Stormwater management plans: steps for Somerset County compliance

A project that disturbs 5,000 square feet or more of soil or involves 100 cubic yards or more of earthwork requires approval of stormwater management and erosion and sediment control plans. A project disturbing 1 acre or more also enters the state construction stormwater permitting system.

The practical consequence is direct: a parcel does not avoid regulation merely because it is rural, low-density, or served by private drainage. The determining factors are disturbance area, impervious surface, grading, discharge pathways, and the applicable state and county approval requirements.

1. Determine whether the project crosses a regulatory threshold

The first step is a quantified site assessment. The applicant must identify the total area that will be affected by clearing, grading, excavation, construction access, utility installation, temporary staging, and impervious surface construction.

The relevant thresholds are:

These categories are not interchangeable. A project can exceed the earthwork threshold without exceeding the acreage threshold. Conversely, a broad but shallow disturbance can trigger plan approval through area alone.

Measure disturbance, not only the building footprint

A common error is to calculate only the area occupied by the proposed structure. That approach understates the regulated footprint. The calculation should account for:

• Building pads and foundations.
• Driveways, parking areas, sidewalks, and patios.
• Septic installation areas, where applicable.
• Utility trenches and service connections.
• Graded shoulders and access roads.
• Temporary construction entrances.
• Soil stockpiles and material storage areas.
• Areas cleared for drainage facilities or outfalls.
• Temporary and permanent slopes.
• Areas altered to connect the site to an existing road or drainage system.

The disturbance boundary should be shown on the site plan. It should not be inferred from the property boundary or from the final developed footprint.

For Somerset County properties, this distinction is material because a rural lot may contain substantial clearing and grading outside the proposed house location. A driveway crossing, drainage swale, septic field, and construction access route can collectively move a project into the mandatory approval category.

Treat earthwork as an independent trigger

The 100-cubic-yard earthwork threshold requires a separate calculation. Cut and fill should be documented using the proposed grading plan, not estimated informally from the apparent size of the site.

The calculation should identify:

1. Existing elevations and proposed elevations.

2. Areas of cut and fill.

3. Imported and exported soil.

4. Temporary excavation.

5. Excavation associated with foundations, utilities, and stormwater facilities.

6. Final grading around structures and pavement.

The purpose is regulatory classification and drainage analysis. Earthwork changes the surface profile, flow direction, storage capacity, and discharge velocity. A project can therefore create a compliance issue even when the added impervious surface is modest.

The regulatory trigger is established by the full disturbance footprint and earthwork volume, not by the size of the house alone.

2. Classify the proposed drainage changes

Once the threshold analysis is complete, the applicant must determine how the project will alter runoff. The central questions are physical:

• Where does rainfall currently infiltrate?
• Which areas will become impervious?
• Which portions of the site will be compacted?
• Will grading redirect sheet flow?
• Will runoff reach a ditch, roadside swale, stream, wetland, or neighboring parcel?
• Will the project increase the rate, volume, or duration of discharge?
• Will construction expose soil during a period of active rainfall?
• Does the receiving system have an existing drainage constraint?

The answer is not limited to whether the site has a visible ditch. Subsurface conveyance, roadside drainage, culverts, depressions, and informal overland flow paths can all affect the design.

For Eastern Shore properties, low relief can make drainage design more sensitive to small elevation changes. A minor grading adjustment may create a persistent wet area, concentrate flow against a structure, or shift discharge toward a neighboring parcel. Flat terrain does not eliminate drainage risk. It reduces the available hydraulic gradient and can make maintenance and overflow routing more consequential.

Review the receiving drainage system

The design should follow runoff beyond the property line. The analysis should identify:

• Existing roadside ditches and culverts.
• Outfalls and discharge points.
• Adjacent agricultural drainage features.
• Streams, wetlands, and other regulated waters.
• Existing stormwater facilities on adjoining parcels.
• Areas subject to nuisance flooding.
• Low points that may retain water after construction.
• Easements that authorize drainage conveyance or maintenance.

An easement delineation is not a substitute for hydraulic analysis. It establishes a property or access interest. It does not, by itself, prove that a proposed discharge is adequately sized, legally authorized, or compatible with downstream conditions.

Where a proposed facility crosses or occupies an easement, the site plan should distinguish the facility footprint, access route, maintenance area, and discharge structure. These areas may affect both the disturbance calculation and the project’s land-use approvals.

3. Apply Environmental Site Design before structural controls

Maryland’s stormwater framework requires new development to use Environmental Site Design to the Maximum Extent Practicable, commonly abbreviated as ESD to the MEP. This requirement derives from the Maryland Stormwater Management Act of 2007 and is implemented through COMAR 26.17.02 and the Maryland Stormwater Design Manual.

The sequence matters. Structural Best Management Practices are not the starting assumption. The plan must first evaluate how the site can be designed to retain, infiltrate, slow, and treat runoff close to its source.

What ESD changes in the design process

ESD is a site-design method. It addresses the origin of runoff rather than treating all runoff at a single downstream facility. The plan should examine whether the project can reduce runoff through:

• Preserving existing vegetation and undisturbed soil.
• Limiting the area of clearing and grading.
• Locating buildings and pavement outside natural drainage features.
• Reducing driveway and parking widths where functional needs allow.
• Directing roof runoff to non-erosive landscape areas.
• Using small-scale infiltration or filtration practices.
• Maintaining natural flow paths.
• Dispersing discharge rather than concentrating it at one point.
• Protecting soil permeability during construction.
• Separating clean water from disturbed areas.

The correct design depends on soil, groundwater, slope, seasonal saturation, existing drainage, and the proposed use. A facility that is technically suitable on a well-drained upland parcel may be unsuitable on a low-lying site with limited infiltration capacity.

ESD and rural residential construction

Single-lot residential construction is not automatically exempt from stormwater regulation. Somerset County Department of Public Works regulates standard stormwater management plans for single-lot residential construction under County Ordinance No. 1033 and Chapter 5 of the Maryland Stormwater Design Manual.

A standard plan may simplify documentation where the project meets the relevant conditions. It does not erase the need to classify the disturbance, address erosion and sediment control, or demonstrate that the proposed drainage arrangement complies with applicable requirements.

For a rural property, the applicant should separate three questions:

1. Does the project exceed the mandatory approval threshold?

2. Can a standard county plan be used for the project type and site conditions?

3. Does the site require a more individualized design because of grading, discharge, environmental constraints, or unusual drainage conditions?

The existence of a standard plan does not establish that the site is suitable for every standard detail. Field conditions remain controlling.

Structural BMPs are not the primary shortcut

A detention pond, infiltration basin, underground facility, or other structural BMP may be necessary. It should not be presented as the first and only compliance measure without documenting the ESD analysis.

The design record should show:

• Which nonstructural measures were evaluated.
• Which measures were selected.
• Which measures were rejected.
• Why rejected measures were infeasible.
• How the selected practices address runoff volume and quality.
• How overflow and bypass conditions are handled.
• Who will maintain the facility.
• Whether access and maintenance easements are recorded or otherwise established.

The phrase maximum extent practicable requires a reasoned site-specific determination. It does not mean that every conceivable ESD feature must be installed regardless of feasibility. It does mean that the plan must demonstrate that the design did not default to a downstream structural solution without analysis.

4. Prepare the county stormwater and erosion control submission

For projects at or above the applicable thresholds, the submission must be developed as a coordinated set of documents. Stormwater management and erosion and sediment control are related but distinct functions.

Stormwater management addresses the long-term condition of the developed site. Erosion and sediment control addresses soil exposed during construction. A project can satisfy one function and fail the other.

The stormwater plan should establish the permanent drainage arrangement

The permanent plan should clearly identify:

• Existing and proposed contours.
• Limits of disturbance.
• Existing and proposed impervious areas.
• Drainage areas and flow directions.
• ESD practices and their locations.
• Structural BMPs, if required.
• Inlets, pipes, swales, channels, and outfalls.
• Emergency overflow routes.
• Discharge points.
• Easement delineations.
• Access routes for inspection and maintenance.
• Stabilization measures for slopes and channels.
• Design assumptions used for runoff calculations.

The drawings should make the proposed system legible without relying on verbal explanations. A reviewer must be able to trace runoff from the roof, pavement, and graded ground surface to the final discharge or treatment point.

A plan that shows a facility but not its maintenance access is incomplete from an operational standpoint. A plan that shows a discharge pipe but not the receiving drainage feature is incomplete from a hydraulic and land-use standpoint.

The erosion and sediment control plan addresses construction risk

During construction, exposed soil can be mobilized before the permanent stormwater system is complete. The erosion and sediment control plan should therefore coordinate:

• Construction sequencing.
• Limits of clearing.
• Stabilized construction entrances.
• Perimeter controls.
• Temporary conveyance.
• Sediment trapping or filtering measures.
• Soil stockpile controls.
• Slope stabilization.
• Temporary stabilization after grading.
• Permanent stabilization at project completion.

