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Civil Engineering

Stormwater / LID / WQMP

Low Impact Development (LID) design and Water Quality Management Plans to meet MS4 Permit requirements and achieve plan check approval for your development project.

What Are LID and WQMP Plans?

LID (Low Impact Development) and WQMP (Water Quality Management Plan) are stormwater quality requirements mandated by the San Diego Regional Water Quality Control Board under the Municipal Separate Storm Sewer System (MS4) Permit. These regulations require development projects to treat stormwater runoff before it enters the public storm drain system — reducing pollutants like sediment, oils, metals, and nutrients that would otherwise reach local waterways and the ocean.

Moment Engineering determines whether your project qualifies as a Priority Development Project (PDP) or Standard Project under the current MS4 Permit, selects the appropriate BMP (Best Management Practice) strategy, and prepares the engineering plans and reports needed for plan check approval. We design bioretention basins, permeable pavement, proprietary filtration systems, and other LID measures that comply with the San Diego BMP Design Manual, Orange County TGD, or LA County LID Standards Manual applicable to your jurisdiction.

PDP vs. Standard

Project classification determines the scope of stormwater requirements

85th %ile

LID design storm volume per San Diego BMP Design Manual (other counties vary)

MS4 Permit

Regional Water Board permit driving stormwater quality requirements

Need LID / WQMP Compliance? Get a fixed-fee proposal — typically within 24 hours.

Request a Proposal ✆ (619) 374-8677

Typical Investment

$2,500 – $5,000

Depends on project size, BMP type, and whether LID or WQMP format is required.

Fees vary by site conditions, scope, and jurisdiction. Request a proposal for a fixed-fee quote tailored to your project.

Scope of Work

What's Included

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Project Classification

We determine whether your project is a Priority Development Project (PDP), Standard Project, or exempt based on the project type, size, and location per the applicable MS4 Permit criteria.

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LID BMP Design

Engineering design of bioretention basins, flow-through planters, permeable pavement, green roofs, or proprietary filtration systems sized to capture and treat the design storm volume.

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WQMP Report

A Water Quality Management Plan (WQMP) documenting the pollutant sources, BMP selection, sizing calculations, and long-term maintenance requirements for your project. Some jurisdictions refer to this as a SWQMP.

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Hydromodification Analysis

Where required, analysis demonstrating that post-development stormwater discharge rates and durations do not exceed pre-development conditions to protect downstream channels.

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BMP Plan Sheets

Detailed plan and section drawings showing BMP locations, piping, overflow structures, planting specifications, and underdrain details — included in the permit plan set.

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Maintenance Agreement

Preparation of the long-term BMP maintenance plan and O&M agreement required by the jurisdiction before permit issuance, ensuring ongoing stormwater compliance.

When You Need LID / WQMP

Stormwater quality requirements apply to most new development and significant redevelopment in Southern California. The scope depends on your project classification.

New Homes & ADUs

Single-family homes and ADUs that create or replace 2,500+ square feet of impervious surface typically trigger Standard Project requirements (source control BMPs and site design measures).

Priority Development

Projects creating 5,000+ sq ft of impervious area, automotive facilities, restaurants, parking lots > 5,000 sq ft, and other categories trigger full PDP requirements with structural BMPs.

Commercial & Industrial

Retail, office, warehouse, and industrial projects almost always exceed PDP thresholds and require full LID design with biofiltration or equivalent treatment.

Subdivisions

Residential tracts and subdivisions require a project-level WQMP addressing the entire development, with BMP locations coordinated with the tentative map.

Redevelopment

Projects that replace 50% or more of the existing impervious surface are treated as new development and must meet current stormwater requirements.

Permit Conditions

Some discretionary approvals and conditions of approval specifically require stormwater compliance documentation before the grading or building permit is issued.

Our Process

From Site Assessment to Stormwater Compliance

Project Classification

We review the project scope and impervious area calculations to classify the project as PDP, Standard, or exempt under the applicable MS4 Permit. This determines the BMP requirements.

BMP Selection & Sizing

We select the most cost-effective and site-appropriate BMPs, then size them to capture the 85th percentile design storm volume per the BMP Design Manual or equivalent standard.

Plan & Report Preparation

We prepare the WQMP report and BMP plan sheets coordinated with the grading plan. The package is formatted per the jurisdiction's submittal requirements and PE-stamped.

Plan Check & Approval

We submit with the grading plan package and respond to stormwater reviewer comments through approval. We also prepare the maintenance agreement required before permit issuance.

Want to learn more about what a stormwater / lid / wqmp involves?

Read: What Is a Stormwater / LID / WQMP? →

Related Services

Often Paired With Stormwater / LID / WQMP

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Grading Plans

LID BMPs are integrated into the grading plan — their locations and grading affect the overall site design and drainage.

Learn More →

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Hydrology Reports

Hydrology reports address water quantity while WQMP/LID addresses water quality — most projects require both.

Learn More →

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Erosion Control Plans

Erosion control addresses construction-phase stormwater pollution, while LID/WQMP addresses permanent post-construction treatment.

Learn More →

Common Questions

Stormwater / LID / WQMP FAQs

LID (Low Impact Development) is a design approach that mimics natural hydrology — using infiltration, bioretention, and permeable surfaces to manage stormwater. A WQMP (Water Quality Management Plan) is the regulatory document that describes the LID strategy for your project. The WQMP is the report; LID is the design philosophy it implements.

PDP classification depends on project type and impervious area. Generally, projects creating 5,000+ sq ft of new impervious surface, restaurants, auto service facilities, and large parking lots are PDPs. Residential projects under 5,000 sq ft of new impervious area are typically Standard Projects with less stringent requirements. We determine the classification as part of our scope.

We commonly design bioretention basins (rain gardens), flow-through planters, permeable pavement (interlocking pavers or pervious concrete), proprietary filtration units (Modular Wetland, StormFilter), and dry wells. The selection depends on available space, soil infiltration rates, maintenance access, and cost.

As a rule of thumb, bioretention basins require about 3–5% of the contributing impervious area. A typical residential PDP bioretention basin might be 100–200 square feet. We optimize the layout to minimize the space impact on your site plan.

Yes. All jurisdictions in San Diego, Orange, and LA counties require a recorded maintenance agreement or covenant that obligates the property owner to maintain the BMPs in perpetuity. We prepare the agreement and maintenance plan as part of our deliverables.

In many cases, yes. Proprietary units like Modular Wetland Systems or Contech StormFilter are accepted alternatives when site constraints (space, soil conditions, or depth to groundwater) make bioretention impractical. We evaluate the trade-offs and help you select the best option.

Need LID / WQMP Compliance?

Stormwater compliance on a deadline? Tell us your jurisdiction and project type and we'll scope the right documents and send a proposal — typically same day.

Request a Proposal ✆ (619) 374-8677