Maryland Stormwater & Erosion Control

The short version

• MDE administers the program statewide. The Maryland Department of the Environment's Stormwater Management Program sets the rules; most day-to-day review is delegated to county and municipal programs approved by MDE.
• Environmental Site Design (ESD) to the Maximum Extent Practicable (MEP) is the core design philosophy under Maryland's law. Contractors and designers must prioritize low-impact, natural-system-based BMPs before resorting to larger structural controls.
• Stormwater Management Act lives in Maryland Environment Article Title 4, Subtitle 2 (§§4-201 through 4-215).
• COMAR 26.17.02 is the implementing regulation.
• Maryland Stormwater Design Manual is the technical design standard contractors and engineers work from.
• General Permit for Stormwater Associated with Construction Activity is MDE's NPDES coverage vehicle for most construction stormwater discharges.
• Soil Erosion and Sediment Control is a separate but coordinated MDE program covering construction-phase controls.

Where to go — primary sources

• MDE Stormwater Management Program — authoritative hub for MD stormwater regulation.
• Maryland Stormwater Design Manual — the technical standard for ESD and structural BMP design. Linked from the MDE hub.
• General Permit for Stormwater Associated with Construction Activity — MD's construction general permit. Linked from the MDE hub.
• Stormwater Management Act — Environment Article §§4-201 through 4-215.
• COMAR 26.17.02 — implementing regulation.
• MDE Soil Erosion and Sediment Control Program — parallel program for construction-phase controls.
• County / municipal stormwater programs — most MD counties and some municipalities run MDE-approved delegated programs handling day-to-day review.

Environmental Site Design (ESD) to MEP — the design philosophy

Maryland's stormwater law, amended significantly in 2007, requires Environmental Site Design to the Maximum Extent Practicable. In practice this means designers must:

• First, minimize runoff at the source — preserve natural drainage patterns, minimize impervious area, disconnect impervious surfaces.
• Then, treat runoff with small-scale, distributed ESD practices — micro-bioretention, green roofs, permeable pavement, swales, disconnection.
• Only after ESD-to-MEP is exhausted, fall back to larger structural BMPs.

The Design Manual enumerates approved ESD practices and their design criteria. Designers must document why ESD could not fully address the site's stormwater management — this is a real burden of proof, not a paperwork formality. MDE and delegated reviewers push back on plans that jump straight to structural BMPs.

When do the rules trigger?

Coverage generally applies to new development and certain redevelopment projects disturbing above the statutory threshold. The exact current threshold, the redevelopment coverage rules, and the list of exempt activities should be verified directly against the current statute, COMAR 26.17.02, and the Design Manual linked above. The 2007 amendments substantially changed coverage; older projects grandfathered under prior rules are treated separately.

Delegated county and municipal programs

Most MD counties — including Baltimore County, Anne Arundel, Montgomery, Prince George's, and Howard — run MDE-approved delegated stormwater management programs. For covered projects in those jurisdictions, the county program handles day-to-day plan review; MDE provides oversight and retains enforcement authority. Baltimore City runs its own program separately.

This means contractors and engineers need to know which jurisdiction reviews which project. The MDE hub maintains the list of approved delegated programs; the specific county's Department of Permitting Services (or equivalent) is the operational front door.

Soil Erosion and Sediment Control — separate but related

MDE's Soil Erosion and Sediment Control Program covers construction-phase controls and is administered in coordination with — but distinctly from — the post-construction Stormwater Management Program. Like stormwater management, E&S plan review is substantially delegated to local programs (Soil Conservation Districts in MD are the typical reviewers). Both programs commonly apply to the same project.

How Maryland differs from neighboring states

• ESD to MEP. MD's explicit ESD-first design requirement is stricter than PA's Chapter 102 or DE's program. This is a design-philosophy difference, not just a paperwork difference — site layout is affected.
• Delegated county programs. MD's delegated programs are more numerous and more operationally capable than the conservation-district delegation in PA. Several counties run substantial, specialized stormwater programs.
• Design Manual prominence. The Maryland Stormwater Design Manual is a prescriptive technical document with specific design criteria for each ESD practice. Treat it as a spec, not reference.
• Statute location. MD's Stormwater Management Act is in the Environment Article; PA's Chapter 102 lives in the PA Code.

Common pitfalls

• Skipping ESD analysis and proposing structural BMPs. Reviewers require documented ESD-to-MEP evaluation first.
• Not knowing which county program reviews a given project.
• Under-designing permeable surfaces or micro-bioretention — the Design Manual's specific criteria drive the design.
• Treating redevelopment projects as exempt when they may trigger stormwater management requirements under the 2007 amendments.
• Coordinating E&S plan and Stormwater Management plan late in design rather than in parallel.

The practical workflow

1. Determine coverage: does the project trigger Maryland Stormwater Management Act requirements?
2. Identify the reviewing jurisdiction (MDE direct, delegated county program, or Baltimore City).
3. Perform ESD analysis early in civil design: evaluate ESD practices per the Design Manual, document why any ESD practice is not practicable on this site.
4. Design remaining stormwater management per Design Manual criteria.
5. Design soil erosion and sediment control per the parallel E&S program requirements.
6. Submit plans; address review comments; revise.
7. Obtain construction general permit coverage.
8. Install perimeter E&S controls before earthwork.
9. Maintain, inspect, and document throughout construction.
10. Install permanent ESD and structural BMPs per approved plan.
11. Close out per the program's termination procedures.

When to get direct help

For ESD analysis or Design Manual interpretation, MDE program staff are accessible through the hub. For day-to-day plan review questions, the delegated county program (or Baltimore City) is the operational contact. For soil erosion and sediment control questions, the Soil Conservation District.

Why we built this

Maryland's ESD-to-MEP requirement is the most significant design-philosophy difference in the Mid-Atlantic. Out-of-state designers who bring a PA- or NJ-style "big pond at the outlet" plan to an MD project get pushed back hard. This page surfaces the ESD framework so designers and contractors set expectations and site layout correctly from the start.

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