Appendix C Stormwater Facility Sizing – BMP L602.a - Roof Downspout Infiltration Trench Sizing The minimum trench length is based upon the soil type in the location of the infiltration trench. The soils report will provide the USDA Soil Type. The table below provides the minimum trench length per 1,000 ft2 of contributing roof area. Roof downspout infiltration trenches shall be designed in accordance with the SWMM and Typical Detail Figure 001 Downspout Infiltration Trench. – USDA Soil Type Minimum Trench Length (ft) per 1,000 ft2 of Roof Area Sand” (more than 50% of sand 20 “Coarse fraction remains on #4 Sand” (more than 50% of sand 30 “Medium fraction remains on #40 Sand 75 Loam 125 Loam 190 Silt Loam 275 Fill (only per SWMM requirements) 60 Roof Area Requiring Mitigation (ft2): USDA Soil Type per Soils Report: Trench Length Required: *Trench Length cannot exceed 100 feet. If trench length exceeds 100 feet, multiple trenches will be required. Number of Trenches: Length of Each Trench:
Appendix C – Stormwater Facility Sizing BMP L602.a - Roof Downspout Infiltration Trench Sizing The minimum trench length is based upon the soil type in the location of the infiltration trench. The soils report will provide the USDA Soil Type. The table below provides the minimum trench length per 1,000 ft2 of contributing roof area. Roof downspout infiltration trenches shall be designed in accordance with the SWMM and Typical Detail Figure 001 – Downspout Infiltration Trench. USDA Soil Type Minimum Trench Length (ft) per 1,000 ft2 of Roof Area “Coarse Sand” (more than 50% of sand fraction remains on #4 20 “Medium Sand” (more than 50% of sand fraction remains on #40 30 Sand 75 Loam 125 Loam 190 Silt Loam 275 Fill (only per SWMM requirements) 60 Roof Area Requiring Mitigation (ft2): USDA Soil Type per Soils Report: Trench Length Required: *Trench Length cannot exceed 100 feet. If trench length exceeds 100 feet, multiple trenches will be required. Number of Trenches: Length of Each Trench: