5
Sources of Pollution in the New York City Watersheds

Like most areas of the United States, the source waters of the New York City supply are affected, to varying degrees, by a range of pollutants. This chapter describes water quality constituents of primary concern in the New York City drinking water supply—microbial pathogens, nitrogen, phosphorus, organic carbon compounds, sediment, and toxic compounds—as well as their ecological and operational significance. Discrete, point sources (sewage treatment plants and other sources with discharge permits) and diffuse, nonpoint sources (namely on-site sewage treatment and disposal systems or OSTDS, agriculture, residential and commercial development, forestry, and atmospheric deposition) are discussed in detail. The chapter concludes by considering (1) the relative proportion of point and nonpoint source pollution in major watersheds of the New York City systems, (2) reservoir water quality and eutrophication, and (3) compliance with the Safe Drinking Water Act (SDWA) and forthcoming amendments.

POLLUTANTS

Microbial Pathogens

Surface water supplies can be affected by pathogenic microorganisms (bacteria, viruses, and protozoa) originating from various sources. Many bacterial pathogens (e.g., Salmonella, Shigella, Vibrio) have long been known to be potentially waterborne (Black et al., 1978; Geldreich, 1990; West, 1989), and they may emanate from both human (wastewater) and nonhuman sources. However, they are at least as sensitive to disinfection with chlorine as are coliforms (Butterfield et al., 1943; Wattie and Butterfield, 1944). Therefore, in disinfected systems



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Watershed Management for Potable Water Supply: Assessing the New York City Strategy 5 Sources of Pollution in the New York City Watersheds Like most areas of the United States, the source waters of the New York City supply are affected, to varying degrees, by a range of pollutants. This chapter describes water quality constituents of primary concern in the New York City drinking water supply—microbial pathogens, nitrogen, phosphorus, organic carbon compounds, sediment, and toxic compounds—as well as their ecological and operational significance. Discrete, point sources (sewage treatment plants and other sources with discharge permits) and diffuse, nonpoint sources (namely on-site sewage treatment and disposal systems or OSTDS, agriculture, residential and commercial development, forestry, and atmospheric deposition) are discussed in detail. The chapter concludes by considering (1) the relative proportion of point and nonpoint source pollution in major watersheds of the New York City systems, (2) reservoir water quality and eutrophication, and (3) compliance with the Safe Drinking Water Act (SDWA) and forthcoming amendments. POLLUTANTS Microbial Pathogens Surface water supplies can be affected by pathogenic microorganisms (bacteria, viruses, and protozoa) originating from various sources. Many bacterial pathogens (e.g., Salmonella, Shigella, Vibrio) have long been known to be potentially waterborne (Black et al., 1978; Geldreich, 1990; West, 1989), and they may emanate from both human (wastewater) and nonhuman sources. However, they are at least as sensitive to disinfection with chlorine as are coliforms (Butterfield et al., 1943; Wattie and Butterfield, 1944). Therefore, in disinfected systems

