Watershed Management for Potable Water Supply Assessing the New York City Strategy (2000) / Chapter Skim
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6 Tools for Monitoring and Evaluation
6 Tools for Monitoring and Evaluation
Pages 206-278
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From page 206... ...
First, as with all other source water protection programs, one goal of the MOA is to comply with local, state, and federal statutes that protect drinking water quality. Thus, the City has developed an extensive water quality monitoring program, active disease surveillance, a Total Maximum Daily Load (TMDL)
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From page 207... ...
developed for watershed inventory and other purposes is critically evaluated. Second, the safety of the drinking water system is considered by reviewing the role of active disease surveillance in New York City and by conducting a microbial risk assessment on the source water.
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From page 208... ...
A full description of all monitoring efforts conducted by NYC DEP is available in the Water Quality Surveillance Monitoring report (NYC DEP, 1997a)
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From page 209... ...
However, the new network is greatly improved over the previous system, which measured precipitation only, and it is adequate for most of the eutrophication and public health questions of concern. Groundwater and Shallow Subsurface Monitoring Regular groundwater monitoring has only occurred in the Kensico watershed, as this area has a high potential for contamination related to urbanization (NYC DEP,1997b)
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From page 210... ...
Because samples are collected at fixed time intervals rather than on the basis of discharge, it is certain that major fluctuations in the loading of chemical and biological parameters are not captured. This issue, which pertains to stream sampling, precipitation measurements, and sampling of shallow subsurface flows, is discussed below with regard to certain parameters, and it is generally addressed later under a separate section titled Flow Proportional Monitoring.
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From page 211... ...
In 1997, concentrations of several pesticides and polychlorinated biphenyls (PCBs) were monitored at two stream sites in the Kensico watershed; compounds were detected at very low levels (NYC DEP, 1998a)
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From page 212... ...
As part of the Process Control-Remote Monitoring Program, sampling of turbidity, pH, conductivity, temperature, free chlorine, and fluoride is automated at 13 aqueduct locations east of the Hudson River. NYC DEP plans to extend automated sampling to aqueduct key points west of the Hudson River when resources are available.
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From page 213... ...
Because DOM can serve as a precursor of trihalomethanes (THMs) and other chlorination byproducts, NYC DEP has spent considerable energy investigating the sources of DOM in the water supply reservoirs.
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From page 214... ...
This trend has been borne out by NYC DEP studies; UV254 data collected in Kensico Reservoir effluents on an irregular basis were found to average around 0.036 OD with little variation (S. Freud, NYC DEP, personal communication, 1998~.
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From page 215... ...
In addition to determining sources of DOM, NYC DEP may want to consider regularly measuring disinfection byproduct (DBP) formation potential in the reservoirs, particularly Kensico Reservoir.
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From page 216... ...
Bromide is currently not measured in the reservoirs. However, should New York City decide to install ozonation, bromide should be measured on a regular basis in the Kensico Reservoir using the IC method with a detection limit of 10 ,uglL or less.
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From page 217... ...
For this reason, the committee encourages the planned monthly sampling of pesticides in the reservoirs, particularly at Kensico Reservoir (NYC DEP, 1997a)
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From page 218... ...
Each month, NYC DEP collects on average 946 compliance samples and 473 surveillance samples, resulting in the sampling of individual sites every 9-14 TABLE 6-2 Sampling Sites in New York City Distribution System Type Bronx Brooklyn Manhattan Queens Staten Island Total Compliance 46 70 56 85 29 286 Surveillance 31 27 32 113 19 222 Total 77 97 88 198 48 508 Source: NYC DEP (1998b)
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From page 219... ...
Wastewater Treatment Plant Monitoring It is apparent from available data that a major source of pollutant loading to the water supply reservoirs emanates from wastewater treatment plant (WWTP) effluents (NYC DEP, 1998c, 1999a)
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From page 220... ...
Only through event-based sampling can the monitoring program accurately assess this possibility. Microbial Monitoring The microbial monitoring programs being conducted by NYC DEP (beyond compliance monitoring)
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From page 221... ...
