Montana Statewide Rule

Montana Erosion & Stormwater: MPDES Construction Permit Rules

Some RestrictionsApplies statewide across Montana (2026)

Key Facts

Governing law: MCA 75-5-401; Water Quality Act
Permit trigger: Disturbing 1+ acre of land
Enforcing agency: DEQ Water Protection Bureau
Required plan: Stormwater Pollution Prevention Plan
Maximum penalty: $25,000 per day of violation

Last verified: July 31, 2026

Summary

Montana requires an MPDES construction stormwater permit before any land disturbance of one acre or more, enforced by the Department of Environmental Quality under the Water Quality Act with erosion-control BMPs and a written pollution prevention plan.

Except as provided in subsection (5), the department shall adopt rules: (a) governing application for permits to discharge sewage, industrial wastes, or other wastes into state waters...

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Full Breakdown

Montana's Water Quality Act requires a Montana Pollutant Discharge Elimination System (MPDES) permit before discharging stormwater or construction sediment into state waters. Under MCA 75-5-401, the Department of Environmental Quality adopts the permit rules, and its Water Protection Bureau administers the General Permit for Storm Water Discharges Associated with Construction Activity. Any construction disturbing one or more acres, or forming part of a larger common plan of development of that size, must file a Notice of Intent, prepare a Stormwater Pollution Prevention Plan, and install erosion and sediment best management practices before ground is broken.

Violations & Penalties

Discharging sediment or stormwater without MPDES coverage exposes the operator to a civil penalty up to $25,000 under MCA 75-5-631, with each day of violation counted as a separate violation; DEQ may also issue compliance and cleanup orders.

Frequently Asked Questions

When do I need a Montana construction stormwater permit?

When your project disturbs one acre or more, or is part of a larger common plan of development reaching that size. File a Notice of Intent with DEQ before discharging.

Who enforces construction erosion control in Montana?

The Department of Environmental Quality's Water Protection Bureau, through the MPDES General Permit for construction stormwater issued under the Water Quality Act.

What is the penalty for discharging without a permit?

A civil penalty up to $25,000, with each day of violation treated separately under MCA 75-5-631, plus possible DEQ compliance and cleanup orders.

Sources

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