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy such as the New York City supply, the presence of bacterial pathogens is not a significant threat compared to other microbial pathogens. There are many human enteric viruses that may be present in surface water supplies, such as the rotaviruses, coxsackieviruses, and echoviruses (Clarke and Chang, 1959; Cooper, 1974; Gerba and Rose, 1990; Melnick et al., 1978). Human wastes (including wastewater discharges) are the most frequently documented sources of human enteric virus in surface waters (Gerba and Rose, 1990). Viruses are more sensitive to disinfection than are cysts of Giardia (Hoff and Akin, 1986), and thus the amount of inactivation provided to viruses during treatment will be at least as great as that provided to Giardia. Thus, like bacterial pathogens, the presence of viruses in water supplies that are disinfected is not of great concern. Sources of Giardia As noted in earlier chapters, two protozoa have received increasing attention in the United States over the past several decades—Giardia lamblia and Cryptosporidium parvum. These organisms form stages, known as cysts and oocysts, respectively, that are resistant to disinfection with chlorine. There is a large body of evidence demonstrating the occurrence of G. lamblia in human wastewater as well as in animal wastes. Some animals are believed to serve as reservoirs for human pathogenic strains, with much attention being given to beavers and other aquatic animals. However, evidence that animal-derived cysts have actually resulted in human outbreaks is not conclusive (Erlandsen and Bemrick, 1988). Nevertheless, it is clear that aquatic animals, domestic dogs and cats, and cattle may serve as sources of measurable cysts in surface waters. Monitoring studies of wildlife in the New York City watershed found that 6.9 percent of those animals tested were infected with Giardia cysts (NYC DEP, 1998a). This correlates well with infection rates of cattle in the watershed. Research conducted by Cornell University measured a 7 percent Giardia infection rate among previously uninfected cattle (NYS WRI, 1997). This study also demonstrated that cattle previously infected with Giardia are more likely to develop infections of other protozoan pathogens. Sources of Cryptosporidium Knowledge of the life history of Cryptosporidium in water is somewhat less developed than that of Giardia. First, there are serious methodological problems with many commonly used environmental detection methods for oocysts (Clancy et al., 1994). Second, there are recently developing lines of evidence suggesting the possibility of different subspecies/strains of C. parvum with different preferential hosts (Carraway et al., 1997). Hence, prior evidence may undergo reinterpretation if the taxonomy of C. parvum is reconsidered.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy The literature indicates that domestic animals, livestock, and wildlife may serve as reservoirs of C. parvum, with infected calves and lambs excreting large amounts of oocysts (Smith, 1992). In the New York City watershed, 0.66 percent of tested wildlife (6,261 total specimens) and approximately 2 percent of cattle tested were found to be infected with C. parvum (NYC DEP, 1998a; NYS WRI, 1997). There have been studies of the cross-infectivity between humans and other animal species (O'Donoghue, 1995). Human C. parvum isolates have been found to infect calves, lambs, goats, pigs, dogs, cats, mice, and chickens. Isolates from calves have been found to infect humans. There is also epidemiological evidence of transmission from cats or pigs to humans (Rose, 1997). Thus, both nonpoint, animal-derived sources as well as human wastewater must be considered as sources of waterborne Cryptosporidium in the New York City watershed. For all microbial pathogens, determining the relative importance of wildlife, domestic animals, and humans as sources is a challenge. To elucidate the contribution of wildlife, field research of the kind demonstrated in Box 5-1 is needed in the Catskill region to document the link between wildlife populations and water quality. In the interim, management practices that encourage increases in wildlife populations (e.g., supplemental feeding of deer, posting to prevent hunting, trapping bans on beaver, and some habitat-enhancement techniques), especially in riparian areas, are ill-advised. A wide variety of forest management strategies are available to enhance wildlife habitat for nongame species (e.g., songbirds), overstory tree growth, and forest health without increasing the size of the deer populations. Beaver populations may require active management in some parts of the watersheds. Occurrence of Infection in Humans There is evidence of the occurrence of both giardiasis and cryptosporidiosis in the New York City population. The most recent surveillance data (NYC DEP, 1999a) show rates of giardiasis and cryptosporidiosis of 25.7 and 2.8 per 100,000 persons per year (over the period 1994–1998), respectively. It should be noted that this includes illness from all causes, not just drinking water. The magnitude of this disease burden can be placed in context with other active surveillance efforts conducted by the Centers for Disease Control and Prevention (CDC). In the Foodnet program, a number of infectious diseases are monitored at several target locations. Although the motivation for this monitoring is understanding foodborne illness, all illnesses from particular pathogens (regardless of source) are tracked. Summaries of incidence rates are indicated in Table 5-2 for cryptosporidiosis and for the total of all infectious diseases tracked. Interestingly, the reported New York City cryptosporidiosis rate is identical to the 1997 Foodnet average cryptosporidiosis rate among all reporting sites, and a number of sites (in Minnesota and California) have higher detected occurrences.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy BOX 5-1 Investigating Wildlife as Sources of Pathogens Wildlife populations in the Catskill region include the species, perhaps as many as 350 vertebrates, typically associated with northeastern forest ecosystems (De Graaf et al., 1992). Once extirpated from the region by marked hunting and trapping, white-tailed deer and beaver have rebounded during the last century. The current distribution and abundance of deer and beaver in the Catskills is not well documented. A recent study (Fraser, 1999; Fraser et al., 1998) in the Saw Kill watershed on the east side of the Hudson River measured fecal coliform bacteria and other water quality constituents in 12 subwatersheds. Two reference subwatersheds had no domestic livestock or residences; the other ten had livestock (beef and dairy cattle, sheep, and horses) ranging in number from 25 to 1,474 and unknown numbers of wildlife and pets (Pinney and Barten, 1997, 1998). Except for the reference subwatersheds, there are scattered residences with septic systems that may confound the fecal coliform data. Table 5-1 summarizes watershed characteristics, animal numbers, and mean fecal coliform concentrations during the summer of 1996. Although fecal coliform concentrations in the reference subwatersheds are lower than most, if not all, of the concentrations in the treatment subwatersheds, the background contamination from wildlife populations is apparent. TABLE 5-1 Summary of 1996 Water Quality and Livestock Data for 12 Subwatersheds of the Saw Kill, Tivoli Bays (Hudson River) National Estuarine Research Reserve, near Red Hook, New York (the italicized rows are the reference subwatersheds with no domestic livestock but unknown numbers or types of wildlife) Subwatershed ID# Area (km2) Total number of domestic livestock Mean fecal coliform (CFU/100 mL) W1 3.0 25 626 W2 4.2 91 797 W3 1.9 0 594 W4 5.9 38 597 W5 1.2 90 389 W6 2.1 122 1,657 W7 2.9 122 341 W8 12.1 54 450 W9 50.0 1,474 1,118 W10 17.0 690 142 W11 1.5 0 167 W12 4.0 600 453   Source: Reprinted, with permission, from Fraser (1999). ©1999 by Fraser.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy TABLE 5-2 Disease Incidence Rates Reported by 1997 Foodnet Surveillance Locale Number of Cases per 100,000 per year All illnessesa Cryptosporidiosis All sites 53.1 2.8 California 89.2 3.4 Connecticut 46.6 1.3 Georgia 44.9 No data Minnesota 51.8 5.2 Oregon 42.9 0.8 a Includes illnesses from Campylobacter, Cryptosporidium, Cyclospora, E. coli 0157:H7, Listeria, Salmonella, Shigella, Vibrio, and Yersinia. Source: CDC (1998). Nitrogen Nitrogen has many forms and functions in watersheds and other environmental systems. As shown in Table 5-3, it is found in nature in all three environmental media (air, water, and soils) and in six of its eight possible oxidation states (+V to –III). Nitrogen can act as a pollutant in surface waters in four principal ways: (1) as a nutrient for photosynthetic activity in streams, lakes, and reservoirs (eutrophication), (2) by producing toxic effects on fish when present as ammonia (NH3), (3) as an acid when present as nitric acid (HNO3), and (4) by exerting an oxygen demand when in the form of organic N, ammonium (NH4+), or NH3. It can also exert a significant chlorine demand and can therefore affect the disinfection process. Sources of nitrogen in the Catskill and Delaware watersheds are diverse. Atmospheric deposition, both wet and dry, is substantial. It can include gaseous NOx [the sum of nitrogen dioxide (NO2), nitrous oxide (N3O), and nitrogen oxide (NO)], HNO3, and NH3, as well as ammonium and nitrate particulates. Other nonpoint sources include septic tanks, agricultural runoff (as discussed below), urban stormwater, and groundwater. These can contain NH4+, NH3, nitrate (NO3-), and organic nitrogen. Point sources of NH4+, NH3, NO3-, and organic nitrogen include municipal wastewater treatment plants, industrial discharges, and stream or reservoir inflows. Point sources of nitrogen are controlled by the limits that have been placed on total ammonia concentrations [NH4+ + NH3] in wastewater discharges. Biological treatment to meet these limits reduces the possibility of fish toxicity related to NH3 and also lowers the nitrogenous oxygen demand entering surface waters by oxidizing reduced nitrogen to NO3-. Nonpoint sources of nitrogen are more difficult to control. Manure is a significant source of nitrogen in agricultural watersheds such as the Cannonsville