The sequence should prevent the contractor from exposing the entire site before controls are functional. Clearing, grading, utility work, and final stabilization should be arranged so that exposed areas remain manageable.

The plan should also distinguish temporary controls from permanent facilities. A sediment trap used during construction does not necessarily satisfy the permanent stormwater requirement. Conversely, a permanent basin may require protection from sediment loading before it is placed into final service.

Coordinate site design with property rights

Stormwater facilities frequently require space beyond the building envelope. The applicant should resolve ownership and access questions before construction begins.

Potential conflicts include:

• A proposed swale placed within an existing utility easement.
• A discharge point located outside the applicant’s property.
• A maintenance route blocked by fencing or landscaping.
• An infiltration facility placed where seasonal groundwater prevents its intended operation.
• A drainage connection that depends on a neighboring parcel.
• A facility whose overflow route crosses a lot line without documented authorization.

The plan should identify each easement by location and function. Utility, access, drainage, and maintenance rights are not interchangeable. A recorded access easement may permit passage but not installation or maintenance of a stormwater facility.

5. Add the state NPDES permit for projects disturbing one acre or more

A project disturbing 1 acre or more requires coverage under the Maryland Department of the Environment’s General Permit for Stormwater Associated with Construction Activity, NPDES Permit No. 12-SW. The project must also prepare a Stormwater Pollution Prevention Plan, or SWPPP.

The NPDES requirement is additional to local plan review. It does not replace Somerset County stormwater management approval, and county approval does not substitute for state permit coverage.

The SWPPP must match the actual construction operation

The SWPPP should be treated as an operational document, not a filing formality. It must correspond to the site plan, construction sequence, disturbed acreage, control measures, inspection obligations, and stabilization procedures.

The document should be consistent with:

• The limits of disturbance shown on the approved plan.
• The construction phasing.
• The location of soil stockpiles.
• The temporary drainage system.
• The permanent BMP installation sequence.
• The points where runoff leaves the site.
• The methods for correcting failed controls.
• The timetable for stabilizing completed areas.

If field operations expand beyond the approved disturbance boundary, the permit analysis may no longer match the actual project. The same problem occurs when a contractor relocates a stockpile, opens an unplanned access route, or bypasses a temporary control.

The permit fee scale identified for NPDES Permit No. 12-SW ranges from $1,600 to $9,600, based on acreage. These are state permit fees. They should not be confused with any local Somerset County Department of Public Works plan-review fees, for which a separate fee schedule must be confirmed.

The current General Permit No. 12-SW has an expiration date of February 28, 2028. Permit conditions and renewal requirements must be evaluated against the operative state documents at the time of application. An applicant should not assume that a permit framework remains unchanged merely because the project was designed under an earlier version.

Construction compliance continues after approval

Approval does not end the compliance obligation. The permittee and contractor must maintain the controls, inspect the site as required, correct deficiencies, and stabilize disturbed areas.

Typical failure points include:

• Silt fencing installed across concentrated flow.
• Construction entrances that do not remove sediment from vehicle traffic.
• Sediment controls overwhelmed by an unplanned drainage area.
• Inlet protection removed before upstream stabilization.
• Exposed soil left inactive without stabilization.
• Permanent stormwater facilities used as sediment traps without authorization or proper protection.
• Discharge points creating erosion at the receiving channel.
• Field changes not reflected in the approved plan.

These are operational failures, not merely drafting defects. The site must function under actual rainfall and construction conditions.

6. Account for Somerset County’s local ordinance and drainage context

Somerset County’s local compliance pathway is governed in part by Ordinance No. 1033, with standard stormwater management plans for single-lot residential construction administered through the County Department of Public Works. The ordinance operates within Maryland’s broader stormwater framework. Local review therefore has to be read together with COMAR 26.17.02, the Maryland Stormwater Design Manual, and applicable MDE permitting requirements.

The applicant should organize the review around the following sequence:

1. Define the project boundary.

Include all clearing, grading, access, utility, pavement, drainage, and staging areas.

2. Calculate disturbance and earthwork.

Document both square footage and cubic-yard quantities. Do not assume that one measurement replaces the other.

3. Identify environmental and drainage constraints.

Map streams, wetlands, low areas, existing ditches, culverts, easements, and downstream discharge paths.

4. Determine the county plan pathway.

Establish whether the project qualifies for a standard single-lot residential plan or requires a more site-specific submission.

5. Develop the ESD analysis.

Evaluate source control, runoff reduction, infiltration, filtration, and flow dispersion before selecting structural BMPs.

6. Prepare erosion and sediment controls.

Sequence construction so that exposed soil is controlled before major grading begins.

