Appraisal of storm-water quality near Salem, Oregon

Water-Resources Investigations Report 87-4064




Stormwater runoff for the period December 1979 to May 1981, at 13 sites (12 basins) in the vicinity of Salem, Oregon, was sampled and analyzed for water quality. Constituent concentrations for urban storm water were relatively small when compared to samples from Portland and Medford, Oregon and to samples from Denver, Colorado. The data indicated that levels of suspended sediment, ultimate CBOD (carbonaceous biochemical oxygen demand), and total lead increased with increased urbanization. Much of the suspended sediment and related turbidity result from transport of basin soils rather than from the wash-off of dry fallout solids from impervious areas. Because of small chemical concentrations and winter high flow and low temperature conditions in the Willamette River, Salem storm water probably has little effect on biological or on most chemical conditions in the Willamette River. An analysis of data from a stormwater detention pond (originally designed to reduce peak flows) indicated that the facility was about 47% efficient in reducing suspended sediment loads. The facility also reduced such sediment-related constituent loads as total lead and total phosphorus. Total Kjeldahl nitrogen and ultimate CBOD loads that are transported mostly in the dissolved phase were not measurably affected by the detention pond. Precipitation samples collected at one site for a year were found to be acidic, with a median pH of 4.6. Median total lead concentration was 8 micrograms/L (ug/L) in precipitation, whereas the median total lead concentration in runoff from the 12 basins ranged from 8 to 110 ug/L. The median dissolved ammonia concentration in precipitation was larger than the median dissolved ammonia concentration at all 13 sites. In contrast, the median total Kjeldahl nitrogen concentration in precipitation samples was about half the median for streamwater concentrations. Median ratios of sulfate to chloride and nitrate to chloride in precipitation were much higher than ratios expected for sea water, suggesting anthropogenic sources for sulfate and nitrate. (Author 's abstract)

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Appraisal of storm-water quality near Salem, Oregon
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Water-Resources Investigations Report
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U.S. Geological Survey,
iv, 29 p. :ill., map ;28 cm.