Stormwater

Preparing for MS4 Changes

April 14, 2025
By Treasure Agbonkhese, Environmental Compliance Specialist, WSB

Expert insights on adapting to upcoming program updates

The Municipal Separate Storm Sewer System (MS4) program is a critical initiative aimed at reducing the pollutants that enter our water bodies through stormwater runoff. Managed under the Clean Water Act, the MS4 program requires regulated entities, such as cities, counties, universities, and even highway departments, to develop and implement a Stormwater Pollution Prevention Program (SWPPP). This ensures that the quality of water discharged from their systems meets the requirements set forth by the local agencies and the EPA.  Organizations need to prepare for MS4 changes and reauthorizations which necessitate both awareness and preparedness from involved stakeholders.  Each state reauthorizes their own permits, for example Minnesota’s expire in 2025 and Oklahoma’s are set to expire in 2026.

MS4 programs will likely see several pivotal updates designed to enhance its effectiveness and expand their scope. Those changes may include:

• Reauthorization of NPDES MS4 permits
• New rules and requirements
• More audits conducted by the MPCA to ensure compliance with the current MS4 permit
• Annual Reporting
• Increased emphasis on TSS, TMDL, and Waste Load Allocation 
• Increased emphasis on the education and incorporation of green infrastructure solutions, such as rain gardens and permeable pavements, which help mitigate stormwater impacts.

These changes underscore the program’s commitment to leveraging sustainable practices to protect our water resources better.

To prepare for these impending changes, municipalities and other regulated entities must take proactive steps. Firstly, reviewing and updating current Stormwater Pollution Prevention Programs to align with the current requirements is crucial. This may involve investing in new technologies for inspection, monitoring and data collection of stormwater infrastructure, as well as training staff to handle more complex reporting and documenting tasks in illicit discharge, construction, and post-construction stormwater management. Secondly, exploring green infrastructure options and integrating them into existing frameworks can provide long-term benefits and compliance with the 2025 updates. Engagement with community stakeholders and public education campaigns will also be essential to ensure widespread understanding and support for these initiatives.

WSB stands ready to assist entities in navigating these changes, offering comprehensive services ranging from full management of MS4 programs to targeted support for specific components. With our expertise in stormwater management and green infrastructure, we can help you assess your current systems, identify areas for improvement, implement solutions that meet the current and future requirements, and help perform self-audits of current MS4 programs. Our team is equipped to handle everything from initial development and management to ongoing construction sites, illicit discharge, facility inspections, and maintenance and reporting, ensuring a seamless transition to the new NPDES MS4 Permit.

In conclusion, changes to the MS4 program represent a significant step forward in protecting our water resources. By preparing now and leveraging the expertise of partners like WSB, municipalities, counties, state departments and other stakeholders can successfully adapt and thrive under the new requirements. Together, we can ensure the continued health and sustainability of our water bodies for future generations.
Treasure is an environmental compliance specialist at WSB. Her background includes water resources engineering, construction site and MS4 permitting, SWPPP design and inspection, and MS4 program development and implementation. Her passion for MS4 coupled with her background in engineering brings a level of engagement, creativity, training, and unique skills to MS4 program development and management.

Monitoring Maintenance

App-based storm water asset management program helps streamline inspections.

By Bill Alms, Project Manager, WSB

Changing permit requirements throughout the country for municipal separate storm sewer systems (MS4) prompted Minneapolis-based design and consulting firm WSB to develop a web-based application for tracking inspection and maintenance of storm water best management practices (BMPs). Launched in 2013, the application has helped dozens of communities meet National Pollutant Discharge Elimination System (NPDES) permit requirements and prioritize maintenance needs for aging storm water infrastructure.

When the Minnesota Pollution Control Agency (MPCA) first introduced a new MS4 permit that required operators to have a standard procedure for annual inspections and maintenance, many communities felt overwhelmed. “We were hearing from municipal clients that there just wasn’t a good practice in place for wrapping your head around these systems,” said Jake Newhall, a water resources project manager at WSB. “Some systems have upward of 1,000 ponds and other BMPs. Communities didn’t have the resources available to inspect every asset.”

Utilizing Geographic Information System (GIS) data, the team at WSB developed an application to prioritize annual storm water BMP inspection and maintenance activities called the Storm Water Asset Management Program, or SWAMP. Specifically, the app provides an easily accessible BMP inventory, tracks and prioritizes annual inspections and maintenance and addresses the NPDES annual reporting requirement.

