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

Chapter: 5 Sources of Pollution in the New York City Watershed

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Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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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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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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-

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Another potential source of turbidity that should be considered is biogenic turbidity generated by phytoplankton in the reservoirs. Colloidal CaCO3, common to hard-water lakes and some of the New York City reservoirs, contributes to both reservoir turbidity and the characteristic blue-green color of the reservoirs. Colloidal carbonates are inorganic particulates that are largely induced by the photosynthetic activities of phytoplankton. Although thought not to be a significant problem at this time, increased algae growth within the reservoirs may eventually lead to increased turbidity, among other things.

Toxic Compounds

Because much of the Catskill/Delaware watershed region consists of undisturbed forest, it is far less likely than industrial regions to harbor hazardous wastes and toxic compounds that might pose a human or environmental health risk. However, there are a few specific types of hazardous compounds used on a regular basis in the watershed region, and there are also a small number of regulated hazardous waste sites. Because of the considerable uncertainty that surrounds the transport, fate, and toxicity of many of these compounds, additional information is needed to better assess and prevent exposure of humans and ecological receptors to these chemicals.

Pesticides are used on a regular basis in the Catskill/Delaware watershed, primarily on agricultural lands in the Cannonsville region. Residential and commercial use of pesticides also occurs throughout the Catskill, Delaware, West Branch, and Kensico watersheds. A comprehensive compilation of pesticide use in the watershed can be found in the 1993 environment impact statement for the watershed regulations (NYC DEP, 1993a). Some of the more prevalent compounds found in the watershed include alachlor, aldicarb, atrazine, carbaryl, carbofuran, chlorpyrifos, cyanazine, 2,4-D, and metolachlor, among others (NYC DEP, 1997b,c; Quentin, 1996). NYC DEP monitoring of pesticides has occurred primarily in the distribution system to comply with the Safe Drinking Water Act (SDWA), in aqueduct entry points (annually), and at Kensico stream sites. Regular and widespread monitoring of pesticides has not been conducted by NYC DEP or the Watershed Agricultural Program.

Sediment and surface water (mainly river water) samples have been found to have low levels of all the pesticides listed above (NYC DEP, 1997b; Quentin, 1996). In almost all cases, measured concentrations were below maximum contaminant levels (MCLs) for those compounds regulated under the SDWA. Concentrations of unregulated compounds were below 2 µg/L. The most frequently detected compound was 2,4-D, a weed-killing herbicide used throughout the watershed region for residential and commercial lawns (Quentin, 1996).

In addition to pesticides, other hazardous substances may be generated, stored, and disposed of in the Catskill/Delaware watershed. As of 1990, there were 35 petroleum storage facilities, 15 hazardous waste storage facilities, 1 haz-

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

ardous waste generator, and no hazardous waste disposal facilities in the West-of Hudson region (NYC DEP, 1993a). The most significant of these are the Richardson Hill Road landfill (a Superfund site) and the Rotron-Olive site, both of which are currently inactive (NYC DEP, 1993a). The Richardson Hill Road landfill lies within 500 ft of a tributary to the Cannonsville Reservoir. Volatile organic compounds and polychlorinated biphenyls (PCBs) have been detected in soil at the site and in groundwater beneath the site. Contaminated groundwater has also been detected in the drinking water wells of residents living in close proximity to the site. Potential health risks from this site are being mitigated by treating contaminated groundwater at private wells, by excavating contaminated sediments at the site, and by collecting and treating landfill leachate (EPA, 1999). In addition, each town in the Catskill/Delaware watershed has a municipal landfill that may or may not be closed. However, information about conditions at these sites is extremely limited.

General information about the types and amounts of hazardous substances generated at the other hazardous substance storage facilities in the Catskill/Delaware region (NYC DEP, 1993a) reveals that 44 percent of the 177,672 gallons of hazardous waste stored west of the Hudson River is acids and bases, 24 percent is inorganic compounds, 23 percent is metals or salts, 5 percent is volatile organic compounds, and 4 percent is unclassified. Those hazardous waste storage facilities that hold SPDES permits (and hence are regulated point sources) are discussed in the next section. It should be noted that none of New York State's top ten facilities for release of toxic compounds is located in either the West-of-Hudson or East-of-Hudson watershed regions (Toxics Release Inventory, 1996).

POINT SOURCES OF POLLUTION

Domestic Wastewater Treatment Plants

Domestic wastewater contains substantial concentrations of pathogenic microorganisms and must be discharged in an area that will ensure removal of pathogens before the effluent reaches groundwater (Veneman, 1996). Individual septic systems (OSTDS) and centralized WWTPs represent the two main strategies used to collect, treat, and dispose of domestic wastewater. Centralized sewage treatment systems collect wastewater from large numbers of residential and commercial facilities through pipes (sanitary sewers). The sewage travels through the pipes by gravity flow (which may be facilitated by occasional "lift stations") to a treatment works. Small-scale treatment works that serve perhaps a single subdivision are known as package plants; larger-scale systems serving entire communities are referred to as municipal treatment plants (Purdom, 1971). WWTPs are considered to be point sources of pollution because they discharge treated wastewater from discrete locations (effluent pipes) into a receiving water. In the Catskill/Delaware watershed, there are 39 WWTPs that discharge waste

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

into adjacent streams and two that discharge to the subsurface. Table 5-4 lists important parameters for the WWTPs in the Catskill/Delaware watershed.

Regardless of size, the basic treatment methodology of a centralized sewage treatment system can be summarized in a few basic steps. The first step involves screening large debris from the wastewater and grinding or macerating the remaining sewage. This slurry is then allowed to settle and the resulting sludge is digested aerobically or anaerobically in large tanks. This process, termed primary treatment, removes about 40 percent of the 5-day biochemical oxygen demand (BOD5) in the wastewater and 50-90 percent of the bacteria (Chanlett, 1979).

During secondary treatment, the liquid fraction of wastewater is subjected to degradation through contact with large numbers of microorganisms in an aerobic environment. Several technologies are used to maintain high levels of oxygen and maximize the contact between the sewage and the microorganisms. These include (1) trickling filters—rocks or plastic media covered with microorganisms, (2) activated sludge—a slurry of microorganisms subjected to intense mixing with atmospheric oxygen, and (3) rotating biological contactors—discs of large surface area colonized by microorganisms. The rotating action of the latter method alternately exposes the microorganisms to the atmosphere and wastewater. Secondary treatment removes approximately 85 percent to 90 percent of the BOD5 and 90 percent to 95 percent of the bacteria from the wastewater (Chanlett, 1979).

