Stormwater treatment in Massachusetts has historically focused on suspended solids, but more attention is being given to phosphorus and other nutrients that contribute to surface water quality issues and affect both ecological and recreational uses.
The US Environmental Protection Agency (USEPA) is proposing to require National Pollutant Discharge Elimination System (NPDES) permits for currently unregulated stormwater discharges from certain commercial, industrial and institutional (CII) properties with one or more acres of impervious cover in three of the major Greater Boston watersheds: the Charles, Mystic and Neponset River watersheds.
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GP Requirements for Affected Properties
USEPA is using a Clean Water Act (CWA) provision called “residual designation authority” to regulate stormwater discharges from certain CII and multi-family residential properties within the Charles, Mystic and Neponset River watersheds that have one acre or greater impervious area (i.e., hard surfaces such as parking lots, sidewalks, roof tops, driveways, etc.). Both existing and new CII sites that meet the impervious area requirements will be required to apply for coverage under a NPDES General Permit (GP). As of October 31, 2024, USEPA provided notice of a draft NPDES GP for CII sites that would require implementation of stormwater best management practices (BMPs), as well as meeting other water quality standard limitations. CII sites applicable to the GP will be required to:
- Submit a Notice of Intent (NOI) for permit coverage, with deadlines based on impervious area size.
- Develop and implement a Stormwater Pollution Control Plan (SPCP) to reduce Phosphorus discharges by specific percentages for each watershed.
- Develop an Onsite Chemical Application Management Plan addressing landscaping and winter maintenance.
- Annual stormwater trainings following Year 2 after permit authorization.
- Annual reporting.
To address the discharge of Phosphorus from a CII site to meet Water Quality Standards, all Permittees must reduce Phosphorus from stormwater discharges from their site by the following percentages based on the watershed into which the site discharges:
- Charles River Watershed: 65%
- Mystic River Watershed: 62%
- Neponset River Watershed: 60%
CII sites have three options for complying with the permit phosphorus reduction requirement:
- Onsite Phosphorus discharge reductions through structural or non-structural stormwater control measures (SCMs) within the watershed. For sites that discharge to more than one watershed, the onsite and offsite reduction must happen proportionally within each watershed.
- Offsite Phosphorus discharge reductions (SCMs are implemented at another location that is not the permitted site) via an agreement with a local watershed management group to fund a regional project.
- Offsite Phosphorus discharge reductions (SCMs are implemented at another location that is not the permitted site) via trading credits reducing Phosphorus loadings on another CII site in the same watershed.
Existing CII sites must meet a 50% Interim Phosphorus reduction goal within 6 years of permit authorization and full compliance within 11 years. Newly developed sites must comply with the Phosphorus load reduction responsibilities within two years of receiving authorization to discharge under the GP.
The public comment period for this proposed action will remain open until January 29, 2025.
Next Steps: TRC Can Help
To meet compliance deadlines, it is critical for large private developments operating (or to be operating) within these watersheds to review these draft regulations and understand the new requirements for compliance with their stormwater discharges. Sites applicable to the GP will need to evaluate their existing SCMs and may need to install new SCMs, which must be constructed in accordance with the Massachusetts Stormwater Standards to be used for treating phosphorus in stormwater.
TRC’s goal when assisting clients with stormwater management and treatment projects is to create the most efficient and sustainable solution possible. Our extensive expertise with stormwater integration into existing and new sites, especially in urban environments, in conjunction with our environmental, permitting and siting capabilities enable us to support the CII GP requirements for a Permittee.
Learn more about our related services or contact us for assistance today.
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This regulatory update is a service to TRC’s utility clients, helping keep you informed of issues that impact your company’s electric system security risks along with related topics regarding future regulatory developments to help you achieve your company’s business goals.
