The Conservation Commission at its meeting Tuesday night mainly discussed two issues with The Trails, a development off Legacy Farms Road North, including an amended notice of intent concerning drainage improvement plans for four lots and a violation or continued problems with stormwater management on the site.

Project engineer Peter Bemis said that the project is undergoing the third phase of construction at Weston Lane. This phase is almost 50 percent complete with approximately 70 units currently constructed out of 175, he said.

Bemis explained that the drainage improvements were needed because the original developer had planned for more triplexes for the development, but the project was downsized so that there will only be five.

In a third-party peer review done by GCG on the Ashland side of the project, Bemis explained that there were deficiencies found with stormwater retention due to a hurricane last year. The soils on that part of the project were highly permeable.

“What we’ve suggested is that we revisit two basins,” he continued, noting that one of them hasn’t been built yet and is part of the fourth phase of the project.

He also said that when Bohler Engineering was involved in the project previously, miscalculations were made.

“They did not treat the receiving watershed as what’s called an outstanding resource water,” he said. “That’s a water supply. It should have had a one-inch infiltrative volume rather than the half-inch one that Bohler designed.”

Asked Chair Jeff Barnes: “So the infiltration volume was understated by fourfold, you’re saying?”

Bemis said that the mistake was not made intentionally, and it is something he is hoping to correct with the new basin design. He requested a waiver to perform work in the 50-foot buffer zone to reconstruct a basin, saying the previous one probably was miscalculated in an attempt to avoid working within the 50-foot buffer zone. He also wanted to convert the sidewalks that have yet to be built to permeable pavement, which Bemis considered “a win-win.”

Added Bemis: “We want to design for the future — not for yesterday.”

A question came up as to why the water would be drained back into the wetlands system. The problem is that the project also impacts Ashland and would send the water to the lagoon driveway. Discussions have not yet begun with the Ashland Conservation Commission.

“Maybe there’s a middle ground there,” Barnes said.

The hearing was continued until the next meeting on Sept. 27.

The Trails chastised for stormwater issues

A violation at The Trails also was discussed after flooding issues from a recent rainstorm.

“We’ve had some issues at the site, quite obviously,” Barnes said. Some of the problems may have been caused by extreme precipitation, he noted, while others may have been caused because of possible miscalculations by former engineers on the project.

“What’s frustrating, I think, for our commission, is that the project is in Hopkinton, but Ashland’s getting the brunt of the erosion problem that’s running offsite,” Barnes continued, noting that both town managers are involved at this point.

The drinking water for both Hopkinton and Ashland has been affected, which is another concern.

“What do we need to do to impress upon you guys that this can’t continue to happen?” Barnes asked regarding the ongoing problems with the project’s stormwater management system.

Bemis said there were six-tenths of an inch of rain in 25 minutes that bypassed the containment bags, went through the embankment and forced silt out onto the street, which he never anticipated.

Bemis said he was “embarrassed” by the situation.

Barnes countered that it “is embarrassing for us as a commission” because the water is going into Ashland.

“I’m sure they’re thinking, ‘What the heck are these folks doing up there?’ ” he said. “We really need to kind of nip this in the bud to make sure this doesn’t keep happening.”

No fine was issued at this meeting.

Eversource certificate of compliance approved

In other news, the board approved a certificate of compliance for improvements to the Eversource liquefied natural gas (LNG) plant at 52 Wilson Street. Barnes noted that the permanent immovable barriers had been installed and the requested plantings have been established, making the approval “pretty straightforward.”

Jean Christy, the senior engineer at Tighe & Bond, spoke on behalf of the applicant. She said that inspections were conducted after the recent rainfalls, which showed that the stormwater basins were working properly.