Arapahoe County, CO Environmental Rules: Grading & Drainage (2026)

Grading and drainage regulations in Arapahoe County are codified at multiple levels. Arapahoe County Land Development Code §4-4 requires grading permits for excavation or fill exceeding 100 cubic yards, or creation of slopes over 3 feet in vertical difference. Aurora City Code §22-170 et seq. applies similar thresholds, with additional requirements for slopes exceeding 3:1 gradient. Centennial requires grading permits for disturbance over 100 cubic yards or slope creation over 5 feet. Colorado's natural topography ranges from plains in eastern Arapahoe County to foothills in the west, creating varied grading challenges. Drainage rules (Colorado common law and C.R.S. §37-83-101 et seq.) prohibit property owners from redirecting natural drainage onto neighboring properties in ways that cause damage. Grading plans must direct stormwater to approved discharge points—typically the public right-of-way or private detention facilities. Retaining walls over 4 feet (measured from bottom of footing to top of wall) require engineering design and separate permits in most Arapahoe County jurisdictions. Walls over 6 feet need specific IBC review. Foundation compaction testing typically required for structural fill (95% Standard Proctor). Colorado's semi-arid climate creates expansive soils (bentonite clay) requiring soil reports for new construction. Freeze depth is 30-36 inches in the Denver metro affecting footings and plumbing. Mile High Flood District criteria govern drainage design.