inventory of point sources of residuals discharges to U.S. waterways. This 

 included some data on baseline values of ambient water quality in terms of 

 total suspended solids (TSS), temperature, and pH. Especially for the work 

 reported here we gathered data on characteristics of U.S. waters by state in 

 terms of ability to support any fish populations at all, and dominant fish 

 populations supported, prior to implementation of the Fish and Wildlife Protection 

 and Conservation Act and the Clean Water Act (FWPCA and CWA) . 



Baseline Discharge Inventory 



Estimates of pollutant discharges from point source sectors were made for 

 1972 levels of control. The basic approach for most point source sectors was 

 to assemble a plant inventory showing county location and plant output for all 

 plants, by industry, in 1972. EPA-developed waste coefficients, based on survey 

 data from actual plants, were then used to estimate total waste generated at 

 the plant in 1972 assuming no end-of-pipe pollution control. The actual end-of- 

 pipe wastewater treatment equipment in place in 1972 was then determined for 

 each plant wherever possible. Standard removal efficiencies associated with 

 this equipment were assumed and application of these efficiencies to estimated 

 raw loads produced estimates of actual discharges for 1972. The basic source 

 of data used in this project was a set of technical reports known as Development 

 Documents , prepared by the Effluent Guidelines Division of the U.S. EPA. 



Estimates of annual pollutant discharges from municipal sewage plants by 

 county were derived from data on Biological Oxygen Demand (BOD) and TSS discharges 

 from 24,209 individual municipal sewage treatment plants surveyed in the 1974 

 EPA's "Needs Survey" (U.S. EPA 1975). 



The pollutants carried in nonpoint source discharges were also estimated 

 for all nonpoint source sectors at the county level of detail. For certain 

 sectors (e.g., irrigation section flow, urban runoff, stream bank erosion, and 

 acid mine drainage), we relied on the analyses of other investigators and 

 accepted their estimates of annual pollutant discharge. For a second set of 

 sectors (e.g., ship ballast cleaning, accidental oil spills, and recreational 

 boating), national estimates of discharges were prorated to counties using 

 detailed information on the location and extent of each sector's activities. 

 For a third set of sectors (e.g., sediment from construction and mining), 

 national estimates of discharge were prorated to counties according to the 

 county's share of employment in these activities weighted by an estimate of 

 runoff per acre. 



A set of county-by-county estimates of sediment loss and sediment-related 

 pollutant discharge from nonirrigated cropland, woodland, pastureland, and 

 rangeland were derived from estimates of gross soil erosion made by the U.S. 

 Department of Agriculture (USDA). The USDA estimates were made by applying 

 the Universal Soil Loss Equation (USLE) to about 200,000 field sample points 

 as part of the 1977 National Resource Inventory. We then estimated sediment 

 delivery ratios and ratios for pollutants attached to sediment for 156 

 geographically homogeneous regions and assumed them to be constant for all 

 counties within each region. 



The county-by-county discharge estimates are linked to a detailed water 

 quality network model. This network model consists of 304 rivers, 175 lakes 

 and reservoirs, and 37 bays. A total of 1,051 nodal points have been established 

 along the rivers included in the model. See the schematic in figure 1. Each 



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