Regulations
Arapahoe County SWPPP Checklist: Concrete Washout & MS4 Compliance
Arapahoe County
Jurisdiction: Arapahoe County & Southeast Metro Stormwater Authority (SEMSWA)
Permit / authority: Governing Permits: Arapahoe County Stormwater Ordinance 2019-02 / SEMSWA
Enforcement Response Plan If you are managing concrete washout within Arapahoe County, including the Centennial and SEMSWA service areas, you are operating under a highly structured Enforcement Response Plan (ERP). SEMSWA acts as the MS4 permit manager and explicitly targets concrete washout compliance.
1. The $2,000 SEMSWA Fine Trigger
The Rule: Arapahoe County adopted Stormwater Ordinance 2019-02 per Resolution 190347 to enforce local stormwater rules and regulations. The Arapahoe Nuance: Under the official SEMSWA Enforcement Response Plan (ERP), an infraction specifically related to "Concrete Washout" carries a stated penalty of $2,000 per day.
2. The Direct Ground Discharge Ban
The Rule: Concrete washout water shall not be discharged to the MS4. The Arapahoe Nuance: The county's Grading, Erosion, and Sediment Control guidelines explicitly state that no concrete waste is to be discharged from a delivery truck, pump truck, or small batch mixer directly onto the ground outside of a designated washout area. Furthermore, all concrete waste and washouts from these vehicles must be discharged directly into the designated washout areas.
3. USDCM Volume 3 Structural Compliance
The Rule: Best Management Practices (BMPs) installed on-site must reflect what is shown in the Stormwater Management Plan (SWMP) and be installed and maintained per the SWMP specifications. The Arapahoe Nuance: Arapahoe County relies heavily on the Urban Storm Drainage Criteria Manual (USDCM), Volume 3, for BMP design standards and Concrete Washout Area (CWA) compliance. If your CWA containment does not meet the structural adequacy concepts outlined in USDCM Volume 3, it risks failing site plan approval.
4. The Cherry Creek Basin Phosphorus Mandate
The Rule: Control measures must be included on the approved site plan to manage other non-stormwater discharges, including wash water, that may contribute pollutants to state waters. The Arapahoe Nuance: Portions of Arapahoe County, including Aurora and Centennial/SEMSWA, are located within the Cherry Creek Basin. The regulated MS4s in this area are subject to a Total Maximum Daily Load (TMDL) requirement that demands a 20 percent reduction in the target load of total phosphorus. Consequently, control measures preventing concrete wash water from discharging into state waters are closely monitored to ensure effluent limitations meet this 20 percent reduction goal.
