Developers tell Stratford commission new stormwater controls will reduce peak flows for 99 Holly Lane proposal

Mountain Development Corp.'s representatives presented revised stormwater plans and mitigation measures for a proposed project at 99 Holly Lane during the Stratford Inland Wetlands Commission meeting. Chris Russo, representing the property owner, said responses to the town engineer's comments were provided and described plan corrections such as accurate pipe sizes and updated calculations. "There's a proposal to add an additional conservation easement area of 60,000 square feet, which 44,000 of it is Upland Review area," Russo said.

Civil engineer Manny Silva walked the commission through hydrology and storage figures, noting the report's 1-inch-storm volume listed in the appendix and clarifying conversions that initially caused confusion. Silva said the report's modeling shows the project's controls would reduce 2-year/3.5-inch peak discharge from an existing roughly 4.6 cubic feet per second to about 3.9 cfs in the proposed condition, a roughly 15% reduction at that storm intensity. "In the proposed condition with our controls and our storage, it's reduced down to 3.9," Silva said. He explained the site uses multiple storage elements (a gallery filtration system, detention basins and an existing basin), and controls are sized to meter out post-construction flows so the downstream peak does not exceed current conditions.

The commission pressed on water quality and contaminant fate. Silva described a treatment train that includes hooded catch basins, swirl concentrators for floatables and oil, and a gallery gravel-and-sand filtration media intended to reduce heavy metals and water-soluble contaminants. He said maintenance obligations would be documented in an operations and maintenance manual with inspection intervals and thresholds for vacuuming accumulations; failure to perform required maintenance would be enforceable. "We put the actual schedule right on the plans... they have to monitor it every six months," Silva said.

Several commissioners raised concerns about downstream erosion and sediment in Bruce Brook and Worcester Pond. Silva responded that the project would reduce this site's net contribution to runoff and noted municipal and state MS4 reporting requirements that require the town engineer to receive and report certain metrics to the state. Commissioners also pressed the applicant on blasting and exposed bedrock. Silva said the team would try to avoid blasting but acknowledged borings will be done for foundation design. He offered to provide pre-blast laboratory sampling and a conditional mitigation plan if blasting is necessary, including lined sediment traps and pH neutralization measures to prevent acidic runoff.

Silva gave an overview of design standards, saying the engineered system is modeled to handle up to a 100-year storm and that catch basin tops were analyzed to at least the 25-year level, exceeding the town's 10-year roadway standard. He emphasized that storage and outlet controls are meant to limit peak discharge and to improve water quality relative to current site conditions.

Next steps recorded in the meeting included the commission moving toward executive session to discuss the matter further. The applicant left the record with specific commitments: (1) supply hydrologic appendix figures and clarifications of volume-to-gallons conversions; (2) provide pre-construction rock-sampling reports if blasting is anticipated and a conditional mitigation plan; and (3) include a detailed operations and maintenance manual with six-month inspection intervals and enforceable thresholds for vacuuming/removal of floatables and sediments.

Provenance: Topic introduced SEG 416; discussion continued through SEG 1114.