Review of the New York City Watershed Protection Program (2020) / Chapter Skim
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4 Current Conditions, Trends, and Future Stressors
4 Current Conditions, Trends, and Future Stressors
Pages 91-134
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From page 91... ...
and other applicable laws and regulations. The water supply system was designed, and is managed and operated, to avoid or minimize fluctuations in drinking water quality.
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From page 92... ...
As shown in Figure 4-1, the total annual water yield for the East Branch of the Delaware River in Margaretville varies widely around a mean of 670 mm, considering 80 years of data from 1938 to 2018. The NYC DEP water supply operations center (and related programs and teams)
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From page 93... ...
for the East Branch of the Delaware River, Margaretville, New York (USGS gaging station 001413500)
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From page 94... ...
Focusing on the challenges associated with very dry and very wet years does not diminish the relatively frequent operational challenges associated with somewhat unusual meteorological events in any given year. For example, several weeks with little or no rainfall can rapidly diminish streamflow and adversely influence water quality (e.g., increased water temperature and BOD)
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From page 95... ...
of record (1937-2018) , East Branch of the Delaware River at Margaretville, New York (USGS gaging station 00141350)
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From page 96... ...
of record (1937-2018) , East Branch of the Delaware River at Margaretville, New York (USGS gaging station 00141350)
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From page 97... ...
of record (1937-2018) , East Branch of the Delaware River at Margaretville, New York (USGS gaging station 00141350)
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From page 98... ...
It convincingly demonstrated the flexible and adaptive nature of both the water supply system and the operations staff and, reassuringly, the capacity to effectively meet the inevitable challenges of the 21st century. LAND USE AND LAND COVER Land use and land cover are key drivers of anthropogenic effects on freshwater ecosystems (Gergel et al., 2002)
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From page 99... ...
appear to have minimized land cover change for almost two decades in both watersheds of the NYC water supply. In absolute terms, the rates of land cover change were ~25 acres per year for the 1-million-acre WOH watershed and ~280 acres per year for the 248,000-acre EOH watershed.
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From page 100... ...
. TABLE 4-3 Further Analysis of Cumulative Land Cover Change, 2001-2016, in the West-of-Hudson Watersheds Land Cover Classesa 2001 Acres 2016 Acres ∆ Acres ∆% Watershed Forest (all age and size classes; 6, 7, 8, 844,866 846,024 1,157 0.12 9, 10, 11)
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From page 101... ...
. TABLE 4-5 Further Analysis of Cumulative Land Cover Change, 2001-2016, in the East-of-Hudson (Croton System)
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From page 102... ...
. Taken together, the very small changes in land cover are likely influenced by the combined effects of the Memorandum of Agreement, Watershed Protection Program, forest and agricultural land conservation efforts, and recent market trends for agricultural and forest products.
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From page 103... ...
SOURCE: Adapted (with permission from the Watershed Agricultural Council) from VanBrakle and Pavlesich (2017)
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From page 104... ...
If overland flow, short residence times, and little or no plant growth predominate, the net effect on water quality is decidedly negative. Given their critical role in influencing stream water quality, mapping, assessing, and protecting riparian areas are foundational components of any watershed protection program.
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From page 105... ...
. Highly turbid water is aesthetically unappealing and possibly a cause for health concerns in drinking water, particularly because particles in water can absorb other pollutants (notably metals, nutrients, and bacteria)
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From page 106... ...
and turbidity is more closely related to particle surface area; hence, turbidity emphasizes smaller particles that are much less likely to settle. In the various reservoirs of the NYC water supply system, turbidity can change, sometimes dramatically, at time scales of minutes to hours and be quite different in one reservoir relative to another.
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From page 107... ...
. Despite these improvements and changes, in the Committee's opinion, turbidity will remain a significant challenge for the NYC water supply for the foreseeable future.
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From page 108... ...
, and present a number of challenges from the perspective of drinking water quality. First, the algae in a eutrophic reservoir results in an increase in turbidity, which, as discussed above, is an important type of impairment that could lead to a determination that filtration is required.
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From page 109... ...
These results suggest that watershed protection strategies, at least over the 2008-2018 period, do not seem to be resulting in progress in terms of reducing this indicator of eutrophication in Cannonsville Reservoir. FIGURE 4-9 Annual geometric mean values of total phospho rus (TP)
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From page 110... ...
Analysis of Phosphorus Data Upstream of Cannonsville NRC (2000a:164) states that "the suppression of phosphorus loading rates to the Catskill/Delaware reservoirs is a particularly important goal for the New York City watershed management strategy." This Committee strongly endorses that statement and further notes that the data on trends in trophic state, reservoir phosphorus concentrations, and new indications of algal toxins place a particularly high priority on the need to suppress phosphorus loading rates to the Cannonsville Reservoir.
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From page 111... ...
The Committee's analysis of the streamflow record for the West Branch of the Delaware River at Beerston indicates an increase in mean discharge of about 33 percent over the three decades of water quality sampling considered here (almost significant at the 0.1 alpha level)
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From page 112... ...
The uncertainty of the overall trend in the flow-normalized flux is that it is "likely" that the trend is upward over this full period,7 FIGURE 4-11 Estimated annual flux (black dots) of total phosphorus for the West Branch of the Delaware River at Beerston, New York, for water years 1988–2018, expressed in metric tons per year.
