Maine Stormwater Management Law: Statewide Environmental Rules Rules (2026)

Key Facts

Permit threshold: 1 acre disturbance
Statute: 38 M.R.S. § 420-D
Rule: DEP Chapter 500
Max civil penalty: $25,000 per day

Full Breakdown

Under 38 M.R.S. section 420-D and DEP Chapter 500 rules, projects disturbing one or more acres, or smaller projects in protected watersheds, must obtain a stormwater permit and implement Best Management Practices for water quality, channel protection, and flooding. Stricter standards apply within Urban Impaired Streams, Most-At-Risk lake watersheds, and the shoreland zone. Municipalities with delegated review authority may issue permits but cannot weaken DEP standards. Construction general permits (Maine Construction General Permit) cover erosion controls. Post-construction operation, maintenance, and inspection plans are required, with reporting to DEP.

Violations & Penalties

Discharges without a permit, or violation of BMPs, can trigger DEP enforcement orders, daily civil penalties up to $25,000, and required restoration of impacted waters.

Frequently Asked Questions

When does Maine require a stormwater permit?

Projects disturbing one acre or more, or any disturbance in a sensitive watershed exceeding lower thresholds, must obtain a Maine DEP stormwater permit before earthwork begins.

Can a Maine town adopt looser stormwater rules?

No. Local stormwater ordinances must meet or exceed Chapter 500 standards. Delegated municipalities can issue permits but must enforce equivalent or stricter water quality protections.

Maine Stormwater Management Law and Chapter 500 Standards