Thornton, CO Environmental Rules: Erosion Control (2026)

Section 22-156(5) of the Thornton City Code makes erosion, sediment, and dust control a direct duty of every permittee under a grading, stormwater quality, or floodplain permit. The permittee must prevent sediment or dust from reaching any watercourse, drainage system, or adjacent property by implementing temporary and permanent best management practices (BMPs), and must maintain every temporary structural BMP until 'final stabilization' of all disturbed ground, defined in Section 22-112 as uniform vegetative cover of at least 70 percent of pre-disturbance plant density, or an equivalent permanent erosion-reduction method.

Once that stabilization threshold is reached, the permittee must promptly remove the temporary controls. Section 22-184 backs this up at the project-approval stage: no construction or building permit may issue for work disturbing more than one acre, or that is part of a larger common plan of development, until the applicant proves it has filed for a Colorado Discharge Permit System (CDPS) stormwater discharge permit, provided a sediment control plan, or shown the stormwater coordinator that no state permit is required. Every grading and stormwater application must include a preliminary or final erosion and sediment control plan under Section 22-141, and the city may attach erosion, sediment, dust, and noise-control conditions, plus requirements for haul routes and work-area traffic control, to any permit issued under Section 22-132(b).

If a permittee fails to control erosion or sediment to the city's satisfaction, Section 22-156(6) lets the city draw on the project's security deposit to remedy the condition or order all work stopped.