New EPA NPDES Permit for Stormwater Discharge

What Developers and Property Owners Need to Know

The Environmental Protection Agency (EPA) has introduced a draft General Permit (GP) for stormwater discharges from private commercial, industrial, and institutional properties in the Charles, Mystic, and Neponset River Watersheds across eastern Massachusetts.  

This new CII GP is designed to improve water quality in these regions by addressing pollutant loading in the waterways. However, while the goal is to enhance environmental protection, the permit will have significant implications for both existing properties and future development projects. 

The new permit mandates increased stormwater treatment measures. Developers should be prepared for stricter requirements in managing stormwater runoff, impacting both project timelines and costs.  

Here’s what Bohler’s New England team knows about the draft permit requirements and how they might impact property owners and development teams across Massachusetts. Stay ahead of the curve by understanding the potential requirements and challenges associated with the new CII GP. 

Impacted Sites and Projects

Existing Properties – Currently Developed

The new CII GP will impact existing privately held properties located within the Charles, Mystic, and Neponset River Watersheds that are classified as “commercial,” “industrial,” or “institutional” in the Massachusetts Tax Codes. Specifically, properties with more than 1 acre of impervious surface will be subject to retrofit stormwater systems to the updated requirements.  

Note that some mixed-use properties may also be subject to compliance. Eligibility depends on how the property is classified, and certain exemptions may apply. 

Approximately 4,000 properties across these watersheds are expected to be affected.  

Newly Developed Sites

In addition to existing properties, the CII GP will apply to newly developed sites and any existing properties that increase impervious coverage beyond the 1-acre threshold. 

Developers will need to account for these changes early in the planning stages. Increased impervious surface coverage will necessitate more extensive stormwater management systems, which could lead to higher costs for planning, design, and construction throughout the project’s lifecycle. These additional measures will need to be integrated into the development process, affecting project timelines and budgets. 

Understanding the New Requirements

Under the new CII GP, impacted properties and projects will be required to take steps to improve how they manage stormwater in order to reduce pollution—specifically, phosphorus — by 60% to 65%, depending on where they’re located. 

This includes using structural measures, like installing underground filters or creating areas where water can soak into the ground, as well as nonstructural measures, like adjusting how the site is maintained or designed to naturally reduce runoff. These changes are meant to help keep local rivers and waterways cleaner by filtering out pollutants before they reach the storm drain system. 

Retrofitting Existing Sites

For existing properties, meeting the new stormwater treatment standards will likely require site modifications. The right solution depends on the amount of treatment needed and the available space. Solutions may include surface or subsurface infiltration systems, low-impact development (LID) strategies like bioretention, or mechanical treatment methods such as underground filtration units.  

Cost and Space Considerations

Each stormwater treatment approach comes with trade-offs in terms of cost and space. Mechanical and underground systems are typically more costly but can be more compatible with retrofit projects, especially when it’s important to maintain existing site operations or preserve buildable area. In contrast, surface and low-impact development (LID) methods are generally more cost-effective but require more space, which may limit future development potential.  

Bohler’s design teams are well-versed in guiding developers and property owners through evolving stormwater regulations. We take a collaborative approach, working closely with project stakeholders to develop strategies that align with the new EPA permit requirements while also supporting broader project goals and budget considerations. By tailoring solutions to each site’s specific conditions, we help clients move forward with confidence and compliance. 

Roll-Out and Implementation

Although the public comment period for the new CII General Permit has closed, the EPA hasn’t yet announced when the new rules will officially take effect. What we do know is that the rollout is expected to happen in phases. Properties with more than five acres of impervious surface will likely be required to meet the new requirements first. 

This phased approach is intended to give property owners and developers several years to prepare—allowing time to apply for the permit, plan for upgrades, and install the necessary stormwater systems. It also takes into account the varying complexity of projects and the time needed to align resources and budgets.  

What to Do Next

To determine if your property may be subject to the new EPA permit requirements, start by using the EPA’s Parcel Level Interactive Mapping Tool. This tool allows you to search by address and check if your property falls within the impacted watersheds—Charles, Mystic, or Neponset—and whether it meets the impervious surface threshold of 1 acre or more. The tool also provides the tax code listing at the time of map preparation, helping you confirm your property’s classification. 

Please be advised that this permit has not yet received approval. The above provides a summary of the legislature’s current intent. We will ensure to keep you informed of any updates as we receive further information.

Concerned about how this may impact your property? Connect with our team today.