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Watershed Management for Potable Water Supply: Assessing the New York City Strategy (2000)

Chapter: 8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

8
Phosphorus Management Policies, Antidegradation, and Other Management Approaches

This chapter discusses four policy tools that New York City is using, or could be using, within its watershed management strategy. Although somewhat unrelated to one another, these tools represent various ways in which protection strategies (both structural and nonstructural) can be implemented. In addition, they each highlight the difficulty of assessing and mitigating nonpoint source pollution in comparison to point source pollution. The Total Maximum Daily Load (TMDL) Program, mandated for impaired waters by the Clean Water Act (CWA), is a powerful tool for determining the relative contributions of point and nonpoint source pollution to the water supply reservoirs. The Phosphorus Offset Pilot Program, or "trading" program, was created to allow new point sources of pollution without increasing the overall level of pollution within a subwatershed. Antidegradation refers to a state and federal policy that is intended to prevent the lowering of water quality within water supply reservoirs (and other waterbodies). Finally, treatment processes beyond chlorine disinfection are being explored for use in the New York City water supply system.

TOTAL MAXIMUM DAILY LOAD PROGRAM

Section 303(d) of the CWA requires states to identify waters that do not meet the goal of "fishable, swimmable water quality" and to develop TMDLs for them. The TMDL process involves identifying the chemical(s) of concern that are causing impairment, defining a water quality standard for that chemical (if a federal or state standard does not already exist), and determining the allowable loading (TMDL) of that chemical such that the standard is not exceeded. If the current pollutant loading to a waterbody exceeds the TMDL, then the state must

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

identify point and nonpoint sources of pollution and suggest ways to decrease loading from these sources.

Participation of all 19 New York City reservoirs in the TMDL program is required under the City's filtration avoidance determination. The New York City Department of Environmental Protection (NYC DEP) has been developing TMDLs for each reservoir in three phases; the TMDLs generated at each phase supersede the previous values and reflect more site-specific data, better modeling efforts, and improved implementation methods for meeting TMDLs. Because the overall goal of the TMDL program is to identify specific polluting areas and land uses and concentrate point and nonpoint source pollution controls to those specific areas, the TMDL calculations are viewed by NYC DEP as a planning exercise that will guide the implementation of best management practices (BMPs) throughout the New York City watershed (K. Kane, NYC DEP, personal communication, 1998). This fact places tremendous importance on the adequacy of the methods and models used in the TMDL program.

NYC DEP has decided to base its TMDL calculations on total phosphorus as the compound of concern. In doing so, it has assumed that phosphorus is the limiting nutrient for plant primary production and that it correlates best with disinfection byproduct (DBP) formation, nuisance algae and eutrophication, hypolimnetic anoxia, and taste and odor problems. Using phosphorus as the target of the TMDL program presents several challenges because it is somewhat ambiguous and controversial as an indicator of drinking water quality. Because there is no national maximum contaminant level (MCL) for phosphorus, NYC DEP has had to interpret qualitative state laws regarding phosphorus. The state currently endorses a guidance value for in-reservoir total phosphorus of 20 µg/L measured in the epilimnion during the growing season (NYS DEC, 1993). This value, based on aesthetic effects for primary and secondary contact recreation, was used for Phase I TMDLs. For Phase II, however, NYC DEP has interpreted the state's narrative standard for phosphorus, which states that, for all classes, "there shall be none in amounts that result in the growth of weeds, algae, and slimes that will impair the waters for their best uses." (NYCRR 701-703). Accordingly, a phosphorus concentration of 15 µg/L has been recommended by NYC DEP and used for Phase II TMDLs (NYC DEP, 1999a).

TMDL Methodology

The TMDL program in New York City was developed in phases in order to generate results quickly with currently available information and also to update TMDLs on a regular basis as more data and sophisticated models become available. The first two phases have been completed; Phase I values have been adopted by the New York State Department of Environmental Conservation (NYS DEC) and approved by the Environmental Protection Agency (EPA), and Phase

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

II values await approval in September 1999. Phase III is not expected to be complete until 2002.

Phase I Methodology

Step 1: Calculating the TMDL. The first step of the TMDL process determines the status of the basin with respect to phosphorus concentration. Phosphorus concentration data were collected from different points in each reservoir and at different depths, both biweekly and monthly. During Phase I, data from the growing seasons (May 1 through October 31) of 1990–1994 were collected, and the median value for each year was calculated.

Median values of phosphorus concentration were converted into annual phosphorus loads using the Vollenweider equation (see Equation 8-1 of Box 8-1). The Vollenweider equation is a simple, steady-state model of chemical flux through a completely mixed waterbody (Vollenweider, 1976). It was originally developed with data collected from Canadian lakes. The derivation of the Vollenweider equation and its use to convert phosphorus concentrations to phosphorus loads is discussed in Box 8-1.

It should be noted that the use of the Vollenweider equation to estimate loadings to the water supply reservoirs is unusual. In most cases, the Vollenweider equation is utilized to estimate the total phosphorus concentration in the reservoirs based on measured or estimated loadings from tributaries and other inputs. Agreement between the measured and calculated phosphorus concentrations indicates appropriate application of the model. In NYC DEP's application of the Vollenweider equation, measured total phosphorus concentration in the reservoirs is utilized to "back-calculate" the loading to each reservoir (and a comparison is made with an independent method, the Reckhow equation, to estimate loadings). This use of the Vollenweider equation requires less information to be gathered because monitoring of storm events from tributary inputs to derive accurate estimates of nutrient loadings is not needed.

The estimated phosphorus loads (L) from each of the five years between 1990 and 1994 were arithmetically averaged to determine one value for the "current load." The state guidance value for phosphorus, 20 µg/L, was also converted into an annual load (the "critical load") using the Vollenweider equation. The TMDL for a reservoir corresponds to this critical load. However, given the uncertainties inherent in the process, a margin of safety (10 percent for the New York City reservoirs) is usually subtracted from the critical load to give the "available load." It is this available load to which the current load is compared to determine if a waterbody is exceeding its TMDL. If the current load is below the available load, then the basin is not exceeding its TMDL. If the current load is greater than the available load, then the amount in exceedance must be reduced in the watershed by reducing the contribution of phosphorus from either point or nonpoint sources.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-1
The Vollenweider Equation

The Vollenweider equation was derived as follows: a simple mass balance for a constituent like total phosphorus in a complete-mix basin (in which a fraction of material is settling at an apparent settling velocity of vs) results in the following steady-state equation:

where P = the total P concentration throughout the reservoir, mg/L

L = the total P loading to the reservoir from all sources, g/m2/day

qs = the overflow rate of the reservoir (flow rate/surface area), m/day

vs = the apparent mean settling velocity of total P, m/day

This mass balance equation can be written in an equivalent form as:

where τw = the mean hydraulic detention time of the reservoir, days

R = the fraction of total P retained within the reservoir system (dimensionless)

H = the mean depth of the reservoir (volume/surface area)

The form of the equation that the NYC DEP utilized varies from Equation 8-2 because it makes use of correlations to account for the fraction of total phosphorus that is not retained in the reservoir. The fraction of total phosphorus that passes through the reservoir is inversely proportional to the square root of the mean hydraulic residence time (Larsen et al., 1976). This empirical relationship, which has been validated on hundreds of lakes, was found to be accurate for the New York City reservoirs (Janus, 1989). Therefore, the final equation that is used by the NYC DEP is:

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Step 2: Modeling All Sources of Pollution. The second step in the Phase I TMDL process is to establish the relative contribution of phosphorus from different sources throughout the basin. In New York City, this step used data from 1993 only. To determine the contribution from wastewater treatment plants (WWTPs), effluent samples were collected on a regular basis and a flow-weighted mean phosphorus concentration was determined. This concentration was then multiplied by the average flow from the WWTP and the number of days in operation during 1993 to determine the annual phosphorus loading from WWTPs. Upstream reservoirs are also considered to be point sources for downstream reservoirs. To determine their contribution, the tunnels connecting the reservoirs were sampled for phosphorus at a point just prior to the receiving reservoir.

Nonpoint sources pose greater difficulties because few methods have been developed to measure their contributions. NYC DEP used the Reckhow model to predict the contributions of agricultural land, forest, urban land, atmospheric deposition, and septic tanks (Reckhow et al., 1980). As shown in Box 8-2, each contribution was calculated by multiplying the area of land devoted to that land use by an export coefficient, which was derived from the literature. For septic systems, only those sited within 100 ft of lakes, reservoirs, and watercourses were assumed to contribute loadings to the reservoirs. Because current state regulations prohibit septic systems within 100 ft of a waterbody, the septic system contribution is made up primarily of preexisting and noncomplying systems.

The Reckhow equation sums up all the point and nonpoint sources and produces an annual phosphorus loading in kg/year, which can be converted into phosphorus concentration, again using the Vollenweider equation. This concentration was compared to the measured annual median phosphorus concentration. If the difference between those values was less than 20 percent, then the Reckhow model was assumed to be an adequate model for that basin.

Although this second step may appear to be strictly academic and not required during the TMDL process, NYC DEP was obliged (because of the filtration avoidance determination and agreements with NYS DEC) to measure point and nonpoint phosphorus loading using the Reckhow model, even for those basins that were not exceeding their TMDLs.

Step 3: Determining Wasteload Allocations and Load Allocations. The last step of the Phase I TMDL process was only done if a basin exceeded its TMDL (as it did in Cannonsville Reservoir). In this step, the waste load allocations (WLA) from point sources and load allocations (LA) from nonpoint sources are determined to help optimize management strategies. NYC DEP determined the Cannonsville WLA by assuming that all WWTPs would meet the effluent phosphorus concentration goals of the Memorandum of Agreement (MOA) as a result of the upgrades. These effluent phosphorus concentrations were then multiplied by the State Pollution Discharge Elimination System (SPDES) permit-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-2
The Reckhow Model

The Reckhow model is a lumped-parameter model that determines the contribution of different land uses to overall pollutant loads. Data on land use in the New York City watersheds are stored in a Geographic Information System (GIS) database derived from Landsat images taken at 30-m resolution. Four land use categories are distinguished in the Reckhow model: urban, forest, agriculture, and water, with the agricultural land use being sometimes subdivided into corn/alfalfa, bare soil, and grass/shrubs. For Phase I, the export coefficients for the Reckhow model were derived mainly from the literature. Slight variations in the Phase I coefficients were used to reflect known differences between the Croton, Catskill, and Delaware watersheds. In Phase II, only the Croton watershed TMDLs utilized the Reckhow model. Export coefficients for this phase were revised to include some site-specific data and information. Coefficients used for Phases I and II are shown below along with the governing equations for the Reckhow model.

where L = the total P loading to the reservoir from all sources, kg/year

ECag = export coefficient for agricultural land (kg/ha/yr)

ECf = export coefficient for forest land (kg/ha/yr)

ECu = export coefficient for urban land (kg/ha/yr)

ECa = export coefficient for atmospheric input (kg/ha/yr)

ECs = export coefficient for septic systems (kg/capita/yr)

Aag = area of agricultural land (ha)

Af = area of forest land (ha)

Au = area of urban land (ha)

As = area of lake surface (ha)

PSI = point source input (kg/yr)

Septic = septic system input (kg/yr)

SR = soil retention coefficient.

Export Coefficients (kg/ha/yr):

Croton Phase I

Catskill

Delaware

Croton Phase II

Urban

0.70

0.70

0.70

0.90

Forest

0.05

0.07

0.05

0.05

Atmospheric

0.53

0.53

0.53

0.10

Agriculture:

0.3

 

 

0.3

Corn/alfalfa

 

2.00

2.00

 

Bare soil

 

0.30

0.30

 

Grass shrubs

 

0.15

0.20

 

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

ted flows to obtain the WLA. The LA was obtained by subtracting the WLA from the available load.

The main purpose of calculating a WLA is to set a permanent upper bound on phosphorus loading that can be incorporated into the SPDES permit of a WWTP. The LA is sometimes used to target best management practices to the appropriate nonpoint sources.

Phase II Methodology

Phase II has a more complex methodology than Phase I, although the three steps of the process are analogous (NYC DEP, 1999b). Details are only provided where differences between Phases I and II exist.

Step 1. In Phase II, the geometric mean of the reservoir phosphorus concentration data was used rather than the median. The geometric mean was thought to be a more accurate representation of the phosphorus concentration data, which follow a lognormal frequency distribution (K. Kane, NYC DEP, personal communication, 1998). Values that were below the detection limit (2–5 µg/L) were set to half the detection limit. Unlike Phase I, phosphorus concentration data from 1992 to 1996 were used in Phase II. The geometric mean from each of these five years was arithmetically averaged to determine the current load.

The margin of safety in Phase II was changed slightly to account for large variations in phosphorus data from year to year (K. Kane, NYC DEP, personal communication, 1998). The margin of safety can vary between 10 percent and 20 percent, depending on interannual variability in phosphorus concentrations (NYC DEP, 1999b).

Finally, the Vollenweider equation was altered slightly for Phase II to accommodate its coupling to the Generalized Watershed Loading Function (GWLF) in Step 2. Unlike the Reckhow model, which does not vary over time, the GWLF can simulate large, storm-related pollutant loadings. These loadings may deliver particulate phosphorus that settles to the bottom of the reservoirs and does not affect midlake phosphorus concentration. As originally formulated, the Vollenweider equation does not take into account this fraction of input phosphorus lost to the sediments. Thus, an additional term representing this fraction was added to the Vollenweider model, resulting in Equation 8-6 (NYC DEP, 1999b).

where P = phosphorus concentration (mg/L)

L = the total P loading to the reservoir from all sources, g/m2/day

τw = the mean hydraulic detention time of the reservoir, days

H = the mean depth of the reservoir (volume/surface area)

fs = the fraction of input phosphorus that is positionally unavailable

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Step 2. Determining the contributions of point and nonpoint sources to phosphorus loading has changed dramatically from Phase I. For reservoirs in the Croton watershed, the nested Reckhow model was used to divide the region into multiple subbasins. The nested Reckhow was adopted because NYC DEP felt that the Phase I approach was not accounting for phosphorus retained in nine large waterbodies upstream of the 13 reservoirs. In Phase II, the waterbodies in these subbasins were assumed to retain 50 percent of the phosphorus and were then considered to be point sources to the downstream waterbodies. A 50 percent phosphorus retention rate was used for all of the subbasins in the absence of data on the water budget, phosphorus concentrations, and residence times for these subbasins. Previous studies on reservoirs with residence times greater than six months show that phosphorus retention tends to plateau around 60 percent (K. Kane, NYC DEP, personal communication, 1998). NYC DEP choose 50 percent because although the East-of-Hudson subbasins have longer residence times than the main East-of-Hudson reservoirs, they are also more eutrophic and may be creating phosphorus near the bottom waters as a result of algal decay.

As shown in Box 8-2, the Phase II Reckhow model was amended to include some locally measured export coefficients, and data from four years were used rather than data from one year. Another major change for Phase II is that the criterion for determining whether the Reckhow model is a good fit to a basin has been increased from 20 percent to 50 percent in some cases. The 20 percent acceptance criterion was thought to be too restrictive, especially in basins where the phosphorus concentration is very low.

In the Catskill/Delaware watershed, the Reckhow model was replaced in favor of the GWLF, which can predict the temporal and spatial variability in phosphorus loading. The GWLF is a numerical model that simulates hydrology, nonpoint source runoff of pollutants, and point source inputs. It is an advancement over the Reckhow approach because it utilizes daily time intervals to generate monthly, seasonal, or annual loadings to reservoirs. Also, it provides separate estimates of groundwater inputs, which are especially important in systems with thin soils such as the Catskill/Delaware reservoirs [in fact, the model was originally developed for the Catskill Region by Haith et al. (1983, 1992) and Haith and Shoemaker (1987) at Cornell University]. Figure 8-1 shows the three submodels that make up the GWLF, and a more detailed description of the model is given in Box 8-3. The model has been calibrated and validated using stream flow data from the Catskill/Delaware reservoirs.

Although the data requirements for the GWLF are extensive, literature values are often used for some of the needed parameters. NYC DEP monitoring program provides required data on precipitation, air temperature, land use, soil type, topography, and point source phosphorus loads. There are 11 land use categories in the GWLF as compared to six in the Reckhow model. Data of other model parameters, including soil erodability and pollutant concentrations in ground-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-1 (A) Water balance submodel of the Generalized Watershed Loading Function.

water and surface runoff, are not currently available and have been derived from the literature up to the present time.

Step 3. During the Phase I TMDL process, the WLA and LA were calculated only for those basins exceeding their TMDLs. However, during Phase II they were calculated for all basins, regardless of their TMDL status. The methods for calculating the WLA and LA are unchanged from Phase I.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-1 (B) Dissolved nutrient submodel of the Generalized Watershed Loading Function.