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From page 113... ...
In contrast, the change in flux is much more influenced by the relatively few days of the year when FIGURE 4-12 Estimated annual mean concentration (black dots) of TP for the West Branch of the Delaware River at Beerston, New York, for water years 1988–2018.
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From page 114... ...
The Cannonsville watershed is not unique in the slowness of watershed-scale response to nonpoint source phosphorus management controls. Smith et al.
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From page 115... ...
For many years after the concern about organic carbon in drinking water supplies was first raised, the NYC DEP measured and reported both TOC and DOC, but the differences were so infinitesimal that they now measure only DOC but report it in the annual drinking water quality reports as the TOC. Further, since the concentration of synthetic organic compounds is extremely low in the NYC DEP system in comparison to the natural organics, the TOC measurement is interpreted to be the NOM concentration.
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From page 116... ...
Of the wide variety of halogenated organics formed as DBPs, two groups are usually dominant on a mass basis, and their concentrations are regulated in drinking water by the EPA. Those two groups of compounds are the trihalomethanes and some of the haloacetic acids.
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FIGURE 4-13 Dissolved Organic Carbon Measurements Throughout the NYC Reservoir System. Figure in color at https://www.
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In their annual public Drinking Water Supply and Quality Report, they list the range of values of all of their measurements of both the haloacetic acid 5 (HAA5) and the total trihalomethane (TTHM)
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From page 119... ...
The data are encouraging, inasmuch as all of the quarterly values are less than the annual average values in the regulation, but the fact that the highest values reflect the hurricane experience of 2011 makes it clear that high-rainfall events reflect a vulnerability of the NYC system. Many utilities in the United States have opted to change the disinfectant used to keep a residual in the dis tribution system from chlorine to chloramines; chloramines drastically limit the production of haloacetic acids.
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From page 120... ...
Indicators of potential pathogen contamination, including total and fecal coliforms, are routinely monitored at various points in the NYC water supply system. As discussed in Chapter 3, the SWTR requires that source water from unfiltered water supplies, sampled prior to disinfection, must have fecal coliform concentrations less than 20 CFU/100 mL (or total coliforms <100 CFU/100 mL)
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From page 121... ...
Nov-17 Sep-07 Jan-18 Nov-07 Mar-18 Jan-08 May-18 Mar-08 Jul-18 May-08 Sep-18 Nov-18 Jul-08 Jan-19 Sep-08 Source Water (DEL18) Fecal Coliform Compliance (2010-2019)
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From page 122... ...
model (Smith et al., 1997) is one formulation that has been effective in a number of regional water quality analyses; it is described and applied to the NYC watersheds in Chapter 12.
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From page 123... ...
Current Conditions, Trends, and Future Stressors 123 FIGURE 4-16 Cryptosporidium levels measured at the outflows of the three systems, prior to UV disinfection. Note the Catskill outflow was closed September 2012.
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From page 124... ...
Key findings that are most germane to NYC watershed protection are summarized here: • Annual average air temperatures have been increasing nationwide, with an average increase of about 1.0°C for the period 1895–2016. • Annual average air temperatures are projected to rise in the future, with a projected 1.4°C increase pro jected for the period 2021–2050 compared to 1976–2005.
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From page 125... ...
The following sections discuss aspects of climate change and their possible linkage to water quality impacts in the New York City watershed. How climate change may affect specific subprograms of the Watershed Protection Program is discussed in Chapters 5 through 11.
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From page 126... ...
The analysis reported earlier in this chapter, on phosphorus inputs to Cannonsville Reservoir, illustrates why considering climate change can be important to the analysis of water quality change. In this case, trends in the flux of TP from 1988 to 2018 showed an increase of 88 percent.
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From page 127... ...
Thermal stratification can contribute to both eutrophication and HABs because the low-oxygen conditions near the reservoir bed can lead to increased mobility of the phosphorus stored in the bed sediments. Analyses of threats, particularly of HABs, should include a long-term analysis of water temperatures in the reservoirs and dates of ice formation and ice breakup.
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From page 128... ...
This may have an impact on the production of compounds that can produce DBPs in the finished water supply. Changes in Air Temperatures and Resulting Impacts on Water Temperatures Increasing air temperatures are of particular importance to NYC watershed protection because of their influence on water temperatures in the streams and reservoirs of the NYC system.
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From page 129... ...
demonstrate the flexibility and robustness of the NYC water supply system to such extreme storm events, as well as the utility of OST (discussed in Chapter 12 and NASEM, 2018)
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From page 130... ...
This underscores the critical importance of full and sustained support of the Water Supply Operations Center and core functions of the Bureau of Water Supply. Land cover and land use changes from forest and farmland to developed areas in the west-of-Hudson watersheds have been minimal, one-tenth the average change for New York State, from 2001 to 2016.
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From page 131... ...
NYC DEP should regularly analyze their monitoring data for trends that would identify such changes and indicate whether water quality parameters could be altered by climate change. New York City's Watershed Protection Program and system operations appear able to more than adequately protect the quality of the city's drinking water source, even under extraordinary storm conditions.
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From page 132... ...
2020. Conterminous United States land cover change patterns 2001-2016 from the 2016 National Land Cover Database.
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From page 133... ...
2014. New York City 2014 Drinking Water Supply and Quality Report.
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From page 134... ...
2013. Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment.
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