Tertiary treatment involves removal of nutrients such as phosphorus and nitrogen, sand filtration, and microfiltration, or other techniques that remove an additional five percent of the BOD5 (Chanlett, 1979). A few WWTPs in the Catskill/Delaware watershed currently use chemical precipitation in conjunction with tertiary sand filters to remove phosphorus, and more plants are expected to require chemical precipitation to comply with the MOA (D. Warne, NYC DEP, personal communication, 1999). Finally, most WWTPs chlorinate (and sometimes dechlorinate) their wastewater prior to discharge.

The entire treatment train (sequence) for one of the larger WWTPs in the region is shown in Figure 5-1. This treatment train, among the most sophisticated in the Catskill/Delaware watershed, includes all of the tertiary treatment upgrades mandated by the MOA, including microfiltration (see discussion below). Figure 5-2 shows a treatment train more typical of one of the smaller WWTPs in the watershed and does not reflect upgrades that will be installed as part of the MOA.

As part of the Watershed Rules and Regulations in the MOA, all sewage treatment plants in the watershed are being upgraded to meet new performance criteria and effluent standards, with upgrades scheduled for completion by 2002 (EPA, 1997). The most significant of these requirements for WWTPs that discharge to surface waterbodies are the following:

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-4 Municipal Wastewater Treatment Plants in the Catskill/Delaware Watershed

Reservoir/Watershed

SPDES Number

SPDES Permitted Flow (gpd)

1998 Actual Flowa (gpd)

1998 Effluent [Phos.]b (mg/L)

Months of Operation

Class of Receiving Streamc

Kensico

None

West Branch

Clear Pool Camp

NY-0098621

20,000

3,858

0.63

Year-round

B

Ashokan

Belleayre Mt. Ski Center

NY-0034169

15,000

2,230

1.61

Year-round

B(T)

 

 

14,000

4,220

1.00

 

D

Camp Timberlake

NY-0240664

34,000

10,000

2.43

June–Oct. 1

B(T)

Chichester

NY-0233943

9,900

NA

NA

Year-round

subsurface

Mountainside Rest.

NY-0251241

3,076

650

3.59

Year-round

B

Onteora Schools

NY-0099856

27,000

9,320

1.88

Year-round

B

Pine Hill

NY-0026557

500,000

285,250

0.43

Year-round

B(T)

E.G.&G Rotron, Inc.

NY-0098281

12,750

0

NV

Year-round

B/B(T)

Schoharie

Camp Loyaltown

NY-0104965

21,000

NV

0.13

June–Oct. 31

C

Colonel Chair Estates

NY-0101001

30,000

14,242

0.58

Year-round

C(TS)

Crystal Pond Twnhs.

NY-0223638

36,000

0

NA

Winter

C(TS)

Elka Park

NY-0092991

10,000

NV

0.77

May–Oct.

C(TS)

Forester Motor Lodge

NY-0100374

3,900

0

1.4

Year-round

C(TS)

Frog House Rest.

NY-0224731

1,788

985.5

17.48

Year-round

subsurface

Golden Acres Farm

NY-0069957

5,800

NV

1.48

July–October

C

 

 

1,100

 

1.73

 

 

 

 

2,300

 

1.99

 

 

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Reservoir/Watershed

SPDES Number

SPDES Permitted Flow (gpd)

1998 Actual Flowa (gpd)

1998 Effluent [Phos.]b (mg/L)

Months of Operation

Class of Receiving Streamc

Grand Gorge

NY-0026565

500,000

114,875

0.06

Year-round

C

Harriman Lodge

NY-0100277

20,000

10,000

0.80

June–Sept.

C(TS)

Hunter Highlands

NY-0061131

80,000

8,414

0.09

Year-round

C

Latvian Church Cmp.

NY-0072192

7,000

NV

1.4

July–August

C(TS)

Liftside at Hunter Mt.

NY-0212288

81,000

29,600

0.24

Year-round

C(TS)

Mountain View Estates Home

NY-0241261

7,000

2,717

4.05

Year-round

C

Mountain View Estates, Inc.

NY-0212407

6,000

2,550

1.8

Year-round

C

Ron-De-Voo Rest.

NY-0124672

1,000

<1,000

0.28

Year-round

NA

Snow Time

NY-0065315

120,000

3,800

2.33

Year-round

C

Tannersville

NY-0026573

800,000

334,714

0.10

Year-round

C(TS)

Thompson House Inc.

NY-0101168

4,775

2,200

5.33

May–Oct.

A(TS)

Whistletree Dev.

NY-0310821

12,450

NV

0.56

Year-round

C(TS)

Cannonsville

Delaware-BOCES

NY-0097446

2,500

1,000

1.35

Year-round

C(T)

Delhi

NY-0020265

515,000

390,000

3.12

Year-round

C(T)

SEVA Institute

NY-0205800

6,600

0

NA

Spring–fall

C(T)

 

 

1,200

 

 

 

 

Allen Center

NY-0029645

20,000

10,477

7.59

Year-round

C(T)

Stamfordd

NY-0021555

500,000

517,075

1.28

Year-round

C(T)

Village of Hobart

NY-0029254

160,000

40,000

3.20

Year-round

C(T)

Waltond

NY-0027154

1,170,000

1,387,125

0.52

Year-round

B(T)

Pepacton

Camp NuBar

NY-0023787

12,500

6,000

1.42

June–August

C(TS)

Camp T'ai Chi

NY-0104957

7,500

0

0.25

July–Sept.

B

Margaretville

NY-0026531

400,000

268,000

1.46

Year-round

A(T)

Mountainside Farms, Inc.

NY-0084590

49,800

11,700

17.44

Year-round

GA & GW

Regis Hotel

NY-0100382

9,600

6,167

1.50

April–Nov.

B(TS)

Roxbury Run

NY-0099562

100,000

37,914

1.59

Year-round

C

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Reservoir/Watershed

SPDES Number

SPDES Permitted Flow (gpd)

1998 Actual Flow a (gpd)

1998 Effluent [Phos.]b (mg/L)

Months of Operation

Class of Receiving Streamc

Rondout

 

 

 

 

 

 

Grahamsville

NY-0026549

180,000

96,666

0.3

Year-round

A(T)

Neversink

 

 

 

 

 

 

None

 

 

 

 

 

 

a Actual flow data are 1998 averages of monthly (30-day average) data from discharge monitoring reports to the NYS DEC. Only those months indicated in the months of operation column are included in the value.

b Average 1998 effluent phosphorus data are averages of monthly or biweekly data reported by NYC DEP. In most cases, these concentrations represent conditions prior to the installation of upgrades mandated by the MOA.

c See Appendix B for explanation.

d WWTP in exceedance of permitted flow on a regular basis.