Phase III Methodology

Although Phase III TMDLs are not due for several years, NYC DEP has been developing more sophisticated models for this process. It is anticipated that the Vollenweider equation will be discarded in favor of a more complex water quality model that has both hydrothermal and eutrophication components. Such a model is currently being designed for the Cannonsville watershed (Cannonsville model), and similar efforts for the other Catskill/Delaware reservoirs are under way. A primary goal of Phase III is to link the GWLF to such a water quality model in order to predict long-term changes in water quality as a result of management practices in the watershed. More information on the hydrothermal and eutrophication models that make up the Cannonsville Model can be found in Auer et al. (1998), Doerr et al. (1998), Owens et al. (1998), and numerous NYC

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-1 (C) Particulate nutrient submodel of the Generalized Watershed Loading Function.

DEP publications. As presently formulated, these water quality models focus specifically on nitrogen, phosphorus, dissolved oxygen, and sediment. Water quality and terrestrial models for simulating fate and transport of microbial pathogens and precursors of disinfection byproducts are not currently under development.

Phosphorus-Restricted Basins

NYC DEP has developed a water quality measure for its reservoirs that is similar in calculation to the TMDL and is used for similar management purposes.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Box 8-3
Generalized Watershed Loading Function

The GWLF is a terrestrial runoff model than can predict contributions of point and nonpoint sources to overall pollutant loading. As shown in Figure 8-1, the GWLF is divided into three submodels that are combined to predict overall pollutant loadings to waterbodies.

In the water balance submodel, stream flow is divided into surface runoff and groundwater contributions. Precipitation, evapotranspiration, infiltration, percolation, snowmelt, and other processes contribute to overall stream flow. This submodel requires data on rainfall, temperature, land use, and soil characteristics. Rather than measuring all of the parameters, NYC DEP has used known data on land cover and soils (from the current GIS databases) combined with parameters derived from literature research to determine the contributions of groundwater and surface runoff to overall flow. The hydrology submodel was calibrated and validated using measured stream flow data from eight drainage basins west of the Hudson River.

The dissolved nutrient submodel generates loadings of dissolved nitrogen and phosphorus in groundwater and surface water and from septics systems. To use this model, NYC DEP has combined GIS data on land cover and septic system numbers with literature values of nutrient concentrations in different types of nonpoint source runoff.

The final submodel is the particulate nutrient submodel, which generates sediment and particulate phosphorus loadings from erosion and surface runoff. This submodel relies on empirical runoff and erosion relationships (e.g., the Universal Soil Loss Equation (USLE) developed by the USDA Agricultural Research Service). Data on land cover and sediment yield were used by the NYC DEP in combination with literature values for soil erodability, slope, vegetation, and other factors to generate loadings.

For all three submodels, the same land cover database used for the Reckhow model was used in the GWLF. Both of the nutrient submodels were calibrated and validated using actual stream loadings measured at one location in the Cannonsville watershed.

There are some important limitations of the GWLF that should be noted and effectively overcome as part of the Phase III TMDL calculations. First, it is not clear that the septic system component of the dissolved nutrient loading submodel accounts for effects of soil type and depth to groundwater. Nitrate concentrations may be much lower in anaerobic soils with high organic content than in sandy soils where most studies of nitrate plumes from septic systems have been conducted.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Second, the SCS Curve Number and USLE do not necessarily yield accurate, absolute values of streamflow, erosion, or sediment delivery. Both methods can be orders of magnitudes off for certain events and soilvegetation complexes because neither was developed for the forested, natural vegetated watersheds with thin soils that are characteristic of the Catskill/Delaware watershed. Using SCS curve numbers to characterize runoff potential can misrepresent true runoff processes in the interest of computational simplicity (D. Booth, University of Washington, personal communication, 1999). The USLE is a poor estimator of upland sediment generation in any watershed save those with predominantly agricultural land uses (for which the USLE was originally developed). Watersheds that generate much of the sediment load to streams via stream-channel erosion will not be represented by this approach. (It should be noted that the USLE has been adapted for forested conditions and has been shown to work well under such conditions. The committee assumes that this adaptation was used in the GWLF for forested parts of the watershed.) Further site-specific testing and validation of both nutrient submodels in each subwatershed are of paramount importance before the GWLF is used in Phase III TMDL calculations.

Source: NYC DEP (1998a).

''Phosphorus-restricted basins" are those which also exceed the state guidance value of 20 µg/L phosphorus. However, there are some fundamental differences between TMDL and phosphorus-restriction calculations. Phosphorus restriction is mentioned here (1) because of its similarity to TMDLs, (2) because it is an important part of the phosphorus offset pilot program to be discussed later, and (3) because it is used in conjunction with the controversial 60-day travel time (see Chapter 11).

The Watershed Rules and Regulations Prohibit new or expanded WWTPs with surface discharges from being located within phosphorus-restricted basins. Thus, phosphorus restriction is a measure of the health of a reservoir. Phosphorus-restricted basins are determined by measuring total phosphorus concentration at all reservoir depths from May to October (NYC DEP, 1997a). It should be noted that because of the seasonality of the data used, the phosphorus restriction analysis as formulated yields the lowest concentrations (or "best picture") of the year. This is because utilization of phosphorus by microbes is highest during the

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

summer and because there are relatively low influents to the reservoirs during summertime.

Measured phosphorus concentrations are expressed as a yearly geometric mean, and the geometric means are then averaged over the five most recent years to determine exceedance. In general, if a reservoir's five-year running average exceeds 20 µg/L for more than two years in a row, it is designated as phosphorus-restricted.

There are significant differences between the concepts of phosphorus TMDLs and phosphorus-restricted basins, although both were designed to protect water quality and to mitigate problems associated with eutrophication, algal blooms, and low dissolved oxygen in the hypolimnion. These differences are summarized in Table 8-1. In addition to the distinctions listed in Table 8-1, it should be noted that the concepts differ in spatial scale and extent. The calculation of phosphorus restriction uses data from a single waterbody, not an entire watershed. Thus, it is really not a "basin concept" like the TMDL process, which considers loading from point and nonpoint sources in the entire watershed.

Phase I and II TMDL Results

For the most part, the reservoirs in the Catskill/Delaware watershed are not exceeding their Phase I or Phase II TMDLs, nor are they phosphorus-restricted. Reservoirs within the Croton watershed, which has undergone rapid development

TABLE 8-1 TMDL Basin Concept vs. Phosphorus-Restricted Reservoir Concept

Governing Agency

TMDL

Phosphorus Restriction

NYS DEC and EPA

NYC DEP

Requirements

Multiple data sets/models required

Phosphorus concentration data

Regulatory Implications

Determines compliance with the Clean Water Act and affects SPDES Permits

Affects siting of WWTPs in the New York City water supply watersheds only

Exceedance Test

Phosphorus load corresponding to 15 µg/L exceeded

Phosphorus concentration of 20 µg/L exceeded

Consequence of Exceeding the TMDL or Phosphorus Standard

Reduction in SPDES-permitted phosphorus loads and nonpoint source loads

No new WWTPs can be constructed in the basin; extra requirements for SPPPs.

Margin of Safety

90% of load is allocated

No margin of safety

Updating

Infrequent revisions

Annual revision

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

during the last 20 years, are considerably less healthy. In general, the basins that are exceeding their Phase II TMDLs are also phosphorus-restricted. Table 8-2 lists the Phase II TMDLs and phosphorus-restricted status of all 19 reservoirs in both watersheds.

TABLE 8-2 Phase II TMDLs and Phosphorus-Restriction Status

Reservoir

Phase II TMDL kg/yr

Available Load kg/yr

Current Load kg/yr

WLAa kg/yr

LA kg/yr

Average [P], 1992–1996 µg/Lb

West of Hudson

Ashokan East

19,542

17,588

16,484

4

17,584

13.4

Ashokan West

45,399

40,859

32,833

264

40,595

15.4

Cannonsvillec

40,237

35,207

52,368

1,059

34,148

21.1

Neversink

16,914

15,223

6,863

0

15,223

6.4

Pepacton

59,375

53,437

37,327

388

53,049

9.7

Rondout

41,413

37,272

23,476

125

37,147

8.7

Schoharie

22,321

20,089

19,864

789

19,300

21.3

East of Hudson

Kensico

28,276

25,448

16,926

0

25,448

9.9

Amawalkc

997

897

1,318

390

507

21.3

Bog Brookc

281

253

321

28

225

18.7

Boyds Cornerc

725

652

687

0

652

14.6

Cross River

1,007

881

717

108

773

12.9

Croton Fallsc

3,565

3,030

5,010

615

2,415

28.7

Divertingc

2,098

1,794

3,844

232

1,562

30.0

East Branchc

2,116

1,851

3,462

449

1,402

26.4

Middle Branchc

712

612

1,020

173

439

24.3

Muscootc

7,048

6,343

11,560

1,405

4,938

24.9

New Croton

9,731

8,758

11,189

209

8,549

17.6

Titicusc

869

739

1,124

0

739

22.8

West Branch

12,760

11,484

8,662

28

11,456

13.0

Note: The Phase II TMDL column lists the TMDL value calculated from the modified Vollenweider model based on the 15-µg/L phosphorus standard. The Available Load column shows the available load, which ranges from 80 to 90 percent of the calculated TMDL. The Current Load column represents the current load derived from phosphorus concentration data collected in each reservoir. The current load must be less than the available load for a reservoir to be in compliance with its TMDL. The WLA and LA columns show calculated waste load allocations (WLA) and load allocations (LA), respectively. The final column shows the 1992–1996 calculation of average phosphorus concentration in each reservoir. Significant figures in the columns differ because of the different units used.

a The WLA was calculated by assuming that upgrades mandated by the Watershed Rules and Regulations would be in effect and that the SPDES-permitted flow would be used.

b Bolded values indicate phosphorus-restricted basins based on two consecutive years of exceedance.

c Basin exceeds its TMDL, which is based on 15-µg/L. Nonpoint sources will have to be reduced to meet the TMDL.

Source: NYC DEP (1997a, 1999c–t).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

All of the basins that were exceeding their Phase I TMDLs are also exceeding their Phase II TMDLs. However, four basins in the Croton watershed that did not exceed Phase I TMDLs exceed Phase II TMDLs. This difference is attributable to the lower phosphorus standard of 15 µg/L and the additional years of phosphorus concentrations data that were used during Phase II. During the Phase I TMDL process, there were only three basins (Diverting, East Branch, and Muscoot) that required a reduction in nonpoint loadings to meet the required TMDL. The other basins in exceedance were able to meet TMDLs by upgrading their WWTPs, as required by the Watershed Rules and Regulations. However, in Phase II, all of the basins that exceed their TMDLs must reduce phosphorus loadings from nonpoint sources in order to comply. As a result, meeting Phase II TMDLs in these basins will be considerably more difficult and challenging than implied from Phase I calculations. In the New York City watersheds, implementation of point source controls is under way in some basins and is planned for all others. Implementation of nonpoint source controls in Cannonsville and the nine Croton subwatersheds as a result of the TMDL calculations is not readily apparent. An important measure of success for the New York City TMDL program (or any TMDL program) is the degree of implementation of protection strategies to help the reservoirs meet their Phase II TMDLs.

Replacing the Reckhow model with the nested Reckhow model and with the GWLF had a significant impact on predicted nonpoint source loadings. In particular, the GWLF consistently predicted greater nonpoint loadings because of its ability to simulate storm events and the associated high loadings of particulate pollutants. Because the GWLF spatially and temporally simulates the inflows of both particulate and dissolved nutrient loads from a large number of land covers, it can be an important tool in targeting management practices for control of nonpoint source pollution.

Analysis of TMDL Program

Methods

Both the Phase I and II TMDL methodologies have received criticism, of varying degrees of validity. These criticisms and others identified by the committee are discussed below.

Needed Data Input for Models. The Vollenweider, Reckhow, and GWLF models are well based, highly functional, and predictive, provided data inputs are accurate. As stressed in Chapter 6, more event-based stream monitoring will improve the accuracy of these models, which are totally dependent upon influent discharge-based loadings and residency times within the reservoirs. The GWLF model is particularly data-intensive, requiring numerous parameter inputs that are currently in minimal supply, are not available, or are assumed from published

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

values from other ecosystems that roughly approximate conditions of the reservoir catchment under consideration (NYC DEP, 1998a). Many of the key elements needed, such as estimations of snowmelt, soil chemistry data, and pollutant concentrations in surface runoff and groundwater, are lacking and can be feasibly collected. Real data for these and other parameters are needed at fine resolution scales (<30 m) within each of the reservoir drainage basins, particularly within half a kilometer of the boundaries of the reservoirs and major tributaries. At the very least, such measurements could be made in representative subwatersheds and generalized with other, less-intensive measurements to the rest of the system. Recent discussions on model data development, particularly using the Landsat imagery data of very high resolution (1 m), are a step in the correct direction (NYC DEP, 1998a).

Model Appropriateness. Critics of the TMDL methodology often point to the Vollenweider model as a significant weakness. The model was first constructed using lakes with residences times of 1–10 years. Thus, the steady-state assumption that is part of the Vollenweider may not be valid for the New York City reservoirs (with residence times of six months to one year). Unfortunately, it is not clear that a better model is currently available. Because the Vollenweider will probably not be used during Phase III (in favor of a time-variable water quality model), its use in Phases I and II is not perceived as a problem by this committee.

NYC DEP's use of the Vollenweider equation was somewhat unorthodox and was less than optimal. By using phosphorus concentration data to back-calculate phosphorus loadings, NYC DEP was forced to estimate an arbitrary net phosphorus retention (50 percent) in the large lakes of the Croton system and use an empirical relationship to determine phosphorus retention in the reservoirs. Simple input–output budgets (measurements of reservoir phosphorus loadings and mass phosphorus exports) could have been used to arrive at a specific net phosphorus retention in each reservoir, which would have been substantially more defensible for the calculation of TMDLs. In addition, NYC DEP's procedure required that two models be used to calibrate one another (Vollenweider and Reckhow) rather than using measurements of input loadings and lake concentrations to calibrate and validate the Vollenweider model. The committee presumes that this was because of a lack of resources required to measure all the inputs and outputs to the 19 reservoirs.

Margin of Safety. The margin of safety that differentiates the available load from the critical load has been judged by some as too low (Izeman and Marx, 1996 a,b, 1998; Novotny, 1996). There can be many purposes of the margin of safety. NYC DEP has stated that the margin of safety should account for yearly variations in hydrology and the reservoir response to the phosphorus load (NYC DEP, 1996). The agency also believes that the margin of safety should take

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

variability in phosphorus concentrations into account, because it specifically altered the margin of safety between Phases I and II to do this.

If NYC DEP wants to determine an appropriate margin of safety given its selection of the Vollenweider model, it should conduct a formal uncertainty analysis. Equation 8-3 or 8-6 could be used in a Monte Carlo simulation to determine how errors in the inputs (total phosphorus concentrations in the reservoirs, mean depth, and mean hydraulic detention time) propagate through the equation and result in uncertainty in the estimated loadings (Reckhow and Chapra, 1983; Schnoor, 1996). In order to do this, frequency distributions with time must be constructed for (1) the measured phosphorus concentrations in the lake, (2) the mean depth (volume/surface area), and (3) the mean hydraulic residence time (volume/discharge).

As many as 10,000 realizations (simulations of the model equation) should be run while sampling the frequency distribution of each parameter using a random number generator in the Monte Carlo approach. The result is a distribution of loading values with its own frequency distribution that can be sorted to yield the median and quartile loading values. Such a distribution provides an estimate of uncertainty, which can then be characterized as a margin of safety. For example, the coefficient of variation (the standard deviation divided by the mean) can be utilized as the margin of safety.

Seasonal Variations. It has been charged that because they are averages of several years of data, the TMDL calculations do not take seasonal variations into account and are not made on a "daily" basis (Izeman and Marx, 1996a,b, 1998). Critics feel that this methodology may not capture important trends in phosphorus loading. NYC DEP has argued that because eutrophication parameters are not acutely toxic, variations in phosphorus concentration (occasionally including high concentrations) will not adversely affect reservoir water quality as long as average phosphorus concentrations are maintained at low levels (NYC DEP, 1999a), an assessment with which the committee agrees. In addition, given NYC DEP's unorthodox use of the Vollenweider model to calculate loads from concentration data, there is little utility in calculating daily loads. A meaningful calculation of daily loads would require daily sampling of all major tributaries and groundwater inputs to each reservoir, activities that are beyond the scope of NYC DEP's current monitoring program and, while desirable, are probably unnecessary for Phase I and II TMDLs.

There are, however, other important seasonal considerations that should have been taken into account. NYC DEP calculates the TMDL over the growing period because this is the time period during which NYS DEC requires that phosphorus concentrations be below the state standard. This requirement is based on the assumption that phosphorus triggers algal growth (and eutrophication) predominantly during summer months because of increased heat and light. However, problems of increased algal growth can occur at all times of the year.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

In addition, it is clear that phosphorus loadings from discharges of rivers are strongly coupled to precipitation events, which are not predictable and certainly not seasonal. As currently conducted, the TMDL program may be underestimating the annual phosphorus loading, a supposition that stems from a comparison of relatively low phosphorus concentration data and high chlorophyll a data (NYC DEP, 1993, 1999a). Thus, the committee does not support limiting the TMDL calculation to the "growing season" only.

