LOWELL – The stormwater controls on the Lowell wind site had to be repaired and upgraded in some locations following a “significant” rain storm May 29, according to a state stormwater specialist.
Kevin Burke with the Agency of Natural Resources said he investigated the situation on Lowell Mountain the day after the storm that dropped between 4.1 and 5.4 inches of rain, most falling within two hours that afternoon.
Green Mountain Power’s contractors were already on the site before 7 a.m. May 30 making repairs when Burke arrived to see what happened. GMP is beginning to pour concrete for the pads of 21 turbine sites on the ridgeline.
The storm caused hundreds of thousands of dollars in damage to local roads and bridges in the town of Lowell to the north of the wind site, closing Vermont Route 100 through the town and several roads connecting Lowell to northern communities.
On the wind site, a culvert intended to direct offsite water away from the site became plugged during the storm and caused a series of overflows through the wind site downhill. The culvert size and situation needs to be examined, Burke stated in a report released online Thursday.
The report didn’t note any major problems other than that.
Some drainage basins were overwhelmed because water flowed differently than predicted when the culvert plugged, he wrote.
“It was determined that the Environmental Protection Stormwater Controls plan had been properly implemented at the time of inspection, however maintenance and/or repair … was necessary … following this significant event,” Burke wrote.
Drainage traps and basins have to be cleaned of sediment and repaired, he wrote. Some of the work has already been done as of May 30 and was continuing, he noted.
“Additional failures may have been the result of increased flows resulting from the upstream plugged culvert and intensity of the storm event,” he wrote.
Also, silt fences were overwhelmed in a few locations because they weren’t designed to handle the flow, he wrote.
There was limited erosion on the ridgeline crane path, with one observed “major blow out” of a perimeter control. Stormwater controls were compromised near the site for turbine 15 “which is where significant hail deposition and wind damage was observed,” Burke wrote.
Burke went back to the site on June 8 with Mike Adams of the U.S. Army Corps of Engineers, which also looks at wetlands impacts of projects. They found that stormwater with sediment carved a gully through a rock/ledge slope, depositing sediment in a buffer zone and wetland area, probably caused by the culvert failure.
The area could be reseeded until a decision is made about whether to remove the sediment, Burke wrote. “Additional sediment control may be necessary at or in the buffer to prevent further migration of sediment following repair,” he wrote.
Another blowout occurred, also because of the culvert plug, causing a minor breach of a pond, he wrote.
The contractors will have to work with the Army Corps to look at corrective action for these areas, he wrote.
The storm also caused damage in other parts of the Northeast Kingdom, causing mud slides near Lake Willoughby and knocked out power in parts of the area.
The series of storms dropped between 1 and 2 inches in the morning of May 29 and another 2 to 4 inches in the afternoon, Burke said. The measurements of 4.1 and 5.4 inches were recorded in rain gauges on the wind site, Burke said.
Some TV weather reports described the storm that hit Lowell in the afternoon as a super cell, uncommon in Vermont, with the capacity for torrential rain in a short period of time.
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