Duration of water quality objective exceedance for storm water runoff in streams
Conference
·
OSTI ID:85947
- Woodward-Clyde Consultants, Oakland, CA (United States)
Storm water runoff data in 4 major streams of Santa Clara County (CA) has been collected for the past 6 years using flow-composite samplers. When flow-weighted concentrations exceed the acute water quality objective (WQO) that is protective of freshwater aquatic life, it was assumed that the duration of exceedance may be as long as the entire duration of the runoff event. Runoff events ranges from 6 to 48 hours. To evaluate the actual duration of exceedance, discrete runoff samples were taken during the rising, peak, and receding limb of the hydrograph over 6 storm events in a large stream. Total and dissolved metals (copper, lead and zinc), hardness, and total suspended solids were analyzed. Hardness changed dynamically during the course of the storm, with decreasing hardness (and correspondingly decreasing WQOs) during high flows due to greater contribution of fresh rainfall, and increasing hardness with low flow as the storm recedes. Comparing results with acute WQOs over the storm showed that the duration of exceedance was shorter than the actual storm duration; average duration of exceedance (expressed as % of runoff duration) is 60% for total copper, 40% for total zinc, and 20% for total lead. None of the dissolved metals exceeded WQOs.
- OSTI ID:
- 85947
- Report Number(s):
- CONF-9410273--
- Country of Publication:
- United States
- Language:
- English
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