NA = not applicable

NV = not available

Note: Bolded entries have received the WWTP upgrades mandated by the MOA. They are all city-owned facilities.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-1 Primary, secondary, and tertiary treatment at the Grahamsville WWTP. Source: NYC DEP (1998b).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-2 Sewage treatment at the Whistletree Development WWTP.  Source: NYC DEP (1998b).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 effluent standards:

1.0 mg/L for <50,000 gallons per day (gpd)

0.5 mg/L for 50,000–500,000 gpd

0.2 mg/L for >500,000 gpd

• 99.9 percent removal and/or inactivation of Giardia and enteric viruses

• upgrades of existing WWTPs to include sand filtration, disinfection, phosphorus removal, and microfiltration (or an approved alternative technology).

Some of these requirements have overlapping goals. For example, microfiltration can be used to achieve particulate phosphorus and microbial pathogen removal. It should be noted that five of the New York City-owned WWTPs are installing microfiltration (as illustrated in Figure 5-1) while most of the plants not owned by New York City will be using an alternative type of technology known as Continuous Backwash Upflow Dual Sand Filtration (EPA, 1998b). The equivalence of this technology to microfiltration and its ability to meet the required effluent standards are discussed in Chapter 11.

One significant benefit of WWTPs is the SPDES permit requirement for a trained operator (see Chapter 3). In addition, samples of the effluent are routinely analyzed to ensure that effluent quality standards are met. These factors are meant to ensure that the system functions as designed at all times and that corrective actions are applied in a timely manner.

In addition to treated wastewater, WWTPs produce partially digested sludge, or residuals. These residuals contain substantial amounts of nutrients and pathogens and some heavy metals. They are typically rendered free of detectable pathogens, or stabilized, by adding lime until the pH is too basic to support pathogenic microorganisms. These residuals must be properly managed to avoid creating a secondary source of contaminants. Though sludge treatment practices vary throughout the watershed, most solid waste generated by WWTPs is eventually buried in landfills within the watershed region or is moved outside the watershed boundaries (Warne, 1998a).

Although combined sewer overflows are not found in the Catskill/Delaware watershed, it is possible that stormwater can impact WWTP flows via inflow and infiltration (I/I) into sanitary sewer pipes and other infrastructure. These processes can greatly increase treatment plant flow, which may result in overflow conditions and a short-circuiting of the treatment processes. Much of the sewerage infrastructure in the Catskill/Delaware watershed predates the advent of sturdy and leak-proof pipe materials. At least 11 WWTPs west of the Hudson River have been identified as having problems with I/I (NYC DEP, 1993a). NYC DEP estimates that nearly every West-of-Hudson WWTP experiences I/I at a level that is approximately 25 percent of its average daily flow, with some plants receiving I/I that is equal to or greater than their permitted flow during large storm events (Warne, 1998b).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Other Point Sources

There are a small number of point sources other than municipal WWTPs in the Catskill/Delaware watershed, some of which are permitted (Table 5-5). Unlike sewage, the composition of industrial wastewater varies widely, depending on the type of industry. In addition, chemical concentrations may be extremely high in comparison to domestic wastewater. The industrial wastewater and cooling water discharges in the Catskill/Delaware region derive from dairy processing plants and hazardous waste treatment processes. There are also stormwater permits for industrial operations. As mentioned in Chapter 3, stormwater permits are often required for construction and industrial activities that affect five or more acres of land. For the purposes of this discussion, these permitted discharges are labeled point sources because they are regulated under Section 402 of the Clean Water Act (CWA).

Although few in number in comparison to municipal WWTPs, industrial point sources may still be responsible for pollutant loadings in the Catskill/Delaware watershed because of high effluent concentrations derived from these sources. For example, the average phosphorus concentration of wastewater from the UltraDairy facility that is sprayed onto nearby fields was 25.7 mg/L in 1998. This effluent phosphorus concentration is considerably higher than that associated with any municipal WWTP during the same year. Thus, industrial point sources cannot be ignored when determining the overall contribution of point sources to pollutant loadings in the water supply reservoirs.

NONPOINT SOURCES OF POLLUTION

Over the last quarter century, water quality across the country has improved dramatically, primarily as a result of technologies that have greatly reduced pollution from point sources. Despite this progress, EPA estimates that 40 percent of the nation's waterbodies still do not meet CWA standards of fishable and swimmable quality (EPA, 1998a). In New York State, 7 percent of rivers and streams and 53 percent of lakes and reservoirs do not fully support their designated uses (NYS DEC, 1996).

The dominant threat to water quality today is nonpoint source pollution, or polluted runoff, which derives from multiple diffuse sources. Technologies for reducing nonpoint source pollution are, in some respects, more difficult to design, implement, and monitor than those for point source pollution. In addition, the regulatory strategies that have proven successful in reducing point source pollution are inadequate for combating nonpoint source pollution (EPA, 1998a). Little regulatory pressure exists specifically to deal with nonpoint source pollution. For these reasons, the states have been slow to develop, implement, and enforce effective strategies for reducing polluted runoff.

Nonpoint source pollution has been blamed for several significant national pollution problems such as coastal eutrophication, leaching of nitrate into ground-

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-5 Other Point Sources in the Catskill/Delaware Watershed

Reservoir/Watershed

Type of Discharge

SPDES Number

SPDES Permitted Flow

Class of Receiving Streama

Ashokan

 

 

 

 

Shokan Post Office

Treated outflow from chemical spill

NY-0233889

 

A(T)

E.G.&G Rotron, Inc.

Treated outflow from solvent-contaminated site

NY-0098281

 

B(T)

Schoharie

 

 

 

 

Agway Petro

Stormwater and tank test water

 

 

C

Falke's Quarry

Stormwater runoff

NY-0223506

 

C(T)

Hunter Synagogue Remediation

Treated outflow from chemical spill

NY-0241041

 

C(TS)

Town of Hunter Landfill

Stormwater runoff from landfill

NY-0103107

 

D

Cannonsville

 

 

 

 

Kraft Inc. Dairy

Cooling water

NY-0008494

1,080,000

B(T)

Walton Town Garage

Discharge from an oil/water separator

NY-0249483

No limit

 

Dairyvest at Fraser (Ultra Dairy/DMV)

Dairy processing waste

NY-0068292

200,000

GA (spray irrig.)

 

Cooling water

 

720,000

C(T)

Mallincraft/Grahm Labs

Water with pharmaceutical and industrial chemicals

 

 

 

Audio-Sears, Inc.

