indicated on Figure 1. In addition, a summary of EPA's ongoing efforts 
to expand the database available for contaminant source 
characterization is presented. 
Sources of Toxic Chemicals 
Toxic chemicals entering Puget Sound originate from two types of 
sources: point sources and nonpoint sources. Point sources are most 
readily identified and monitored as they are associated with an outfall 
pipe. Point sources include inputs such as municipal and industrial 
outfall discharges. There are over 350 permitted discharges in the 
Puget Sound basin (USEPA, 1985). Approximately 180 discharge directly 
to the Sound with the remainder discharging to rivers that drain to the 
Sound (USEPA, 1985). Nonpoint sources are not associated with an 
outfall pipe; rather they are spread out over a large land area. These 
sources include riverine flow, urban runoff, agricultural runoff 
containing animal wastes as well as agricultural chemicals, runoff from 
logging operations, shoreline erosion, atmospheric inputs from car 
exhausts or industrial emissions (atmospheric deposition), contaminated 
groundwater entering the Sound, septic systems, sewer overflows, 
spills, and boat discharges. Point sources and some nonpoint sources 
such as runoff from dairy farms are regulated under the National 
Pollution Discharge Elimination System (NPDES) permit system. 
Relative Source Contributions 
Preliminary estimates of toxic chemical mass loadings have been 
computed for the following five subcategories: municipal; industrial; 
riverine; shoreline erosion; and atmospheric deposition. Loadings 
have been computed for select metals, for the polychlorinated biphenyls 
(PBCs), and for polynuclear aromatic hydrocarbons (PAHs). The results 
of these loading computations are presented below. First, however, the 
limitations of available contaminant concentration data will be 
summarized to emphasize the preliminary nature of the computed 
contaminant loadings. Estimates of inflow and material input are 
subject to similar limitations which will not be detailed in this 
report. 
Riverine 
Available metals data were limited both in the numbers of rivers 
sampled and in the numbers of samples per river. The available data 
were used to develop single values for riverine metals concentrations. 
A crude estimate of the possible organic concentration in Puget Sound 
rivers was obtained from limited data available for the upper Duwamish 
(Green) and Puyallup Rivers and the Lake Washington Ship Canal. 
15 