Implementation

The most frequently cited criticism of TMDL programs across the country is the failure of states to implement pollution control measures following calculations of waste load and load allocations. There is little information regarding implementation of Phase I TMDLs in New York City (see NYC DEP, 1998b), and none regarding Phase II (expected after September 1999). The City, via New York State, is currently under legal pressure to commence implementation. Although ongoing WWTP upgrades in the Cannonsville watershed were sufficient to meet Phase I TMDLs for the Catskill/Delaware system, meeting Phase II TMDLs will likely require implementation of nonpoint source controls in several watersheds, including the Cannonsville and Croton watersheds.

In those instances where water quality models indicate that TMDLs can be met entirely by point source controls, such improvements should be rapidly planned and implemented. Where nonpoint source reductions are needed, NYC DEP must embark on a vigorous plan to understand how BMPs can be employed to reduce phosphorus loading to the reservoirs. This is a difficult task because most watershed management actions required by the MOA are not tied quantitatively to the load reductions necessary to improve water quality. That is, there is little understanding of which BMPs should be used, how many are needed, and where they should be located to obtain a desired phosphorus loading reduction or water quality objective (e.g., 15 µg/L). These frustrations are particularly apparent in Delaware County where it is unclear what specific quantitative source reductions are needed and how to link BMP performance to such reductions.

Public Health and Ecological Protection

Phosphorus Guidance Value. The 20-µg/L guidance value for phosphorus used during Phase I has been the target of much criticism because the value is based on aesthetic and recreational concerns rather than on the use of a waterbody for drinking water (NYS DEC, 1993a). There is nothing sacred about the guidance value of 20 µg/L total phosphorus. In 1934, Clair Sawyer originally proposed a criterion of 30 µg/L of orthophosphorus at spring turnover as a criterion to prevent algal blooms in the spring and summer seasons for New England Lakes (Sawyer, 1947). Vollenweider's research on European and North American

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

lakes indicated that the boundary separating so-called eutrophic lakes from mesotrophic lakes was about 20 µg/L, and the boundary between mesotrophic lakes and oligotrophic lakes was about 10 µg/L (Dillon and Rigler, 1974). The committee feels that the 20-µg/L guidance value is not sufficiently conservative, because it would allow the reservoirs to exist under mesotrophic and mildly eutrophic conditions. For filtration avoidance, it is desirable to have water supply quality with better than meso-eutrophic conditions.

Recently, the NYC DEP assessed the 20-µg/L guidance value by collecting data on phosphorus and chlorophyll a concentrations in all 19 reservoirs and relating these data to use-impairment criteria like taste, odor, algae, and other incidences of eutrophication (NYC DEP, 1999a). In order to ensure high-quality drinking water to the City's distribution system, these criteria specified that cyanobacteria cannot be the dominant algal class, and that algal numbers cannot exceed 2,000 SAU/mL, in more than 25 percent of all samples. Analyses indicated that a phosphorus guidance value of 15 µg/L would be required to meet these criteria and maintain eutrophication at or below an acceptable level, and this value was used to calculate all Phase II TMDLs. For the many reasons discussed above, the committee enthusiastically supports this value.

Other Parameters. It would be desirable to extend the TMDL calculations on phosphorus to water quality parameters that more directly influence health effects and the protection of the New York City drinking water supply. Phosphorus controls aid in the protection of ecological health of the reservoirs, they prevent taste and odor problems, and they help control sources of DBP precursors. The committee also believes that phosphorus controls can help prevent anoxia in bottom waters, although this is not the primary goal of the TMDL program.

However, for a major drinking water supply such as New York City's there are other public health concerns, including DBPs and pathogens, that may not be fully protected using phosphorus controls alone. The remainder of this section focuses on approaches that the NYC DEP might take to model trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP), and other parameters for protection of the water supply. These analyses are targeted at Phase III of the TMDL program and as such will complement the use of time-variable models.

Phase III TMDLs

In Phase III, the Vollenweider model should be discarded in favor of a modeling approach where event-based, time-variable reservoir loadings (Longabucco and Rafferty, 1998) are used as input to a fully dynamic reservoir model (Schnoor, 1996). If phosphorus continues to be used as the priority pollutant, both particulate and dissolved forms of phosphorus must be modeled. Indi-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

vidual input–output models (which could have benefited Phases I and II) should be constructed and validated using site-specific data in order to estimate the fraction of phosphorus retained in each reservoir and the fraction of phosphorus retained in each reservoir and the fraction of phosphorus returned to the water column from the sediment by internal regeneration processes (scour, resuspension, and mineralization/diffusion). Thus, monitoring of phosphorus loading from all prominent sources and monitoring of in-reservoir phosphorus concentrations must occur for each Catskill/Delaware reservoir.

NYC DEP has moved in this direction with the development and adaptation of a hydrothermal model (Owens, 1998), a nutrient/phytoplankton model (Doerr et al., 1998), and the GWLF. As shown in Figure 8-2, the nutrient/phytoplankton model considers nitrogen, phosphorus, dissolved oxygen, phytoplankton, and zooplankton and their interrelations. It is a dynamic mechanistic model that can be coupled with the GWLF to simulate hydrology and nutrient loading from tributaries. To date, these two models have been calibrated and validated using data from the Cannonsville watershed and have been extended to the other basins. Gathering site-specific data to validate these models in each watershed will be a necessary part of the Phase III TMDL process. For example, data on phosphorus bioavailability and phosphorus cycling similar to data collected in the Cannonsville Reservoir (Auer et al., 1998) are needed for each reservoir.

The models currently under development by New York City do not incorporate DBPs or DBP precursors (organic carbon compounds), even though compliance with future EPA rules may require modeling of these compounds. NYC DEP should make substantial efforts during Phase III to develop TMDLs for trihalomethane and haloacetic acid formation potential (THMFP and HAAFP). In order to calculate TMDLs for these parameters, it will be necessary to use numerical water quality models capable of predicting THMFP, HAAFP, dissolved organic carbon (DOC), turbidity, and taste and odor. These are the water quality parameters that affect drinking water quality directly. Such models should be developed now so that they can be tested prior to use in decision-making on the New York City water supply in the next decade.

Figure 8-3 is a schematic that shows some of the interactions that may be modeled. Soluble reactive phosphate and particulate phosphorus must both be simulated as state variables because of the need to account for nonbioavailable fractions of phosphorus. Vertical profiles of dissolved oxygen will be needed in order to estimate the internal phosphorus regeneration from sediments under anoxic conditions. Data on chlorophyll a (or phytoplankton biomass) will be needed because chlorophyll a measures ecosystem impacts and authochthonous (internally generated) DBP precursors. Knowledge of vertical variations in phytoplankton would be helpful for understanding the potential impairment of uses by excessive algae growth. DOC should be modeled both for the quantity and quality of carbon compounds that react to form DBPs, including the relative fractions of allochthonous and autochthonous sources of DOC. Dissolved silica is an important nutrient for diatom growth, and information on nitrogen species

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-2 Conceptual submodels of the nutrient/phytoplankton model for Cannonsville Reservoir: (a) phosphorus, (b) nitrogen, (c) phytoplankton, (d) zooplankton, and (e) oxygen. Source: Doerr et al. (1998). Reprinted, with permission, from Doerr et al., 1998. © 1998 by the North American Lake Management Society.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-3 Modeling of THMFP, HAAFP, and other parameters.

may also be required to accurately simulate the growth and decay of phytoplankton standing crops. It remains to be seen whether taxonomic distinctions are necessary (green algae, diatoms, and cyanobacteria) to adequately simulate THMFP, HAAFP, and taste and odor thresholds.

Taste and odor are the most challenging parameters of all because little is known about the sources and fate of organic molecules that cause taste and odor. The redox status of sediments, bacteria assemblages such as Actinomycetes spp., and certain algal species are reported to influence taste and odor formation. Fortunately, there has not been a large problem with taste and odors in the New York City water supply to date, probably because turbidity and algae have been maintained at low levels.

It is not clear whether additional trophic levels, such as zooplankton grazing and fish predation, will be needed to simulate chlorophyll a concentrations accurately. In general, it is best to develop the simplest model that accurately simulates important drinking water quality variables. The required modeling of DBP precursors, DOC, color, and taste and odor goes beyond the current state of the art and will require development.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

NYC DEP has made a good start on relating phosphorus concentrations and DOC concentrations to THM precursors in the Cannonsville Reservoir (NYC DEP, 1997b; Stepczuk, 1998a–c). The relationships between these parameters, however, need to move beyond simple correlations to deterministic models. Results to date indicate that it is a complicated problem; further research and development of these models is strongly encouraged.

Conclusions and Recommendations

  1. In general, methods that were used for Phases I and II of the TMDL program were adequate. The Vollenweider model was the best choice for a water quality model given the limited data available and the time constraints placed on the program. It should be kept in mind that the phosphorus loading calculations are limited by the lack of real data used for the Reckhow and GWLF models.

  2. Phase I and II TMDLs would have been improved if the following had been taken into consideration:

  • The calculations should have used phosphorus concentration data for the entire year rather than for just the growing season.

  • The modeling should have taken into account all septic systems, not only those septic systems within 100 ft of the reservoirs.

  • Phosphorus retention should have been determined using input–output measurements rather than through selection of an arbitrary phosphorus retention value of 50 percent.

  • The margin of safety should have been determined by conducting an uncertainty analysis to show how variability in phosphorus concentration, hydraulic detention time, and reservoir depth propagates through the Vollenweider model.

  1. The new 15-µg/L phosphorus guidance value is appropriate for Phase II TMDLs. The Phase I goal of 20 µg/L was not adequately conservative for a drinking water supply, as it is based on ecological and aesthetic considerations. Conservatism in the choice of phosphorus standard is necessary because data for some of the New York City reservoirs (Cannonsville, Croton system) show that algal productivities, estimated from average and maximal summertime algal biomass as chlorophyll a, are in excess of recommended values for any drinking water system (NYC DEP, 1993, 1999a).

  2. NYC DEP should place a high priority on implementing all necessary nonpoint source control measures to reach Phase II TMDLs. Currently, it is unclear what specific measures are being taken to reduce nonpoint source phos-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

phorus loading to the Cannonsville Reservoir and several Croton reservoirs other than WWTP upgrades. Ongoing watershed management actions in the Catskill-Delaware watershed must be quantitatively linked to the source reductions necessary to improve water quality prior to successful implementation of the nonpoint source TMDLs.

  1. In Phase III, time-variable analyses should be performed using dynamic reservoir models and the GWLF (or equivalent model) for inputs. This will require construction of input–output models for total phosphorus, measurements of dissolved and particulate phosphorus loadings and concentrations, and assessment of individual phosphorus retention coefficients for each reservoir. NYC DEP's efforts in this regard for the Cannonsville Reservoir are to be commended.

  2. Data collection to support and validate the GWLF and other Phase III water quality models should be given a high priority. Currently, the use of the GWLF is limited by a lack of site-specific data on soil chemistry, pollutant concentrations in runoff and groundwater, and other factors. At the very least, such data should be collected in representative subwatersheds and should be generalized with other, less-intensive measurements to the rest of the system. The use of event-based monitoring data rather than fixed-frequency sampling, and increasing the spatial resolution of the collected data, would greatly improve model accuracy. Given the pervasiveness of the GWLF in many facets of the City's watershed management program, the time and money spent to improve the accuracy of this model through intensive data collection would be well justified.

  3. NYC DEP should focus Phase III of the TMDL program on public health protection by developing models that can link phosphorus to DBP precursors and other relevant parameters. New York City should consider doing a TMDL calculation for THM and HAA formation potential by deriving models that can link phosphorus and other inputs to THMFP, HAAFP, algae, chlorophyll, and taste and odor.

  4. The method for determining which reservoirs are phosphorus-restricted should use phosphorus concentration data for the entire year, not just for the growing season. In addition, the criterion for determining whether a basin is restricted should be set at 15 µg/L rather than at 20 µg/L. The phosphorus guidance value determined for the Phase II TMDL program is relevant to the calculation of phosphorus restriction, which is also used to express the degree of use impairment.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

PHOSPHORUS OFFSET PILOT PROGRAM

The New York City MOA includes a five-year phosphorus offset pilot program that allows for the construction of new or expanded WWTPs in phosphorus-restricted basins, areas otherwise closed to further construction of WWTPs. The purpose of the offset program is to allow for some continued growth in these phosphorus-sensitive basins while preventing a net increase in phosphorus loading.

The phosphorus offset pilot program is similar to effluent trading programs for water and emissions trading programs for air, in which a discharger of pollution is allowed to increase its pollutant discharge if another party will concomitantly reduce its discharge. In general, these programs require that an overall net reduction of pollutant loading be achieved by the trade. Most programs specify a trading or offset ratio that indicates the amount of pollutant reduction that must occur to balance the increase in pollutant discharge. Offsets are provided by a variety of mechanisms that reduce pollutant loadings from other sources, either point or nonpoint.

The objective of this section is to assess the scientific and technical basis for the New York City phosphorus offset pilot program. The effectiveness of trading as an approach to pollution reduction is discussed, using lessons learned from elsewhere. The potential reliability of the program is evaluated by addressing the following issues:

  • Are the offset ratios specified by the MOA scientifically sound?

  • How is ''surplus" phosphorus defined?

  • Are the proposed offset mechanisms appropriate?

  • Can the phosphorus offsets be effectively quantified?

  • What are the expected net effects of offsets on reservoir water quality?

  • How can offsets be integrated within the TMDL process?

  • Will the proposed offset program be sufficiently cost-effective or include sufficient incentives to be successfully implemented?

Overview of Watershed-Based Trading

Since 1996, EPA has been promoting effluent trading as an innovative way to develop cost-effective, common-sense solutions for water quality problems in watersheds. Trading is an agreement between parties contributing to water quality problems on the same waterbody in which the allocation of pollutant-reduction responsibilities among the parties is altered (EPA, 1996).

Proponents of Effluent Trading

Effluent trading has been proposed as an alternative to command-and-control environmental regulation, which attempts to reduce emissions at all point sources.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Proponents of trading argue that mandated discharge reductions for WWTPs are not efficient mechanisms for reducing pollutant loads because they force dischargers to adopt identical practices for pollutant reduction and to bear identical shares of the pollution-control burden regardless of their relative impacts (Jacobson et al., 1994). Under this system, every discharger is required to reduce pollutant loading to a certain level, which is likely to be more costly for some discharges than for others. In contrast to command-and-control regulations, effluent trading attempts to control overall pollution in a given area (such as a watershed) by assuming that particular pollutants disperse evenly across the area. Some have argued that these two systems of control can achieve the same result but that trading is more flexible and achieves pollution control more efficiently than existing command-and-control policies (Hoag and Hughes-Popp, 1997; Jacobson et al., 1994).

Opponents of Effluent Trading

Effluent trading has received substantial criticism, primarily because it assumes that a certain level of pollution will always exist and thus does not lead to the elimination of all emissions (Lapp, 1994). Likewise, Mann (1994) argues that pollutant trading has the undesirable effect of shifting the terms of debate from public health and industry responsibility to economics and finances. Many environmental groups feel that effluent trading is inconsistent with the goals of the CWA for attaining fishable/swimmable waters because it would allow pollutant loadings from some sources to increase (see EPA, 1996). The spatial distribution of the remaining pollutants also presents an environmental justice dilemma. For example, pollution rights from low-polluting sources in affluent areas might be traded to high-level polluters in poor areas. If residents of poor areas are unable to resist such transactions, they may be exposed to greater pollution than their more affluent counterparts. These and other benefits and criticisms of effluent trading are considered below, with specific reference to the phosphorus offset pilot program mandated by the MOA.

Trading Frameworks and Their Implementation

EPA Guidance

EPA has developed a framework for effluent trading that allows for five types of trades: (1) point source/point source trading, (2) intraplant trading, (3) pretreatment trading, (4) point source/nonpoint source trading, and (5) nonpoint source/nonpoint source trading (EPA, 1996). Trading programs developed by the states must meet CWA water quality requirements by ensuring a number of important conditions. Trading partners must meet applicable technology-based treatment requirements. Thus, no participant is allowed to

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

operate treatment processes at suboptimal levels and engage trading partners to compensate for their lack of efficiency. Trades must be consistent with federal and state water quality standards throughout a watershed, and they should be used only for certain appropriate types of pollutants. A TMDL or similar process should provide the framework for developing trades, because of the ease with which pollutant loadings are accounted for under such programs. Trades must be supported by regulatory and enforcement mechanisms, which can be a challenge when nonpoint source pollutant reduction is involved. Performance monitoring is needed to track the success of trading programs and the effectiveness of BMPs. In order to maintain desired water quality, trading areas should align with waterbody segments or watersheds. And finally, any trade must include stakeholder involvement and public participation.

Existing Applications of Trading

Pollution trading was first implemented for air emissions control under the Clean Air Act, and it has been widely utilized in that arena. Efforts to use pollution trading to protect water quality are more recent and are relatively uncommon. A few water pollution trading programs have existed since the 1980s and early 1990s (e.g., Fox River, Wisconsin; Cherry Creek Basin, Colorado), the most notable being the Tar-Pamlico program in North Carolina (Harding, 1993; Hoag and Hughes-Popp, 1997; Jacobson et al., 1994; Stephenson, 1994). Typically, the trades are initiated by WWTPs as a means of reducing overall phosphorus and nitrogen loads in the watershed. In effect, the WWTPs invest in off-site measures to reduce pollutant loads. These investments are expected to remove at least as much of the pollutant in question as innovations that the WWTP might make to reduce point source emissions, but at a lower cost to the WWTP. Boxes 8-4 and 8-5 present case studies of two effluent trades being implemented in the United States. Because most programs have only recently been developed, in general it is too early to judge their success.

