Material spilled during the rescue of a worker last month at a Trempealeau County sand mine contained elevated levels of arsenic, lead and other metals.
The Wisconsin Department of Natural Resources released initial results late Wednesday afternoon of water samples taken after the May 21 spill at the Hi-Crush frac sand mine in Whitehall.
The tests show lead concentrations of more than 70 times the Environmental Protection Agency's drinking water limit in water sampled near where the spill entered Pocker Creek, which runs into the Trempealeau River. Arsenic was measured at more than 6 times the EPA limit.
There also were elevated levels of beryllium, cadmium, chromium, copper, and selenium; however, samples taken from the Trempealeau River show concentrations that meet surface water standards, said DNR spokesman Jim Dick.
The Trempealeau River was colored orange in the days after the spill as sediment from the mine made its way to the Mississippi River.
Dick said dissolved oxygen levels in both Pocker Coulee and the Trempealeau River were ”above the level needed to sustain aquatic life” and that the DNR is not aware of any fish kills resulting from the spill.
The tests were done on water samples taken within hours of the spill. Dick said additional samples have been taken since and the DNR will evaluate results as they come in to better understand the environmental impacts.
The DNR did not say if the contamination presents a threat to human health. On Monday the DNR said initial tests showed no signs of “immediate toxicity.”
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The Trempealeau County Health Department on Friday issued a release stating water in the Trempealeau River "does not pose an immediate health risk," although state and local officials are still evaluating the overall health concerns associated with the spill.
Public health officials say people should avoid swallowing contaminated sediments and included the following recommendations:
- Avoid areas that have orange sandy material, as they might be contaminated.
- Wash after wading or swimming.
- Watch children closely to make sure they do not eat any sand or sediment from the river.
Workers at the Hi-Crush mine in Whitehall drained a holding pond after a bulldozer slipped into the water. The driver escaped uninjured after about 2½ hours in the air-tight cab.
Hi-Crush officials said the pond contained mostly water, silt, clay and sand, though it could contain trace amounts of a polyacrylamide, which is used to remove silt from the water.
Jay Zambito, a geologist with the Wisconsin Geological and Natural History Survey, said the minerals identified in the test results are commonly found in the rock formations being mined in Trempealeau County and could be a source of the contaminants found in the process water.
“However, the spatial variability of the trace metal-bearing sulfide minerals in these rocks suggests that the potential for water contamination at a given mine would be site specific, and further detailed study is needed,” Zambito said.