Water/air with acids, heavy metals, electroplating

 

 

 

Pepacton

 

 

 

 

Railway Laundry Dry Cleaning

Water/air with dry cleaning chemicals

 

 

 

General

 

 

 

 

Town/County

Water via floor

 

 

 

DPW Buildings

drains from garage areas

 

 

 

a See Appendix B for an explanation.

Sources: Marx and Goldstein (1993) and Warne (1999a).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

water, and siltation of riverways and waterbodies. Consistent with national trends showing increased awareness of nonpoint source pollution, New York City has acknowledged the role of polluted runoff in degrading water quality in the Catskill/Delaware watershed (NYC DEP, 1998c). Both the New York State Department of Environmental Conservation (NYS DEC) and NYC DEP have developed programs for combating nonpoint source pollution from a variety of sources.

The activities that produce nonpoint source pollution in the Catskill/Delaware watershed are similar to those across the nation. In general, the predominant land uses of an area will determine what the major types of nonpoint pollution are. Table 2-6 reveals that agriculture, forestry, and urban development are likely contributors to nonpoint source pollution in the Catskill/Delaware watershed. The following section discusses these activities as well as the contributions of OSTDS and atmospheric deposition.

Agriculture

Modern agriculture focuses large amounts of energy, materials, and management on relatively small portions of the landscape. The high productivity gained in this way also leads to the potential for nonpoint source pollution. In general, as agriculture is practiced in most parts of the United States today, row crops are treated with fertilizers and pesticides and have the potential for contaminating surface waters with nutrients, pesticides, and sediment. Animal-based agriculture typically involves land application of manures or manure mixed with bedding material, which may contaminate surface waters with nutrients, organic matter, and biological pathogens. Both row-crop agriculture and animal-based agriculture can supply nutrients to groundwater.

Loadings per unit area of nonpoint source pollutants to surface water and groundwater resources are greater for most agricultural land uses than they are for undisturbed areas. Certain nonpoint source pollutants such as pesticides are wholly human-made and will not occur at all in unmanaged areas unless they are transported there through atmospheric or hydrologic processes. Other types of nonpoint source pollution such as sediment, nutrients, and organic matter may be increased as a result of agricultural management but also occur in unmanaged areas.

Agricultural land uses in the Catskill/Delaware watershed are primarily dairies; thus, pollutants associated with animal manure and dairy barnyards are the main concern. Manure contains high concentrations of nutrients, particularly nitrogen and phosphorus. Manure is also a potential source of parasitic protozoa such as Giardia and Cryptosporidium, pathogenic viruses and bacteria, and organic chemicals used for promoting animal survival (such as antibiotics). The other major sources of nonpoint pollution from dairy operations are row crops, hayfields, and pastures that are commonly grown for silage. Nonpoint source

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

pollution can result from the application of fertilizers, manures, and pesticides to these lands. There is also the threat of erosion and sediment transport from crops or pasturelands to nearby waterbodies. This may be exacerbated by agricultural activities such as plowing, harvesting, building of roads, and the movement of animals.

Agriculture comprises 4.5 percent of the total land use in the Catskill/Delaware watershed. The greatest impacts of agricultural runoff occur in the West Branch of the Delaware River and the Cannonsville Reservoir, where agriculture occupies 10 percent to 11 percent of the watershed. Runoff from barnyards, overland and shallow groundwater flow from manured fields, inundation of manured fields during floods, and general enrichment of groundwater phosphorus related to agriculture have been shown to contribute to eutrophication of the Cannonsville Reservoir (Brown et al., 1984; NYC DEP, 1997d; Robillard and Walter, 1984). Runoff from dairy barnyards was found to have an average total phosphorus concentration of 11.9 mg/L (Robillard and Walter, 1984). Mean phosphorus concentrations measured in surface water at a farm site (Robertson Farm) were as high as 3.8 mg/L compared to concentrations of less than 0.1 mg/L at a nearby control site (Shaw Road) (WAP, 1997). Finally, mean phosphorus concentrations during baseflow conditions on the West Branch of the Delaware River were estimated to be twice as high as mean phosphorus concentrations in groundwater from undisturbed areas (Brown et al., 1984).

Monitoring of streams above and below a dairy farm has also demonstrated that downstream water is enriched with Cryptosporidium oocysts in comparison to reference sites (NYC DEP, 1998a). Pesticides are also found in surface waterbodies of the Cannonsville watershed, but almost always at levels well below their regulated MCL.

Urban Stormwater

A second important class of activities that produce nonpoint source pollution are classified as ''urban." This term encompasses a wide variety of commercial, residential, and industrial activities such as road building, construction of housing, and the creation of golf courses, among other things. There are discrepancies regarding the amount of land in the Catskill/Delaware watershed that is urban. According to calculations done for the Total Maximum Daily Load (TMDL) Program, the amount of land classified as urban is less than 1 percent of the land area west of the Hudson River, 3.8 percent of the West Branch watershed, and 15.1 percent of the Kensico watershed (NYC DEP, 1999c–j). This analysis is likely to underestimate the total percentage of land in urban uses because it includes only impervious surfaces. (In fact, the TMDL documents state that some residential land was classified as forests.) Other analyses (Table 2-6) indicate a much higher percentage of the Catskill/Delaware watershed (17 percent) is urban.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Urban development can have a profound influence on the local hydrologic cycle and water quality. The hydrologic changes begin during the clearing and grading that accompany construction. Trees that had intercepted rainfall are felled, and natural depressions that had temporarily ponded water are graded to a uniform slope. The leaf litter and organic layer on the soil surface are scraped off, eroded, or severely compacted. Having lost its natural storage capacity, a cleared and graded site can no longer prevent rainfall from being rapidly converted into runoff.

Roof tops, roads, parking lots, driveways, and other impervious surfaces prevent rainfall from soaking into the ground. Consequently, most rainfall is directly converted into stormwater runoff. This phenomenon is illustrated by the strong correlation between site imperviousness and the runoff coefficient (Rv), which expresses the fraction of rainfall volume converted to stormwater runoff (rather than infiltrating into the soil). For example, a one-acre parking lot produces on average about 15 times more annual runoff than does a one-acre meadow in good condition (Schueler, 1995). Extensive drainage networks (using curbs and gutters, enclosed storm sewers, and lined channels) are necessary to rapidly collect and convey this additional stormwater runoff.

