Erosion and Sediment Control
Erosion and Sediment Control
Erosion and sediment control (ESC) practices prevent soil loss during construction. Candidates must understand best management practices (BMPs): silt fences, sediment basins, check dams, erosion control blankets, and stabilized construction entrances. Key principles: minimize disturbed area, phase construction, stabilize promptly, and manage runoff. Regulations include NPDES Construction General Permit, which requires a Stormwater Pollution Prevention Plan (SWPPP) for disturbances ≥1 acre.
Traps include: confusing erosion control (preventing soil detachment) with sediment control (capturing soil after detachment). Silt fences are sediment control, not erosion control. Another trap is silt fence installation: it must be trenched into the ground, not just staked, and placed on the contour. Also, sediment basin sizing: typically 67 cubic yards per acre of disturbed area for the 2-year, 24-hour storm (varies by state). A common error is to forget construction entrance requirements: a stabilized pad of crushed stone, often 50 ft long, to prevent tracking onto roads.
Worked example: A 5-acre construction site requires a sediment basin. Using the rule of 67 cy/acre, basin volume = 5 × 67 = 335 cy. If the basin has a 6-ft depth, surface area = 335 / 6 = 55.8 sq ft? That seems too small; actually 335 cy is volume, so area = volume/depth = 335 yd³ × 27 ft³/yd³ / 6 ft = 9045 ft³ / 6 = 1507.5 sq ft. So basin surface area ≈ 1,508 sq ft. Ensure the basin has a proper dewatering device and emergency spillway.
Rule of thumb: Silt fence should be installed on the contour, with a maximum slope length of 100 ft and a maximum drainage area of 0.25 acre per 100 ft of fence.