SWPPP Requirements in Montana

Who needs a SWPPP in Montana?

Any construction project that disturbs one acre or more — or is part of a larger common plan of development reaching one acre — needs a SWPPP under Montana permit MTR100000.

Montana runs its own delegated stormwater program. Operators obtain coverage from Montana Department of Environmental Quality (DEQ), Water Protection Bureau under MPDES General Permit for Storm Water Discharges Associated with Construction Activity (SWC) (MTR100000), not directly from the EPA. A small subdivision, a solar pad, and a road-widening project all clear the same one-acre line.

Montana adds requirements worth flagging early: Submit the NOI-SWC package — NOI with topographic map, signed SWPPP with site maps, Sage Grouse consultation letter if applicable, and fee — through DEQ’s FACTS e-permitting system before construction starts; the SWPPP is part of the application (MTR100000 Parts 1.2.1–1.2.2); Post a public sign at the site entrance/exit from the authorization date until termination: at least 1-inch lettering, visible from the nearest road, showing the MPDES SWC authorization number and DEQ’s contact and complaint statements (MTR100000 Part 1.5); Projects in designated sage grouse habitat must include the Montana Sage Grouse Habitat Conservation Program consultation letter (MTR100000 Parts 1.2.2 and 3.5); For disturbance of five acres or more, the site description must estimate pre- and post-construction runoff coefficients and the increase in impervious area (MTR100000 Part 3.3.a.5); Document each major construction activity and its BMP phasing in a table or narrative with timeframes (MTR100000 Part 3.7); Dewatering discharges to state surface waters need separate coverage under the Construction Dewatering General Permit or an individual permit (MTR100000 Parts 2.1.4 and 3.6); Notify DEQ in writing within 15 calendar days of any change to the SWPPP Administrator’s name, address, or phone number (MTR100000 Part 2.6.1); Sites within Indian country are not covered; they fall under the EPA CGP (MTR100000 Part 1.1.1).

What the plan must contain

A Montana SWPPPis the site's compliance binder — the document an inspector opens first. It documents:

1. 1Site & project descriptionTotal and disturbed acreage, soils, slopes, and the sequence of construction.
2. 2Receiving waters & discharge pointsWhere stormwater leaves the site and the waterbodies it reaches.
3. 3Erosion & sediment control BMPsSilt fence, stabilized entrances, inlet protection, and stabilization measures.
4. 4Inspection schedule & recordsDated, signed inspection logs and the corrective actions taken.
5. 5Operator certificationThe SWPPP is signed by the legally responsible party before work begins.

Required and conditional BMPs

Filing your Notice of Intent

Submit a complete NOI-SWC package (NOI with topographic map, signed SWPPP with site maps, Sage Grouse consultation letter if applicable, and fee) through DEQ’s FACTS e-permitting system before the proposed construction start date; discharge is authorized once DEQ receives a complete package.

A Notice of Termination closes coverage once the site reaches final stabilization. Keeping the SWPPP and its inspection records on site is what keeps a project clear of stop-work orders.

Inspection requirements

The permit allows 2 inspection schedules; the operator follows one and records the choice in this plan: (a) Weekly routine inspection schedule — inspect at least once every 7 calendar days (during the project’s normal business hours; document any schedule change in the SWPPP or inspection report) (MTR100000 Part 2.3.3); or (b) Biweekly routine and post-storm event inspection schedule — inspect at least once every 14 calendar days and within 24 hours of the end of a storm producing 0.25 inch of rain or more (and within 24 hours of runoff from snowmelt (any snowmelt event resulting in a discharge); during normal business hours; determine rainfall with an on-site rain gage or a representative weather service and record the method and the calendar-day total for any day of 0.25 inches or more; a post-storm inspection may serve as the biweekly routine inspection, but routine inspections resume no later than 14 calendar days after the last post-storm inspection) (MTR100000 Part 2.3.4). The chosen schedule is documented in the SWPPP (MTR100000 Part 2.3.2); reductions to once every 30 calendar days for inactive or stabilized areas and delayed inspections for severe winter conditions are in Parts 2.3.5–2.3.6. Every inspection is dated and signed, and any failed control is corrected before the next storm.

How Montana differs from the federal permit

Because Montana administers its own program, the federal EPA Construction General Permit does not apply directly here — the state permit governs. Sites inside a regulated municipal storm sewer system may carry additional local ordinance requirements on top of the state permit.

Frequently asked questions