10200 19TH AVE SE COSTCO FUEL STATION 2022-05-23

BMP C220: Storm Drain Inlet Protection Purpose Storm drain inlet protection prevents coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area. Conditions of Use Use storm drain inlet protection at inlets that are operational before permanent stabilization of the disturbed drainage area. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless conveying runoff entering catch basins to a sediment pond or trap. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters in new home construction can add significant amounts of sediment into the roof drain system. If possible delay installing lawn and yard drains until just before landscaping or cap these drains to pre- vent sediment from entering the system until completion of landscaping. Provide 18- inches of sod around each finished lawn and yard drain. Table 11-4.2.2 Storm Drain Inlet Protection (p.358) lists several options for inlet protection. All of the methods for storm drain inlet protection tend to plug and require a high frequency of maintenance. Limit drainage areas to one acre or less. Possibly provide emergency overflows with additional end-of-pipe treatment where stormwater ponding would cause a hazard. Design and Installation Specifications Excavated Drop Inlet Protection - An excavated impoundment around the storm drain. Sediment settles out of the stormwater prior to entering the storm drain. • Provide a depth of 1-2 ft as measured from the crest of the inlet structure. • Slope sides of excavation no steeper than 2H:1V. • Minimum volume of excavation 35 cubic yard. • Shape basin to fit site with longest dimension oriented toward the longest inflow area. • Install provisions for draining to prevent standing water problems. • Clear the area of all debris. • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. • Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter- A barrier formed around the storm drain inlet with standard concrete blocks and gravel. See Figure 11-4.2.8 Block and Gravel Filter (p.360). • Provide a height of 1 to 2 feet above inlet. • Recess the first row 2-inches into the ground for stability. Page 154