8925 AIRPORT RD MUKILTEO SCHOOL DISTRICT 2018-01-02 MF Import

�s s �,�� . Oil can accumulate in bypass catch basins and flow �ut ��9 through the bypass pipe during high flows if these structures are designed improperly. The attached sketches show some acceptable alternatives for the bypass catch basin. The choice of structures is somewhat dependent on the size of the orifice required to control flow to the oil/water separator, the distance required between the grate elevation and structures within the catch basin, and the depth of cover required over the bypass pipe. • If the orifice needed to control flow to the oil/water separator is 4 inches in diameter or greater, and adequate cover will be provided over the bypass pipe, the structure will not accumulate oil and no special design of �he bypass pipe is required. if a pipe or orifice less than 4 inches in diameter is required to control flow to a water quality device, a restrictor unit is generally needed to requlate the flow. In this case bypassed flows may contain accumulated oil. To address this problem, a floatable material separator (City std #`411) without a vent hole can be used on the bypass pipe, if enough clearance exists between the crown of the bypass pipe and the ground/rim elevation. Pipe cover and City installation requirements need to be met (required pipe cover depends on the pipe material and a minimum of 1.5 feet is necessary between the rim elevation of the manhole/cb and the crown of the bypass pipe to meet all city standards regarding installation) . A third alternative is to install a second restrictor-type unit on the bypass pipe equipped with a baffle, made of a larger diameter Yipe, welded to the standpipe. The space between the baffle and the overflow standpipe needs to be large enough to not restrict flows. The baffle should be stiffened by welding a "rib" from the standpipe to the baffle, and should extend a minimum of 4 inches above and 6 inches below the overflow elevation. The water quality device restrictor standpipe should also be capped and provided with a one inch vent hole. Fuelina Facilitv: i {�(,��`� The fueling facility i�: required to meet City standards rUe�,aa � �regarding these types of areas. The applicant should refer 1 �C� to section 4-5.2 af the City's current standards manual for S�' �rq specific requirements. Th�s fac� � itv would be reqarded as a Gj. � �� t± VO�H3A6 ll�o far31 it�+. � ��,II � � if the applicant proposes undergrovnd storage tank overfill � � protection under section 4-5.2 (3) (B) , a narrative should be �