Increased stormwater runoff can significantly alter stream geometry. Following urban development, stormflow frequency and magnitude increase dramatically, causing a greater number of bankfull and sub-bankfull flow events. When streambeds and banks are exposed to destabilizing flows for long periods of time, their cross-sectional area increases (either by channel widening, down cutting, or both). Under extremely high flows, streams may undergo severe streambank erosion and habitat degradation. Indeed, the presence of impervious surfaces has been linked to declines in nearby stream insect, freshwater mussel, and fish diversity (Maxted et al., 1994; May et al., 1997; Schueler, 1995).

During storm events, accumulated pollutants are quickly washed off of impervious areas and are rapidly delivered to downstream waters. Some common pollutants found in urban stormwater runoff are profiled in Table 5-6. Although variable from storm to storm, in general the concentrations of pollutants in urban stormwater can be characterized by an event mean concentration (EMC) on an annual basis. Research indicates the EMC is the same for most pollutants, regardless of storm size, intensity, antecedent conditions, or other factors (EPA, 1983). Consequently, most models of urban stormwater runoff have pollutant loads increase in direct proportion to the amount or percentage of impervious cover in the watershed (Schueler, 1987). It should be noted that this relationship does not hold true for other types of stormwater (e.g., agricultural or forestry runoff).

There are few direct measurements of pollutant concentrations in urban stormwater in the Catskill/Delaware watershed. Efforts have been made to compare the incidence of polluted water samples from "urban" areas to those from "pristine" areas. Monitoring of Giardia and Cryptosporidium in stream samples across the watershed has revealed that ''urban" sources are enriched in both cysts

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-6 Average Event Mean Concentrations (EMC) Found in Urban Stormwater

Pollutants

EMCa

Total Suspended Solids

80 mg/L

Total Phosphorus

0.30 mg/L

Total Nitrogen

2.0 mg/L

Total Organic Carbon

12.7 mg/L

Fecal Coliform Bacteria

15,000–20,000 MPN/100 mL

E. coli

1,450 MPN/100 mL

Petroleum Hydrocarbons

3.5 mg/L

Cadmium

2 µg/L

Copper

10 µg/L

Lead

18 µg/L

Zinc

140 µg/L

Chlorides (winter only)

230 µg/L

Insecticides

0.1–2.0 µg/L

Herbicides

1–5.0 µg/L

a These concentrations represent mean or median storm concentrations measured at typical suburban sites, and may be greater during individual storms. Also note that mean or median runoff concentrations from stormwater hotspots are 2–10 times higher than those shown here.

Source: MDE (1999).

and oocysts as compared to stream samples from undisturbed areas (NYC DEP, 1998a). In fact, Cryptosporidium was detected in urban watersheds more frequently than in agricultural watersheds and in effluent from sewage treatment plants. These studies clearly demonstrate the importance of urban areas and impervious surfaces in contributing to pollutant loading. Urban sources of pollution are expected to be more significant in the Kensico and West Branch watersheds, which have a much higher percentage of urban land than the West-of-Hudson watersheds.

Forestry

The Catskill/Delaware watershed includes 667,517 acres of forest land or 68 percent of the total area. NYS DEC lands comprise about 22 percent of the forest land, mostly in the Catskill Forest Preserve. The largest contiguous block of forest preserve includes high-elevation and mountainside lands in the Esopus Creek (Ashokan Reservoir) watershed. NYC DEP owns a small percentage, largely adjacent to reservoirs, while private landowners hold the remaining acreage, usually lower slope and valley bottomland between state and city holdings. Ephemeral and intermittent streams link these lands to perennial tributaries and

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

downstream reservoirs. Hence, inappropriate land use in these areas can directly affect water quality.

It has been known for decades that without the careful application of best management practices (BMPs), the effects of forest harvesting on site stability and aquatic ecosystems can be severe. Numerous studies of traditional logging and farming practices have demonstrated that removal of riparian vegetation, haphazard road and skid trail construction, careless clearcutting and high-grading (cutting only large, valuable trees), and little or no professional supervision can lead to significant degradation of terrestrial and aquatic resources (Anderson et al., 1976; Satterlund and Adams, 1992; Swank and Crossley, 1988; Verry, 1986). In general, the largest relative impact is associated with roads, followed by skidding, site preparation, and then felling operations (Satterlund and Adams, 1992). The felling operation may cause appreciable short-term increases in water yield without corresponding increases in soil erosion and sediment transport (Bosch and Hewlett, 1982).

Reducing the density and biomass of forest cover increases rainfall reaching the soil surface, snowmelt rate in openings, and soil water content in the root zone. All three changes combine to increase water yield. The magnitude of the change is proportional to the area harvested, the biomass removed, and species composition of the stand (whether coniferous, deciduous, or mixed). However, the response rate is not uniform or incremental. Partial cuts produce comparatively smaller water yield increases than do seed-tree or overstory removal cuts. That is, although the same quantity of wood is harvested, a 100-acre clearcut generates more water than do 300 acre thinned by one-third of the original biomass. Because of reduced competition for water, light, and nutrients, partially cut stands tend to recover more quickly, as forest regeneration, herbaceous plants, and changes in microclimate (greater solar radiation and wind velocity at the surface) combine to restore evapotranspiration to pre-harvest levels in as little as three years (Brooks et al., 1997).

It has been more difficult to determine water yield response in relation to the fraction of the watershed subject to harvesting or conversion to another land use. Because of the biophysical and financial limitations associated with classical paired watershed experiments, most of what is known or hypothesized comes from retrospective analyses of streamflow and land use data for very large watersheds. The few convincing studies suggest 30 percent to 40 percent of a forested watershed must be clearcut before a substantial water yield or peak discharge increase is noted. The response rate increases between 30 percent and 60 percent to 70 percent harvested until stabilizing at 70 to 100 percent removal (Verry, 1986).

Due diligence in the application of forestry BMPs is the key to preventing adverse environmental impacts. These BMPs are discussed in more detail in Chapter 9.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

On-site Sewage Treatment and Disposal Systems

Individual septic systems (on-site sewage treatment and disposal systems or OSTDS) are frequent alternatives to sewage treatment plants in less densely populated areas where the costs of constructing sewage treatment systems are prohibitive. Properly sited and functional OSTDS receive, treat, and dispose of wastes in a manner that does not contaminate the environment or expose humans to pathogens. OSTDS are often considered nonpoint sources of pollution because they are small-scale and widely dispersed, and they discharge to relatively large subsurface areas. As with other nonpoint sources of pollution, measuring the impact of these systems on nearby water quality can be difficult. Performance monitoring of OSTDS effluent in the Catskill/Delaware watershed has not occurred on a regular basis and has only recently become a goal of NYC DEP's septic siting study (see Chapter 11).

The term OSTDS encompasses several technologies ranging from cesspits to aerobic treatment units. The most common OSTDS is the septic tank and drainfield shown in Figure 5-3. The septic tank is a watertight container with a typical capacity of 1,900–4,550 L, and it is designed to detain raw sewage discharged from a home or building. The septic tank is essentially a settling basin, in which the suspended solids are separated from the liquid fraction (EPA, 1980). The solids settle to the bottom of the tank where they are degraded by anaerobic bacteria. Lighter material, including fats, oils, and grease, accumulates at the

FIGURE 5-3 Septic tank and drainfield. Both parts of the system are generally underground.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

liquid surface. The liquid portion of the waste flows from the tank through an outlet near the top. This liquid is then distributed through perforated pipes into a subsurface drainfield or infiltration system. The removal of solids in the tank allows the effluent to be disposed to the subsurface drainfield without clogging the perforated pipes and soil, which would cause failure of the system (Canter and Knox, 1986).

The purpose of the drainfield is to distribute wastewater evenly to the soil. The soil beneath the drainfield filters out pathogenic microorganisms from the OSTDS effluent before it reaches groundwater. Once in the soil, pathogens on soil particles may succumb to unfavorable environmental conditions or be destroyed by aerobic microorganisms. Because aerobic conditions enhance destruction of pathogens, drainfields are usually placed only 61–76 cm beneath the surface. Properly sited and maintained septic tanks and drainfields remove approximately 80 percent of the BOD and virtually all of the total suspended solids. Removing pathogens from OSTDS effluent before it reaches groundwater is important because various studies have shown that bacteria and especially viruses can travel long distances (15–60 m) in groundwater down gradient of a properly sited and functioning OSTDS (Hagedorn et al., 1978; Moe et al., 1984; Parker et al., 1978; Paul et al., 1995; Vaughn et al., 1983; Yates et al., 1986).

The aerobic treatment unit (ATU) is the most effective OSTDS technology that is backed by third-party certification. It uses mechanical devices to mix atmospheric oxygen into the tank, which allows aerobic microorganisms to colonize the tank rather than the anaerobic microorganisms found in the conventional septic system. This results in more effective removal of pathogens and higher treatment efficiencies (Derge, 1983). Other innovative types of OSTDS that make use of aerobic environments include the Ruck system, which uses aquatic vegetation to aid degradation of the effluent, the Peat Moss filter, the recirculating sand filter, and a variety of waterless and composting toilets. However, unlike the ATU, these technologies have received limited testing and are not yet endorsed by most regulatory agencies across the country, including the New York State Department of Health (NYS DOH). Thus, they are not considered further in this report.

Among other types of OSTDS, the least efficient is the cesspit. This is simply an underground tank without a bottom that allows the liquid fraction of the wastewater to percolate into the soil with little or no degradation by soil organisms. Cesspits are not legal in the New York City watershed, although old or illegally installed cesspits may be of concern.

One of the primary limitations of OSTDS is that they provide little removal of nutrients (details provided in Chapter 11). A variety of experimental systems that remove nutrients are being studied, including those that use small rotating biological contactors or recirculating sand filters. The latter system attempts to maintain colonization of the treatment media for vacation homes or other facilities not subject to regular dosing with domestic sewage. As with WWTPs, solid

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

waste that accumulates in OSTDS must be properly disposed of on a regular basis. The six New York City-owned WWTPs in the Catskill/Delaware watershed can accept and treat the sludge generated by OSTDS (known as septage), but the extent to which this is carried out is not known (D. Warne, NYC DEP, personal communication, 1998).

The 31,270 OSTDS in the Catskill/Delaware watershed (NYC DEP, 1993a, Table VIII.F-1) represent a significant potential source of contamination to the reservoirs. Individual systems (22,454) have flows of less than 1,000 gpd and are regulated by NYS DOH and the County Health Departments under 10 NYCRR Appendix 75A. Intermediate systems (59) discharge more than 1,000 gpd and thus operate under SPDES permits, necessitating oversight by either NYS DOH or NYS DEC. Small, nonresidential systems (such as restaurants) with flows of less than 1,000 gpd (7,754) are classified as "other" systems and are regulated by NYS DOH. Regardless of the classification, failing OSTDS must be detected and repaired rapidly through a vigorous enforcement effort if contaminants are to be prevented from degrading surface water quality.

Atmospheric Deposition

Atmospheric deposition is a source of nonpoint pollution that is difficult to quantify and control. Both wet and dry deposition of chemicals, such as acids and nitrogen compounds, can result from industrial activities that produce large amounts of airborne pollutants. Atmospheric deposition onto land areas can be transported to waterbodies via surface runoff. For this reason, some atmospheric deposition may be treated by the BMPs primarily designed to treat land-based sources of nonpoint pollution. However, direct deposition into reservoirs also occurs, and this source of pollution is much more difficult to control.

As shown in Table 5-7, dry and wet deposition are relatively important sources of nitrogen, sulfate, and acids. In particular, atmospheric deposition is the primary mechanism for transporting SO2 (gas), sulfate particles, and sulfate-containing aerosols to the watershed region. When dissolved in precipitation, sulfate is a major component of acid rain. Sulfate ions do not substantially influence the total alkalinity and stability of the water that New York City receives. However, the associated acid rain may result in changes in species composition within forested areas. Fortunately, atmospheric deposition of sulfate has been decreasing in the watershed region since the late 1980s, probably a result of sulfur emission controls on power plants in the Midwest and East following the 1990 Clean Air Act Amendments (Murdoch et al., 1998).

Nitrogen, and the associated acidity, is the primary pollutant of concern in atmospheric deposition in the Catskill/Delaware watershed, as discussed previously. In contrast to the atmospheric deposition of sulfur, the atmospheric deposition of nitrogen has been increasing in the watershed region because of increasing vehicular emissions (number of cars and number of miles driven), despite the

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-7 Speciation of Atmospheric Deposition in the Northeastern United States

Processes

Nitrogen Species

Sulfur Species

Hydrogen Ions

Other Inorganics

Wet Deposition

NO3, NH4+

SO42–

H+

Ca2+, Mg2+, K+, Na+, Hg2+

Dry Deposition, Particles and Aerosols

NH4NO3, (NH4)2SO4NH4HSO4

NH4HSO4(NH4)2SO4CaSO4MgSO4

H2SO4

Ca2+, Mg2+, K+, Na+, carbonates/ oxides (dust)

Dry Deposition, Gases

NOx, NH3

SO2

HNO3

Hg(O)

Note: Largest contributions are in bold type.

