Point versus Nonpoint Source Pollutant Loads in the 1990s

Municipal wastewater discharges account for only one source of pollutants to the Hudson River. In order to properly place the magnitude of municipal wastewater loads in the context of the total pollutant loads discharged to the Hudson River, estimates of the contributions from the Upper Hudson and Mohawk river basins discharging over the dam at Troy, New York and nonpoint sources from the middle and lower Hudson basins have been compiled as a budget based on conditions during the 1990s. Loadings were based on estimates from Johnson (1994), Johnson and Hetling (1995), and HydroQual (1991) as described in Hetling et al. 2003. Point sources include municipal and industrial WTPs and CSOs. Nonpoint sources include land-use-dependent surface runoff of water and pollutant loads. Land uses of the Hudson basin are broadly categorized as urban, forest, crops, and pasture lands to estimate nonpoint source loading rates (Johnson and Hetling, 1995). Annual averaged flow and nonpoint pollutant loading rates for the Upper Hudson and Mohawk basin at the Troy Dam and the middle Hudson basin are taken from Johnson (1994) and Johnson and Hetling (1995). Estimates of annual average flow and nonpoint and CSO flow and pollutant loads to the lower Hudson New York-New Jersey metropolitan region are taken from HydroQual (1991).

Over 79 percent of the population served by WTPs in the Hudson River watershed is from the lower Hudson metropolitan area (Fig. 23.4). The less densely populated middle and upper Hudson watersheds contain only 19 percent of the basin's totalpopulation. However, thepredominantsource of flow (67 percent) in the watershed is from its major subbasin, the upper Hudson above the Troy Dam.

In part reflecting this geographic disparity in distribution of population and sources of flow, the principal components of loading to the Hudson River watershed vary considerably by the type of contaminant. For example, the Upper Hudson contributes 71 percent of the TSS to the system (Fig. 23.4). With solids loads greatly reduced by upgrading to full secondary treatment, the solids contribution from WTPs (ca. 90 mt d-1) represents only 6 percent of the total solids budget.

While flows and TSS are dominated by contributions from above the Federal dam at Troy, sources ofBOD5 are more evenly distributed between lower Hudson point sources (38 percent), middle and lower Hudson nonpoint sources (33 and 34 percent), and contributions from above the dam (25 percent). Lower Hudson point sources dominate loadings of nitrogen and phosphorus at 57 percent and 65 percent, respectively. The other nutrient sources in order of significance include the upper Hudson, and middle Hudson point and nonpoint sources (Fig. 23.4).

Note that CSOs contribute 1-3 percent of the total input of TSS, BOD5, and nutrients. However, as noted below, they are the dominant source of fecal coliform bacteria and floatables. Thus the principal reason for controlling CSOs is not to reduce TSS and BOD5or nutrients, but rather to alleviate impacts from floatables and pathogens.

Population 67%

Flow Total Suspended Solids

□ Metropolitan Wastewater

P Metropolitan Non Point

E3 Metropolitan CSO

H Mid Hudson Wastewater

gH Troy Dam

HE Mid Hudson Non Point Source

Figure 23.4. Percentage distribution of population served (8.41 million), flow (4.78e7 m3 d 1), and effluent loads of BOD5 (238 mt d-1),TSS (1,469 mtd-1), TN (145 mt d-1) and TP (17.1 mtd-1) for point and nonpoint sources of the middle Hudson and lower Hudson basins ca. 1990s.

Figure 23.4. Percentage distribution of population served (8.41 million), flow (4.78e7 m3 d 1), and effluent loads of BOD5 (238 mt d-1),TSS (1,469 mtd-1), TN (145 mt d-1) and TP (17.1 mtd-1) for point and nonpoint sources of the middle Hudson and lower Hudson basins ca. 1990s.

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