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy TABLE 5-3 Forms of Nitrogen Compound Media Oxidation State Elemental nitrogen Air 0 Ammonia(um) Soils, air, water –III Nitrate Soils, water V Nitrate Soils, water III Amino acids Soils, water –III Nitric acid Air, atmospheric precipitation V Nitrous acid Air III Nitrogen oxides Air, water II, III Dissolved organic N Water III Nitrous oxide Air I watershed. Although nitrogen is lost through ammonia volatilization and denitrification, there can be large amounts of organic and inorganic nitrogen in runoff from barnyards and manured fields. Additionally, both manured and fertilized fields tend to have high levels of nitrate leaching to groundwater. The Cannonsville Reservoir shows a tendency to nitrogen limitation on algal production during mid-to late summer (Effler and Bader, 1998), indicating that nitrogen loading, in some instances, is important. Deposition of nitrogen currently exceeds the biological demand for nitrogen in the Catskills because vegetative growth rates have slowed as the forest has matured (Murdoch, 1999). Nitrogen in excess of demand is stored in the soil and/or leached into streams. Increases in nitrate concentrations in streams have been accompanied by measured decreases in pH in the East Branch of the Neversink River. The effects of atmospheric deposition of nitrogen in the Catskill/Delaware watershed include impaired fish habitat in streams. In addition, the associated soil acidification can lead to slower growth rates for vegetation, less nutrient retention in the forest, and greater erosion and nutrient leaching to streams. Previous work has shown enhanced eutrophication in downstream reservoirs when nitrate concentrations increase in the presence of high phosphorus concentrations (Dodds et al., 1989; Morris and Lewis, 1988). Finally, temporary acidification of the reservoirs themselves is possible. This is most likely in the Neversink Reservoir, which is not sufficiently alkaline to buffer acid inputs from the Neversink River (Murdoch, 1999). Phosphorus The pollutant in the New York City water supply system that has received the most attention is phosphorus. Phosphorus has been identified as the dominant

