Inland Wetland Agency approves Student Incorporated bus-parking and infiltration basin with conditions

The South Windsor Inland Wetland Agency and Conservation Commission voted to approve application 2617P from Student Incorporated to create a gravel bus parking area, install fueling infrastructure and construct a shallow infiltration basin to manage additional runoff.

The commission’s discussion centered on stormwater calculations, the scope of parcels analyzed, and water‑quality protections for the proposed fueling area. The applicant’s engineer explained the site is divided into three parcels and that the drainage calculations treat Parcels 2 and 3 as a 2.71‑acre drainage area while the permitted work affects a roughly 21,134‑square‑foot (about 0.49‑acre) gravel parking area on Parcel 2. The engineer said the proposed recharge basin is shallow (about 2 feet) and was designed to accept the project’s increased runoff and to meet the town’s expectation for a 100‑year storm standard.

Commissioners probed the underlying soils and infiltration assumptions. The engineer said borings measured groundwater near 5 feet and found permeable fill near the surface over thicker clay, that measured permeability was about 10–15 feet per day, and that the design conservatively uses the Connecticut stormwater guidance conversion (effectively limiting exfiltration to the manual’s allowable rate).

Members raised water‑quality concerns tied to hydrocarbons from fueling or the long‑established adjacent parking areas that discharge to the same basin. One commissioner asked whether spills on gravel could migrate into the basin; the applicant’s representative said tanks would be double‑walled, the fueling area would be paved and include spill prevention supplies and trained staff, and the operation would report monthly monitoring overseen by a third‑party monitor. The applicant also said the fueling area would not be covered. Commissioners discussed retrofit options for existing outfalls, including hydrodynamic separators or oil‑water pretreatment, and asked staff to confirm whether state or town requirements would trigger additional water‑quality units.

The vice chair’s written questions — read into the record — specifically asked about fueling‑site containment and delivery procedures. The applicant’s representative read answers: proposed tank capacities are 2,000 gallons for unleaded gasoline and 3,000 gallons for diesel; fueling areas would be double‑walled and paved; spill response procedures and absorbents are planned; and fuel handling would be by trained staff rather than untrained drivers.

Several commissioners said the infiltration basin as designed appeared adequate for the increased impervious coverage on Parcel 2, while also noting Parcel 1 (the front parcel) currently lacks water‑quality controls and will be addressed through planning and zoning reviews because it is outside the immediate wetlands review area. Staff and commissioners agreed that applicant responses submitted to staff should be posted to the commission record for review prior to permit issuance.

After discussing draft permit conditions — including seed/planting specifications for the basin, construction erosion controls, and maintenance requirements — a commissioner moved to approve application 26‑17P subject to the 12 draft conditions provided by staff. The motion was seconded and carried by the commission.

Next steps: staff will ensure the applicant’s written responses and technical materials are included in the record, confirm any required water‑quality units against the current Connecticut guidance, and coordinate outstanding parcel‑level questions with planning and zoning. The commission adjourned with no further business.