New Massachusetts Stormwater Measures Are Coming: Top Takeaways for Developers and Municipalities
by Chris Broyles
The Massachusetts Department of Environmental Protection (DEP) has recently proposed new stormwater regulations. Aimed at bolstering resilience to flooding and incentivizing the use of nature-based solutions, the regulatory changes will have significant impact on new and redevelopment projects in the Bay State. Here are five critical elements of the new regulations that we believe our clients should pay particular attention to and which we are monitoring to ensure that they remain in compliance.
New Rainfall Benchmarks
Up until now, rainfall estimates were based on data from 1961. Under proposed amendments (pending approval) to the Wetlands Protection Act (310 CMR 10.00), that would be updated to rainfall estimates based on 2019 National Oceanic and Atmospheric Administration (NOAA) data. As climate change has increased significant precipitation events, the practical impact of this shift for developers would be a need to design for larger volumes of water, from larger pipes to more and/or larger stormwater facilities, such as surface stormwater basins and underground chamber systems. Some municipalities, agencies, and developers have already been preparing for greater stormwater volume; under the amended regulations, those who have not will be required to do so.
A New Groundwater Recharge Requirement
A second proposed change would increase the required amount of groundwater recharge, which can happen via the natural downfall of water into the earth during storms and/or by human-built systems to divert stormwater into specified areas. In Massachusetts, developers or organizations who pave an area must balance out the lost groundwater recharge due to the impervious surface by storing that same volume of would-be groundwater elsewhere on the site in an amount equal to half an inch across the paved surface area. To protect against drought-based problems, the new requirement would increase that groundwater recharge requirement by twofold, for a mandated one inch across the paved surface. As a result, new site development projects will need to consider more and/or larger groundwater systems, and in many cases, permeable ground surfaces may become more attractive.
Changes to Sediment and Pollution Requirements
Another proposed change relates to the amount of total suspended solids (TSS) – sand, silt, etc. – that must be removed before water may be discharged from a stormwater facility. Currently, facilities must have an 80 percent TSS removal rate. To protect waterways from runoff, the new regulations propose raising that requirement to 90 percent of sediment. In addition, proposed changes include a new regulation: the total and documented removal of phosphorus. Many stormwater facilities already achieve this through chemical or biological treatments (or both); under the proposed changes, facilities would now be required to comply with and document this process. A similar compliance and documentation proposal extends to any contributions to a body of water’s total maximum daily load (TMDL), which is the maximum amount of a pollutant permissible in a body of water while still meeting water quality standards.
New Standard for Land Subject to Coastal Storm Flowage
A change impacting coastal development includes MassDEP’s new standards for Land Subject to Coastal Storm Flowage (LSCSF). These Resource Areas extend from the mean low water line to the farthest landward extent of the coastal floodplain. LSCSF buffers the effects of coastal storms on property, infrastructure, and the natural shoreline. Modifications to this area can adversely impact its ability to reduce storm damage, resulting in threats to public health and safety. The new standards promote coastal resiliency against worsening impacts of storms, flooding, and sea level rise. Its intent is to reduce damage to properties, infrastructure, and the natural shoreline by preserving and restoring natural floodplain functions of the area. In certain flood zones, proposed LSCSF standards require additional protections, such as elevating structures on open piles to preserve floodplain function and prevent damage.
New Credits for Low-Impact Development (LID) and Environmentally Sensitive Site Design (ESSD)
Some costs associated with adhering to these new requirements may be offset by a proposal to offer seven new credits for those who implement LID or ESSD practices. Examples include protecting or enhancing tree canopies and buffer areas, reducing impervious surface areas, strategically directing runoff, and incorporating environmentally sensitive site design. While these priorities are not new, the proposed changes would give them “teeth.” Until now, implementing these measures resulted in little more than a “pat on the back” from DEP. Under the proposed changes, adopting
and documenting these actions would yield credits that can mitigate a developer or owner’s requirements in other areas.
Turning Challenges into Opportunities
The aim of these new regulations is to future-proof Massachusetts properties, waterways, and resource areas in the face of a changing climate that may include more severe weather events. Many businesses have already begun planning for such scenarios with proactive measures such as moving mechanical units from basements and ground floors to higher floors within buildings, or even roofs.
Still, the average developer or municipality is unlikely to have an encyclopedic knowledge of land subject to coastal storm flowage, the Massachusetts Stormwater Handbook, the Wetlands Protection Act, the Massachusetts Clean Waters Act, and the state’s Water Quality Certification Regulations. By consulting an integrated civil engineering, land surveying, and landscape architecture firm as early as possible in the development process, developers and municipalities can be sure that land planning, site development, and infrastructure design takes place in a manner that will be compliant and cost-effective. Regulatory changes can cause some discomfort, particularly when standard operating procedures are well-established, but when those changes are presented to a knowledgeable, creative team, such land and water challenges can become opportunities.
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Link to MassDEP Presentation: 
Proposed Stormwater Updates
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..Key Takeaways:
1. Rainfall benchmark estimates would update from 1961 to 2019 NOAA data, requiring design for larger water volume, from larger pipes to more and/or larger stormwater facilities
2. Groundwater Recharge: Proposal would double requirement (from half to one inch).
3. Sediment and Pollution: Total suspended solids (TSS) – sand, silt, etc. – removal rate would increase from 80 to 90 percent, plus “total” and “documented” removal of all phosphorus.
4. MassDEP’s new standards for Land Subject to Costal Storm Flowage intends to reduce damage to properties, infrastructure, and the natural shoreline by preserving and restoring natural floodplain functions of impacted area(s).
5. Get some credit! Some costs can be offset by implementing LID and ESSD, such as tree canopies, buffer areas, and reducing impervious surface areas, among others.
6. Turn your challenge into an opportunity! By design, Meridian offers integrated civil engineering, survey, and resiliency-focused landscape architecture. Together, our experts deliver permittable designs that balance development with nature, protecting your project now – through permitting and construction – and later via stormwater system supports calibrated to a changing and challenging climate
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About the Expert
Chris Broyles, PE
PROJECT MANAGER, CIVIL ENGINEERING
Christopher Broyles, PE is a civil engineer, project manager and stormwater expert at Meridian Associates with experience in the design of site layouts, stormwater management facilities, erosion and sedimentation control, sanitary sewerage disposal systems, roadways, and utilities.