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy limiting macronutrient for algal and other plant growth in the New York City reservoirs (NYC DEP, 1999b). When phosphorus concentrations become elevated in these waters, enhanced growth of algae, photosynthetic and heterotrophic bacteria, and higher aquatic plants can occur. In turn, the increased production of organic matter by these organisms can alter conditions within the reservoirs and lead to eutrophication. The most important negative consequences of eutrophication include (1) an increase in water turbidity caused by algal material and algal byproducts, (2) an increase in total organic carbon derived from algal biomass that can lead to formation of disinfection byproducts (DBPs), (3) algal production of potentially toxic compounds, some of which may create taste and odor problems, and (4) a decrease in dissolved oxygen levels within the reservoirs and the associated negative impacts on fish habitat. Many of these conditions are particularly difficult to overcome in water supplies that do not undergo extensive treatment. Thus, the suppression of phosphorus loading rates to the Catskill/Delaware reservoirs is a particularly important goal for the New York City watershed management strategy. Total phosphorus is divided into soluble and particulate forms. Particulate phosphorus (PP), which must be mineralized or hydrolyzed prior to uptake by algae, is much less bioavailable than soluble phosphorus, and it often settles to reservoir sediments. Therefore, it is less likely to lead to increased algal growth and eutrophication. The fraction of particulate phosphorus that can be hydrolyzed and mineralized to release soluble reactive phosphorus back to the water column varies. Studies in the Cannonsville watershed found that 25 percent to 48 percent of tributary particulate phosphorus was bioavailable (Auer et al., 1998). Soluble forms of phosphorus include soluble organic phosphorus, total dissolved phosphorus, and soluble reactive phosphorus (SRP). Soluble reactive phosphorus is the most commonly measured dissolved form because of its important role in eutrophication. Phosphorus sources in the Catskill, Delaware, and Croton watersheds are many and varied. As with most of the pollutants discussed in this chapter, phosphorus emanates from a variety of point and nonpoint sources such as wastewater treatment plants (WWTPs), OSTDS, agriculture, urban stormwater, and (in low concentration) forests. However, the dominant form of phosphorus created by each of these activities can be very different. Sewage treatment plants are the primary point source of phosphorus in the New York City water supply system because of the paucity of industrial waste discharges. Effluent from municipal sewage treatment plants consists mainly of soluble reactive phosphorus (essentially phosphate) plus some particulate phosphorus from plants that do not have efficient secondary sedimentation and/or filtration of the effluent. Similarly, OSTDS with poorly operating drain fields can result in leaching and discharge of soluble reactive phosphorus to streams. Stormwater transports both particulate and dissolved phosphorus. In par-

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy ticular, runoff from agricultural lands treated with manure and from barnyard areas has high levels of dissolved phosphorus with average volume-weighted concentrations of 230 µg/L (Robillard and Walter, 1984). Model calculations for Cannonsville Reservoir in the early 1980s estimated that 77 percent of the dissolved phosphorus load to Cannonsville Reservoir came from either direct runoff (both surface and subsurface) or baseflow. Urban stormwater has been shown to contribute approximately equal loadings of particulate and dissolved phosphorus (Schueler, 1995). Organic Carbon Compounds Organic carbon compounds in water supply reservoirs are problematic because some can react with chlorine to form DBPs in the water distribution system. Before describing important sources of organic carbon in the Catskill/Delaware watershed, it is necessary to define the many parameters used to measure organic carbon concentrations. The most generic classification is natural organic matter (NOM). This term has been used to differentiate between organic carbon compounds from natural versus human-synthesized sources. The most common measure of organic carbon compounds used in environmental engineering is total organic carbon (TOC). TOC includes all particulate and dissolved organic matter, ranging in size from simple dissolved molecules to particles several millimeters in diameter and larger, and it includes both natural organic matter as well as artificial human created compounds. Organic carbon is often characterized by dividing it into dissolved and particulate forms. Particulate organic carbon matter (POC) is organic carbon in particulate form greater than 0.5 µm in diameter. Dissolved organic carbon (DOC) is analytically separated from POC by filtration through 0.5-µm glass fiber filters and includes both dissolved and colloidal organic carbon. Both TOC and DOC refer only to organic carbon and should not include inorganic compounds such as CO2, HCO3–, and CO3–2. In addition, volatile organic compounds removed from samples during TOC analyses are not reflected in these measurements. DOC is the dissolved (and colloidal) portion of TOC and is the primary focus of the following discussion. DOC can be a precursor to the formation of DBPs in chlorinated water supplies. Reservoirs, including those in the Catskill/Delaware system, have two general sources of such precursors: (1) allochthonous organic carbon (both dissolved and particulate) that flows into the reservoirs with surface and groundwater runoff and (2) autochthonous organic carbon that is created within the reservoirs as a result of microbial activity. Allochthonous organic carbon is largely imported in dissolved and colloidal form as humic substances and is derived from partial microbial degradation of lignin-cellulose based carbon compounds of higher plants. These compounds are chemically recalcitrant to rapid biodegradation. (However, rates of biological

