2320 106TH ST SW 2022-08-29 - Laserfiche WebLink

Stormwater Pollution Prevention Plan • If discharge is occurring during a storm event equal to or greater than the 10-year, 24-hour event, the allowable discharge rate is the peak flow rate of the 10-year, 24-hour event. • Discharge to a stream should not increase the stream flow rate by more than 10 percent. • If the discharge is directly to a lake, a major receiving water listed in Appendix C of Volume I, or to an infiltration system, there is no discharge flow limit. • If the discharge is to a municipal storm drainage system, the allowable discharge rate may be limited by the capacity of the public system. It may be necessary to clean the municipal storm drainage system prior to the start of the discharge to prevent scouring solids from the drainage system. • Runoff rates shall be calculated using the methods presented in Volume 3, Chapter 2 for the pre-developed condition. If no hydrologic analysis is required for the site, the Rational Method may be used. Monitoring The following monitoring shall be conducted. Test results shall be recorded on a daily log kept on site: Operational Monitoring • pH, conductivity (as a surrogate for alkalinity), turbidity and temperature of the untreated stormwater • Total volume treated and discharged • Discharge time and flow rate • Type and amount of chemical used for pH adjustment • Amount of polymer used for treatment • Settling time Compliance Monitoring • pH and turbidity of the treated stormwater • pH and turbidity of the receiving water Biomonitorinq: Treated stormwater shall be tested for acute (lethal) toxicity. Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. The 17 17576.003.doc