The New York City Phosphorus Offset Pilot Program

The phosphorus offset pilot program for the New York City watershed is one of only a few programs in the northeastern United States. On Long Island, a trading program to improve marine water quality is in its initial stages (M. Tedesco, EPA, personal communication, 1997). A New Jersey program, in which copper is discharged from small industrial facilities into WWTPs, is reported as the first trade in the country between indirect dischargers (i.e., facilities that discharge effluent to a WWTP) (C. Tunis, EPA, personal communication, 1997). Box 8-5 describes a trading agreement that has recently been approved in Massachusetts.

Under the terms of the MOA, construction of six new WWTPs within phos-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-4
Effluent Trading in Minnesota

The Minnesota Pollution Control Agency has identified four critical elements that constitute an effective effluent trading program:

  • Cost-effectiveness. Trades must be cost-effective or provide sufficient incentives for trading to occur. Trading costs may include capital and operation/maintenance costs of trading mechanisms, transaction costs, and time associated with the complexities of involving multiple parties in the trade.

  • Equivalence. Proposed trades must be equivalent, or sufficiently similar in physical attributes, to substitute for one another. Physical conditions that must be considered in determining equivalency include timing of discharges, spatial differences, and chemical differences (e.g., dissolved versus particulate forms).

  • Additionality. The condition of additionality requires that load reductions credited to a source in a trade would not have occurred in the absence of the trading program. That is, reductions are "surplus" or beyond those already required by other regulatory programs.

  • Accountability. Conditions of the trade must be met over time. For example, BMPs proposed to achieve trading reductions must actually be implemented and maintained at the proposed levels of effectiveness over time. The degree of monitoring associated with a trading program will depend on the degree of accountability desired.

These conditions have recently been put to the test as part of the first trading permit ever issued in Minnesota. The Rahr Malting Co. plant, which produces barley malt, discharges wastes into the Minnesota River under a National Pollutant Discharge Elimination System (NPDES) permit. The river, certain sections of which are highly degraded, must meet a Total Maximum Daily Load of Carbonaceous Biological Oxygen Demand (CBOD) of 53,400 lbs/day for the section just downstream of the Rahr plant. After approval of the TMDL in 1988, many upstream discharges, including Rahr, were required to reduce loading of CBOD by as much as 40 percent. At the same time, Rahr Malting Co. requested a new permit that would allow additional wastes to be discharged into a lower section of the river.

In designing an effluent trading scheme that would satisfy the chemical characteristics of the Rahr plant's treated wastewater and the Minnesota River, it was assumed that the plant's wastewater would provide nutrients (such as phosphorus) to the river that would be utilized by microorganisms and eventually would result in higher CBOD levels. Positive correlations between phosphorus, chlorophyll, and CBOD were dem-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

onstrated for the Minnesota River to support the trade. The conversion of nutrients from wastewater into CBOD was assumed to be more rapid in stagnant areas of the river because organic material derived from decaying microorganisms would have a chance to accumulate.

The actual trade appears to be a 1:1 trade using phosphorus as the parameter that will be measured both by the point source (Rahr) and participating nonpoint sources. The trade assumes that a one-pound reduction of phosphorus could yield an 8-to 17-pound reduction in CBOD, depending of which sections of the river are involved. Nonpoint sources that have been targeted for participation include soil erosion BMPs, livestock exclusion, rotational grazing, set-asides of highly erodible land, and wetland treatment systems. However, trading partners have yet to be confirmed and approved by the Minnesota Pollution Control Agency. There is no indication of how difficult it will be to attract trading partners and monitor appropriate nonpoint source control measures.

Source: Adapted from Anderson et al. (1997).

BOX 8-5
Effluent Trading in Massachusetts

An effluent trading program has recently been approved in Massachusetts involving an office complex that discharges treated sewage into the Sudbury River. As with the New York City phosphorus offset pilot program, this trade requires a 3:1 offset for all new discharges of phosphorus, utilizing load reductions from other sources. The trading partners in this case are the office complex (Congress Group Ventures) and dozens of neighboring properties that house failing septic systems. The septic systems will be connected to the new sewerage service rather than have the office building install additional, expensive wastewater controls at its plant.

The trade, which was recently approved by EPA, the Massachusetts Department of Environmental Protection, Congress Group Ventures, and the town of Wayland, will be implemented over a two-year period. Although heavily contaminated by a variety of pollutants, the Sudbury River is most noteworthy for its bacterial pollution.

Source: Clean Water Report (1998).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

phorus-restricted basins is allowed as part of the five-year pilot program (NYC DEP, 1997c). These plants must provide a 3:1 phosphorus offset through the reduction of existing point or nonpoint source discharges. In other words, every kilogram of additional phosphorus loading allowed from new WWTPs and accompanying nonpoint source discharges from associated new development must be offset by three kilograms of phosphorus reduction from elsewhere within the phosphorus-restricted basin.

The pilot program allows for the construction of up to three new surface-discharging WWTPs within the Croton watershed (totaling no more than 0.15 mgd) and up to three new or expanded surface-discharging WWTPs (0.10 mgd total) in the Catskill/Delaware watershed. Proposed WWTP discharges must lie outside the 60-day travel-time boundary and must be in basins that have committed to comprehensive water quality protection planning (such as the Croton Plan). If the pilot program successfully achieves water quality and regulatory goals, it will serve as the basis for establishing a permanent phosphorus offset program in the future.

A similar but separate program has been established to allow existing surface-discharging WWTPs in phosphorus-restricted basins to expand, given a 2:1 offset. This program does not place a limit on the number of participating WWTPs (NYC DEP, 1997d). In all cases, if it can be shown that a new or expanding WWTP can safely discharge its effluent to the subsurface, then it is not eligible for participation in either program.

Program Basis

The New York City phosphorus offset pilot program includes two of the trading mechanisms allowed by EPA: (1) point source/point source trading, in which an existing point source undertakes more stringent reductions than required and trades those credits to the new point source, and (2) point source/nonpoint source trading, in which the new point source arranges for stricter pollutant control from nonpoint sources. The responsible party for the new WWTP must identify appropriate offsets for the new phosphorus discharge. As described below, four important criteria must be satisfied by the proposed phosphorus offsets (NYC DEP, 1997c).

Surplus. Proposed offsets must be demonstrated as "surplus" before they can be included within the pilot program. NYC DEP guidance on the program has defined surplus as those phosphorus reductions that are "not otherwise required by federal, state, or local law" (NYC DEP, 1997c). Baseline, or minimum, requirements for phosphorus reductions that cannot count as surplus include (1) upgrades of existing WWTPs mandated by the MOA and (2) implementation of stormwater pollution prevention plans (SPPPs) for new developments larger than five acres and for new SPDES-permitted facilities. Reductions achieved by

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

retrofitting developed areas with effective stormwater quality controls can qualify as surplus. In addition, any phosphorus reductions achieved under the Catskill Fund for the Future and the Stormwater Retrofit Program can qualify as surplus offsets.

Quantifiable. An offset is quantifiable if a reasonable basis exists for calculating and verifying the amount of reduction in phosphorus. Models can be used to estimate phosphorus reductions, but these reductions must be verified through routine monitoring. Some methods for calculating quantifiable phosphorus reductions are provided in program guidance (NYC DEP, 1997c).

Permanent. An offset is permanent if the phosphorus reduction is ongoing and of unlimited duration. Adequate maintenance and routine inspections are required to ensure the permanence of offsets. A contingency plan must identify alternative measures to be taken if the existing offset mechanisms fail.

Enforceable. The offset must be incorporated into a legally valid and binding agreement to qualify as enforceable. At a minimum, the offsets must be incorporated into the SPDES permit for the new WWTP.

Offset Mechanisms

The following text describes offset mechanisms found in NYC DEP guidance. Program applicants are free to suggest additional mechanisms, which must be approved by NYC DEP.

Stormwater Best Management Practice Retrofits. Best management practices (BMPs) can be added to reduce phosphorus loadings associated with stormwater runoff from existing sites, particularly those that were initially developed without BMPs. Stormwater retrofits are structures, such as ponds and wetlands, that remove urban pollutants through sedimentation, adsorption, and biological methods (Claytor, 1996). When properly located, designed, constructed, and maintained, stormwater retrofits can be an effective element of a phosphorus-trading program.

Land Reclamation. Lands that generate significant phosphorus loads can be altered to a condition that reduces overall phosphorus generated on the site. An example of land reclamation would be to remove impervious surfaces and replace them with a vegetated landscape that would export less phosphorus.

Reductions of Phosphorus Discharge from Existing WWTPs. Phosphorus from existing WWTPs can be reduced in several ways. Plant retrofits can provide an offset if they reduce phosphorus discharges below the levels to be

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

achieved by City-funded upgrades of existing WWTPs (i.e., below 0.2 mg/L). Diversion of effluent flows from existing WWTPs outside of the City's water supply watershed can also provide offsets. Phosphorus reductions can be achieved by flow reductions of existing WWTPs, including complete elimination through facility closure. Finally, conversion of surface discharges from existing WWTPs to subsurface discharges, through a subsurface absorption field, can provide an offset. All WWTP flow reductions must be reflected in revised SPDES permits.

Removal of Septic Systems. Improperly functioning septic systems that contribute measurable amounts of phosphorus are generally subject to enforcement proceedings from a local health authority. For this reason, repair or replacement of such systems does not qualify as an offset. However, NYC DEP will allow the complete removal of improperly functioning and irreparable septic systems to qualify as an offset (Warne, 1999). In this case, the offset is determined by multiplying the volume flux (volume/day) of discharge from the septic system (based on the number of residents) by the phosphorus concentration in septic effluent (as determined by the New York State Department of Health).

Wetland Restoration. Restoration of degraded wetlands to reestablish stormwater runoff treatment functions can accomplish phosphorus reductions that qualify as surplus.

Offset Calculation Methodology

WWTP Phosphorus-Load Increase. The first step in calculating the appropriate offset is to determine the phosphorus load from the new WWTP. This load is calculated as the product of the maximum SPDES-permitted flow and the effluent limits for new WWTPs, or the flow increase and new effluent limits for WWTP expansions.

Nonpoint Source Phosphorus-Load Change. Associated changes in nonpoint source phosphorus loading that result from WWTP and all associated construction are then calculated. The incremental change in nonpoint source loadings is the difference between the phosphorus load generated under existing or predevelopment conditions and the phosphorus load generated under postdevelopment conditions. The guidance suggests the Simple Method (Schueler, 1987), the P8 Urban Catchment Model (EPA, 1997), or the Stormwater Management Model (EPA, 1997) to calculate nonpoint pollutant loads from development activities. The use of generalized runoff coefficients and pollutant loading coefficients developed from data collected in the Nationwide Urban Runoff Program (Schueler, 1987) is also recommended. If controls on nonpoint source runoff from the new development actually achieve a net decrease in

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

phosphorus loading over predevelopment conditions, this decrease can be applied as an offset.

Net Change in Phosphorus Load. The phosphorus loads attributed to the new WWTP and the associated nonpoint sources are combined. If nonpoint sources are projected to decrease, the nonpoint portion of the equation is set equal to zero, not less than zero.

Offset Requirement. To determine the offset requirement, the net increase in the phosphorus load from the new WWTP and associated nonpoint sources is multiplied by 3.

Offset Mechanism Reductions. The final step of the process is to calculate the phosphorus reductions to be achieved through the proposed offset mechanisms. The calculation of offset reductions for modifications of existing WWTPs is straightforward: the reduction in flow is multiplied by the effluent limit. For nonpoint source discharges, the guidance allows for "any reliable method to predict their removal rate" and provides a few examples (NYC DEP, 1997c). For stormwater BMP retrofits, the reduction in the phosphorus load is a function of the predevelopment loading rate and estimated BMP removal rates. For land reclamation and wetland restoration mechanisms, the reductions are calculated as the difference in loads generated by the land in its restored form versus the load generated in its current form.

Existing Applications for the Phosphorus Offset Pilot Program

As of April 10, 1999, three applications are being considered by NYC DEP for the pilot program. Each of these applications has undergone extensive revision in order to comply with the requirements of the program. The applications concern developments in Putnam County, within the Croton system, where development pressures are greatest. Although no applications from the Catskill/Delaware watershed have been received, it is expected that the town of Delhi in the Cannonsville basin may choose to participate in the near future.

NYC DEP has developed criteria for evaluating all applications (NYC DEP, 1998c). First, the proposed plan must have technical merit. The project must be adequately described, and the models used to calculate offsets must be valid. This includes all calculations of pre- and postdevelopment phosphorus loading. In addition, technical merit must be found in the monitoring plan, the quality assurance/quality control (QA/QC) plan, the contingency plan, and the inspection and maintenance plan. The other major criterion for each application is that the plan can be implemented. Finally, the application must help further the goals of the phosphorus offset pilot program. NYC DEP is particularly interested in projects in which credible efforts are made to monitor the offset mechanisms and

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

in which water quality changes will result from the construction of the WWTP and from the offset mechanisms. Box 8-6 describes one application currently under consideration by NYC DEP. For all the projects, the new source of phosphorus is a WWTP designed to treat wastewater from proposed new development. The phosphorus offset mechanisms include a variety of stormwater BMPs (e.g., wet ponds, compost filters, extended detention basins) and street sweeping. All the proposed mechanisms are claimed to achieve reductions in phosphorus loading that are at least three times the increase in loading attributable to the new WWTP.

The three applications appear to meet the eligibility requirements of the pilot program, and most have gained NYC DEP approval. However, the success of the proposed projects will depend almost entirely on the effectiveness and long-term reliability of the offset mechanisms. The analysis below suggests that many offset mechanisms will be difficult to monitor and that some cannot achieve the pollutant reductions claimed in the applications.

Analysis of the New York City Program

The committee has reviewed the phosphorus offset pilot program and provides recommended improvements to address concerns in several areas.

Ensuring that Reductions are Surplus

One of the most critical aspects of the offset program is ensuring that proposed offset mechanisms are actually surplus reductions. In order to make such assurances, baseline or minimum requirements for WWTP upgrades and SPPPs must be in place and operating effectively before offsets are identified and accepted. NYC DEP may need to develop criteria that will help determine whether baseline requirements are currently in place and operational, as none are specified in the current guidance materials.

Detailed recommendations for designing and implementing SPPPs are presented in Chapter 9, and should be considered for the phosphorus offset pilot program. In general, baseline stormwater practices, as required by SPPPs, must be permanent and well maintained. When reviewing program applications, NYC DEP must ensure that the reductions are not overstated because of insufficiently conservative assumptions. Because estimates of pre- and postdevelopment stormwater runoff loads are complex and rely on many assumptions, a careful review is required to ensure that proposed offsets are accurately quantified and that they qualify as surplus. The committee recommends that NYC DEP provide further explanatory language and more specific criteria to better define surplus. If possible, this definition should be flexible and receptive to changes and improvements in technology.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-6
Applicant for the Phosphorus Offset Pilot Program: Terravest Phase 3 - Highlands

This application was initially rejected because it proposed that the offset mechanism be subsurface discharge. This was controversial because in order for a WWTP to participate in the program, it has to be shown that subsurface discharge is not possible. NYC DEP has subsequently decided that subsurface discharge cannot be used as an offset mechanism, and the applicant has chosen a new offset mechanism.

New Phosphorus Load. After its initial application was turned down, the applicant proposed a second, smaller WWTP, the Highlands WWTP, to serve a retail center of 384,000 square feet. The anticipated phosphorus loading from the WWTP is 10.95 lbs/yr. The operator of the plant is confident that with a recycling system in place, the WWTP's phosphorus load can be reduced to 3.7 lbs/yr. This is because recycling will cut the effluent flow volume by two-thirds (from 36,000 gpd to 12,000 gpd) while maintaining the low phosphorus concentration of 0.1 mg/L. A SPDES permit for 0.1 mg/L has been requested. (The site had previously obtained a SPDES permit for 0.2 mg/L phosphorus.)

Offset Mechanisms. Predevelopment phosphorus loadings were calculated to be 45.1 lbs/yr, while postdevelopment loadings are 11.96 lbs/yr. These reductions in phosphorus loading are based on a series of stormwater BMPs. Two detention basins are expected to achieve 60 percent removal of phosphorus, while one extended detention basin is expected to achieve 40 percent phosphorus removal. Four additional water quality basins are also included and are credited with 60 percent phosphorus removal. Because the predevelopment loading is greater than postdevelopment loading (by 33.1 lbs/yr), this difference can be used as credit toward the required offset.

Required Offset. Assuming that recycling is used for the new WWTP, the required offset will be 3.7 × 3 = 11.1 lbs/yr. If recycling is not used, the required offset will be 32.85 lbs/yr (10.95 × 3). The phosphorus load reductions achieved with the stormwater control practices (33.1 lbs/yr) should be able to satisfy either offset requirement.