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy degradation are increased markedly if the dissolved organic compounds are exposed to ultraviolet radiation [Wetzel et al., 1995]). Loading of allochthonous TOC to reservoirs is directly correlated with rainfall intensities (e.g., Jordan et al., 1985; Mickle and Wetzel, 1978; Wetzel and Otsuki, 1974). Autochthonous organic carbon is produced largely by algal and cyanobacterial photosynthesis in reservoirs with little or no development along the shoreline. As a result, autochthonous organic carbon has a definite seasonal cycle and is relatively readily biodegradable. Several studies have attempted to compare the DBPs formed from allochthonous versus autochthonous carbon precursors (Briley et al., 1980; Hoehn et al., 1980; Hoehn et al., 1984). DBP yields from humic substances were found to fall within the ranges reported for algal biomass and extracellular products (Hoehn et al., 1980). Recent studies by the New York City Department of Environmental Protection (NYC DEP) have shown that allochthonous precursor carbon produces DBPs that are primarily dissolved (94 percent) and are primarily chloroform (98 percent) (Stepczuk et al., 1998). The same was found for autochthonous sources of precursor carbon (NYC DEP, 1997a). If the types of DBPs formed from these different sources are similar, then the most important factors affecting DBP formation are the overall quantities of autochthonous and allochthonous precursor carbon present in each reservoir and their relative rates of degradation. However, if one of these sources has a greater tendency to form DBPs than the other [which is possible for haloacetic acids (HAAs) and other DBPs that have yet to be studied], then successful precursor control will depend heavily on identifying the most significant source. In all natural lakes, most (> 60–80 percent) of the DOC occurring at any one time in the reservoirs is composed of recalcitrant allochthonous DOC. Because of its complex structural chemistry, allochthonous DOC degrades more slowly than autochthonous carbon and dominates in-reservoir DOC. Allochthonous DOC has been shown to degrade at a rate of about 1 percent per day with a turnover time of about 80 days (Cummins et al., 1972; Wetzel and Manny, 1972). This is not to say that autochthonous sources are not, during certain seasons, in greater abundance than allochthonous sources. DOC production by phytoplankton certainly increases during the summer relative to allochthonous DOC production, but it is not dominant until hypereutrophic conditions are reached. Thus, on an annual basis, allochthonous DOC will dominate the pool of precursor carbon that is available to react with the disinfectants in the water supply system. Determining which source of precursor carbon is more important to DBP production in the Catskill/Delaware watershed has recently become a priority for NYC DEP. In 1997, modeling of the West Branch of the Delaware River and the Cannonsville Reservoir suggested that autochthonous sources of DBP precursors are more important than allochthonous sources (NYC DEP, 1997a). Other data in the report, however, demonstrated that allochthonous precursors are present and should not be ignored. The report states that ''net autochthonous production