Nationally, the list of impaired waters steadily grows. In Minnesota alone, the MPCA recently added more than 500 waterbodies to the list. The app can be used to track the BMPs’ performance toward water quality improvements upstream of impaired waters, as well as performance related to Total Max Daily Load (TMDL) waste load allocations.

The web-based application utilizes a series of inputs that allow communities to customize their storm water maintenance programs. Since it was developed, national and local MS4 permitting requirements have continued to change. The program easily adapts to help clients meet these new standards, such as a recent requirement for reporting total suspended solids and total phosphorous.

Most communities have readily available data to utilize the program: a pond inventory, subwatershed and storm sewer maps and historic survey information. The result is a user-friendly snapshot of a community’s storm water system maintenance needs, which can be used to help decision-making as well as respond to staff, elected officials and residents.

How the program works:

• Data collection and application set-up: WSB begins the process by inputting data on all construction as-builts, MS4 ponds, drainage areas, land use maps, field inspection reports, storm sewer maps and BMPs. This data serves as the foundation of the client’s storm water asset management program.
• Prioritization: Once the data is compiled, the application analyzes BMPs and prioritizes them based on pollutant removal efficiencies, cost-benefit, downstream receiving water, etc.
• Surveying: Once the priorities are identified, surveying begins. The highest priority BMPs are surveyed to determine if there are maintenance needs. Following the survey, SWAMP is updated to reflect survey information and further calibrate the application.
• Budgeting: Once a SWAMP action plan is created, a budget can be made. Storm water inspection and maintenance activities can be budgeted based on the community’s capital improvement plan (CIP), making funds readily available for improvements as needed.
• Construction: With the action plan and budget identified through the app, municipalities can begin hiring contractors or allocating staff to perform construction and maintenance.
• Updates and tracking: The SWAMP application is updated to reflect the maintenance performed as well as track all historical activities.

WSB meets with multiple communities annually to review their programs and determine upcoming survey and maintenance needs. Prior to the app, clients would have to invest significant dollars in studies and models to prioritize storm water infrastructure needs. By utilizing the information within SWAMP, each client can efficiently prioritize BMP maintenance based on their preferred metrics, such as total cost, cost effectiveness and pollution removal effectiveness.

Many clients report that the program makes it easier to upgrade and maintain their BMPs. The SWAMP action plans for each community also make it easier for staff to address citizen concerns. If a resident wants to know when a pond will be maintained, the staff member or official can point to the framework and showcase how the priority of that pond compares to other assets within the system and when it will be due for maintenance.

“For developed communities, many of these BMPs that were installed in the 70s and 80s after the Clean Water Act are nearing their life expectancy,” said Newhall. “These are assets for the community–reducing pollution and ensuring safe, clean water–and we need to manage the benefits provided by this infrastructure in perpetuity.”

This article was originally published in the February 2020 issue of Storm Water Solutions magazine.

MPCA Releases Revised Soil Reference Values (SRVs)

Jake Newhall, Senior Project Manager, WSB

In early April 2020, the Minnesota Pollution Control Agency (MPCA) released revised SRVs for contaminated sediment. These revised values slightly relax regulations placed on sediment disposal.  The graphic below compares the new regulations with the old regulations.

SRV levels indicate the concentration of polycyclic aromatic hydrocarbons (PAHs) that have accumulated in some stormwater pond sediments around the state. PAHs break down over time and can be transported via stormwater runoff.

The adjustment in regulations creates cost-saving opportunities when managing stormwater maintenance projects.

Basic steps to flood prevention

Minnesota’s aging stormwater infrastructure is forcing communities across the state to re-evaluate their action plan.

As water levels continue to increase, so does the need for effective stormwater management systems. The Star Tribune pointed out some of the struggles facing Minnesota communities in their recent story, published on September 22. At WSB, we’re working closely with municipalities to help develop stormwater management planning. Here are a few ways communities can respond to the rising water levels:

1. Plan ahead. Identify areas of highest risk in your city early. Develop action plans that include back-up generators and pumps, sandbags, and resident notification.
2. Identify, map and maintain overland overflow routes for water bodies where feasible. These routes allow runoff to follow streets, property lines, and backyards while protecting homes from high flood levels. Inspect and enforce keeping these overflows clear – no fences or outbuildings that may block drainage.
3. Look for opportunities to build resiliency into the system. This may mean allowing for parking lot flooding to protect structures; constructing additional ponding retention with new developments; utilizing park space, public open space, and golf course greens for flood retention.