Contingency Plan. The contingency plan for the project lists eight options, three of which NYC DEP thinks are most promising: (1) chemically treating any malfunctioning detention basin until corrective measures restore the basin's functional capabilities, (2) creating another stormwater basin for short-and long-term use, and (3) pumping the effluent from stormwater basins back through a series of basins. The applicant must expand on these options before the project can commence.

Comprehensive Plan and Town Approval. Putnam County is in the process of preparing the required Croton Plan, and the town of Southeast has signed a letter approving the project.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
Appropriateness of Offset Mechanisms

NYC DEP guidance describes several offset mechanisms that can be used to achieve reductions in phosphorus loading. The committee has reviewed each mechanism and gives comments below, particularly for those mechanisms that require substantial improvement before they are able to provide the reliable, long-term protection needed for the program.

Stormwater BMP Retrofits. Stormwater retrofits can be an effective element of an overall watershed strategy to reduce phosphorus loads in stormwater runoff generated by existing urban development. Given the applications received by NYC DEP to date, they are the most popular mechanism chosen for achieving a phosphorus offset. However, the guidance document for the program (NYC DEP, 1997c) needs to be greatly strengthened in several areas to ensure that stormwater retrofits are effective.

  1. The guidance appears to permit the use of any urban nonpoint source practice as an eligible stormwater retrofit, such as might be found in the ''Urban/Stormwater Runoff Management Practices Catalogue for Nonpoint Source Pollution Prevention and Water Quality Protection" (NYS DEC, 1996). In fact, only four of the 43 urban nonpoint source practices that are summarized in the NYS DEC catalogue appear to meet the quantifiable and/or permanent removal criteria of the pilot program. Sufficient research is presently available only to quantify the expected phosphorus removal capability of ponds, wetlands, sand filters, and swales (Brown and Schueler, 1997). The phosphorus offset pilot program should restrict eligible stormwater retrofit BMPs to these four groups until further independent research indicates that other practices have quantifiable phosphorus removal capability. In practice, most stormwater retrofitting employs stormwater ponds and wetlands that can cost-effectively treat large catchment areas.

  2. The table of expected phosphorus removal rates provided in Appendix F of the guidance document for the phosphorus offset pilot program (NYC DEP, 1997c) is outdated and has been superseded by more recent data. Updated stormwater BMP removal rates are provided in MDE (1998).

  3. The sizing of stormwater retrofit BMPs is not explicitly addressed in the offset program. The guidance document bases the phosphorus credit solely on the presumed pollutant removal capability of the stormwater retrofit that is ultimately designed. It does not specifically require that the retrofit have an adequate storage or treatment volume to actually accomplish the desired removal. The computational methodology needs to be revised to ensure that the stormwater retrofit has a minimum stormwater treatment volume to accomplish the desired degree of pollutant removal.

  4. Program applications have assumed that BMP removal rates are constant for BMPs placed in series. (That is, if a BMP has a 40 percent removal rate, effluent pollutant concentrations will be decreased by 40 through each BMP

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

used.) However, removal efficiencies of individual BMPs generally decline when placed in series, based on the handful of performance research studies that have examined the issue (Gain, 1996; McCann and Olson, 1994; Oberts, 1997; Urbonas, 1994). Removal efficiencies vary in accordance with the changing composition of stormwater as it passes through multiple BMPs. For example, the first BMP may accomplish 50 percent removal of sediment and sediment-associated particles. But because larger particles are more effectively removed, subsequent BMPs will be treating stormwater enriched with finer particles, and removal efficiency will drop below 50 percent. At some point, the incremental removal is negligible, and the pollutant concentration from the final BMP reaches an irreducible concentration, which represents the maximum treatment limit for gravity-driven practices (Schueler, 1996). Upper bounds on the amount of pollutant removal from BMPs in series vary depending on the specific pollutant, but none approach 100 percent.

  1. Current stormwater treatment technology cannot reduce pollution loads to below predevelopment levels. In most cases, the asserted pollutant removal shown in stormwater offset applications is a result of computational methods that have no real basis in engineering or science (e.g., using BMPs in series, use of curve numbers rather than runoff coefficients, and over-sizing). Also, the committee is unaware of any field study that has actually documented that stormwater BMPs (or groups of BMPs) were actually able to reduce phosphorus loads to predevelopment levels for forest or meadow conditions. In a modeling study, Caraco et al. (1998) found that predevelopment nutrient loadings could not be achieved through any combination of better site design and stormwater BMPs.

  2. Although the Simple Method (Schueler, 1987) used to compute pre-and postdevelopment pollutant loads is a general model that has been widely used across the country, it is important to utilize regional data for phosphorus event mean concentrations (EMCs) and background loads. The guidance relies heavily on stormwater EMCs developed from the mid-Atlantic Region and also employs the annual background phosphorus load of 0.5 1bs/ac/year that was derived from a mix of rural land from the Chesapeake Bay region. Stormwater monitoring data have been collected to derive more accurate stormwater EMCs for the Catskill/Delaware region. Derivation of a regional background load should also be a priority, since a higher or lower regional background load will have a profound influence on the offset calculations.

  3. The current guidance requires that applicants consider several physical feasibility factors, but it does not address several feasibility factors that are unique to stormwater retrofitting. Examples include locational factors (e.g., are retrofits allowed within watershed setbacks? Within jurisdictional wetlands?), public acceptance factors (acceptance by adjacent landowners, potential habitat/restoration benefits, long-term maintenance capability), and watershed significance (minimum size or load reduced per retrofit). Implementation of stormwater retrofits in other regions of the country has generally been done in a watershed

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

context to ensure that retrofits not only meet phosphorus reduction targets, but also meet other restoration and community objectives. In addition, nearly all stormwater retrofits to date have been constructed on public lands and therefore require a much greater level of public involvement, agency coordination, and environmental permitting than is normally needed to construct BMPs to serve a new development (Claytor, 1996).

  1. Language in the current guidance should be added to ensure regular inspection of stormwater BMPs and long-term (beyond the first few years) maintenance of these facilities, even if they are designed correctly. The magnitude of institutional commitment, in terms of funding and trained staff, needed to achieve effective pollutant reduction will be high.

Land Reclamation. Land reclamation is a preferred offset mechanism because of its long-term nature, because of the ability to effectively quantify load reductions from this mechanism, and because of the direct water quality benefits. Land reclamation should be given high priority as an offset mechanism.

Reductions of Phosphorus Discharge from Existing WWTPs. This mechanism holds considerable potential because available treatment technologies can significantly reduce phosphorus concentrations. The following caveats should be considered:

  1. The diversion of phosphorus effluent to other watersheds must be carefully evaluated to ensure that the applicant is not transferring phosphorus problems to another area.

  2. Reductions in flow at existing facilities must also be accompanied by overall reductions in phosphorus loadings (e.g., no increases in phosphorus concentrations) in order to be protective.

  3. The transfer of discharges from the surface to subsurface should not be allowed as an offset since groundwater may also be a source of phosphorus to down-gradient surface waters.

Repair/Replacement of Improperly Functioning Septic Systems. As stated in NYC DEP guidance material, repair or replacement of improperly functioning septic systems is not allowed as an offset mechanism because these units are subject to enforcement proceedings by the local health authority. However, complete removal of failing septic systems is an option.

In the committee's opinion, the complete removal of failing septic systems is not an acceptable offset mechanism for the program. First, it goes against the idea that baseline treatment requirements should be met prior to identifying offsets. Septic systems should first be rehabilitated to use best available control technology (BACT), and suggestions for doing so are given in Chapter 11. Second, complete removal of septic system may have the unintended consequence of converting the watershed population to more expensive central sewerage

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

systems. Such shifts in infrastructure use often precede increases in development and population. Finally, the incremental phosphorus load reduction to be gained from individual septic systems is small. The phosphorus offset pilot program should focus on more effective and substantial offset mechanisms.

Wetland Restoration. The microbiota and higher aquatic plants of wetlands and littoral areas can function effectively to sequester phosphorus from runoff if they are designed and maintained specifically for that purpose. Thus, wetlands used effectively as stormwater BMPs are constructed, rather than restored. Constructed wetlands generally require large land areas and special design enhancements to achieve significant phosphorus removal (EPA, 1993a; Knight et al., 1995; Reed et al., 1995). Although not stated in NYC DEP guidance material, constructed wetlands are an acceptable offset mechanism for the pilot program (Warne, 1999), which the committee supports.

Restored wetlands are generally less amenable to specific design criteria and are usually ineffective in long-term net phosphorus removal. They may even increase phosphorus loadings under certain hydrologic conditions. Their effectiveness fluctuates seasonally, with more phosphorus removal being observed during the warmer growing season. Restoration of wetlands to treat stormwater could have associated regulatory and permitting requirements, as they are likely to be considered waters of the United States, which would require CWA certification and a Section 404 permit for any modifications. Finally, it is important to note that using natural or restored wetlands to treat stormwater runoff can result in long-term adverse effects on natural wetland functions (Azous et al., 1997; Kadlec and Knight, 1996; Richter and Azous, 1995).

Quantification of Offsets and Assessing the Impact of the Program on Water Quality

For all the offset mechanisms allowed under the program, there must be sufficient techniques to monitor their performance and demonstrate compliance. The collection and analysis of performance monitoring data provide the only sure method for assessing the impact of the program on long-term reservoir water quality. In particular, monitoring should be designed to take the cumulative impacts of various offsets and of development within the watersheds into account.

The establishment of a reliable, long-term monitoring program is probably the most challenging aspect of the New York City pilot phosphorus offset program. NYC DEP allows for the application of models to estimate phosphorus removals, but these estimates must be confirmed with actual data. A brief overview and analysis of monitoring requirements is presented below for stormwater runoff controls (stormwater BMP retrofits, land reclamation, and wetland restoration) and wastewater controls (WWTPs and septic systems).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Stormwater Runoff Controls. Phosphorus load reductions associated with stormwater runoff controls are a function of two factors: (1) storm flow volume and (2) removal effectiveness or percent reduction in concentration. For BMP facilities, data on phosphorus concentrations in the inflow and outflow should be collected during and shortly after storm events using paired flow-compositing automated samplers. Performance monitoring for phosphorus removal should be conducted for a minimum of ten storm events per year to adequately characterize the range of storm conditions. In addition, flow data should be collected over the entire year to estimate the total storm flow and baseflow volume. BMP effectiveness may change over time, depending on storm size, level of BMP maintenance, age of facility, influent concentrations, and conditions in the contributing watershed. To confirm continued removal effectiveness, it is recommended that estimates of load reduction be reviewed periodically (i.e., every 5-7 years).

The above recommendations on stormwater BMP monitoring also hold for wetlands and land reclamation with the following caveats. Because wetlands are not effective in reducing phosphorus during base flow conditions, it may be appropriate to incorporate only storm flow volumes in estimates of annual load reductions for wetlands. To estimate phosphorus removal benefits associated with land reclamation, information on event mean concentrations and runoff coefficients before and after reclamation is required.

Point Source Controls. Documenting pollutant load reductions from point sources such as WWTPs is relatively easy, and such documentation should be captured during regular SPDES monitoring. Septic systems are much more difficult to monitor. For this reason (and for those reasons mentioned previously), septic systems should not be used to provide offsets.

Offset Ratios

A trading ratio specifies how many units of pollutant reduction a source must achieve to receive credit for one unit of load reduction (EPA, 1996). A trading ratio of 1:1 indicates an equal exchange between sources. Typically, trading ratios exceed 1:1 to provide a margin of safety in the event that traded reductions are less effective than expected. Higher trading ratios can also reflect a net reduction strategy, although this is not a stated goal of the New York City pilot phosphorus offset program.

Establishing a scientific basis for trading ratios is an important component of any credible trading program. Unfortunately, detailed guidance for developing ratios is extremely limited to date. The 3:1 and 2:1 ratios found in the New York City program were chosen after negotiations among government agencies (S. Amron, NYC DEP, personal communication, 1998; D. Warne, NYC DEP, personal communication, 1999). The ratios apply to all program applicants, regardless of the nature of the trade and the proposed offset mechanism. The following

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

cursory evaluation of the New York City ratio is based on information available from trading programs in Colorado (see Box 8-7), Minnesota, and Massachusetts.

The New York City ratio of 3:1 for new WWTPs is among the largest ratios found among the four state programs. The Cherry Creek Basin program (Box 8-7), which more explicitly discusses the types of uncertainty that should be considered when setting trading ratios, has developed ratios between 1.5:1 and 3:1 (Paulson, 1997). The ratio being used in Minnesota seems to be a 1:1 ratio, while that in Massachusetts is 3:1. Thus, at first glance, it appears that the New York City ratio may be sufficiently protective. However, because the scientific basis of the trading ratio is not stated, its protectiveness cannot be adequately evaluated by such a simple comparison.

The Cherry Creek Basin program justifies its trading ratio as providing a safety margin against several relevant uncertainties, including variability in phosphorus loading and BMP performance, uncertainties associated with laboratory analysis and data evaluation, and institutional uncertainties. All these uncertainties exist in the New York City phosphorus offset pilot program as well. In addition, there are several specific scientific uncertainties in the New York City watershed that must be taken into account. These issues, which are not mentioned in the program's guidance material, suggest that the 3:1 ratio may not be sufficiently protective of water quality.

First, the New York City program does not make a distinction between the forms of phosphorus that are used to acquire offsets. Generally, phosphorus discharged from WWTPs is in a soluble, reactive form. Phosphorus removed by many of the proposed offset mechanisms, particularly stormwater runoff controls, is predominantly particulate in form. A shift in the existing balance of phosphorus toward a larger soluble fraction could have significant implications for downstream reservoirs, such as higher concentrations in the water column and enhanced algal growth. This could in turn aggravate eutrophication problems in these already phosphorus-restricted basins. Monitoring of the soluble fraction of total phosphorus concentrations, both in reservoirs and tributary streams, is recommended before and after proposed offsets to track this possible outcome.

The second consideration is spatial—the location of the proposed offset versus the location of the proposed WWTP discharge. Natural losses of phosphorus released to a stream would be expected to occur, at varying levels, with transport to a downstream reservoir. The closer a WWTP is located to a downstream reservoir, the less time for potential retention en route. Unfortunately, no distinctions in the trading ratio are made for new WWTPs built closer to, or further from, terminal reservoirs, nor are relative locations of the WWTP and the proposed offsets discussed. A related issue is that diffuse sources of phosphorus experience more opportunities for phosphorus retention than single-point sources of equivalent concentration. In order to demonstrate that point source and nonpoint sources are spatially "equivalent," a proposed offset should be located

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-7
Trading Ratios in the Cherry Creek Basin, Colorado

Trading ratios in the Cherry Creek Basin program have been developed primarily to reflect uncertainty associated with specific phosphorus removal facilities. The ratios do not reflect a net reduction strategy. The Cherry Creek Basin trading ratios incorporate two aspects of uncertainty associated with the trading program—scientific and institutional. The ratios are facility-specific and range from about 1.5:1 to 3:1.

In the Cherry Creek Basin program, scientific uncertainty stems from the variability in phosphorus load reductions that occurs from one year to another as well as from uncertainty in the estimate of reductions. A variability factor accounts for annual variations in load reductions, and is a function of both flow volume and removal effectiveness (i.e., concentration reduction). The variability factor is based on the relationship between the 95th and 50th percentile estimates of load reduction to ensure that the load reductions could be expected to occur 95 percent of the time. In addition, a best professional judgment (BPJ) factor is applied to account for the degree of uncertainty in the estimate. For example, if data on a given facility were limited, it would have a higher BPJ factor than if the facility had extensive site-specific data. The ratio associated with scientific uncertainty for a given facility is the product of the variability and BPJ factors [e.g., scientific uncertainty = (variability factor)(BPJ factor)].

Institutional uncertainty is a function of the entity responsible for implementation of the trading program and the degree to which the trades are documented and enforceable. Institutional uncertainty will be low if the entities responsible for the trading program are permanent and well established. In the Cherry Creek Basin program, the ratio associated with institutional uncertainty was set equal to 1:1, meaning that no institutional instability could adversely influence the continued effectiveness of the trades over the long term.

For most programs, a number of factors can determine the level of institutional uncertainty. These include finances, staffing, and general administrative stability, all of which play important roles in the regular functioning of any program. For example, a trading program needs some capacity for monitoring, verification, and enforcement of trading arrangements. Institutional uncertainty is lowest if trading programs have clearly defined tasks, unambiguous assignment of responsibilities, qualified personnel, and regular funding linked to performance of program activities. Conversely, institutional uncertainty rises when no clear lines of responsibility and authority are identified, personnel are appointed informally, and funding decisions are politically motivated.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

within proximity of a proposed WWTP discharge or at some point further downstream toward the reservoir.

Finally, there are temporal considerations that must be reflected in the trading ratio. It is likely that reductions in phosphorus as a result of the offset mechanisms may not coincide with WWTP discharges of phosphorus. Phosphorus associated with stormwater runoff occurs intermittently, with storm events. In contrast, wastewater discharges are more consistent. Also, there is considerable seasonal variability in the performance of BMPs (especially wetlands). For a downstream reservoir with a relatively long residence time (i.e., longer than one year), temporal differences in offsets are of less consequence. The average residence times of the New York City reservoirs suggest that temporal fluctuations may be significant.

