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(557) Effects of Urbanization on Water Quality in a Small Watershed.
Majewski, Michael*,1, Foreman, William2, Mendez, Gregory3, Baranov, Peter4, 1 US Geological Survey, Sacramento, CA, USA2 US Geological Survey, Denver, CO, USA3 US Geological Survey, San Diego, CA, USA4 Sweetwater Authority, Spring Valley, CA, USA
ABSTRACT- The air, water, and reservoir bed sediments in a small, southern California, urban watershed have been sampled regularly since 1998 and analyzed for chemical contaminants including volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons (PAHs), pesticides, and trace elements. The Sweetwater watershed contains two drinking water reservoirs where recreational boating and swimming are not allowed. A variety of projects protect the water quality in the reservoirs including a runoff diversion system that channels all urban and first flush watershed runoff around the primary water supply reservoir. These management practices offer a unique opportunity to investigate the effects of air quality on an urban drinking water supply. Pesticides (average concentration) routinely found in the reservoir water are simazine (17 ng/L), prometon (14 ng/L), and diazinon (5 ng/L). In air, chlorpyrifos (0.7 ng/m3), diazinon (1.8 ng/m3), malathion (0.4 ng/m3), maloxon (0.2 ng/m3), DDE (0.05 ng/m3), dacthal (0.06 ng/m3), trifluralin (0.09 ng/m3) are frequently detected. VOCs routinely found in air include the gasoline components methyl tert-butyl ether, benzene, ethylbenzene, toluene, and xylenes. The water concentrations for these compounds appear to be in equilibrium with the atmosphere because of their Henry's law values. The bed sediment cores contained a wide variety of PAHs with concentrations that show a steady increase since about 1933, based on 137Cs age dating, coincident with urbanization in the watershed. Atmospheric deposition appears to be a likely source for many of the contaminants found in the water.
Key words: urban watershed, water quality, atmospheric deposition
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