More studies planned for contaminated groundwater plume

SALT LAKE CITY — The operator of the White Mesa Mill in San Juan County has agreed to do more tests to determine the source of groundwater contamination that has led to a nitrate plume.

A plan outlining those tests will be reviewed this week by state regulators after causes blamed in a lengthy Contamination Investigation Report were rejected by the state Division of Radiation Control.

The state said the report was incomplete and allegations by mill operator Denison Mines over the source of contaminants were unsubstantiated.

At issue is a 40-acre nitrate plume south of Blanding in an agricultural area that has the potential to contaminate 16.2 billion cubic feet of groundwater.

Sampling at 19 monitoring wells showed levels in some cases as high as four times the water quality standard established by the Environmental Protection Agency.

Nitrate results from ammonia when bacteria break down nitrogen. In unsafe levels it has been linked to a disorder that causes elevated amounts of hemoglobin in the blood. That condition in severe cases leads to developmental delays and retardation.

Denison contends a municipal sewage plant operated by Blanding City allowed wastewater to flow to a pond, where it was then piped to other ponds for mill operations from the mid 1980s to the early 1990s, when Recapture Reservoir then began to supply the water.

The plant is uphill from the mill more than 1.2 miles away.

In its investigatory report submitted to the state, Denison claims the wastewater subsequently flowed into two unlined ponds, leading to the contamination.

Because of that, Denison says it should not be required to remediate the contamination since it originated from a source off-property and not caused by mill activities.

The state countered that operators of the sewage facility said it had a "total containment system" with no discharge, and the claim that the pond was the sole source of contamination is "unsubstantiated."

Given the disagreement how the groundwater was contaminated, state regulators have agreed to review plans for additional studies Denison will be required to do.

e-mail: amyjoi@desnews.com