Source of Pathogens. As discussed in greater detail in Chapter 12, the primary goals of the NYC DEP pathogen monitoring program should be to (1)
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From page 222... ...
There are currently no wildlife population data available to assess the relative contributions of different animal source terms to the overall pool of pathogenic protozoa in the Catskill/Delaware watershed. A study to determine the population of mammals with high protozoan infection rates has recently been initiated (NYC DEP, 1999a)
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From page 223... ...
NYC DEP has been measuring for fecal streptococci in the Kensico Reservoir to help determine the relative contributions of human and avian sources of fecal bacteria to this important reservoir. It is not clear from available reports (NYC DEP,1999b)
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From page 224... ...
Intensive sampling of the West Branch of the Delaware River during both base flow and storm events demonstrated that stream flow during storm events contains significantly higher concentrations of several pollutants than base flow, including all measured forms of phosphorus, total suspended solids, and total ammonia nitrogen (Longabucco and Rafferty, 1998~. In addition to increased pollutant concentrations, storm events were also found to deliver the bulk (from 55 percent to 95 percent)
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From page 228... ...
Samples collected by flow proportional monitoring must be properly preserved and retrieved in accordance with the vulnerability of the assays being
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From page 229... ...
The use of flow proportional sampling for microorganisms (indicators such as coliforms and pathogens such as Cryptosporidium) is technically feasible with the use of refrigerated field samplers.
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From page 230... ...
Once a sufficient concurrent record of fixed-frequency and event-based monitoring exists, a wide range of advanced statistical techniques can be used for retrospective modeling and analyses of historical data (Clarke, 1994; Haan, 1977; Hosking and Wallis, 1997~. For some time, NYC DEP has recognized the need to include event-based sampling in their water quality monitoring program (NYC DEP, 1997a)
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From page 231... ...
Although some performance monitoring of the shallow subsurface has occurred in the New York City watersheds, it has been relatively infrequent. Given data on groundwater flow rates in the Kensico watershed, there is a general assumption that subsurface flows and their attendant pollutant loadings to the reservoirs are minor in comparison to surface (river)
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From page 232... ...
Performance monitoring can also be conducted on a larger-scale, in order to assess the "performance" of a region or subwatershed. This larger-scale strategy is being used by NYC DEP in monitoring agricultural areas.
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From page 234... ...
If NYC DEP wants to conduct this type of large-scale mass balance with accuracy, data need to be collected over long time periods and during storm events to reduce both variability and the risk of systematic sampling bias.
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From page 235... ...
In addition, water quality within individual reservoirs is uncertain because of variable basin morphometry, natural and managed hydrology, climatic conditions, and fluctuations in pollutant loadings. As noted earlier, temporal variations in water quality typically occur over small time scales.
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From page 236... ...
These discussions are found in Chapter 8. Monitoring of the Kensico Watershed As the collection point for Catskill/Delaware system water prior to chlorination and distribution, the Kensico Reservoir is critical in controlling the quality of the New York City drinking water supply (Figure 6-2~.
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From page 237... ...
, NYC DEP (1998d) , and Owens (1998)
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From page 238... ...
238 WATERSHED MANAGEMENT FOR NEW YORK CITY FIGURE 6-2 Kensico Reservoir and watershed. Courtesy of the NYC DEP.
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From page 239... ...
and the standard operational monitoring that takes place in all Catskill/Delaware reservoir basins. Given its influence on the quality of drinking water in New York City, Kensico Reservoir and its watershed should continue to be the focus of intensive monitoring by NYC DEP.
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From page 240... ...
Source: NYC DEP (1997a)
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From page 241... ...
In this regard, NYC DEP could benefit by assimilating work done on pathogen inactivation under variable environmental conditions and by making use of approaches to watershed modeling developed for nonpathogens (e.g., nutrients)
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From page 242... ...
7. If NYC DEP wants to determine the effectiveness of managed riparian buffer zones, septic system drainfields, and agricultural and urban stormwater BMPs, performance monitoring using paired measurements is needed.
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From page 243... ...
A cooperative study by NYC DEP and the Catskill Watershed Corporation (CWC) , fully supported by the GIS group, would greatly advance this key task.
