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Eastern Washington Phase 11 Marnicipal Slorinivater Permit <br />they are inspected/maintained/cleaned at least once per year or more frequently as needs are <br />identified: <br />• A customer or visitor parking lot with an expected trip end count equal to or greater than <br />300 vehicles (best professional judgment should be used in comparing this criterion with <br />the preceding criterion); and <br />• Commercial on -street parking areas on streets with an expected total ADT count equal to or <br />greater than 7,500; or <br />At all other high -use sites and high ADT traffic areas subject to the oil treatment <br />requirement, sorptive technologies, not separators, are required. Basic treatment methods with <br />sorptive properties, such as swales or filters, may be selected to fulfill this requirement; or catch <br />basin inserts may be used at these sites. A catch basin preceded by passive oil control vault, such <br />as a chamber with a turned -down elbow, may be applied at sites with ADT greater than 30,000 <br />as long as they are inspected/maintained/cleaned at least once per year or more frequently as <br />needs are identified. <br />High -use roadway intersections shall treat lanes where vehicles accumulate during the signal <br />cycle, including left and right turn lanes and through lanes, from the beginning of the left turn <br />pocket. If no left turn pocket exists, the treatable area shall begin at a distance equal to three car <br />lengths from the stop line. If runoff from the intersection drains to more than two collection areas <br />that do not combine within the intersection, treatment may be limited to any two of the collection <br />areas where the cars stop. <br />High -use sites and high ADT roadways and parking areas must treat runoff from the high -use <br />portion of the site using oil control treatment options in Chapter 5 of the Stormwater <br />Management Manual for Eastern Washington prior to discharge or infiltration. For high -use sites <br />located within a larger project area, only the impervious area associated with the high -use site is <br />subject to oil control treatment, but the flow from that area must be separated; otherwise the <br />treatment controls must be sized for the entire area. <br />Exceptions: Preservation/maintenance projects and some improvement or safety enhancement <br />projects that do not increase motorized vehicular capacities as defined in the sections <br />"Exemptions" and "Partial Exemptions" above are exempt from Oil Treatment Requirements. <br />Any of these exemptions may be negated by requirements set forth in a Total Maximum Daily <br />Load (TMDL) or other water cleanup plan. <br />Phosphorus Treatment <br />Requirements: Phosphorus treatment is required only where federal, state, or local government <br />has determined that a water body is sensitive to phosphorus and that a reduction in phosphorus <br />from new development and redevelopment is necessary to achieve the water quality standard to <br />protect its beneficial uses. Where it is deemed necessary, a strategy shall be adopted to achieve <br />the reduction in phosphorus. <br />Appendix 1- Minimum Technical Requirements <br />Eastern Washington Phase HMunicipal Stormwater Permit —August 1, 2014 <br />Page 14 <br />