Clean Air Act Amendments of 1990. Wet deposition of nitrogen falls primarily as nitrate ions, while dry deposition occurs as NOx gas, HNO3, and ammonium nitrate and ammonium sulfate aerosols. Deposition of nitrate and ammonia are important contributions to overall watershed nitrogen budgets in forested watersheds, but are relatively insignificant in agricultural settings where nitrogen fertilizers are often used. Total nitrogen modeling and load allocation in the New York City watershed region has not been performed because the reservoirs have been shown to be primarily phosphorus-limited and because nitrogen water quality standards have not been exceeded.

Finally, there is the potential for atmospheric deposition of mercury into the water supply reservoirs and associated detrimental effects on fish health. A few fish caught in the Neversink and Rondout reservoirs have been found to have high mercury levels in their tissues, most likely attributable to mercury deposition into these acidic watersheds (Murdoch, 1999). NYC DEP monitoring of the water supply has detected mercury in concentrations near the detection limit, suggesting that it is not a cause for concern at this time (Warne, 1999b).

WEIGHING POINT AND NONPOINT SOURCES

Assessing the contributions of point and nonpoint sources to overall pollutant loading is a critically important watershed management task. Such an analysis can direct monetary, personnel, and other resources toward the most polluting sources. In the New York City watershed, this type of evaluation is easily conducted using models developed for the Total Maximum Daily Load (TMDL) program. A thorough description of the TMDL program, including data requirements, modeling efforts, and evaluation, is found in Chapter 8.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

This discussion is limited to total phosphorus because, as of 1999, TMDLs have been calculated only for that priority pollutant. Table 5-8 and Figure 5-4 show TMDL model predictions of the relative contributions of point and nonpoint sources of phosphorus for each Catskill/Delaware basin. For the purposes of this analysis, point sources include WWTPs and the contributions from upstream reservoirs. Nonpoint sources include agriculture, urban runoff, OSTDS, ambient conditions emanating from pristine areas (forestland), groundwater (which reflects other nonpoint sources), and atmospheric deposition over water. For the six West-of-Hudson reservoirs, the predictions were generated by the Generalized Watershed Loading Function, a terrestrial runoff model that is discussed in detail in Chapter 8. The Reckhow model was used for the Kensico and West Branch watersheds.

Table 5-8 clearly demonstrates that sources of pollution in the six West-of-Hudson basins, West Branch, and Kensico are very different from one another. The more terminal reservoirs (Ashokan, West Branch, Kensico, and Rondout) receive almost their entire phosphorus loading from upstream reservoirs. This fact underscores the importance of watershed management in upstream areas to the maintenance of high water quality in these reservoirs. Schoharie and Pepacton reservoirs receive phosphorus from multiple sources of approximately equal magnitude: groundwater, agriculture, and forest land. Cannonsville, the most developed of the West-of-Hudson watersheds, is affected primarily by agriculture and then by forest land, groundwater, and WWTPs including several dairy-processing plants. Finally, runoff from undeveloped areas (forests) comprises the majority of phosphorus loading to the Neversink Reservoir. Impervious surfaces, septic systems, and atmospheric deposition over water contribute relatively little total phosphorus to the reservoirs. It should be noted that the groundwater category in the Generalized Watershed Loading Function may contain dissolved phosphorus derived from urban, agricultural, and forest sources as well as OSTDS. Because of its relatively significant contribution, further differentiation of the groundwater category should be a goal of future modeling efforts. The implications of the relative contributions of point and nonpoint source pollution for New York City's overall watershed management strategy are discussed in Chapter 12.

CURRENT STATE OF HEALTH OF THE WATERSHED AND WATER SUPPLY

This chapter closes with an overview of current conditions in the New York City watershed and water supply. As introduced in Chapter 3, there are important ecological and human health concerns related to drinking water supply systems. Water quality in the water supply reservoirs has a direct impact on aquatic ecosystems and habitats, particularly during eutrophication events. Although few epidemiological studies have conclusively linked waterborne DBPs to human

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-8 Predicted Range of Percent Contributions of Point and Nonpoint Source Total Phosphorus Loading into Individual Reservoirs from 1993 to 1996

Reservoir

WWTP

Upstream Reservoirs

Urban Areas

Septic Systems

Agriculturea

Forest Landb

Groundwaterc

Atmospheric Deposition over Water

Ashokan W

<1

5–30

<1

1–3

3–4

38–74

12–25

<1

Ashokan E

<1

84–94

<1

1–4

1–3

2–7

1–3

1–4

Cannonsville

7–20

0

<1

1–2

43–57

13–20

13–21

<1

Neversink

0

0

<1

<1

15–19

48–61

19–33

<1

Pepacton

1–2

0

<1

1–2

29–34

39–51

14–27

<1

Rondout

0–1

26–58

<1

1–2

14–29

16–33

6–10

<1

Schoharie

2–5

0

1

2–4

25–30

31–45

19–32

<1

Kensicod

0

95

2

<1

2

<1

ND

<1

West Branchd

<1

93

2

1

1

2

ND

1

Note: All values are percentages (%) of basinwide phosphorus loading (mass/time). The West-of-Hudson contributions are derived from the Generalized Watershed Loading Function.

a Agriculture is the combination of six subgroups: grass/shrub, grass, bare soil, corn, alfalfa, and barnyard.

b Forestland is the combination of three subgroups: deciduous forest, coniferous forest, and mixed forest.

c Sources of pollutants in groundwater are not defined in the GWLF. They may derive from multiple other nonpoint sources.

d Kensico and West Branch point and nonpoint source contributions were calculated using the nested Reckhow model, which does not include groundwater as a category.

Source: NYC DEP (1999c–j).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-4 Relative contributions of point, nonpoint, and upstream sources to phosphorus loading in the Catskill/Delaware reservoirs. The thickness of the arrow represents the relative contribution to total inflow (Table 5-8).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

health problems, some of these compounds are known carcinogens and are regulated by the SDWA. Finally, waterborne microbial pathogens, most notably Cryptosporidium and Giardia, are a constant concern, particularly for systems using disinfection as the sole treatment process.

Reservoir Water Quality

Direct human access to the New York City water supply reservoirs is limited to recreational fishing from row boats, shores, or bridges. However, human activities within the drainage basins have significantly influenced reservoir water quality. The poorest water quality is associated with areas that have significant population growth (see Chapter 2), particularly east of the Hudson River in the Croton system. Water quality in the Catskill and Delaware systems is better, in relative terms, because population densities are lower and a larger proportion of the watersheds is forested. The greatest threats to the reservoirs from watershed uses are microbial contamination and eutrophication caused by nutrient enrichments.