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From page 244... ...
and NYC DEP maintain a Waterborne Disease Risk Assessment Program that encompasses both active disease surveillance and outbreak detection. Acute diseases of microbial origin are the focus of this program, rather than chronic conditions that have been linked to long-term exposure to chemical contaminants (such as trihalomethanes)
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From page 245... ...
Source: NYC DEP (1999c)
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From page 246... ...
. Interview data from giardiasis cases during July 1994 to May 1995 indicated that the most commonly reported exposure risk was travel outside the United States, with other prevalent risk factors being contact with a household member having diarrhea, recent immigration, and adult male homosexual activities (NYC DEP, 1997e)
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From page 247... ...
These limitations apply to active disease surveillance programs nationwide. To illustrate these effects, Table 6-7 compares the expected number of endemic Cryptosporidium cases reported per month among immunocompetent persons in New York City to the expected number of reported Cryptosporidium cases in a situation where there is an outbreak affecting one percent of the population.
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From page 248... ...
NO FIGURE 6-4 Sources of loss of information during active disease surveillance. Note: In the case of cryptosporidiosis, the health care provider must specifically request that a stool specimen be tested for Cryptosporidium because this is not included in routine parasitic examinations of stool specimens.
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From page 249... ...
This time lag reinforces the argument that this type of active surveillance system is limited in recognizing and managing an outbreak in real time and can only provide retrospective information. Outbreak Detection Aware of the fact that active, laboratory-based surveillance is neither sensitive enough nor rapid enough to detect waterborne disease outbreaks, New York City has developed three independent and complementary diarrhea!
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From page 250... ...
Although the sensitivity of these systems is potentially far greater than that of active surveillance, in some cases (monitoring of medication sales and number of stool specimens examined) , the data collected are surrogate measures for cases of gastroenteritis and do not have the specificity of laboratory-confirmed infections.
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From page 251... ...
Although surveillance data are limited because of the newness of the program, results so far indicate very low numbers of new gastrointestinal illness cases per day (NYC DEP, l999c)
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From page 252... ...
under what circumstances these investigations include checking source water quality and informing the public. Response to Consumer Complaints As in many other water systems, NYC DEP and NYC DOH respond to consumer complaints about water quality by collecting and testing a water sample from the consumer's home.
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From page 253... ...
In New York City, it is not clear what concentration of contaminants triggers a boil-water advisory or other public health response. According to NYC DEP, should any elevated level of Cryptosporidium be detected in the water supply, NYC DEP, working with the City and State Departments of Health and EPA, will evaluate factors included in the 1995 CDC guidance to determine what action, if any, to take in response (Ashendorff, 1999~.
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From page 254... ...
Both of these studies utilized cases identified from the active disease surveillance program. Giardiasis Case-Control Study In June and July 1995, NYC DOH compared 120 patients suffering from giardiasis with a control group of 120 persons (NYC DEP, 1997e)
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From page 255... ...
were collected, and 331 stool specimens were collected. Only 1.2 percent of the stools tested positive for Cryptosporidium, while 28 percent of the blood samples were seropositive for a Cryptosporidium antibody (NYC DEP, 1998e)
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From page 256... ...
Because of the wealth of water quality monitoring data, NYC DOH and NYC DEP should consider conducting time series studies that compare patterns of illness with various water quality parameters over time (as in Schwartz et al., 1997~. This could be easily accomplished with the data that are already collected in the active disease surveillance, outbreak detection, and water quality surveillance monitoring programs.
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From page 257... ...
The results are summarized briefly in Table 6-8 and are explained in greater detail below. TABLE 6-8 Recommendations for Improving the New York City Waterborne Disease Risk Assessment Program Goal 1, Program General Limitations Recommendations 2, or 3?
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From page 258... ...
4. NYC DOH and NYC DEP should develop a plan of action to define spikes in surveillance and outbreak detection data and trigger investigation of these peaks after eliminating the possibility of reporting error.
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From page 259... ...
5. NYC DOH and NYC DEP should develop a plan of action for tracking and investigating consumer complaints about water quality and waterrelated illness that goes beyond collecting and testing a household water sample for routine parameters.
