Legal Terrain

MassDEP Proposes Updates to Stormwater Management Standards

February 26, 2024


In addition to amending the Wetlands Protection Regulations to add performance standards for the Land Subject to Coastal Storm Flowage wetland resource area, MassDEP wants to update the Massachusetts Stormwater Management Standards as part of its efforts to promote climate resiliency.

The Stormwater Management Standards are contained in Chapter 1 of Volume 1 of the Massachusetts Stormwater Handbook.[1] Volume 1 lays out the legal and regulatory framework for stormwater management in the Commonwealth. Volume 2 discusses the elements of stormwater management, particularly Best Management Practices (BMPs). Volume 3 describes how to prepare a stormwater report for submission with a wetlands Notice of Intent under the Wetlands Protection Act.

According to MassDEP’s Public Summary document, the proposed updates would replace the precipitation data upon which stormwater systems are designed with modern information that accounts for the increased intensity of storm events due to climate change. The updates would also require that stormwater system designs be based on the 90% value of the upper end of the historical precipitation range instead of the mid-point or average of the range. This would ensure that systems are designed to handle more frequent extreme precipitation events expected due to climate change. Other design requirements would require that more stormwater be infiltrated into the ground to reduce surface water flooding and pollution and replenish groundwater and would incentivize the use of ecological processes to handle stormwater runoff. Finally, the updates would better align the Commonwealth’s stormwater management with EPA stormwater management requirements for small municipal separate storm sewer systems (MS4s).

After significant stakeholder input, MassDEP extended the public comment period for the entire suite of proposed resiliency regulations for 60 days. The public comment period now runs from March 1 to April 30, 2024, and MassDEP will hold three virtual “office hours” sessions to take questions on the proposed amendments on February 26 from 1:00 p.m. to 3:30 p.m.; on March 14 from 1:30 p.m. to 4:00 p.m.; and on April 3 from 1:30 p.m. to 4:00 p.m.

Follow Legal Terrain as we dig deeper into the other provisions of the proposed regulations, and contact us if you need guidance on what these regulations could mean for your project.


[1] There are 10 Stormwater Management Standards which are also expressly incorporated into the Wetlands Protection Regulations at 310 CMR 10.05(6)(k):

  1. No new stormwater conveyances may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth.
  2. Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates.
  3. Loss of annual recharge to groundwater shall be eliminated or minimized through the use of infiltration measures including environmentally sensitive site design, low impact development techniques, stormwater best management practices, and good operation and maintenance.
  4. Stormwater management systems shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids (TSS).
  5. For land uses with higher potential pollutant loads, source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable.
  6. Stormwater discharges within the Zone II or Interim Wellhead Protection Area of a public water supply, and stormwater discharges near or to any other critical area, require the use of the specific source control and pollution prevention measures and the specific structural stormwater best management practices determined by the Department to be suitable for managing discharges to such areas, as provided in the Massachusetts Stormwater Handbook.
  7. A redevelopment project is required to meet the following Stormwater Management Standards only to the maximum extent practicable: Standard 2, Standard 3, and the pretreatment and structural best management practice requirements of Standards 4, 5, and 6.
  8. A plan to control construction-related impacts including erosion, sedimentation, and other pollutant sources during construction and land disturbance activities shall be developed and implemented.
  9. A long-term operation and maintenance plan shall be developed and implemented to ensure that stormwater management systems function as designed.
  10. All illicit discharges to the stormwater management system are prohibited.

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