SWPPP Requirements in Idaho

Who needs a SWPPP in Idaho?

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 Idaho permit IDR100000.

Idaho runs its own delegated stormwater program. Operators obtain coverage from Idaho Department of Environmental Quality (DEQ), IPDES Program under IPDES Construction General Permit (IDR100000) (IDR100000), not directly from the EPA. A small subdivision, a solar pad, and a road-widening project all clear the same one-acre line.

Idaho adds requirements worth flagging early: Develop the SWPPP before submitting the NOI, and submit the NOI through the IPDES E-Permitting System at least 14 calendar days before commencing construction (IDR100000 Sections 1.4.2–1.4.4, Table 1); Post notice of permit coverage at the site (IDR100000 Section 1.5); Turbidity monitoring when an unstabilized portion of the site discharges directly to a water of the U.S. during operating hours: sample upstream background and downstream daily; 50 NTU instantaneous over background is an exceedance requiring corrective action (IDR100000 Section 3.4); Dewatering discharges directly to a water of the U.S.: daily turbidity sample; stop and correct if over 50 NTU above background, or a 10-day running average over 25 NTU above background (IDR100000 Section 3.3); Assemble a storm water team and keep its training records with the SWPPP (IDR100000 Sections 6.1–6.2 and 7.2.2); Keep a corrective action log: record the condition within 24 hours of identifying it and the actions taken within 24 hours of completing them (IDR100000 Section 5.4); Sites on tribal reservations are not eligible; they are covered by the EPA CGP (IDR100000 Section 1.1.3).

What the plan must contain

An Idaho 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

Develop the SWPPP, then prepare and submit the NOI electronically through DEQ’s IPDES E-Permitting System at least 14 calendar days before commencing construction; coverage begins at least 14 calendar days after DEQ notifies you it has received a complete NOI, when DEQ sends the authorization with your IPDES permit number (paper NOI only with a DEQ waiver).

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) 7-day schedule — inspect at least once every 7 calendar days (inspections are only required during the site’s normal working hours) (IDR100000 Section 4.2.1); or (b) 14-day schedule with storm-discharge inspections — inspect at least once every 14 calendar days and once each day that there is a discharge from the site to a water of the U.S. from a storm producing 0.25 inch of rain or more (during normal working hours; keep a properly maintained rain gauge on site or use a representative weather station, and record the total rainfall for any day of rainfall during normal business hours measuring 0.25 inches or greater; footnote 55 describes the storm inspection as “within 24 hours of the occurrence of a storm event” that has produced 0.25 inches within a 24-hour period, and for a multi-day storm within 24 hours of the first day and within 24 hours after the end of the storm) (IDR100000 Section 4.2.2 and footnotes 54–55). Reduced frequencies for stabilized areas, arid or drought periods, and frozen conditions are in IDR100000 Section 4.4. Every inspection is dated and signed, and any failed control is corrected before the next storm.

How Idaho differs from the federal permit

Because Idaho 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