Roxbury wetlands commission continues hearing on 65 Minor Bridge Road after engineers clash over infiltration treatment

The Roxbury Inland Wetlands and Watercourses Commission on Oct. 27 continued the public hearing on a proposed single-family residence at 65 Minor Bridge Road to Nov. 12, 2024, after engineers debating the project’s stormwater approach disagreed over whether underground infiltration systems alone will prevent long-term pollution of the nearby watercourse.

The applicant’s engineer, identified in the record as Paul, told the commission the revised plan adds phasing, extra sediment traps and stone check dams and that the design includes three underground infiltration galleries that “fully retain and fully infiltrate” the project’s water-quality volume. Paul said his corrected calculations show the infiltration systems provide several times the manual-required retention—citing figures such as “550%” and “746%” for different galleries—and argued that those volumes, together with swales and catch basins, meet the Connecticut stormwater guidance.

“On-site infiltration of stormwater is fundamental to preserving predevelopment hydrology,” Paul said, adding that the design follows the state stormwater manual and that the applicant will provide monitoring and phased inspections before and after rainfall events.

The commission’s contracted reviewer, consulting engineer Steve Trinkus, disputed that characterization. Trinkus told commissioners he reviewed the applicant’s earlier submission and said he had not had time to fully review plans presented for the first time at the meeting. He said retention volume alone is not treatment and warned that sand‑and‑gravel soils commonly found on the site do not reliably attenuate soluble pollutants such as nitrogen and phosphorus.

“If you fill your bathtub up with the water-quality volume, is there any treatment in your bathtub? No,” Trinkus said, arguing that infiltration on steep slopes or in sloped trenches can convey runoff to the watercourse and that pre‑treatment (for example bioretention or wider vegetated swales) is required before discharging to underground galleries.

The applicant’s environmental consultant, Dr. Steve Danzer, who submitted a supplemental environmental report, disagreed with Trinkus’ conclusion. Danzer said he reviewed the field conditions and the revised erosion-control phasing and concluded the measures, together with added monitoring and sediment traps, were consistent with Connecticut erosion- and stormwater‑control guidance and in his professional opinion would prevent an adverse impact to wetlands and watercourses.

“The erosion controls are in accordance with Connecticut guidelines for soil erosion and sediment control,” Danzer said, summarizing his view that the phased approach and additional barriers reduce the likelihood of construction‑period discharges.

Commission members repeatedly asked for clarification about (1) which trenches and galleries will be level versus sloped; (2) where stormwater runoff will be pre‑treated (bioretention cells, grassed swales, hooded deep‑sump catch basins); and (3) how inspections and “exit” criteria between construction phases will be documented. The applicant described a pre‑construction field staking and a photo‑journal inspection protocol; the enforcement officer and staff will perform periodic inspections and report to the commission before the applicant begins the next construction phase.

Several commissioners and reviewers noted a practical enforcement concern: well‑designed erosion controls can fail in high‑intensity storms or if a contractor does not follow phases, so the commission must weigh potential risk against the applicant’s mitigation measures. Trinkus characterized the risk as real and potentially cumulative; Danzer and Paul argued the combination of measures—physical barrier wall, phasing, extra sediment traps and monitoring—substantially reduces that risk.

Because reviewers received revised materials only immediately before the meeting, the commission voted to keep the hearing open and asked staff and the reviewers to submit written comments on the latest plans. The public hearing was continued to Nov. 12, 2024, at 7:00 p.m. at Town Hall; applicants and reviewers were asked to provide updated documentation to the commission before that date.

Other business: the commission voted on unrelated matters during the same meeting, approving another regulated activity (voice vote; no roll-call tally recorded) and discussing several new applications and site visits.

Next step: the hearing on 65 Minor Bridge Road will resume Nov. 12; the commission requested written reviewer comments on the newly revised plans in advance of that session.