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What Has Changed For Stormwater Management Facilities?

On July 12, 2023, the Environmental Protection Agency (EPA) issued a final rule that clarified that urban areas are ‘locations with 50,000 or more people’. This clarification has implications for what can be classified as a small municipal separate storm system (MS4), meaning that stormwater management facilities may now be required to implement stricter guidelines, including bioretention facilities.

If your facility now falls under the MS4 program, your bioretention facility might be subject to additional stormwater management rules.

What Are The Requirements For Stormwater Management Facilities?

If you are an existing or new stormwater management facility under the MS4 program, you might need an SMW Site Development Plan. This plan includes critical items that are needed to meet storm management approval, including:

  • A Storm Drain Plan checklist
  • A Flood Plain Checklist
  • Geotechnical investigations
  • Drainage area maps

What Does This Mean For My Bioretention Facilities?

If you own a rain garden to collect runoff from nearby impervious surfaces, you may fall under the new MS4 guidelines. You may need to provide an SMW Site Development plan for your site and ensure that your facility meets the required guidelines. This includes conducting textural, chemical, pH and organic analyses for plants and topsoil in your bioretention system.

State guidelines for bioretention outline what checks bioretention facilities must have in place, although a brief overview follows below.

Sand Filter Testing Specifications

Underground sand filters must be watertight and have no leakage for a period of eight hours. All overflows and channels must also be tested to ensure the facility is watertight and equally distributes flows.


Manholes must be provided to underground channels and must comply with OSHA guidelines. Steps and height clearance guidelines must be adhered to, and steps must be drilled into the wall or cast in place below each manhole.

Planting Soil

Planting soil must be free from stones, stumps, or roots over two inches. The soil must be a uniform mix with no contaminants that might impact vegetative growth. No noxious weeds can be present in the soil.

Plant Installation

Shredded hardwood mulch must be used in plant installation and be well-aged for over 6 months. Trees must be set at the appropriate planting distance, and the plant bed must be thoroughly watered after installation.

How Can I Get Support In Maintaining My Bioretention Facility?

Muller is the region’s leading stormwater maintenance specialist, with a qualified team of stormwater-certified professionals who can meet the new guidelines for your bioretention facility. Whether you are creating a new bioretention facility, redeveloping an existing one, or simply want to ensure you are within the new federal, state and local guidelines, our team is on hand to help.

Some of the services we can provide include:


Our team can conduct routine inspections on your underground overflows, planting soil, and plant installations to ensure you align with existing requirements. Our team is equipped to assist with any repair or cleaning.


We are certified to carry out VSMP, MDE, and DOEE inspections. Work with us directly to ensure that when the site inspection occurs, you are ready to pass with flying colors. Our team can carry any recommendations out as part of our services if any changes are needed.


After routine maintenance and inspections, our team will provide detailed reports and information you can provide to the regulatory authorities as evidence of compliance with the new legislation.

Erosion Inspection

Don’t let erosion pose a threat to your stormwater management system. We provide erosion inspection and can help repair areas where loose sediment impacts your rain garden. Silt fencing and slope stabilization are just some of the services we offer.

Manage Stormwater Confidently with Muller, Inc.

The amendments to federal, state, and local laws regarding stormwater management may impact whether your bioretention facility falls under stormwater management guidelines.

Ensure you’re compliant with the new guidelines by contacting Muller today. Our expert team will ensure that you align with federal, state, and local rules for stormwater management.