Oak Bluffs exploring stormwater remediation

Oak Bluffs is looking to improve and showcase stormwater resiliency methods on Hudson Avenue.

James Houle, program director at the University of New Hampshire’s Stormwater Center, proposed the use of a so-called bioretention and permeable parking concept design on Hudson Avenue during a Tuesday, Oct. 24, Oak Bluffs Select Board meeting. 

While further permitting is needed, the infrastructure would help remove bacteria from stormwater before it gets into Lagoon Pond.

The proposed project is a joint venture between the UNH Stormwater Center and the Martha’s Vineyard Commission. 

The board unanimously approved the project, and tasked Oak Bluffs town administrator Deborah Potter with awarding a permit to the MVC and UNH Stormwater Center to conduct modifications on Hudson Avenue as presented, although the Oak Bluffs conservation commission still needs to sign off.

“We do have a grant to work with communities on the Island to reduce impacts from stormwater and stormwater pollution,” Houle said, adding that such installations have been made already in Tisbury. 

Currently, stormwater runoff going down Hudson Avenue picks up sediments, nutrients, oils, greases, and other materials that are then deposited into Lagoon Pond. 

“That road going down to Lagoon Pond is an active drainage way. Runoff comes down the road, it erodes the sides, and essentially discharges into the bay,” Houle said. “The idea here is to intercept that with these structural controls.” With the proposed systems, the runoff would be filtered before reaching the bay. 

Houle introduced two designs to the board. One was a bioretention system, which he described as a dug-out depression backfilled with “engineered soil” — consisting primarily of sand, topsoil, and woodchips — with a stone reservoir to hold the water as it is filtered through the soil. “It can be planted with essentially anything that will grow in that type of medium,” he said. 

The other was the permeable pavement, which Houle said would act as a “turnaround point” that can sustain vehicle traffic. 

“One of the things I wanted to highlight is there’s a lot of driveways on the Island that are permeable, or have shells or have stones away from the paved infrastructure,” Houle said. He continued that this was an engineered infrastructure that provides a system that can be backfilled with desired and appropriate materials, like crushed shells, and keep the substrate from compacting. “The subbase materials would hold it in place.” 

According to Houle, the systems are designed to be drained of water within 24 hours. A part of this is to prevent the proliferation of mosquitoes, which Houle said need at least three days of standing water. 

If the approval is finalized, the system could be installed in either the fall or spring. 

Martha’s Vineyard Commission executive director Adam Turner said the partnership with the University of New Hampshire to look at water issues started around four years ago. “We have been very vocal with [the Environmental Protection Agency] that there is an Island here, it’s not just the Cape,” Turner said. “They seem to recognize that the Cape has nitrogen problems, the Cape has drainage problems, but they don’t really recognize us. That’s still a problem.” 

Turner said the proposed project was not a “one-shot deal,” and improvements will be made. 

Before giving their approval, some board members wanted further details about the plan. 

When board chair Emma Green-Beach asked for more specifics regarding plantings, Houle said the default would be a grassy plant to stabilize the system, but what was planted in the area could change.

“The vegetation, it can provide additional things — pollinator species, or a habitat, carbon sequestration — but from my perspective, the large function of the vegetation is stabilization of those soils,” Houle said. 

Green-Beach also asked whether there was a storm drain on the site, and Houle said there were shallow catch basins on the road linked to each other by six-inch pipes. “It doesn’t go anywhere,” Houle said, who suspects they were initially installed as a leaching catch basin, which would dissipate the water into the native soil. This infrastructure would be maintained as a backup, according to Houle. 

The board also asked about the impact of stormwater runoff in the area. Houle said there was evidence of beach erosion caused by stormwater runoff that eliminates some soils. Additionally, alongside the assortment of materials stormwater collects on its way to Lagoon Pond, it can also carry along bacteria.

“Lagoon Pond is impaired [by] nitrogen,” Houle said. “Those nutrients tend to create algae growth, and when the algae dies, it affects the dissolved oxygen and the livability, if you will, for other species in that pond.” 

When asked about maintenance costs by board member Thomas Hallahan, Houle said the bioretention and permeable parking areas were traditionally low-maintenance systems that need annual inspections. 

Houle said this technology demonstration would help to spread the usage of bioretention and permeable parking systems at the numerous “end of road” areas on the Island, leading to reductions in erosion impact from stormwater runoffs. “We keep it in the native soil,” Houle said. 

Potter said a spring installation seemed the most likely to allow proper vetting with the conservation commission.