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1 <br /> BMP C107: Construction Road/Parking Area Stabilization <br /> Purpose <br /> Stabilizing subdivision roads, parking areas, and other on-site vehicle transportation <br /> routes immediately after grading reduces erosion caused by construction traffic or runoff. ' <br /> Conditions of Use <br /> Roads or parking areas shall be stabilized wherever they are constructed,whether per- I <br /> manent or temporary,for use by construction traffic. <br /> . High Visibility Fencing (see BMP C103: High Visibility Fence (p.269))shall be ' <br /> installed, if necessary,to limit the access of vehicles to only those roads and park- <br /> ing areas that are stabilized. I <br /> Design and Installation Specifications <br /> . On areas that will receive asphalt as part of the project, install the first lift as soon ' <br /> as possible. <br /> . A 6-inch depth of 2-to 4-inch crushed rock, gravel base, or crushed surfacing base I <br /> course shall be applied immediately after grading or utility installation. A 4-inch <br /> course of asphalt treated base (ATB) may also be used, or the road/parking area <br /> may be paved. It may also be possible to use cement or calcium chloride for soil <br /> stabilization. If cement or cement kiln dust is used for roadbase stabilization, pH <br /> monitoring and BMPs (BMP C252: High pH Neutralization Using CO2 (p.409)and <br /> BMP C253: pH Control for High pH Water(p.412))are necessary to evaluate and <br /> minimize the effects on stormwater. If the area will not be used for permanent <br /> roads, parking areas,or structures, a 6-inch depth of hog fuel may also be used, I <br /> but this is likely to require more maintenance.Whenever possible, construction <br /> roads and parking areas shall be placed on a firm, compacted subgrade. <br /> . Temporary road gradients shall not exceed 15 percent. Roadways shall be care- <br /> fully graded to drain. Drainage ditches shall be provided on each side of the road- <br /> way in the case of a crowned section, or on one side in the case of a super- <br /> elevated section. Drainage ditches shall be directed to a sediment control BMP. <br /> . Rather than relying on ditches, it may also be possible to grade the road so that run- <br /> off sheet-flows into a heavily vegetated area with a well-developed topsoil. Land- <br /> scaped areas are not adequate. If this area has at least 50 feet of vegetation that <br /> water can flow through, then it is generally preferable to use the vegetation to treat I <br /> runoff, rather than a sediment pond or trap. The 50 feet shall not include wetlands <br /> or their buffers. If runoff is allowed to sheetflow through adjacent vegetated areas, it <br /> is vital to design the roadways and parking areas so that no concentrated runoff is <br /> created. <br /> 1 <br /> 2014 Stormwater Management Manual for Western Washington <br /> Volume 11- Chapter 4 -Page 277 <br />