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy of precursors in the epilimnion, apparently driven by primary productivity of phytoplankton, was found to be a major source of precursor for the reservoir (Cannonsville), representing about two-thirds of the cumulative mass input over the April to mid-summer interval." This finding indicates that about a third of the precursor pool in the epilimnetic water was allochthonous. Although the volume of the epilimnion is less than half of the total, it is not a trivial quantity. It is also clear from the data presented that these ratios are highly dependent on seasonal variations. For example, the ratio of autochthonous precursors to allochthonous precursors was estimated to vary from a high of 2.5 in June 1995 to a low of 0.75 in November 1995. This work has focused on trihalomethane formation; information about HAA formation derived from DOC in the water supply is not yet available. There are other important considerations. During dry years, the contribution of allochthonous precursors may be low because of limited streamflow. Also, because algae tend to accumulate at the surface of waterbodies, there can be significant variations in the ratio of autochthonous to allochthonous precursors throughout the depth of a reservoir. This stratification may have played a role in the observed results. Management strategies for controlling allochthonous versus autochthonous precursor carbon are significantly different. If allochthonous sources are suspected, best management practices that reduce DOC loadings from rainfall and snowmelt runoff will be beneficial. In addition, if it is exposed to sunlight, the recalcitrant, allochthonous DOC within reservoirs will degrade faster (both photochemically and microbially) than if it is not exposed (Tranvik and Kokalj, 1998; Wetzel et al., 1995). Thus, management practices to reduce the pool of allochthonous DOC should strive to increase reservoir residence time and exposure to light in the epilimnion. Despite the more rapid decomposition of autochthonous DOC compared to allochthonous DOC, it is essential that algal growth be controlled, especially during those times in which autochthonous precursor carbon dominates. For the New York City reservoirs, this has usually been accomplished by reducing phosphorus loadings to the reservoirs from both point and nonpoint sources. Sediment Sediment decreases the clarity of water, thereby increasing turbidity and its undesirable effects, such as interference with chlorination. In addition, other pollutants (e.g., nutrients, metals, and pathogens) may be adsorbed to sediment particles, which can mask a fraction of the total pollutant load from detection. Wind-induced mixing can disperse sediment and associated pollutants throughout the reservoir. This may be especially pronounced when the reservoirs are thermally stratified and vertical mixing is largely limited to the epilimnion. Coarse-textured sediment (sands and larger silt particles) and bedload may settle

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy to the bottom of a reservoir near the point of entry. However, clay particles may remain in suspension for days to weeks. In the absence of anthropogenic disturbance, the Catskill and Delaware watersheds, like most forest ecosystems, have very low rates of sediment production (Patric, 1976; Patric et al., 1984). Forest vegetation occupies virtually all of the available growing space. Forest fires and insect and disease outbreaks severe enough to kill overstory trees are rare in the region and throughout the eastern deciduous forest. Therefore, the loss of the forest's protective influence occurs infrequently and over relatively limited areas. Soils in the region have high hydraulic conductivity augmented by extensive, interlocking root systems, by an organic litter layer beneath the forest vegetation, and by actions of organisms ranging from microbes to small mammals. Hence, overland flow is exceedingly rare. Even when overland flow occurs, unless there is significant detachment of soil particles by raindrop splash and subsequent transport by overland flow, erosion and sediment production occur in minuscule amounts in areas away from the stream channel network (e.g., the upturned root mass of a fallen tree, the exposed soil below a rock outcrop). Hence, the primary source of sediment in forested watersheds (not subject to landslides and other forms of mass erosion) is erosion occurring within the stream channel. Under present conditions, most turbidity problems in the Catskill/Delaware supply are caused by inorganic particles and sediment derived from surface and channel erosion during heavy precipitation events, primarily in the Schoharie and Ashokan watersheds (Longabucco and Rafferty, 1998). Further problems with sediment could arise if land use in the region changes. When changes in land use lead (1) to the removal of vegetation (or the conversion of forest vegetation to lawns), (2) to disruption or removal of the litter layer, (3) to disintegration or compaction of the soil surface, or (4) to concentration of stormwater from impervious surfaces, overland flow supplants subsurface flow as the dominant pathway. Reductions in interception and transpiration exacerbate the process by increasing stormwater volumes. Roads and storm drain systems frequently short-circuit natural pathways of flow to discharge into nearby streams or wetlands. Unless management practices are used to limit the force of raindrop splash and overland flow (by seeding and mulching exposed soil, dispersing overland flow into forested areas, terracing slopes, etc.) or to collect and clarify water (riparian buffers, settling ponds, created wetlands, catch basins), the downhill path of sediment and associated nonpoint source pollutants is inexorable. Changes in the quantity and quality of flow affect the dynamic equilibrium of stream channels. Sediment deposition in low-velocity stream reaches limits cross-sectional area when larger flows occur. As variation in water level and velocity increases, channel scour and realignment become commonplace. Sedimentation of particulate matter from nonpoint source runoff can cause ecological impacts because of siltation and destruction of habitat for fish and macroinvertebrates.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy FIGURE 5-5 Monthly average free residual chlorine levels in the entry points to Tunnels 1 and 2 during 1998.  Source: NYC DEP (1999k). FIGURE 5-6 Inactivation ratios measured in Tunnel No. 2 during January 1997. Source: NYC DEP Compliance Reports.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy FIGURE 5-7 New York City quarterly running averages for total trihalomethanes within the distribution system of the Catskill/Delaware supply. (Data are averages of multiple locations.) Source: NYC DEP Compliance Reports. Site-Specific Criteria: Waterborne Disease. The ultimate purpose of watershed management is to protect drinking water quality and public health by reducing the amount of contaminants entering the water source. Thus, the filtration avoidance criteria of the SWTR mandate no waterborne disease outbreaks shall occur among the population served by an unfiltered water supply. A disease outbreak can be defined as an increase in the observed number of cases of disease relative to the expected number of cases (background level) over a specific time period. Waterborne disease transmission refers to human exposure to a pathogenic agent (microbial or chemical) via consumption of or contact with contaminated water. Investigations of recognized waterborne disease outbreaks by state and local health departments are reported voluntarily to CDC and EPA. This system, based on voluntary reporting by state health departments, clearly represents only a fraction of the true incidence of waterborne disease outbreaks. There have been only three reported waterborne disease outbreaks in New York City since 1941 (Table 5-10). All these outbreaks were due to cross-connections or back-siphon-age rather than to contaminated source water. One outbreak of unidentified etiology in 1942 resulted in 225 cases; another outbreak in 1949 resulted in 31 cases of shigellosis in an apartment building; and in 1974 an outbreak of 20 cases of illness related to high levels of chromium occurred in an office building. These data indicate New York City is in compliance with the SWTR relating to waterborne disease outbreaks. However, it is possible that additional waterborne disease outbreaks may have occurred and were not recognized. There also may be unrecognized endemic disease associated with the New York City water

