5 county-level rules, plus city-specific rules for 4 cities in Arapahoe County, Colorado.
Verified from official government sources
Arapahoe County is MS4-permitted under the Clean Water Act and Colorado Discharge Permit System. New development requires stormwater management per Urban Drainage and Flood Control District (UDFCD/Mile High Flood District) standards. Cherry Creek Watershed Reg. 72 imposes stricter requirements. Water quality capture volume (WQCV) required.
Arapahoe County and cities require erosion and sediment control per Colorado Discharge Permit System (CDPS) and Mile High Flood District standards. Projects over 1 acre need state CDPS Stormwater Construction Permit. Silt fencing, stabilized entrances, and BMPs required. Cherry Creek Watershed imposes stricter controls.
Arapahoe County is landlocked—no coastal rules apply. However, Cherry Creek Reservoir, Cherry Creek, Plum Creek, Sand Creek, and the Highline Canal receive riparian and floodplain protections. Buffer setbacks 50-100 ft from waterways. FEMA floodplain rules and Cherry Creek Watershed Regulation 72 govern development near water.
Arapahoe County regulates the 100-year floodplain in unincorporated areas under LDC Sections 2-4.10 and 4-3.5. SEMSWA administers floodplain rules for the county. The county participates in the National Flood Insurance Program. New FEMA flood maps were updated in 2023.
Arapahoe County Land Development Code §4-4 requires grading permits for excavation or fill over 100 cubic yards or slopes over 3 feet. Aurora City Code §22-170 thresholds similar. Drainage must not redirect water to neighbors. Retaining walls over 4 feet require engineering. Colorado freeze depth 30-36 inches affects foundations.
4 cities in Arapahoe County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
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Arapahoe County Ordinance Hub →