The inflow of nutrients, particularly phosphorus, to the New York City reservoirs is sufficient to promote moderate to abundant phytoplankton growth. Average chlorophyll a concentrations are a reasonable estimate of phytoplanktonic biomass, and these data have been coupled to the average total phosphorus (TP) concentrations contained in reservoir water. As shown in Table 5-9, phosphorus concentration data indicate all reservoirs are either moderately productive (mesotrophic) or productive (eutrophic). To date, none of the reservoirs has reached levels of productivity that raise serious health problems related to algal toxicity. However, decomposition of phytoplankton can increase dissolved organic carbon and subsequent DBP formation.

Long-term analyses suggest average total phosphorus concentrations within some of the reservoirs are slowly increasing (NYC DEP, 1993b). In some of the reservoirs, the average annual total phosphorus concentration exceeds 20 µg/L, a concentration known to induce eutrophic development of phytoplankton. The problem is particularly severe in the Cannonsville Reservoir, which is routinely taken offline during the summer and fall because of high algae levels (NYC DEP, 1993b). Current phosphorus levels and the associated formation of DBPs meet regulatory requirements in the other Catskill/Delaware reservoirs. However, reductions of phytoplankton in all reservoirs may be essential to meet regulatory standards for DBPs by 2002.

Another significant water quality impairment in the Catskill/Delaware watersheds is sediment loading and turbidity. The Ashokan and Schoharie reservoirs intermittently evince problems from erosional loading of quartz and clay particles that cause unacceptably high turbidity levels (Effler et al., 1998). Although this problem is largely attributed to geologic characteristics of some tributary streams (e.g., Stony Clove in the Esopus Creek watershed), opportunities to

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 5-9 Estimate of Phosphorus Concentration, Chlorophyll a Concentration, and Watershed Phosphorus Loading to New York City Reservoirs

Reservoir

Averagea P µg/L

Averagea Chl a µg/L

Vollenweider RMb Current Loading g/m2 y

Reckhow RMb Current Loading g/m2 y

Trophic State

Catskill/Delaware System

Ashokan

13

4.3

0.50

0.52

Mesotrophic

Cannonsville

22

11.6

1.49

1.55

Eutrophic

Neversink

6

3.5

0.39

0.31

Mesotrophic

Pepacton

12

5.3

0.80

0.61

Mesotrophic

Rondout

10

4.5

2.04

1.91

Mesotrophic

Schoharie

14

4.4

2.13

1.78

Mesotrophic

Kensico

12

 

3.09

3.14

Mesotrophic

Croton System

Amawalk

19

8.9

0.53

0.58

Eutrophic

Bog Brook

16

4.6

0.19

0.30

Eutrophic

Boyd Corners

18

4.5

0.67

0.75

Eutrophic

Cross River

15

7.4

0.26

0.34

Eutrophic

Croton Falls

22

9.5

0.75

0.72

Eutrophic

Diverting

30

13.7

3.92

4.43

Eutrophic

East Branch

22

12.0

1.27

1.29

Eutrophic

Middle Branch

17

8.1

0.48

0.54

Eutrophic

Muscoot

22

11.5

2.02

2.08

Eutrophic

New Croton

20

8.7

1.34

1.24

Eutrophic

Titicus

14

6.9

0.35

0.38

Eutrophic

West Branch

14

5.0

0.49

0.51

Eutrophic

a Average of data measured in the epilimnion of the lacustrine zone from May through October (growing season) from the period 1988–1996.

b RM = reservoir model. The Vollenweider and Reckhow reservoir models use data on in-reservoir phosphorus concentration to determine phosphorus loading. Phosphorus concentration data from the period 1984–1991 were used.

Sources: NYC DEP (1993b, 1999b).

control sediment emanating from unpaved roads, stormwater from impervious surfaces, and unstable streambanks should not be neglected. Water diversions from the Schoharie Reservoir to the upper Esopus Creek via the Shandaken Tunnel also may contribute to sediment transport.

Finally, accidental spills of hazardous or other materials in the watershed can have acute, short-term effects on water quality in the water supply reservoirs. During the last five years, there have been no substantial spills of hazardous material that resulted in a discharge to the water supply reservoirs (Warne, 1998b).

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

Compliance with the Safe Drinking Water Act

The ambient quality of New York City's drinking water is also indicated by its ability to comply with all provisions of the SDWA and the Surface Water Treatment Rule (SWTR). This includes meeting regulatory standards for chemical and microbial parameters, as well as demonstrating an absence of waterborne disease. This section discusses both current and potential future compliance with specific provisions of the SDWA.

Surface Water Treatment Rule

Disinfectant Residual. Because disinfection with chlorine is the only regular treatment given to New York City's drinking water, NYC DEP ensures chlorine residuals are sufficient to comply with federal regulations. The SWTR currently requires water at the entry point to the distribution system to have a disinfectant concentration of at least 0.2 mg/L. As shown in Figure 5-5 (chlorine residual at two entry point locations in the distribution system during 1998), New York City is currently meeting this requirement. These data indicate chlorine residuals so far above the minimum requirement that little difficulty is expected in meeting this requirement in the future as long as the City maintains its current disinfection practice.

CT. The chlorine concentration multiplied by the contact time, or CT, is the metric used to comply with the SWTR requirement for 3-log removal of Giardia and 4-log removal of viruses. NYC DEP calculates actual CT values for the City's distribution system and divides them by the CT value dictated by EPA regulations, generating an Inactivation Ratio (IR). New York City is required to keep this ratio above 1.0; however, NYC DEP strives to achieve an IR of 2.0. Vigilance is most necessary during winter, when low temperatures reduce the effectiveness of chlorine. New York City drinking water is currently meeting CT requirements. Typical data, collected during January 1997, are shown in Figure 5-6.

Total Trihalomethanes. DBPs such as trihalomethanes are of considerable concern for water supplies that rely on chlorine as the sole treatment process. The current MCL for total trihalomethane (TTHM) in drinking water is 0.10 mg/L. Since NYC DEP began measuring this parameter in 1993, this standard has been met (Figure 5-7). As discussed in Chapter 3, the Stage 1 Disinfectants/Disinfection By-Products (D/DBP) Rule MCL for TTHM is 0.080 mg/L, although this standard will not become effective until November 2001. Based on the quarterly compliance data from the Catskill/Delaware system (March 1993 through December 1998) New York City drinking water should meet this TTHM requirement.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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-

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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 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

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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.
×

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.

Suggested Citation:"5 Sources of Pollution in the New York City Watershed." 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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