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy TABLE 5-10 Waterborne Outbreaks Reported in Community Water Systems in New York State and New York City: 1941–1994 Year New York State excluding NYC New York City New York State Total 1941–1950 27 2 29 1951–1960 2 0 2 1961–1970 3 0 3 1971–1980 3 1 4 1981–1994 6 0 6 Total 41 3 44   Source: Reprinted, with permission, from Craun (1998). supply. The City's surveillance systems and epidemiologic studies are reviewed in Chapter 6. Total Coliform Rule Because Kensico Reservoir is the terminal reservoir for the Catskill/Delaware system prior to disinfection, much of the compliance monitoring conducted by NYC DEP occurs in this basin. Under the SWTR, Kensico is considered the source water of the Catskill/Delaware systems and is subject to strict standards for fecal coliforms. During 1988–1992, Kensico Reservoir experienced elevated fecal coliform concentrations (Figure 5-8). However, although Kensico has shown seasonal increases in fecal coliform bacteria, usually beginning in October or November and continuing through December or January, NYC DEP has managed to not violate the Total Coliform Rule. During the fall and winter of 1991–1992, 1992–1993, and 1993–1994, this was accomplished by bypassing the Kensico Reservoir. Because bypassing is not an ideal solution given the operational and water quality benefits Kensico provides, in 1991 the City began a study to identify and eliminate the cause of seasonal coliform increases at Kensico Reservoir. Field investigations and limnological sampling showed that an increase in waterfowl populations coincided both temporally and spatially with increases of fecal coliform bacteria in the reservoir. These data also showed that the seasonal increases occurred only in Kensico Reservoir and not in upstream Catskill and Delaware reservoirs. In response to these findings, the city embarked on a waterfowl management program. Mitigation (e.g., landscaping changes and fence construction to reduce foraging) and the use of noisemakers to frighten the birds were implemented in 1991 and 1992. In the winter of 1993, the City strengthened its efforts with implemen-

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy FIGURE 5-8 Total coliform concentrations in Kensico Reservoir from 1991 to 1998. The arrow marks the commencement of the bird harassment program. Source: Ashendorff et al. (1997). Adapted from Journal AWWA, Volume 89, No. 3 (March 1997), by permission. © 1997 by American Water Works Association. tation of a round-the-clock harassment program using boats, hovercraft, and noisemakers. These efforts simultaneously reduced both the bird populations and coliform densities. Since waterfowl management began, NYC DEP has not observed seasonal increases in fecal coliform bacteria in Kensico. Both bird populations and fecal coliform bacteria levels were low in the fall and winter of 1994–1995 and 1995–1996, making the bypass of Kensico Reservoir unnecessary (Ashendorff et al., 1997). Disinfectants/Disinfection By-Products Rule Although the D/DBP Rule will not be promulgated until 2002, it is worthwhile to evaluate this regulation to determine whether the New York City water supply system would be in compliance based on current conditions. Bromate. In waters containing bromide, ozonation can produce bromate through the oxidation of bromide to hypobromous acid. Bromate is not expected to be a problem for New York City because the water supply is not currently

