Kootenai County, ID Environmental Rules: Stormwater Management (2026)

101 requires a permit for new driveways, private roads, structure excavation, commercial or industrial access construction, and most other grading or excavation, though it exempts permitted mining and forest-practice work, agricultural practices in common local usage, cemetery graves, emergency work, and small jobs such as under fifty cubic yards of fill in a twelve-month period outside a stream buffer or shoreline area, or grading on less than ten percent slope more than five hundred feet from surface water that disturbs under a third of the parcel.

105 sets the engineering targets: conveyance sized for a 50-year storm without flooding, and detention sized so the site's peak runoff for a 25-year storm does not exceed pre-development levels, factoring in both impervious and pervious surfaces. 105(D) adds that runoff needing treatment before infiltration has to be routed to treatment areas with limited infiltration first, protecting the sole-source aquifer the county shares with Spokane County. 106 layers on water quality: the first half inch of runoff from impervious surfaces must be treated, commonly through bioinfiltration swales drawn from Idaho DEQ's best-management-practices catalog or existing natural vegetation, before it reaches ground or surface water; rooftop runoff is exempt from treatment BMPs but still has to be managed to infiltrate or otherwise meet the detention rule.

The county does not require on-site post-construction testing of BMP efficiency, relying instead on the design professional's calculations. 603: a misdemeanor under section 1-4-1, plus a civil penalty of up to $1,000 per incident per day, capped at $20,000 per incident.