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(ND)

"Range of urban runoff concentrations reflects variability of coefficient of variation of event mean concentrations for median urban sites. Data from USEPA (1983) presented in Novotny and Olem (1994, Table 1.3, p.36).

b Range of urban runoff concentrations for total N and total coliforms from Novotny and Olem (1994, Table 1.3, p. 36).

c Range of CSO concentrations for BOD5, TSS, total N, and total coliforms from Novotny and Olem (1994, Table 1.3, p. 36).

d Mean CSO concentrations of BOD5, TSS, and total lead from USEPA (1978) presented in Novotny and Olem (1994); median CSO concentrations of nitrogen constituents from Driscoll (1986); mean CSO concentration of total phosphorus from Ellis (1986).

"Range of urban runoff concentrations reflects variability of coefficient of variation of event mean concentrations for median urban sites. Data from USEPA (1983) presented in Novotny and Olem (1994, Table 1.3, p.36).

b Range of urban runoff concentrations for total N and total coliforms from Novotny and Olem (1994, Table 1.3, p. 36).

c Range of CSO concentrations for BOD5, TSS, total N, and total coliforms from Novotny and Olem (1994, Table 1.3, p. 36).

d Mean CSO concentrations of BOD5, TSS, and total lead from USEPA (1978) presented in Novotny and Olem (1994); median CSO concentrations of nitrogen constituents from Driscoll (1986); mean CSO concentration of total phosphorus from Ellis (1986).

e CBOD :BOD5 ratio from Thomann and Mueller, 1987.

dependent on many complex, and interacting, processes within a drainage basin. In contrast to the relatively continuous input of pollutants from point sources, the timing of loading from diffuse sources is highly variable with intermittent loading related primarily to meteorological events (storms and snowmelt). The magnitude of pollutant loads is dependent on the area of the drainage basin, the characteristics of land uses, including ground cover, and distribution of the volume of precipitation between infiltration into shallow aquifers and surface runoff into streams and rivers.

Within a watershed undisturbed by human activities, naturally occurring biogeo-chemical processes account for the continual cycles of organic and inorganic materials (as uncontrollable nonpoint source loads) transported from the land to rivers, lakes, and estuaries, with eventual discharge of these materials to the coastal ocean. Since it is the uses of the land and the associated activities that occur on the land within a drainage basin that contribute anthropogenic organic and inorganic materials to surface waters, nonpoint source loading rates have been related to the type of land use (Table 2-16). The most critical factor, however, in understanding the management of nonpoint source loading is characterizing the transition from one land use to another (e.g., forest to agriculture, agriculture to suburban/urban).

Beginning with the four natural land classifications (arid lands, prairie, wetland,

TABLE 2-16 Nonpoint Source Runoff Export Coefficients for General Land Uses

Parameter

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