7. Add NPDES coverage and the SWPPP when disturbance reaches 1 acre.

State permit coverage is a separate requirement.

8. Resolve easement and maintenance rights.

Confirm that the proposed facilities can be accessed, inspected, repaired, and legally maintained.

9. Keep field operations within the approved design.

Changes to the disturbance boundary, grading, drainage, or construction sequence may require revised review.

This sequence prevents the most common administrative error: treating stormwater approval as a single document instead of a connected set of land-use, drainage, construction, and maintenance obligations.

Local drainage is not only a private-lot issue

Somerset County’s nuisance flooding planning, including the 2019 Somerset County Nuisance Flooding Plan, reflects the broader relationship between individual site design and public drainage conditions. A private project can increase pressure on a roadside ditch, culvert, or low-lying conveyance route even when the added runoff appears limited in isolation.

The design review should therefore consider cumulative location-specific constraints:

• Existing roadside flooding.
• Limited ditch capacity.
• Undersized culverts.
• Repeated maintenance problems.
• Tidal or coastal backwater conditions.
• High seasonal groundwater.
• Downstream properties receiving concentrated flow.
• Existing failures in public or private drainage infrastructure.

The plan should not claim that a new facility resolves a wider public drainage deficiency unless that conclusion is supported by an engineering analysis. A parcel-level BMP can manage the project’s runoff without correcting a countywide conveyance limitation.

7. Monitor regulatory changes to COMAR 26.17.02

The Maryland Department of the Environment has initiated an Advanced Notice of Proposed Rulemaking concerning updates to COMAR 26.17.02 and the Maryland Stormwater Design Manual. Listening sessions continued through January 2026, with the final session identified as January 20, 2026.

An ANPRM is not the same as an adopted regulation. It signals regulatory review and possible future amendments. Until a new rule is formally adopted and becomes operative, project teams must work from the requirements in force for the application and construction period.

The compliance implications are practical:

• Do not treat discussion materials as binding law.
• Confirm the operative version of the design manual.
• Check whether permit forms or submission requirements have changed.
• Reconcile county plan review with current MDE requirements.
• Avoid finalizing a long-duration project on an outdated regulatory assumption.
• Preserve the technical basis for the ESD and BMP selections.

For projects with extended design or construction schedules, the permit expiration date and transition rules matter. A design prepared well before construction may require revision if the governing permit or technical standard changes.

ESD is a statutory design priority. A structural facility is a component of the solution, not a substitute for site planning.

Typical compliance failures

Somerset County stormwater submissions tend to become difficult when the documents describe a different project from the one that will be built. The following defects are avoidable:

• The limits of disturbance omit the driveway, septic area, or temporary access route.
• The earthwork estimate excludes foundation or utility excavation.
• The plan shows a BMP without an access or maintenance area.
• The drainage narrative stops at the property line.
• The proposed outfall lacks a defined receiving feature.
• The project uses a standard residential plan despite site-specific grading or discharge conditions that the standard details do not address.
• ESD measures are listed but not located or quantified.
• A structural basin is proposed without documenting why source-control measures are infeasible.
• The SWPPP does not match the construction sequence.
• The contractor expands the disturbed area without revising the permit documentation.
• An easement is shown graphically but does not authorize the proposed stormwater use.
• Local county review and state NPDES coverage are treated as one approval.
• State permit fees are confused with local plan-review charges.
• A pending regulatory proposal is presented as though it were already enforceable.

The corrective principle is simple: every material design assumption should appear in the drawings, calculations, narrative, or recorded property documentation. Unstated assumptions become field disputes.

Final determination

The stormwater management plan requirements in Somerset County are controlled by measurable thresholds and layered authority. The applicant must first establish the full land-disturbance area and earthwork volume. At 5,000 square feet of disturbance or 100 cubic yards of earthwork, plan approval is mandatory. At 1 acre of disturbance, MDE General NPDES Permit No. 12-SW and a SWPPP are also required.

The design must implement Environmental Site Design to the Maximum Extent Practicable before relying on structural BMPs. Single-lot residential construction may use a standard county pathway under Ordinance No. 1033 when the applicable conditions are met, but rural location does not create a blanket exemption. Easement delineations, drainage outfalls, construction sequencing, maintenance access, and downstream conveyance must be resolved as part of the compliance record.

The controlling standard is not whether a proposed facility appears adequate on a sketch. It is whether the complete project satisfies state stormwater law, county ordinance requirements, erosion and sediment control obligations, NPDES conditions where applicable, and the physical constraints of the Somerset County site.