Despite objections from nearby residents, the Wisconsin Department of Natural Resources (WDNR) has approved capping the source of a massive groundwater contaminant plume that flows several miles beyond the plant boundary to the Wisconsin River just north of the Village of Prairie du Sac. The March 17 approval will allow the Army to leave more than 15,000 cubic yards of contaminated subsurface soils in place at the Propellant Burning Grounds, a hazardous waste disposal area located on the west side of Badger in the rural township of Sumpter.

During active production years, the Army dumped and burned as much as 500 gallons per week of the explosive dinitrotoluene (DNT) and other carcinogenic chemicals in three 40-foot diameter unlined pits dug in the ground.  Affected soils extend from a depth of 13 feet to more than 100 feet below the surface, reaching the water table at 110 feet.  Concentrations of DNT in subsurface soils are as high as 17,000 parts per million (ppm) compared to the 1 ppm cleanup goal that was previously approved by environmental regulators. In 1995, both the WDNR and U.S. Environmental Protection Agency approved an Army proposal to excavate all contaminated soils at the Propellant Burning Grounds but neither agency enforced the required cleanup.

The WDNR rejected CSWAB’s petition to require excavation of another 10 to 20 feet of the most contaminated soils before allowing the Army to install a permanent cap over the entire hazardous waste site.  In addition to removing readily-accessible contamination, CSWAB maintains that additional source removal could save millions of dollars by significantly reducing the number of years groundwater extraction is required – a process that annually costs in excess of $1 million.

In its response, the WDNR said that the landfill cap is intended to prevent the downward migration of soil contamination to groundwater and that the additional costs associated with partial excavation would “exceed the potential benefits” to the environment.

CSWAB also cites the failure of a similar hazardous waste site that was capped in 2003.  Groundwater monitoring wells at the Deterrent Burning Grounds, located in the northeast corner of Badger in the rural township of Merrimac, recently detected total DNT at 5.14 parts per billion (ppb) which is more than 100 times the health advisory level of 0.05 ppb for drinking water.

The WDNR said that the current approval applies only to contaminated soil at the Propellant Burning Grounds and that the associated groundwater problems will be addressed in a separate future plan approval.  The Army is required to regularly test more than 80 residential and groundwater monitoring wells in the neighboring townships of Sumpter, Prairie du Sac, and Merrimac.

WDNR Final Determination Letter (.pdf file)