In a last-minute addition to its agenda, the Conservation Commission on Tuesday responded to a stormwater management violation reported by the conservation administrator at the Charleswood School project site.

Conservation administrator Judy Day told the commission that on Monday she observed “significant siltation” at an off-site jurisdictional pond adjacent to the school construction site. This occurred after a weekend deluge, with rain persisting into Monday.

“The entirety of the pond was inundated with silty water,” said Day as she displayed a picture.

She observed water coming from the project’s southwest corner near two overflow dry wells. While erosion wasn’t seen on the land’s surface, she said turbid water was flowing into the pond from that point.

Project manager counters claim

Vertex project manager Chris Eberly disputed Day’s report.

“This is a weird one,” he said. “And I think Judy and the team disagree slightly about exactly what’s going on here.”

Eberly said that while there is “clearly silt discharging at that location,” it appears to be “previously settled.”

Added Eberly: “I don’t have a reason for why the previous silt is there.”

In pictures and videos, he demonstrated that clear water was running over the silt. There did not appear to be pathways through which the water flowed. Sediment was not visible on silt sacks or stone meant to deter infiltration.

This was the site of “a previous breach” 11 months ago, he added. Since then, a dry well, silt socks and core logs were installed to reinforce this area.

During the weekend, Eberly said there had been “a separate breach.” On the opposite side of the site, a pump failed over the weekend, leading to a sediment basin overflowing.

“Connected to those two locations [are] drainage manholes that go back into recently completed infiltration systems,” Eberly explained.

Between the infiltration system, the detention system and previously installed “water quality structures,” he said, “100% of suspended solids” should have been removed.

Eberly added that he will be discussing a plan with a civil engineer from Samiotes Consultants to investigate the source of the problem.

Said Eberly: “There’s no smoking gun on this one.”

Stormwater management questioned

Chair Melissa Recos told Eberly that the commission had seen fine silt from previous projects in that area evade stormwater management tactics.

“There really is no method of erosion control to filter out that kind of sediment,” she explained.

“Once the water’s in the pipes, it’s going where the pipe takes it,” commented Eberly.

At that point, co-vice chair Matt Moyen interjected. He explained that underground infiltration basins and the installed water quality structures should not be taking water from a construction site.

Said Moyen: “That is a big no-no.”

“Those are post-construction stormwater management practices,” he stressed.

Fine sediment would disrupt the system’s long-term function. To prevent this, Moyen advised that temporary stormwater controls and sediment traps be put in place to manage stormwater runoff and prevent the infiltration basins from being compromised.

Joe Amara, the project manager from Brait Builders, stressed that the construction team worked hard to prepare for the storm. New silt sacks were installed, and a silt fence was placed around stockpiles.

Recos reiterated that silt sacks would not be a helpful barrier for fine soil. Rerouting and pumping water are better methods.

“I just want to be clear,” emphasized Eberly. “I’ve been no defender of Brait through most of this job. They’ve done a lot of things which have very much frustrated me. But they did spend a good chunk of both Thursday and Friday preparing for this storm on site.”

After the issue is investigated, Eberly said he will ask the contractor to address any permit violations found.

Recos requested that the stormwater pollution prevention plan be updated after the investigation. She also said the team should look into how sediment got into the pond and address it.

Culvert hearing continued

The commission voted 6-0 to continue a notice of intent hearing on a culvert replacement project proposed by the Department of Public Works off Granite Street.

DPW Director Kerry Reed explained that a culvert assessment and inventory identified that this culvert was undersized. This causes it to run over, which is a safety hazard.

The area of work will affect Hayden Rowe Street and Deer Run, she said. It is in the vicinity of the Granite Street Cemetery and the Echo Brook Trail.

This project simultaneously will address structural concerns with the culvert as well as stormwater runoff issues and road repairs, Reed added.

One challenge has been the construction of the Charleswood School affecting Hayden Rowe Street. Reed said she had hoped to start it earlier. Instead, she is pursuing the necessary permits now. Work likely will begin next fall.

Environmental scientist Lucas Acaba from Tighe & Bond explained that this is a limited project because it is addressing maintenance issues. It will allow the culvert to meet current stream crossing standards.

Moyen called the plan “a vast improvement for both the stream and stormwater treatment.”

He requested that a memo be included that explains how the work meets limited project standards. Reed and Acaba agreed to provide one.

Most of the work will be done on town property, Reed explained. The town will seek an access agreement for work that extends into private property, as well as documentation approving any work going into Milford.

Co-vice chair Ted Barker-Hook pointed out that a flood contingency plan is needed. It is particularly relevant given the recent storm, he noted.

Acaba said additional information will be provided at the next meeting on Oct. 20.

Dam repair NOI approved

The commission unanimously approved a notice of intent by Agilitas Energy to repair an earthen dam off Frankland Road. It will be returned to the town when the work is completed. It is impacting the solar energy company’s photovoltaic array at 69 Frankland Road.

Engineer Jeff Bellino represented the applicant. He said the plan has been revised to restore the stop log channel system.

Engineer Craig Curtain noted that the project initially was proposed as an industrial project. He considered it a limited project. Recos and Day agreed.

Some vegetation and tree removal may be required to maintain the dam’s safety, Curtain added.

Hearings continued

The hearings on the Masumeen Charitable Trust’s request to raze and rebuild the mosque at 115 Wood Street and proposed improvements to the Sandy Beach parking lot at 4 Lakeshore Drive were continued at the request of the respective applicants to Oct. 20.

Also, the hearing on 12 North Mill Street for access for soil testing was continued to Nov. 3.