The company responsible for destructive stormwater overflow at a Scandia solar farm in September 2018 has reached an agreement with authorities to pay for wetland protection elsewhere as remediation. BHE Renewables has also spent the last year-and-a-half working at the site, overhauling the stormwater management system to prevent similar incidents in the future.
The site is owned by Dr. James Zavoral. He previously leased it to Tiller Corp. for a controversial gravel pit, and now leases it to BHE Renewables for the three megawatt solar facility.
The washout occurred during a four-inch rainstorm when a holding pond overflowed, sending a torrent down a bluff, into a wetland, and down a creek to the St. Croix River. It eroded the bluff and deposited massive amounts of sand along its path, inundating about 6,500 square feet of a black ash swamp, a few hundreds yards of Middle Creek, and formed a large sandbar in the river.
St. Croix 360 was the first to report news of incident at the time.
At a Scandia city council meeting on January 21, the council unanimously approved a plan reached between BHE Renewables, the Washington Conservation District, Carnelian-St. Croix-Marine Watershed District, and others. The mitigation measures were put forward by a Technical Evaluation Panel (TEP) made up of agency representatives.
The company will not attempt to remove the sand because of difficult access to the steep bluff and wetland, which abuts the Canadian National Railroad. The railroad has not provided access from its property to access the site.
“Based on the site review on July 30, 2019, the denuded slopes have begun to self-stabilize and with the removal of the surface water flow, the TEP feels this trend will continue,” the regulators wrote. “Bringing in heavy equipment to remove trees and attempt to install erosion blankets may worsen the condition and the TEP no longer recommend additional stabilization.”
The company has conducted some minor activities to stabilize the slope, such as cutting several trees near the railroad embankment to lay down across washouts and hold back future water flows.
The loose sand deposits in the wetland are also expected to continue slowly settling, whether or not vegetation is planted.
“With regards to the wetland fill, some of the fill has already flushed to the St. Croix and much of the additional fill is not revegetating naturally,” the group reports. “Even if stabilized at the surface, the TEP does not feel surficial vegetation will prevent the sediment from moving downstream.”
Instead, the Iowa-based subsidiary of Berkshire Hathaway has agreed to pay nearly $30,000 into the watershed district’s new restoration fund and purchase $10,000 in wetland credits as part of a state program.
Wetlands are protected by law in Minnesota, and may not be destroyed without a permit, and usually some sort of mitigation. This often includes paying for wetland restoration and protection somewhere else.
“Wetland banking is a convenient way to replace wetlands that are drained or filled for agriculture or urban development,” the Board of Soil and Water Resources says. “The program connects people who need to replace wetlands with people who have already restored or created high-quality wetlands.”
The wetlands used for mitigation in this case are also in the St. Croix River watershed.
The credits acquired and contributions made by BHE Renewables will result in a six-to-one ratio of wetland replacement, with the company essentially paying enough to protect six times as much land as was affected.
The agencies could have asked for up to a 12-to-one ratio, but pointed out the wetland is still somewhat functional, and the company had invested large amounts of resources in fixing stormwater management at the site.
Scandia’s city council was responsible for approving the mitigation measures. The Washington Conservation District recommended approval.
“From the very beginning, BHE has been very responsive and has been working well with all of the different parties involved,” said councilmember Steve Kronmiller. “They really have stepped up and done what’s needed.”
The council voted 5-0 in favor.
BHE has improved existing stormwater holding ponds around the solar farm, and constructed new areas where runoff can infiltrate into the ground. The point where the water went over the top of the bluff has also been raised several feet.