Appendix C Stormwater Facility Sizing – BMP L602.b - Roof Downspout Drywell Sizing The minimum rock volume and dry well rock layer height are based upon the soil type in the location of the drywell. The soils report will provide the USDA Soil Type. The table below provides the volume of washed rock and height of washed rock required. Roof downspout dry wells shall be designed in accordance with the SWMM and Typical Detail Figure 002 Downspout Infiltration Drywell. – USDA Soil Type Volume of Washed Rock Drywell Rock Layer (ft3) Height Sand” (more than 60 4’9” “Coarse 50% of sand fraction remains on #4 sieve) Sand” (more than 90 7’2” “Medium 50% of sand fraction remains on #40 sieve) Roof Area Requiring Mitigation (ft2): USDA Soil Type per Soils Report: Volume of Washed Rock Required: Rock Layer Height Required:
Appendix C – Stormwater Facility Sizing BMP L602.b - Roof Downspout Drywell Sizing The minimum rock volume and dry well rock layer height are based upon the soil type in the location of the drywell. The soils report will provide the USDA Soil Type. The table below provides the volume of washed rock and height of washed rock required. Roof downspout dry wells shall be designed in accordance with the SWMM and Typical Detail Figure 002 – Downspout Infiltration Drywell. USDA Soil Type Volume of Washed Rock (ft3) Drywell Rock Layer Height “Coarse Sand” (more than 50% of sand fraction remains on #4 sieve) 60 4’9” “Medium Sand” (more than 50% of sand fraction remains on #40 sieve) 90 7’2” Roof Area Requiring Mitigation (ft2): USDA Soil Type per Soils Report: Volume of Washed Rock Required: Rock Layer Height Required: