Needham group reviews concept designs to reduce phosphorus and local flooding at DeFazio parking lot

On Feb. 4, 2025, the Town of Needham Stormwater Working Group heard concept designs for a green stormwater infrastructure project at the DeFazio parking lot aimed at treating runoff that flows into Alder Brook and, ultimately, the Charles River.

The presentation, led by Town sustainability manager Gabby Queenan with technical staff from engineering firm Beta Group and outreach staff from the Charles River Watershed Association (CRWA), described a bioretention (rain garden) and grading plan intended to reduce phosphorus loading, improve water quality and reduce localized ponding in a corner of the gravel lot adjacent to wetlands.

"The goal of the presentation this evening is to give folks a chance to learn a little bit about the project. And the focus is getting some feedback on concept designs for the project," Queenan told the working group. The plan focuses on the DeFazio lot as phase 1 of a larger Alderbrook watershed effort identified through the Charles River flood model.

Beta Group project manager Phil Paradis and project engineer Chris Braynard described the proposed layout and sizing. Braynard said the existing drainage area for the lot is "roughly an existing area of 0.82 acres, and the proposed area, for the catchment with this bioretention or rain garden is what we're proposing is roughly 0.92 acres." He said the gravel lot totals about 98,000 square feet and that the design reduces the number of parking spaces at the corner to make room for the rain garden.

The design calls for modest regrading to create a 2–2.5% slope toward basin inlet structures, a sediment pretreatment forebay, an engineered soil media for infiltration and an overflow weir grading into adjacent woodlands. Braynard said the soils at the site are in a hydraulic soil group A, "ideal for infiltration or bioretention" designed primarily to capture a half-inch storm event; the team cited studies showing removal of phosphorus improves significantly above about 0.4 inches.

Aruna Prea of CRWA, who is leading community outreach, said the project was selected through the Charles River Climate Compact and the Charles River flood model and emphasized public engagement: "We need everyone, especially people who are experiencing the climate impacts firsthand to be a part of the planning, designing and implementation process." Queenan noted the town received a Coastal Zone Management Coastal Habitat and Water Quality grant of about $125,000 to fund the design work and that the grant covers design only.

Project timeline presented to the group anticipates final concept work in February, then a March–June window to produce 25% through 100% design. The team said construction funding has not been identified; Queenan and Beta staff said they will seek additional grants and noted CRWA submitted a larger EPA grant application that would cover multiple projects across towns but that federal funding remains uncertain.

Design details discussed with the committee included two basin inlet structures for pretreatment (easy to maintain, the team said), native New England plantings such as switchgrass and coneflower, and signs explaining the planting and stormwater function for nearby school users. Committee members raised maintenance concerns (snow plowing, sediment buildup in a gravel lot, winter operations) and the project team said maintenance requirements and an operations plan will be developed with the Parks/Forestry and DPW staff during the final design phase.

Committee members also asked how the DeFazio lot project relates to broader flood capacity and the larger Alderbrook package of projects. Queenan and Beta staff said the parking-lot bioretention is a small, water-quality–focused phase intended to be one piece of a phased approach; larger scope elements such as culvert work, wetland and stream restoration and potential building relocation would be subsequent phases requiring more funding and coordination.

The working group was invited to provide feedback ahead of a public meeting the design team scheduled for Feb. 10, 2025 at 7 p.m. on Zoom. The group also approved administrative minutes from the Jan. 29 meeting by roll call (motion and second recorded; vote recorded in the transcript as approved; individual roll-call entries were not consistently captured in the audio record).