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Stormwater Pollution Prevention Plan <br /> 1 <br /> particles down to 0.5 pm. Filters should be sequenced from the largest to the smallest pore <br /> opening. Sediment removal efficiency will be related to particle size distribution in the <br /> stormwater. <br /> Treatment Process Description <br /> Stormwater is collected at interception point(s) on the site and is diverted to a sediment pond or <br /> tank for removal of large sediment and storage of the stormwater before it is treated by the <br /> filtration system. The stormwater is pumped from the trap, pond, or tank through the filtration <br /> system in a rapid sand filtration system. Slow sand filtration systems are designed as flow <br /> through systems using gravity. <br /> If large volumes of concrete are being poured, pH adjustment may be necessary. <br /> ' Maintenance Standards <br /> Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set <br /> pressure drop across the filter. If the backwash water volume is not large or substantially more <br /> turbid than the stormwater stored in the holding pond or tank, backwash return to the pond or <br /> ' tank may be appropriate. However, land application or another means of treatment and <br /> disposal may be necessary. <br /> ' ■ Screen, bag, and fiber filters must be cleaned and/or replaced when they <br /> become clogged. <br /> ■ Sediment shall be removed from the storage and/or treatment ponds as <br /> necessary. Typically, sediment removal is required once or twice during <br /> a wet season and at the decommissioning of the ponds. <br /> 3.2 Site Specific BMPs <br /> Site specific BMPs are shown on the TESC Plan Sheets and Details in Appendix A. These site <br /> specific plan sheets will be updated annually. <br /> t <br /> 1 <br /> 1 <br /> ' 19 16580.006.doc <br />