Gilpin County SWPPP Checklist: Concrete Washout & Excavation Compliance

The Rule: Any land alteration or clearing activity requires formal county authorization to ensure proper erosion controls are established. The Gilpin County Nuance: Gilpin County enforces an incredibly low threshold for earthwork. A formal Grading and Excavation Permit is explicitly required if a site exceeds 50 cubic yards of excavated/filled earth OR 3,000 square feet of total disturbance on a single parcel. Digging a temporary in-ground concrete washout pit directly subtracts from this minimal 50-cubic-yard allowance. Exceeding the threshold without a permit triggers an immediate Stop-Work Order.

The Rule: Stormwater discharges must not introduce pollutants into state waters or soils. The Gilpin County Nuance: A massive portion of Gilpin County (including Black Hawk, Central City, and Gregory Gulch) sits squarely inside the 400-square-mile Central City/Clear Creek EPA Superfund Site. Because the EPA and CDPHE are actively engaged in treating soil, mine tailings, and surface water for heavy metals, the environmental scrutiny here is uniquely severe. Any alkaline concrete washout that breaches containment and leaches into the soil or North Clear Creek tributaries invites direct federal and state environmental oversight, far beyond standard MS4 administrative penalties.

The Rule: Site access must be stabilized to prevent sediment tracking and runoff onto public roadways. The Gilpin County Nuance: Because Gilpin County relies on steep, narrow mountain roads, it actively enforces the International Wildland-Urban Interface (WUI) Code alongside strict local driveway standards. County code explicitly dictates that "Driveways shall not drain onto County-maintained roads." If a washout pit breaches or a mixer truck tracks concrete mud down a steep site approach (which can have up to a 12% maximum gradient) and onto a public roadway, it is prosecuted as a direct violation of both drainage and WUI access codes.

The Rule: Construction footprints must accurately reflect the surveyed site plan and maintain property line setbacks. The Gilpin County Nuance: Many residential and commercial builds in Gilpin County take place on historic, oddly shaped mining claims described by metes and bounds. The county mandates that contemporary surveys (conducted within the last 10 years) dictate exact property lines. Excavating a temporary pit on the steep edge of a mining claim often risks violating structural setbacks or altering the precarious drainage patterns affecting downslope properties. Any retaining structure required to keep an earth-dug washout pit from sliding down a steep slope must be formally engineered.