Integration of Offset Program with TMDL Program

EPA has recognized that trades should occur in the context of a TMDL or SPDES permit to help meet water quality requirements more cost-effectively. As such, the New York City program requires all offsets to be reflected in revised SPDES permits for involved WWTPs. The TMDL program provides another opportunity for consolidating monitoring efforts and ensuring the protectiveness of the pilot phosphorus offset program. Phosphorus TMDLs are expressed in terms of allowable annual loads that are allocated among several components: point sources, nonpoint sources, future growth, and a safety factor. Phosphorus offsets, along with allowed increases in point source discharges, should be incorporated into the wasteload and load allocations and/or the control strategy of a TMDL.

Economic Considerations

The attractiveness of the phosphorus offset program is that it allows increases in some sources of pollution to be offset by reductions in other sources. The immediate intention is to allow increased urbanization within phosphorus-restricted basins by allowing growth in WWTP capacity, provided that phosphorus reductions are realized elsewhere within the basin. Because offset programs typically require a more-than-proportional reduction for an increase in discharge of the pollutant, the quality of the water in targeted waterbodies can be maintained while accommodating demands for economic development within the watershed.

It should be kept in mind that the New York City program is not a "market-based" trading program and will not necessarily result in the greatest pollutant reduction per dollar. The BMPs that are chosen as offsets are determined more by the applicant's familiarity with operating and monitoring them and the potential pollutant reduction abilities of the BMPs rather than their cost-effectiveness.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

There is the possibility that offset programs may be inappropriately relied upon to achieve water quality goals. It is important that they do not become substitutes for effective regulatory and environmental management actions by local government, which may want to shift the costs of environmental cleanup to elements of the private sector as opposed to carrying out discharge reductions itself or requiring existing pollutant discharges to change their practices.

A final economic consideration for the phosphorus offset pilot program is whether offset mechanisms can be identified. In the Cannonsville watershed (which is the only eligible West-of-Hudson watershed), interest in the program has been low because of an inability to identify surplus phosphorus and appropriate offset mechanisms and because of limited demand for additional WWTPs. Agricultural BMPs implemented as part of the Watershed Agricultural Program cannot be used as offsets, although BMPs constructed outside the program are allowed. In the absence of identified offsets, the trading program is likely to remain untested in the Catskill/Delaware watershed during its five-year timeframe. This would leave the program unprepared for future full-scale implementation.

Conclusions and Recommendations

The phosphorus offset pilot program as currently formulated contains significant weaknesses that prevent the committee from endorsing it fully. However, improvements in the existing program can be achieved by addressing a few key areas. These recommendations should be incorporated into the program before it is expanded to full scale.

  1. Baseline minimum requirements for phosphorus reduction must be in place and operating effectively before additional reductions can be defined as surplus. This refers to such activities as all planned upgrades to WWTPs that will reduce phosphorus loadings and to phosphorus reduction mechanisms that are part of an SPPP, among others. NYC DEP should develop clear criteria to determine whether baseline requirements are in use and operational and to further define surplus reductions.

  2. NYC DEP should update its guidance on the use of stormwater retrofits to achieve offsets, as the stormwater retrofits currently allowed under the program are unreliable and scientifically indefensible.

  • Specifically, the program should restrict eligible stormwater retrofit BMPs to ponds, wetlands, sand filters, and swales until further independent research indicates that other practices have quantifiable phosphorus removal capability;

  • the methodology for calculating the phosphorus load reduction must ensure that a stormwater retrofit uses the minimum stormwater treatment volume required to accomplish the desired degree of pollutant removal;

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
  • the pilot program should not give credit for reducing postdevelopment phosphorus loads to below predevelopment levels; and

  • the appendixes of the NYC DEP guidance document should be updated to provide more recent, region-specific estimates of pollutant loading coefficients and BMP removal effectiveness, to discuss the limitations in their application, and to discuss regular inspection and long-term maintenance of BMPs.

  1. Two offset mechanisms—transfer of WWTP discharges from the surface to the subsurface and removal of improperly functioning septic systems—are not adequate and should be dropped from the offset program. Subsurface discharge of phosphorus to groundwater is not acceptable because groundwater may be a source of phosphorus to down-gradient surface waters. NYC DEP has recognized this problem and is likely to alter its guidance document accordingly. Removal of septic systems is inappropriate as an offset because monitoring of this mechanism is difficult and because the baseline requirement should include effectively operating septic systems.

  2. NYC DEP should reevaluate the 3:1 and 2:1 ratios and develop a technical basis for the ratios that reflects the unique conditions associated with specific proposed offset mechanisms. The offset ratios of 3:1 and 2:1 currently have neither scientific basis nor explanatory justification. In addition to providing a safety margin for BMP performance variability, erroneous data collection, and institutional uncertainty, the offset ratio should reflect conditions present in the New York City watershed such as the spatial and temporal variability of offset mechanisms, the relative locations of the offset mechanisms and the WWTPs, and the different forms of phosphorus produced in the effluents of WWTPs and the offset mechanisms. Because the ratios do not explicitly take these issues into consideration, they are likely to be underprotective.

  3. There is no evidence that the phosphorus offset pilot program will result in a net reduction in phosphorus loading to the water supply reservoirs, because the offset ratios do not currently incorporate an additional factor to provide for net reductions in phosphorus. If this becomes a goal of the phosphorus offset pilot program, the offset ratio should be made more conservative.

  4. NYC DEP must develop performance monitoring to document offset mechanism effectiveness and overall net effects on downstream reservoirs. NYC DEP guidance material describes the elements of such a monitoring program, but puts the burden of monitoring entirely on the program applicant. Monitoring and maintenance of BMPs often suffer in the absence of an enforcement presence or when accountability is unclear. Because program applicants generally do not have the needed equipment and technical expertise, and are not respon-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

sible for overall watershed health, NYC DEP should assist and supplement the monitoring efforts of the program applicants.

  1. Phosphorus offsets, along with allowed increases in any point source discharges, should be incorporated into the wasteload and load allocations that have been developed as part of the TMDL program.

  2. NYC DEP should establish a comprehensive set of criteria to systematically evaluate the effectiveness of the phosphorus offset pilot program after five years. Criteria for program evaluation might include (1) reduction in phosphorus loadings directly resulting from the BMPs implemented, (2) relative effectiveness of the different BMPs implemented, (3) the adequacy of the 3:1 offset ratio in achieving net phosphorus reductions, and (4) technical adequacy of local planning to support the program.

ANTIDEGRADATION

Unlike the other three programs that form the core of this chapter, antidegradation is a watershed management policy that is not directly part of the MOA. As described in detail in Chapter 3, antidegradation is a federal regulation related to the CWA stating that waterbodies must not be allowed to degrade in quality. The implementation and enforcement of this policy at the state level is highly variable, with some states creating a separate antidegradation program, while others use existing environmental programs to comply with federal requirements. In New York State, there has been considerable interest in updating antidegradation policy to explicitly protect the water quality of the New York City reservoirs (Izeman, 1998). This section compares the antidegradation policy of New York to other states, assesses its compliance with federal guidelines, and makes recommendations regarding implementation and enforcement of antidegradation that will positively impact the New York City reservoirs.

Federal Antidegradation Policy

As set forth in federal regulations, antidegradation dictates that waterbodies cannot be allowed to sustain pollutant loadings that will prevent them from meeting their specific use classification and associated water quality criteria. It is considered one of the three points to the ''Clean Water Act triangle," along with waterbody use classifications and water quality criteria (EPA, 1994). Although antidegradation has been used for many purposes and supports a wide variety of regulatory activities, its most important role is to describe the necessary steps that must be taken when additional pollutant loading is proposed that would eliminate part or all of a waterbody's assimilative capacity (R. Shippen, EPA, personal communication, 1998).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

States are required to develop and adopt antidegradation policies that mirror the EPA policy. As described in Chapter 3, state policy must define Tier 1 waters (quality below fishable/swimmable), Tier 2 waters (fishable and swimmable), and Tier 3 waters (outstanding natural resources) and discuss whether and how their assimilative capacity can be used. When deciding whether to approve new discharges into their waterbodies, the states are required to conduct an "antidegradation review" that will weigh economic, social, and public concerns and suggest alternatives to the proposed activities.

State Antidegradation Policies

All states have submitted antidegradation policies to EPA, and a wide range of effort is apparent. Some states such as Pennsylvania have devised an elaborate antidegradation review process; others, including New York, have made minimal efforts to establish any oversight activities unique to an antidegradation program. One reason for these disparities is that detailed guidance from EPA on when and how to conduct antidegradation reviews has been lacking. Some states have developed more comprehensive policies in response to legal challenges from environmental advocacy organizations. Common concerns from environmental organizations are that state antidegradation policy (1) does not define a distinct antidegradation review that goes beyond current regulatory processes, (2) does not assure the highest statutory and regulatory requirements for all new and existing point sources, and (3) does not assure that cost-effective and reasonable best management practices to control nonpoint sources will be used.

EPA recently contracted with consultants to compare the antidegradation policies of 26 states, including New York (Cadmus Group, 1998). The study considered how each state has interpreted the three tiers of the EPA guidance and related them to their existing use classifications and water quality criteria. This report (summarized in Box 8-8) illuminates very interesting and important strategies regarding state implementation that are discussed below.

The Cadmus study reveals important trends in state antidegradation policy. First, states have focused antidegradation almost exclusively on point sources because of the ease in accounting for their pollutant contributions. In addition, antidegradation is generally applied to new and expanding point sources rather than being applied retroactively to existing point sources. Very few activities that cause nonpoint source pollution have been subject to an antidegradation review.

Tier 2 waters were identified in Chapter 3 as being the most controversial because they have assimilative capacity. For this reason, federal regulations require discharges into tier 2 waters to be supported by considerations of economic and social benefits and proposed alternatives. Table 8-3 shows that the criteria for determining social and economic benefits of a discharge vary from state to state and are extremely vague. Another important subtlety regarding

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 8-8
Review of State Antidegradation Policies

Following a request from EPA, 26 state antidegradation policies were compared. The study evaluated how the states classify waters into tiers 1, 2, and 3 and how discharges into those waters are regulated via an antidegradation review.

Tier 1

In tier 1 waters, existing uses—and water quality to protect those uses—must be maintained and protected. These waters are usually not fishable/swimmable for any or all parameters. The states have taken one of two general approaches to tier 1 waters:

  1. Do not specifically assign any waters to tier 1, and simply state that all waters are protected for their existing uses (20 states). Because most states do assign waters to tiers 2 and 3, this means that, by default, all other waters are in tier 1. Fishable/swimmable waters can be assigned to tier 1 if they have no assimilative capacity.

  2. Specifically assign waters to tier 1 (6 states). This has been accomplished in one of two ways: the waterbody approach and the parameter approach. In the waterbody approach, the tier 1 classification is assigned to the entire body of water without considering the concentrations of individual parameters. Antidegradation is implemented by making sure that water quality criteria in these waters are not violated. For parameters of higher quality than the applicable criterion, these parameters can be degraded to the criterion without an antidegradation review. Thus, assimilative capacity is not protected.

In the parameter approach, certain water quality parameters are assigned to tier 1 and others to tier 2. Tier 2 parameters have assimilative capacity; the tier 1 parameters do not. Here, even when states have use classifications, they do not coincide directly with antidegradation tiers. Antidegradation is implemented by conducting an antidegradation review for those parameters that have assimilative capacity. For those that do not, antidegradation is implemented by making sure that water quality criteria for those parameters are not violated. Massachusetts is an example of a state that uses the parameter approach.

Tier 2

For fishable/swimmable waters, assimilative capacity cannot be used without an antidegradation review that assesses the economic and social impacts of the discharge. In addition, the state should consider whether alternatives to the discharge exist. Most states specifically assign waters to tier 2 using the same two approaches mentioned for tier 1. That is,

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

under the waterbody approach, all parameters must meet or exceed the criteria for fishable/swimmable for a body of water to be assigned to tier 2. Under the parameter approach, if any parameter is above its criterion for fishable/swimmable, then its assimilative capacity is protected, even if the whole body of water is not fishable/swimmable because of other parameters.

Some states have introduced "extra" conditions that must be met for a water to be classified as tier 2. This appears to be an effort on the part of some states to avoid classifying waterbodies as tier 2 (which would necessitate time-consuming antidegradation reviews and place limits on development). For example, Colorado's definition of a tier 2 water is more stringent than simply having fishable/swimmable quality, thereby allowing 43 percent of Colorado waters to be tier 1. Florida has no tier 2 waters whatsoever.

Tier 2 waters are protected by conducting an antidegradation review that analyzes the social and economic benefits of a discharge that would use some of the assimilative capacity of a body of water. The criteria for determining the social and economic benefits of a discharge vary from state to state and are extremely vague. Of the 26 states included in the study, 21 have statements regarding economic and social benefits that provide some guidance (see Table 8-3).

To refine the antidegradation process, only those discharges that are judged to be "significant" undergo an antidegradation review. The states have developed three different approaches for deciding when a discharge is significant: (1) defined numerical values for the percent assimilative capacity used (11 states), (2) qualitative descriptions of the percent assimilative capacity used, or (3) there are no criteria and cases are judged individually.

Finally, some tier 2 waters receive protection beyond that of justifying social and economic benefits of a discharge. In North Carolina and Pennsylvania, discharges into tier 2 waters must be pretreated with best available technologies. Ohio, Oklahoma, and North Carolina have multiple tier 2 levels with increasingly strict requirements.

Tier 3

The federal antidegradation policy states that water quality shall be maintained in outstanding national resources. Many states have not used this terminology, but do have a category of water that corresponds to tier 3. Although EPA envisioned only one category of tier 3 waters where no discharges would ever be allowed, the states have developed four basic categories of protection for tier 3 waters:

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
  1. No discharges allowed.

  2. Discharges allowed only if they meet some special condition and do not lower water quality.

  3. No lowering of water quality allowed.

  4. Lowering of water quality allowed in some circumstances.

In reviewing state antidegradation policies, EPA has generally not considered the fourth category to be tier 3. Rather, waters falling into that category are termed tier 2.5. Categories 2 and 3 are also somewhat controversial, but in most cases, EPA has not yet made a final determination as to whether they qualify as tier 3.

In determining whether a discharge will "lower" a water's quality, some states require that the discharge meet "background" pollutant concentrations that currently exist in the water, while others insist that only pure water can be discharged.

Stormwater is a type of discharge that has traditionally been exempt from antidegradation polices. Most states do not consider stormwater inputs into tier 3 waters to be a violation of antidegradation. However, in Massachusetts, stormwater discharges into tier 3 waters are prohibited. Connecticut only allows stormwater discharge to tier 3 waters after significant pretreatment has occurred. These actions likely limit development around tier 3 waters.

A final consideration for tier 3 waters is whether drawdown of these waters is lowering water quality. If so, the states may want to consider allowing discharges into tier 3 waters to maintain water quantity. Arizona is the first state that has addressed this issue.

Additional Complexities

There is an interesting tradeoff between water quality criteria and antidegradation. If water quality criteria are very strict, then there will likely be no assimilative capacity to deal with in an antidegradation review (as is the case in Virginia). This must be taken into consideration when evaluating individual state policies on antidegradation. In states with strict water quality criteria, antidegradation may prove to be of little value.

In a related matter, some of the states surveyed have a particular drinking water use classification that specifically prohibits discharges into these waters (e.g., Massachusetts and Connecticut). These use classifications have been highly effective in preventing new development around these waters and are more protective than a tier 2 antidegradation review would be.

Source: Adapted from The Cadmus Group (1998).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 8-3 State Economic and Social Benefits Analysis

Arizona

There are five categories of social benefit that a proposal must discuss, including improved community tax base and employment benefits.

California

Social or economic benefit is determined on a case-by-case basis. State guidance suggests that the community's baseline socioeconomic profile be compared to the projected profile that would exist after the discharge is in place.

Colorado

Submitted evidence is evaluated to determine whether a proposed discharger demonstrates important social and economic development for the area that would be affected by the discharge.

Connecticut

A discharger must demonstrate that it will produce overriding economic and social benefits to the state. Such evaluations rarely occur.

Delaware

Social or economic benefit is determined on a case-by-case basis.

Florida

The state does not apply a tier 2-equivalent test of economic or social benefits.

Maine

Examples of social or economic benefits include increased employment, increased production, improved tax base, correction of an environmental or public health problem, pollution prevention, and increased conservation of energy and natural resources.

Massachusetts

Examples of social or economic benefits include new production by a discharger that cannot be accommodated by existing treatment or permit limits, and increased loading to a publicly owned treatment works because of community growth that cannot be accommodated by existing treatment facilities.

Montana

The applicant must demonstrate that important economic or social development spurred by the activity outweighs the cost to society of allowing the proposed change in water quality. In determining whether a proposed activity is necessary, the department considers the economic, environmental, and technological feasibility.

Nebraska

A discharger must demonstrate that a proposed activity is as minimally polluting as reasonable and is beneficial to the surrounding community.

