Draft state MS4 permit would require site-review procedures; towns warn of inspection burden

Vermont Department of Environmental Conservation officials presented the draft General Permit 3-9014 for small MS4 stormwater discharges to the Chittenden County MS4 Subcommittee on May 2, 2023, outlining a 30-day public comment period expected in early May, a July 27, 2023 permit expiration and NOI deadline, and staggered deadlines for updated stormwater management plans and post-construction plans.

The draft would tighten requirements on construction review and inspections (MCM#4), require permittees to adopt regulatory mechanisms or policies to ensure erosion and sediment controls and sanctions for noncompliance, and add procedures for site-plan review, comment receipt, and site inspection and enforcement, DEC staff said. Sam Hughes, a DEC representative, said permittees will need to demonstrate a plan to create these regulations rather than have them fully enacted within six months.

The proposed MCM#5 language shared in the meeting chat lists the scope for post-construction stormwater controls for developments that disturb one acre or more, "utiliz[ing] a combination of structural, non-structural, and low impact BMPs (e.g. green roofs; infiltration practices, such as rain gardens, curb extensions, planter gardens, porous and pervious pavements, and other designs to manage stormwater using landscaping and structured or augmented soils; water harvesting devices, such as rain barrels and cisterns; and the use of stormwater for non-potable uses)," and requires long-term operation and maintenance of those BMPs, DEC staff (Christy Witters) posted.

Municipal representatives flagged practical challenges. "I am uncomfortable with this continuing burden being placed on the towns," Christine Dougherty (Williston) said, urging clearer limits on inspection frequency and municipal staffing expectations for hundreds of BMPs that may require ongoing oversight.

On crediting for shared projects that span municipal impervious areas and larger non-municipal sites (for example, projects partly in an MS4 and partly under a 3-acre individual permit), DEC staff described two current options and proposed allowing an MS4 to assume "partial legal responsibility" under an individual operational permit so phosphorus-credit assignment and maintenance responsibilities can be described among co-permittees. Municipal members said the separate schedules and differing rules of the MS4 general permit and the 3-9050 operational permits complicate crediting and asked whether co-permittee credits could be implemented without obligating a town to absorb unrelated operational duties.

DEC and CCRPC staff discussed modeling and data tools tied to permit implementation. The BMPDSS tool has been offline; DEC plans an RFI to evaluate model alternatives and an RFP for model setup. Criteria include the ability to produce hourly time-series output, convert outputs to flow-duration curves, calibrate to precipitation and flow records, and model new treatment practices, Hughes said. Emily Schelley (DEC) encouraged permittees to provide hydrocad or other model files to help interim evaluations; she said DEC cannot grant formal NOI deadline extensions but may delay enforcement while municipalities work to submit required materials.

Street sweeping crediting and municipal road standards also drew attention. DEC staff summarized recent Region 1/UNH and USGS work on street sweeping and catch-basin cleaning and said DEC has not formally adopted changes but is open to adjusting crediting (for example, additional fall credit). CCRPC staff noted that REI reassessments for municipal roads are due April 1, 2028, and recommended use of the Survey123 app for data collection and uploads; CCRPC planned training for early June and offered to partner on data collection for Burlington and Winooski.

Next steps: DEC expected the EPA review and a public comment period to start in early May, with the current permit expiring July 27, 2023 and NOIs due by that date; updated SWMPs, PCPs and FRPs were described as due roughly six months after the permit start (mid-January 2024). The subcommittee scheduled a June 6 meeting with an MCM#1 update on the agenda.