6101 23RD DR W NORPRO 2025-07-29

• Since the Narbeck Creek basin is only 0.31 acres, no flow rate BMPs are proposed during the construction phase of this project. Element 4: Install Sediment Controls I Powdermill Gulch Creek: • A temporary sediment pond and associated interceptor swales are proposed for sediment I control. Also, silt fence will be installed around the perimeter of the site to capture any sediment that isn't conveyed to the sediment pond. Narbeck Creek: • Due to the small tributary area of the Narbeck Creek basin onsite, only silt fence is proposed for structural sediment control. I • Natural vegetation along the eastern edge of the development will be left in the predeveloped state to the maximum extent possible to provide a vegetated filter for site runoff. Element 5: Stabilize Soils • All exposed and unworked soils shall be stabilized by application of effective BMPs that I protect the soil from the erosive forces of raindrop impact and flowing water, and wind erosion. • From October 1 through April 30, no soils shall remain exposed and unworked for more 1 than 2 days. From May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. This condition applies to all soils on site, whether at final grade or not. These time limits may be adjusted by the local permitting authority if it can be shown that the average time between storm events justifies a different standard. • Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. • Applicable practices include, but are not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, soil application of polyacrylamide (PAM), the early111 application of gravel base on areas to be paved, and dust control. • Soil stabilization measures selected should be appropriate for the time of year, site conditions, estimated duration of use, and potential water quality impacts that stabilization agents may have on downstream waters or ground water. • Soil stockpiles must be stabilized from erosion, protected with sediment trapping measures, and when possible,be located away from storm drain inlets, waterways and drainage channels. Element 6: Protect Slopes , • Runoff should be diverted from the tops of slopes to avoid erosion caused by upstream flow. • Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations. • Check dams shall be placed at regular intervals within channels that are cut down a slope. I • Stabilize soils on slopes, as specified in Element#5. 6/16/2011 Stormwater Site Plan Page 12