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R(J(~(iops, parking lots and sidewalks in urban an'as shed precipitation instantly, carryillg motor oil, litter. pesticides and other pollution illlo storm drains and. ultimately. rhers, lakes or lhe ocean. More Runoff More Pollutants To some degree, pollutants in runoff are a natural occurrence. But development of the natural land. scape has increased both the amount of runoff and the sources of pollution. Lands that are stripped of their natural vegetation, graded to eliminate the variation in topography, or covered with hard surfaces lose their ability to absorb, hold, or even slow down runoff. As much as 80 percent of an urban landscape typically is covered by impervious surtaces. Rooftops, parking lots and sidewalks virtually shed precipitation instantly. increasing the pace and peaks of runoff. To accommodate the faster and higher peak flows, creeks are widened and channelized, further accelerating currents. Marshes and ponds - natural reservoirs that store runoff and capture sediment - have for the most part been drained, filled or leveed to accommodate urban development and farming. Besides more flooding, the higher stream flows increase erosion and diminish the ability of streams and surviving wetlands to filter pollutants. Changes to the landscape continue. While Califor- nia has lost a greater percentage of its wetlands than any other state, it is still losing wetlands and riparian areas. Over the next 45 years, the state's popula- tion is expected to grow by another 30 million people - that is, by 15 million residential rooftops. The consequences of these hydrological changes are SAN FRANCISCO BAY Only 10 percent of the runoff fhat flows into San Francisco Bay comes from fhe hills and valleys immediately surrounding the bay. Most of the water is delivered fa the bay from the Central Valley through the Delta. Nevertheless, the bay has nearly all of the nonpoint problems in the book - agriculture, old mines, growing cities, heavy industry. In the North Bay, the Napa River, which captures runoff from vineyards and growing cities, is the largest single polluter. Each year between 67,000 and 220,000 tons of sediment are washed down the river, according to EPA and fhe San Francisco Regional Water Quality Control Board. Forty of the river's 55 miles are considered impaired because of eutrophication, excess sedimentation and habitat degradation. multiplied by the pollutants that are washed into streams - pesticides, motor oil, litter. In some places, urban development will trade one set of problems for another. In the Central Valley. for instance, the American Farmland Trust estimates that 1 million acres of agricultural land will be converted to urban uses over the next 45 years - ex- changing the runoff problems associated with agriculture for the different pollut- ants associated with cities. Rural or urban, how- ever, may not matter much to the Ceriodaphnia - a small water flea used to measure toxicity at the lower end of the food chain, which the higher end of the food chain depends upon. In studies of Central Valley streams that capture both urban and farm runoff, researchers from the Central Valley Regional Water Quality Control Board consistently have found pesticides washed into streams by rain and irrigation water at concentra- tions that are lethal to Ceriodaphnia. In the South Bay, historic mercury mines continue to pollute the Guadalupe River. Fish pulled from the stream exceed the federal health standards for mercury. Surrounding the bay, particularly in the high-tech communities on the peninsula, industrial solvents have leaked into the groundwater, damaging a valuable water supply for an area that depends in large measure on imported water. All of the communities, however, share in common the problem of urban runoff. Between 30 percent and 70 percent of the pollutants flowing into the bay come from city streets and urban gardens - heavy mefals like copper fhat are not easily washed out of the bay, oils and soaps, and even pesticides more commonly associated with agricultural regions. 7