New Hampshire

A discharger must show a "preponderance of evidence" that the discharge provides a net social benefit. The benefits, in terms of new jobs or increased taxes, must be greater than increased infrastructure costs.

North Carolina

The state may request, from a local government affected by a discharge, documentation that the discharge is necessary for important economic and social development.

Ohio

Social or economic benefit is determined on a case-by-case basis by considering factors such as condition of the local economy, the number of potential jobs, expected tax revenues, and the projected overall impact on the community.

Oklahoma

Until recently, social or economic benefits were not justifiable reasons for allowing degradation. Little information on future evaluation procedures is available.

Pennsylvania

There is a social or economic benefits checklist. A net present value is assigned to both the proposed discharge and to one that causes no degradation. The net present value of the social or economic benefit must be greater than the associated cost for the discharge to be accepted.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Rhode Island

Few tier 2 social or economic benefit analyses have been performed.

Texas

The procedure does not refer to social or economic benefits.

Vermont

The project associated with a proposed discharge cannot produce substantial social or economic costs unless those costs are offset by equal or greater benefits of maintaining or improving water quality. The state must also find that the discharge is necessary to prevent substantial adverse economic and social impacts.

Virginia

There are five categories of social or economic benefits, including an increase in the number of jobs and an increase in tax revenues.

Wisconsin

There are seven categories of social or economic benefits, including increasing production level and avoiding employment reductions.

Wyoming

Formal evaluation of social or economic benefits through the Wyoming Continuing Planning Process has not yet taken place because new dischargers are encouraged to use zero-discharge techniques.

 

Source: The Cadmus Group, Inc. (1998). Reprinted, with permission from The Cadmus Group, 1998. ©1998 by The Cadmus Group.

discharges into tier 2 waters is that only those discharges that are judged to be "significant" undergo an antidegradation review. According to the Cadmus study, states have developed very different approaches for deciding when a discharge is significant. In some states, significance is defined as the use of a certain percentage of a water's assimilative capacity. In others, the judgment is entirely sitespecific

Finally, the study reveals that some states perceive antidegradation reviews as unnecessary and duplicative. For example, they argue that national and state permitting requirements imposed on point sources result in a level of protection as high as would be achieved under a tier 2 antidegradation review. The main drawback to this approach is that the concept of assimilative capacity may not be made apparent to interested stakeholders. Assimilative capacity of waters is not always considered during the NPDES permitting process, nor is the applicant necessarily required to seek less-polluting alternatives to the proposed activity, both of which are required by antidegradation policy.

Antidegradation in New York State

Antidegradation Policy

Although it is one of the states reviewed by the Cadmus Group study, New York is not specifically mentioned at any point in the report. This is likely to be

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

because the New York State policy is a minimal and simple restatement of a portion of the federal regulation:

"It is recognized that certain waters of New York State possess an existing quality which is better than the standards assigned thereto. The quality of these waters will be maintained unless the following provisions have been demonstrated to the satisfaction of the Commissioner of Environmental Conservation: (1) that allowing lower water quality is necessary to accommodate significant economic or social development in the affected areas; and (2) that water quality will be adequate to meet the existing usage of a waterbody when allowing a lowering of water quality.

Where waters are meeting higher uses or attaining quality higher than the current classification, the Department will use the SEQR process to assure that potential adverse environmental impacts are adequately mitigated and higher attained uses are protected.

In addition, the highest statutory and regulatory requirements for all new point sources and cost effective and reasonable best management practices for nonpoint sources shall be achieved: and the intergovernmental coordination and public participation provisions of New York's continuing planning process will be satisfied.

Water that does not meet the standards assigned thereto will be improved to meet such. The water uses and the level of water quality necessary to protect such uses shall be maintained and protected." (NYS DEC, 1985)

New York does not define the State's waters as tier 1,2, or 3 waters, although the classification system devised for measuring stream quality (i.e., AA, A, B, C, D) could be used to do so. For example, Class N and AA-S waters in New York are comparable to EPA's tier 3 waters (outstanding natural resources). Paralleling the federal mandate to protect tier 3 waters, Article 17, Title 17, of the New York Environmental Conservation Law prohibits discharges into waterbodies with those classifications. Classes A, A-S, AA, B, C, and D are all fishable/swimmable waters and could correspond to EPA tier 2 waters (although it might be useful to create multiple tier 2 categories to differentiate between the existing use classifications). There does not appear to be a New York State use classification equivalent to EPA's tier 1. Figure 8-4 shows the current use classifications of the New York City water supply reservoirs.

Implementation

New York relies on three existing regulatory programs to implement its antidegradation policy: (1) SPDES permitting, (2) reclassification of waters, and (3) the State Environmental Quality Review (SEQR) Act. There are also some state laws that contain protection clauses for certain named waters, waters classi-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 8-4 Use classifications of New York City reservoirs.

fied as AA-S or N, and waters in some agricultural and forest lands. However, none of the New York City reservoirs fall into these categories.

SPDES Permitting Process. As in many other states, the SPDES permitting process is used to help prevent degradation of waters by assessing the impact of nearby point source discharges. In New York, such discharges are not allowed to degrade water quality below the standards associated with a water's use classification. Depending on its complexity, the SPDES permitting process can be analogous to an antidegradation review for some types of discharges.

Reclassification of Waterbodies. Waterbodies can be reclassified sometime during the state's triennial water quality standards review process. An entire round of classifications generally takes ten years given the number of waters that must be assessed and the size of the NYS DEC staff. This process recently resulted in several waters moving from D to C and being afforded an extra level of protection from further degradation. Because reclassification does not deal

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

directly with new discharges, its use as an antidegradation tool is limited to the designation of waters as 1,2, or 3. It is not considered further in this analysis.

State Environmental Quality Review Act. The SEQR process, which is triggered when any State agency undertakes, approves, or funds actions with environmental consequences (such as permitting a WWTP), provides another level of antidegradation protection. SEQR requires that an environmental impact statement (EIS) be drawn up if it is determined that the activity will have a significant effect on the environment. SEQR is the only mechanism by which New York can implement its antidegradation policy for activities that cause nonpoint source pollution.

Analysis of New York State's Antidegradation Policy

NYS DEC currently argues that having a separate, distinct antidegradation review process is redundant because the SEQR process and the SPDES permitting process can accomplish the goals of maintaining high water quality (Cronin, 1997; N. G. Kaul, NYS DEC, personal communication, 1998). Most large-scale activities (such as business park construction) that produce both point and nonpoint source pollution will require review under SEQR. It is, however, possible that some small-scale activities will not trigger action under either regulatory program (N. G. Kaul, NYS DEC, personal communication, 1998).

Over the last 15 years, New York State has wavered on the issue of antidegradation. EPA, NYC DEP, and NYS DEC have irregularly noted that the State's policy and implementation procedures are deficient, although no action has been taken to correct the situation (EPA, 1988a,b, 1993b, 1994; NYS DEC, 1990, 1991). In fact, in 1993, a Proposed Antidegradation Review Process for New York State was abandoned (NYS DEC, 1993b). The only substantive action on antidegradation that has occurred in New York regards its participation in the drafting of an antidegradation policy for the Great Lakes Initiative (NYS DEC, 1997). However, this policy will only apply to watersheds feeding the Great Lakes.

In determining whether New York State's antidegradation policy is effective in fulfilling the intent of the CWA, many issues must be considered. These are discussed below, with particular reference to protecting water quality in the New York City drinking water reservoirs. When possible, the policies of other states are compared to that of New York for perspective.

Policy Document

As is evident from the previous discussion, New York's antidegradation policy is minimal in requirements, relying entirely on existing programs for implementation. This is in stark contrast to the lengthy procedures required

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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elsewhere, particularly Ohio and Pennsylvania. Thus, outward appearances indicate that New York is less focused on antidegradation than are other states. This position is likely to translate into a less effective policy because of the lack of public interest and stakeholder participation in the process (see below).

Potential Applicability

Antidegradation is most useful when water quality criteria are less strict and allow waterbodies to have assimilative capacity, as discussed in Box 8-8. As shown in Table 3-7 for a limited number of parameters, New York's water quality criteria are similar to those of other eastern states and are slightly more strict than western states. Thus, there are likely to be fewer tier 2 waterbodies in New York that might benefit from antidegradation than there are in western states. However, without an accurate estimate of the state's assimilative capacity, this conclusion must remain entirely speculative.

Do Existing State Regulations Effectively Implement Antidegradation?

The SEQR and SPDES permitting processes are used to implement antidegradation in New York State. An analysis of how these programs function and what they achieve should be the best indication of the effectiveness of New York's antidegradation policy. The most important considerations include (1) whether these programs assess the economic and social benefits of proposed activities, (2) whether they consider all relevant alternatives to the proposed project, (3) how they determine the significance of proposed activities, and (4) whether they consider the assimilative capacity of the receiving waterbody through a quantitative assessment of background conditions and the pollutant loading from proposed discharges.

SEQR. The State Environmental Quality Review Act (Article 8 of the Environmental Conservation Law) is New York's most powerful tool for protecting water quality from adverse environmental impacts. It applies to all activities that require government funding, approval, or action, with some notable exceptions (such as agricultural activities). Because the SEQR process is described in Box 3-5, only those portions relevant to antidegradation are discussed here.

The SEQR process requires that the social and economic benefits of a proposed activity be discussed in a draft environmental impact statement (EIS). Minimal guidance for what relevant social and economic benefits are can be found in the SEQR Handbook (NYS DEC, 1992). This guidance describes benefits as satisfying a ''need" or "perceived need" such as having a convenience store in the neighborhood or supplying water to an area that is being developed for residential housing. For the most part, the guidance is extremely limited regarding potential benefits, concentrating much more on what is not an accept-

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

able social or economic benefit. For example, the profitability of the proposed project is not considered to be an appropriate benefit for mention in the draft EIS. Compared to the specific social and economic benefits that are considered by other states during an antidegradation review (Table 8-3), the SEQR guidance document is considerably less comprehensive.

The draft EIS must consider all relevant alternatives to the proposed action. SEQR guidance material is very explicit about the range and types of reasonable alternatives, discussing the use of alternative locations, alternative technologies, actions of a different scale, alternative project designs, alternative timing, and completely different substitute actions. Most importantly, all draft EISs must contain a consideration of the no-action alternative.

Determining the environmental significance of a proposed activity takes place early in the SEQR process. For those activities classified as Type I, the environmental assessment form is used to make an initial determination of significance. SEQR guidance stresses the importance of two factors: magnitude of the impact and importance of the impact in relation to its setting. The cumulative impact of multiple actions and long-term effects must be considered. Although a "substantial adverse change in existing water quality" is listed as an important criterion, SEQR does not define a particular percent change in assimilative capacity as significant, unlike 11 other states' antidegradation policies.

The use of the phrase "assimilative capacity" does not appear in the SEQR process, nor is there an explicit consideration of a waterbody's assimilative capacity. However, many of the provisions of SEQR imply that assimilative capacity is important, such as the determination of significance required in the environmental assessment form, and the description of the environmental setting and the consideration of the "no-action" alternative in the draft EIS. The guidance material associated with SEQR is general because it targets a wide variety of activities that go beyond those impacting water. As discussed below, the construction of new point sources, which almost always triggers review under SEQR, involves a more explicit consideration of assimilative capacity because of the additional oversight afforded by the SPDES permitting program.

SPDES Permitting Program. WWTPs that discharge to surface waters must obtain a SPDES permit. In addition, all WWTPs discharging greater than 1,000 gpd to the subsurface are required to have a SPDES permit. All applicants for a SPDES permit must undergo the initial steps of the SEQR process and submit an environmental assessment form. Thus, the SPDES permitting program and the SEQR review must be considered jointly when assessing New York State's antidegradation policy.

The SPDES permitting program does not require an explanation of the social and economic benefits of a proposed discharge above and beyond that required of a draft EIS. Thus, the SPDES permitting program satisfies this criterion of an antidegradation policy to the same extent as does SEQR. Similarly, because all

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

applicants for a SPDES permit must fill out an EAF, the environmental significance of all proposed point source discharges must be assessed.

The SPDES permitting program includes an explicit call for considering the assimilative capacity of receiving waterbodies. That is, for those plants that discharge into surface waterbodies, the SPDES program may require that applicants conduct a "waste assimilative capacity analysis." This analysis is very similar to the mathematical calculations done under the TMDL program to determine waste load allocations (WLAs) (NYS DEC, 1998). The waste assimilative capacity analysis helps determine whether a proposed point source discharge will cause a waterbody to violate water quality criteria. If so, it is then used to develop alternative waste load scenarios that will achieve water quality standards. NYS DEC has developed multiple guidance documents for calculating waste assimilative capacity under a variety of conditions.

SPDES permits are required to be renewed by the state every five years. However, because of the large number of point sources holding SPDES permits in New York and the limited staff available for conducting reviews, NYS DEC has devised a scheme to prioritize permits for renewal. Under the Environmental Benefit Permit Strategy, NYS DEC ranks all permits by considering the size of the discharge, the present water quality of the receiving water, the nature of the discharged pollutants, and the time since the last review (NYS DEC, 1992). At the time of renewal, the waste assimilative capacity analysis is recalculated and best available technologies are assessed for possible inclusion.

Other Criticism

In addition to comments on the use of the SEQR process and the SPDES permitting program for implementing antidegradation, some other comments about the New York State antidegradation policy are warranted. First, as noted by others (Izeman, 1998), the New York antidegradation policy does not adequately address tier 3 waters. No procedures for assigning waters to tier 3, or for determining what discharges are allowed into tier 3 waters, are given. As demonstrated by the wide variation observed among the states, how tier 3 waterbodies are defined takes on great importance. Second, the antidegradation policy is not referenced in the State's water quality standards, nor is it a part of the standards, as required by federal regulations. This omission, however, is not particularly damaging and would be relatively simple to correct.

Conclusions and Recommendations

  1. NYS DEC should define how tier 3 waterbodies are assigned, as the necessary criteria are currently not stated. This definition may have a significant impact on the New York City drinking water reservoirs if their use classification and water quality criteria are sufficiently high to allow them to qualify for tier 3 status.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
  1. The SPDES permitting program and the SEQR process are adequate tools for implementing antidegradation, but both would benefit from minor changes. For the most part, these regulations take into account the reasonable alternatives to a proposed action, the social and economic benefits of a proposed action, and the significance of potential environmental impacts. The latter two issues require additional attention, as recommended below.

  2. NYS DEC should provide additional guidance on the types of economic and social benefits that should be part of draft environmental impact statements. Although limited information is available, the guidance material should be considerably more comprehensive.

  3. NYS DEC should better define what a significant lowering of water quality is in a tier 2 waterbody. That is, it should set a quantitative criterion for altering the assimilative capacity of a waterbody. Other state antidegradation programs suggest that a 5 percent to 25 percent change in a water's assimilative capacity is significant.

  4. An explicit consideration of a receiving water's assimilative capacity should be required as part of draft environmental impact statements. Consideration of assimilative capacity should be stated clearly to facilitate understanding by the public in written guidance documents, within draft EISs, and during public hearings. The stated purpose of antidegradation is for communities, regulators, and discharges to consider the assimilative capacity of waterbodies. However, this language is not part of federal regulations and, as a consequence, most state antidegradation policies do not require an explicit consideration of assimilative capacity. Although such a consideration is an integral part of the SPDES permitting program, it is less obvious during the SEQR process. Because SEQR is the only avenue for regulating nonpoint sources that will impact water quality, this requirement for addressing assimilative capacity is critical if the SEQR process is to be relied upon for implementing New York's antidegradation policy. Further guidance from EPA on how to implement antidegradation policy for nonpoint source activities should be taken into consideration as soon as it is made available.

ADDITIONAL TREATMENT OPTIONS

Dual-Track Approach

When EPA gave New York City its second conditional waiver from filtration in 1993, it required (in addition to various watershed management activities) a series of studies on filtration of the Catskill and Delaware systems, leading up to completion of conceptual and draft preliminary designs of a filtration plant.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Activities also included a study on alternative disinfectants that might be used in the absence of filtration. These activities have been carried out in parallel with all the other filtration avoidance determination watershed management activities. In 2002, EPA will decide (using the results of these studies) whether filtration or other treatment processes are needed for the Catskill/Delaware water supply.

Simultaneously carrying out watershed management and planning for filtration, a relatively new policy concept, has been dubbed the "dual-track approach" by EPA (Krudner, 1997). This approach, as applied to New York City, was designed to ensure that no time is lost if filtration is later determined to be necessary. Although not completely analogous, the dual-track approach is similar to the multiple-barrier approach to producing high-quality drinking water introduced in Chapter 4, provided that both tracks continue into the foreseeable future.

Filtration Plant for the Catskill/Delaware Water Supply

Phase I Pilot Plant Study

To determine optimal conditions for building a filtration plant for the Catskill/Delaware system, NYC DEP has recently completed a two-year pilot study. Several different treatment trains were investigated, including conventional treatment, ozone/direct filtration, and ozone/dissolved air flotation (DAF)/filtration. All the treatment trains contain ozonation followed by filtration, but some have additional clarification processes such as sedimentation or flotation. Phase I consisted of several different sources of water being tested in small, mobile treatment units comprised of these various treatment processes. Treatment goals were to inactivate 99 percent of Cryptosporidium oocysts, 99.9 percent of Giardia cysts, and 99.99 percent of viruses (via the combined action of ozonation and filtration). Goals were also set for chemical and physical parameters such as turbidity, DBPs, inorganic compounds, and taste and odor.

