OU III Freon-11 ESD

August 2012

This Explanation of Significant Differences (ESD) was prepared to describe a change to the final remedy for the remediation for groundwater for the BNL site as described in the April 14, 2000, Operable Unit III Record of Decision (ROD). The changes are the addition of Trichlorofluoromethane, known by the trade name Freon-11, to the volatile organic compounds (VOCs) to be remediated under the OU III ROD, the addition of one new extraction well and an air stripping treatment system to address the Freon-11 contamination, and the designation of the Building 452 Freon-11 Source Area and Groundwater Plume as Area of Concern (AOC) 32.

In 2011, Freon-11 was discovered in the groundwater in the vicinity of Building 452, a site maintenance facility located in the central portion of the BNL site. The extent of the contamination, which is located entirely on BNL property, was fully characterized. The recommendation for active remediation was made for the 300-foot by 600-foot long plume. Groundwater modeling indicates that the plume can be successfully remediated in 2 to 5 years based on the assumption that there is no longer a significant continuing release of Freon-11 into the groundwater at the Bldg. 52 area. If groundwater monitoring indicates a continuing source, additional remediation of the area will be evaluated. If monitoring results indicate that Freon-11 concentrations in groundwater could exceed the MCL beyond the BNL site boundary, additional measures will be taken.

Neither the existing OU III treatment goals nor the performance period in the OU III ROD are modified by this ESD. A Freon-11 capture goal of 50 g/L has been established for shutdown of the extraction wells. Shut down determination will be based on concentrations detected in the extraction wells and individual monitoring wells at the source area and within the capture zone.

The Final OU III Explanation of Significant Differences for Area of Concern 32 Building 452 Freon-11 Source Area and Groundwater Plume was approved by the U.S. DOE, the EPA with concurrence by the NYSDEC on August 2, 2012.

Documents / Links

Freon-11 ESD