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From page 260... ...
is considered to result in a statistically independent risk of infection (Regli et al., 1991; Haas et al., 1993~. In performing this risk assessment, it is assumed that the oocyst levels in the Kensico Reservoir raw water (at the CATLEFF and DEL 18 sampling locations)
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From page 261... ...
Data courtesy of the NYC DEP. the data record than in the more recent part of the data record.
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From page 262... ...
Using maximum likelihood, and treating all observations less than or equal to 0.721 oocysts/100 L as being "censored" (for all censored observations, 0.721 oocysts/100 L was regarded as being the detection limit) , the parameters of lognormal distributions were determined.
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From page 263... ...
suggests a potential correlation between the oocyst levels at CATLEFF and DEL 18, the rank correlation coefficient (for observations in excess of the detection limit only)
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From page 264... ...
<,? Ct.$~ ~'1 FIGURE 6-8 Summary of mean oocyst levels (#/100 L)
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From page 265... ...
In combining these contributions to assess exposure, they were flow weighted by the average daily flows to the Hillview reservoir 521 and 800 mad, for CATLEFF and DEL 18, respectively (NYC DEP, 1997a)
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From page 266... ...
First, the daily risk estimate is calculated for each individual year, given a single water dose, dose-response parameter, and average oocyst concentration. Four oocyst concentrations are used, representing the different methods for considering data points below the detection limit.
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From page 267... ...
That is, risk values derived from using the full detection limit and half detection limit methods are likely to be overestimates of the true risk, while those derived from using a zero detection limit method are likely to be underestimates. TABLE 6-10 Computed Point Estimates for the Daily Risk of Infection from Cryptosporidium (all numbers x 1 0-5)
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From page 268... ...
Statistic Individual Daily RiskDaily # of Infectionsa Mean 3.4255 Median 0.753 Standard Deviation 19.81,485 Lower 95% confidence limit 0.0342.6 Upper 95% confidence limit 21.91,643 aBased on an exposed population of 7.5 million persons. TABLE 6-12 Rank Correlation of Input Parameters with Daily Risk of Infectiona Input Parameter Rank Correlation with Daily Risk DEL 18 oocyst density CATLEFF oocyst density Water consumption Dose-response "k" value 0.61 0.56 0.24 -0.20 a Rank correlation is the correlation between two sets of data when the individual observations in each set are replaced by the rank in that set.
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From page 269... ...
Oocyst Viability and Recovery The above analysis used total oocysts found in the Kensico Reservoir raw water sampling locations to assess exposure. Not all of the total oocysts represent viable, human, infectious forms.
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From page 270... ...
The endpoint for this risk assessment infection is different than the endpoint measured by active disease surveillance frank illness that is diagnosed and reported. This is one of the reasons that the risk estimate predicts a higher rate of infection than is observed in the active disease surveillance program.
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From page 271... ...
For both treatment processes and watershed management activities, a 1-log reduction in oocyst concentration translates directly into a 1-log reduction in the risk estimate because the dose-response relationship is linear at low dose. In other words, any process that reduces oocyst levels in the Kensico Reservoir by a factor of ten will reduce the risk estimate to 0.34 x 10-5 per person per day, or 25.5 infections per day, in a population of 7.5 million persons.
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From page 272... ...
This level should be arrived at after full and open discussion with the various stakeholders. Should an annual risk level of greater than 10= be regarded as acceptable by NYC DEP or other relevant risk managers, then the risk estimates computed in this report can be compared to such alternate yardsticks.
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From page 273... ...
NYC DEP. E-mail memorandum to the National Research Council dated January 6, 1999.
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From page 274... ...
1998. A survey of risk factors for cryptosporidiosis in New York City: drinking water and other exposures.
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From page 275... ...
1996. Detection and identification of microcystins in the drinking water of Haimen City, China.
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From page 276... ...
Washington, DC: National Academy Press. New York City Department of Environmental Protection (NYC DEP)
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From page 277... ...
1997. Drinking water turbidity and pediatric hospital use for gastrointestinal illness in Philadelphia.
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From page 278... ...
NYC DEP. E-mail memorandum to the National Research Council dated November 16, 1998.
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