San Francisco Stormwater Design Guidelines
Treatment Trains A single treatment BMP may not adequately treat the entire range of pollutants from its contributing watershed, especially in large developments involving diverse activities. For example, some treatment BMPs are designed to remove fine suspended sediment but may not be able to remove dissolved metals. Because of this, a combination of several BMPs in succession may be needed to treat all of the pollutants on a given site. A combination of BMPs, constructed in a series to target specific pollutants, is called a treatment train. Treatment trains not only improve water quality, they also improve the long-term efficiency and reduce the maintenance requirements for each treatment BMP involved in the train. Heavy sediments and trash can negatively impact BMP performance, thus silt traps and sediment forebays are commonly used as a first step in the treatment process. In the same way that pre-rinsing dirty dishes increases the efficacy and efficiency of a dishwasher, removing sediment prior to infiltration of stormwater will improve the longterm capacity of the underlying soils to infiltrate water by preventing sediment from clogging pore spaces that allow the movement of water through the soil. Common treatment train configurations include: Silt trap Swale Wetland Cistern Rain garden Retention basin Sand filter Vegetated strip Infiltration trench
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The Stormwater Control Plan