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy ozonated. However, trial studies with ozone conducted by NYC DEP indicate an interest in switching to this disinfectant. Unfortunately, bromide concentrations were not measured as part of these studies. If ozone is eventually used and bromide is detected in the water supply, bromate may become a pollutant of concern in the New York City drinking water system. Chlorite. Chlorite ion in drinking water has two possible sources: (1) from the use of chlorine dioxide and (2) from the breakdown of sodium hypochlorite (NaOCl). NYC DEP currently uses chlorine gas rather than chlorine dioxide at all disinfection locations except on Staten Island. Hypochlorite is used at that location, raising the possibility of chlorite problems in the future. Haloacetic Acids. The Stage 1 D/DBP MCL for HAA5 is 0.060 mg/L. HAA5 quarterly data for December 1993 through 1998 (Figure 5-9) suggest that New York City may have difficulty in meeting the new HAA5 MCL for the Catskill/Delaware system. Note that since June 1994, the quarterly HAA5 concentrations in the Catskill/Delaware system were higher than the quarterly compliance TTHM concentrations (compare Figures 5-7 and 5-9). These trends have been observed in North Carolina waters (Singer et al., 1995) and in New England waters (McClellan et al., 1996) and may result from the characteristics of the DOC. Because the Stage 1 HAA5 MCL is lower than the TTHM MCL, and undoubtedly will continue to be so in the Stage 2 D/DBP Rule, this finding has potentially serious consequence for New York City in the future. FIGURE 5-9 Quarterly running averages of the sum of five haloacetic acids measured within the distribution system of the Catskill/Delaware supply. The 1994–1997 data were collected from a limited number of sites while the 1998 data were collected from all sites that will be required by the SDWA amendments. Source: NYC DEP Compliance report.

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Watershed Management for Potable Water Supply: Assessing the New York City Strategy Chlorine. Because disinfectants were not historically thought to pose health risks, upper bounds on chlorine concentration in drinking water have not been included in regulations. Any imposed upper bound on disinfectant residuals was generally determined by the taste and odor of the finished water. However, new evidence indicates some disinfectants can cause harm to humans (EPA, 1994a,b). Thus, the proposed D/DBP Rule includes maximum residual disinfectant levels (MRDLs) for chlorine, chloramine, and chlorine dioxide. The MRDL for chlorine, the primary disinfectant used in New York City, will be 4 mg/L. Based on 1998 data (Figure 5-5), New York City drinking water should not have difficulty meeting this requirement. Best Available Technology. The proposed D/DBP Rule makes recommendations for improving the performance of best available technologies to achieve new MCLs, MCLGs, MRDLs, and maximum residual disinfectant level goals (MRDLGs). No direct impact on New York City is expected because the treatment technologies recommended for control of TTHMs are enhanced coagulation and granular activated carbon adsorption, which must supplement filtration. Conclusions This chapter has discussed the types and sources of pollution that may have an impact on water quality in the New York City reservoirs. Predictions derived from the Generalized Watershed Loading Function (Table 5-8) indicate that the most important sources of phosphorus differ from basin to basin. The same is likely to be true for other priority pollutants. Some actual measures of reservoir water quality indicate a growing problem with the eutrophic health of the New York City water supply reservoirs (Table 5-9). All are classified as either mesotrophic or eutrophic, and some have variably high concentrations of phosphorus, chlorophyll a, and turbidity, particularly after large storm events and during certain seasons. Reservoir conditions are routinely more severe in the Croton reservoirs than in the Catskill/Delaware system reservoirs. Despite these conditions, source water and drinking water in New York City are in compliance with the SDWA. The Catskill/Delaware water supply currently meets the necessary criteria for disinfectant residual, inactivation ratio, TTHM, and total coliforms. No waterborne disease outbreaks have been recognized and documented. Given current water quality data and upcoming amendments to the SDWA, the Catskill/Delaware system may have difficulty complying with the newly promulgated D/DBP Rule, particularly the MCL for haloacetic acids. It is also likely that EPA will propose new regulations for microbial pathogens, particularly Cryptosporidium, in the next few years. Such regulations could cause the City to alter its disinfection process or use additional treatment facilities. Areas where the City may have difficulty maintaining compliance should be given high priority as the watershed management strategy is implemented.

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