In order to provide flexibility in the potential siting of a filtration plant, water from several locations was tested during the pilot studies: (1) Shaft 18, effluent from the Kensico Reservoir, (2) Millwood, upstream from Kensico in the Catskill aqueduct, and (3) Shaft 17, upstream from Kensico in the Delaware aqueduct. Tested waters had a turbidity around 1–3 NTU, an average TOC of 1–3 mg/L, and source water particle concentrations between 4,500 and 8,000/mL in the 2–30 µm range (Hazen and Sawyer, 1996). No significant differences existed among the chosen water sources, except during one winter season when the Catskill aqueduct source had higher turbidity.

At Shaft 18 and Shaft 17, all three treatment trains produced low levels of turbidity (<0.1 NTU), particle counts(< 30/mL in the 5–15 micrometer range)1,

1  

 No information was provided for particle removal in the 2–30 µm size range.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

and total trihalomethanes (TTHMs) and the sum of five haloacetic acids (HAA5s) (less than 0.040 mg/L and 0.030 mg/L, respectively). During the season in which the Catskill aqueduct experienced higher turbidity, only DAF/filtration was effective in meeting established water quality goals at the Millford location during the entire year. As a result of Phase I, conventional treatment was eliminated from further consideration because of its high cost and its inability to reliably lower turbidity in the Catskill aqueduct water.

Phase II Pilot Plant Study

The objective of Phase II of the pilot plant study was to further test and optimize filtration technologies. In addition, consultants were hired to determine how many filtration plants would be necessary and to find a proper location for the treatment plant(s). These activities were conducted simultaneously in order to meet EPA deliverables. First, seven configurations for a treatment facility were designed that included from one to three plants located at several different points along the Catskill and Delaware aqueducts. The water demand was projected to be 1,700 mgd. Second, sites within the watershed region that were suitable for a treatment plant were identified. Of 577 initial locations, most were eliminated by taking into consideration such issues as distance from the aqueducts, acreage of land available, and vacancy of the land. Twelve (12) sites that could not be eliminated from consideration were then combined with the seven configurations to produce 25 treatment schemes. A weighted matrix analysis of the schemes was conducted, taking costs, acceptability, site considerations, flexibility and reliability, implementation, and water quality into account. The preferred treatment scheme consisted of one filtration plant at the Eastview location, which had been identified previously by NYC DEP as a potential site.

Eastview is located downstream from Kensico Reservoir and upstream from Hillview Reservoir. Its location would allow water from both the Catskill and Delaware aqueducts to be diverted into the filtration plant. The advantages of the Eastview location are that the appropriate aqueduct connections are possible, the use of Kensico as a settling basin can be maximized, and minimal pumping would be necessary.

DAF/filtration and direct filtration were tested further using water derived from sources downstream of Kensico that would be similar to Eastview water. The treatment requirements for the combined ozonation/filtration processes were made more stringent: 99.9 percent inactivation of Cryptosporidium, 99.9 percent inactivation of Giardia, and 99.99 percent inactivation of viruses. It was also required that finished water turbidity be less than 0.10 NTU 95 percent of the time. Ozone doses were chosen that would achieve a 1.5-log removal of oocysts, as determined by a literature review. Filtration was expected to achieve a 1.5-log removal of cysts and oocysts, and this was tested by determining percent removals of surrogate particles of many size ranges during filtration. Overall treatment

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

was optimized by varying the filtration rate (gallons per minute per square foot), the filter bed depth, the ozonation time and dose, the flocculation time, and the DAF rate (gpm/ft2).

Direct filtration achieved the expected 1.5-log removal of particles in the size range of Cryptosporidium (2–30 µm) (Hazen and Sawyer, 1998). The ozone dose was varied between 1.4 and 3 mg/L. FeCl3 was the primary coagulant, a cationic polymer was used (1.5 mg/L), and a filtration rate between 10 and 13 gpm/ft2 was found to be best. In this test, 84 inches of 1.5-mm anthracite were used for filter media. DAF/filtration was also successful in achieving at least a 1.5-log removal of Cryptosporidium-sized (2–30 µm) particles. Because DAF removes natural organic matter prior to ozonation, the required ozone dose was somewhat lower (between 0.75 and 2 mg/L). A filtration rate between 12 and 16 gpm/ft2 and 58 inches of 1.3-mm anthracite for filter media were found to be acceptable.

The engineering consultant has recommended, and NYC DEP has approved, one plant at the Eastview location using direct filtration (because of its lower cost) combined with pre-ozonation, as shown in Figure 8-5. The filtration rate would be 13 gpm/ft2 (10 gpm/ft2 in the winter), which would be unprecedented for the East Coast. Hillview Reservoir, the posttreatment storage facility, would need to be covered to protect the superior quality of the filtered water. Cost estimates for construction of the recommended plant range from $2–3 billion (Nickols, 1998) to $4 billion (J. Miele, NYC DEP, personal communication, 1999). A key to this low cost estimate is the use of Hillview as a storage reservoir so that the system does not have to be engineered to meet peak daily demands.

Disinfection Study

The filtration avoidance determination also includes a study of alternative disinfectants to assess their ability to render inactive Cryptosporidium oocysts in raw water from the Catskill/Delaware system. The motivation for such research was threefold. First, disinfection with chlorine is the primary chemical treatment received by Catskill/Delaware water, but there have been no previous attempts to

FIGURE 8-5 Proposed treatment train for direct filtration of the Catskill/Delaware water supply. Source: NYC DEP (1998d).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

demonstrate that chlorine is the most effective disinfectant. Second, if regulations for TTHMs and HAA5 in finished water are tightened, then the current reliance on chlorine could take Catskill/Delaware water out of compliance with the Safe Drinking Water Act (SDWA). Third, future regulations for Cryptosporidium log inactivation in water supply systems are likely; a system relying solely on chlorine, in the absence of filtration, would find itself illprepared to comply.

The first phase of an ongoing study of alternative disinfectants was recently completed (NYC DEP, 1998e). A major assumption was that the New York City water supply would continue to be of high enough quality to qualify for filtration avoidance. The study evaluated ozone, chlorine dioxide, and chlorine for their disinfecting abilities. However, no actual experiments were performed in which the inactivation of either indicator organisms or pathogens in water samples was measured. Rather, the literature was used to develop target CT (disinfectant concentration multiplied by contact time) values that corresponded to (1) 3-log Giardia inactivation and 4-log virus inactivation (the EPA requirement for unfiltered systems), (2) 1-log inactivation of Cryptosporidium, and (3) 2-log inactivation of Cryptosporidium. These CT values are given in Table 8-4. The suitability of disinfectants was determined solely by comparing the estimated CT values (measured in actual water samples) to the estimated requirements for inactivation of pathogens (gathered from the literature).

TABLE 8-4 Target CT Values for the Disinfection Study Developed from Multiple Literature Sources. CT values are in (mg/L)(min).

Disinfectant

Season (°C)

CT

3-log Giardia or 4-log virus

1-log Cryptosporidium

2-log Cryptosporidium

Ozone

November 1997 (13°)

1.1

6.5

13

 

March 1997 (7°)

1.9–1.5

8.5

16

 

July 1998 (19°)

0.8

5

10

Chlorine

November 1997 (13°)

86–100

1.4 × 106

 

 

March 1997 (5–9°)

139–182

 

 

 

July 1998 (19°)

52–68

3,000–4,000

6,000–8,000

Chlorine

November 1997 (13°)

28

 

 

Dioxide

March 1997 (5°)

33.4

60–80

120–160

 

July 1998 (20°)

15

30

40

 

Source: NYC DEP (1998e).

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

In order to determine achievable CT values for New York City water, decay rates were measured for ozone, chlorine, chlorine dioxide, and disinfectant combinations in water from the Kensico Reservoir Shaft 18 location. Three sets of tests were conducted, using water collected in November 1997 and in March and July 1998. Chlorine decay and chlorine dioxide decay profiles were generated using a variety of initial doses in batch systems. From this, the integrated CT value was computed (using a first-order decay model fit to the data) and was compared to the target levels shown in Table 8-4. Ozone decay experiments were conducted in a continuous-flow sparged pilot plant comprising five columns in series (with ozone application to the first column only). To obtain varying times, the pilot plant was run at different flow rates, and samples were obtained at multiple intermediate times within the ozonation train. Tracer studies were also conducted to obtain the T10 value (time of exit of the fastest 10 percent of the influent). The consultants then used the T10 values at each sampling location along with the observed ozone residual at each point to estimate an apparent "first order" decay rate.

The conclusions of the study are that the "CT goals were satisfied for all three conditions established…with reasonable ozone and chlorine dioxide doses and contact times. The applied ozone doses and the contact times used to meet the high CT goal were 1.5 mg/L and 21 minutes in the cold water (5°), and 1.7 mg/L at 25 minutes and 1.9 mg/L at 9 minutes in the warm water (19°). The chlorine dioxide doses and contact times used to meet the high CT goal were 1.0 mg/L at 240 minutes and 1.2 mg/L at approximately 200 minutes in the cold water (5–9°) and 1.7 mg/L at 30 minutes in the warm water (19°). Chlorine disinfection and sequential disinfection (ozone followed by chlorine) were not effective in meeting the established CT goals" (NYC DEP, 1998e).

Analysis

Use of Literature Review Data. The primary literature used to estimate Cryptosporidium CT values consisted of conference papers by Finch and colleagues, and details of the CT computations were not provided. The use of conference proceedings for CT values is questionable, particularly because there is recent published information on oocyst inactivation. In addition, the limited information on oocyst inactivation used for this study (in which all data were obtained on buffered, demand-free water) is apparently being used to compute a "best estimate" CT value, with no recognition of the uncertainty surrounding this estimate. The CT values computed by EPA ranged from 1.5 to 3 mg/L × min because of varying safety factors. Furthermore, recent work on oocyst inactivation indicates a considerable variability in ozone inactivation efficiency for Cryptosporidium (Oppenheimer et al., 1999), which may result in a large safety factor for regulatory purposes. Hence, the CT values for Cryptosporidium used

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

in this study may be not on a commensurate scale with the Giardia and viral CT values derived by EPA.

Decay Rate Experiments. The methodology used to analyze the ozone decay process is problematic. The use of a semilog plot to extract data from a reactor with backmixing is inappropriate, as it confounds the processes of hydrodynamic dispersion and reaction. Hence, the computed "CT" values achievable via this method are not entirely accurate. A more appropriate methodology to analyze the data should be employed (i.e., use of the full mathematical solution for a reactor with reaction and dispersion).

Use of Ozone. The committee questions the use of ozone for treating New York City's drinking water in the absence of other treatment processes. Although ozone is a powerful disinfectant for many microbial pathogens, it can react with dissolved organic matter to produce ketoacids, carboxylic acids, and aldehydes. The reaction of ozone with dissolved organic matter can also change largely refractory humic materials into biodegradable products that can support bacterial regrowth in the distribution system. (It should be noted that regrowth is much less apparent in ozonated systems that carry a distribution system residual provided by another disinfectant.) In addition, in the presence of bromide ion, ozone can lead to formation of bromate and bromine-substituted organic compounds. Because bromide levels were not measured in the disinfection study, the potential for bromate formation in the Catskill/Delaware water supply is currently unknown.

To avoid these problems, ozone should only be applied to water with the lowest possible organic content, and ozonation should be followed by a granular media step or secondary disinfection. (The results of using sequential ozone–chlorine disinfection are not encouraging, suggesting that other combinations of disinfectants should be investigated.) Granular media would provide filtration as well as a surface on which heterotrophic organisms can grow and degrade newly formed DBPs and other biodegradable matter. In the absence of these steps, ozonation is not recommended.

Conclusions and Recommendations

  1. The dual-track approach allows New York City to focus the bulk of its resources on improvements in the watershed. This initial focus will help establish a strong source water protection program without diverting attention and resources toward the details of a filtration plant. The pollution prevention achieved through watershed protection reduces influent pollutant concentrations that would be treated via filtration. If the source water protection program is effective, the cost of filtration can be reduced.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
  1. The results of the filtration pilot plant study show that the present New York City water supply can be effectively treated by ozonation combined with coagulation/filtration. Treated water from direct filtration had a turbidity of less than 0.1 NTU, average particle (2–30 µm) counts ranging from 8 to 153/mL, and total trihalomethane and total trihalomethane and haloacetic acid formation potential of less than 0.040 mg/L and 0.030 mg/L, respectively. At least 3-log oocyst inactivation/removal is expected for the entire treatment train. These low effluent pollutant concentrations from a potential filtration plant and dependent on maintaining high source water quality via aggressive watershed management. The construction cost of such a treatment facility ranges from $265 to $400 per capita.

  2. New York City should conduct studies on the actual inactivation of pathogens in its water under potential design conditions. In view of the potential effect of as yet unknown water quality factors on inactivation efficiency, and in view of the large potential investment that enhanced disinfection might require, it is not prudent to rely upon literature values for oocyst inactivation efficiency. These studies should be conducted using best available methodology for assessing cyst, oocyst, and virus viability and for virus viability and for susceptibility testing

  3. Additional studies to assess the potential of ozone as a treatment technique are required. Any consideration of ozonation should include measurements of bromide in the source waters to determine the potential for bromate formation. The literature to date suggests that ozone has the potential to increase biodegradable organic carbon in finished water and to foster regrowth of heterotrophic plate count organisms and possibly coliforms, although distribution system disinfectant residuals may counter this phenomenon. Without assurance that such regrowth would occur, it is imprudent to consider ozone as a sole treatment method.

  4. A decision to construct a filtration plant should in no way deter New York City from pursuing an aggressive watershed management program. If a coagulation/filtration plant is put in place, it should be treating the best-quality source water possible. For that reason, high water quality in the Catskill/Delaware system must be maintained via aggressive implementation of the watershed management strategy.

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

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Clean Water Report. 1998. Nation's first pollutant trading water permit approved by EPA Region I. Clean Water Report 36(23):224.

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

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NYC DEP. 1999a. Development of a water quality guidance value for Phase II Total Maximum Daily Loads (TMDLs) in the New York City Reservoirs. Valhalla, NY: NYC DEP.

NYC DEP. 1999b. Methodology for Calculating Phase II Total Maximum Daily Loads (TMDLs) of Phosphorus for New York City Drinking Water Reservoirs. March 1999. Valhalla, NY: NYC DEP.

NYC DEP. 1999c. Proposed Phase II Phosphorus TMDL Calculations for Ashokan Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999d. Proposed Phase II Phosphorus TMDL Calculations for Cannonsville Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999e. Proposed Phase II Phosphorus TMDL Calculations for Neversink Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999f. Proposed Phase II Phosphorus TMDL Calculations for Pepacton Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999g. Proposed Phase II Phosphorus TMDL Calculations for Rondout Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999h. Proposed Phase II Phosphorus TMDL Calculations for Schoharie Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999i. Proposed Phase II Phosphorus TMDL Calculations for Kensico Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999j. Proposed Phase II Phosphorus TMDL Calculations for West Branch Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999k. Proposed Phase II Phosphorus TMDL Calculations for Amawalk Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999l. Proposed Phase II Phosphorus TMDL Calculations for Bog Brook Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999m. Proposed Phase II Phosphorus TMDL Calculations for Boyds Corner Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999n. Proposed Phase II Phosphorus TMDL Calculations for Cross River Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999o. Proposed Phase II Phosphorus TMDL Calculations for Croton Falls Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999p. Proposed Phase II Phosphorus TMDL Calculations for Diverting Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999q. Proposed Phase II Phosphorus TMDL Calculations for East Branch Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999r. Proposed Phase II Phosphorus TMDL Calculations for Middle Branch Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999s. Proposed Phase II Phosphorus TMDL Calculations for Muscoot Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999t. Proposed Phase II Phosphorus TMDL Calculations for New Croton Reservoir. Valhalla, NY: NYC DEP.

NYC DEP. 1999u. Proposed Phase II Phosphorus TMDL Calculations for Titicus Reservoir. Valhalla, NY: NYC DEP.

Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"8 Phosphorus Management Policies, Antidegradation, and Other Management Approaches." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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In 1997, New York City adopted a mammoth watershed agreement to protect its drinking water and avoid filtration of its large upstate surface water supply. Shortly thereafter, the NRC began an analysis of the agreement's scientific validity.

The resulting book finds New York City's watershed agreement to be a good template for proactive watershed management that, if properly implemented, will maintain high water quality. However, it cautions that the agreement is not a guarantee of permanent filtration avoidance because of changing regulations, uncertainties regarding pollution sources, advances in treatment technologies, and natural variations in watershed conditions.

The book recommends that New York City place its highest priority on pathogenic microorganisms in the watershed and direct its resources toward improving methods for detecting pathogens, understanding pathogen transport and fate, and demonstrating that best management practices will remove pathogens. Other recommendations, which are broadly applicable to surface water supplies across the country, target buffer zones, stormwater management, water quality monitoring, and effluent trading.

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