Three Superfund sites on base do not need to be cleaned up because they do not pose a threat to human health or the environment, according to base environmental officials.
Contamination at two contaminated evaporation ponds and a wastewater sludge drying bed is very low, said Andrew Gem-per-line, project manager for Hill's Superfund Operable Unit 3, of which the three sites are a part.The legal standard for mandatory cleanup is whether a contaminated site would increase the chances of a future site resident or construction worker contracting cancer by a measure of one in a million.
Gemperline said the level of contaminants at the three sites is much lower than the legal standard. The primary toxin is the suspected carcinogen dichlorethylene (DCE).
Hill contains eight operable units, or areas of contamination, for which Superfund cleanup alternatives are currently being studied.
These are the other three Superfund sites in Operable Unit 3, as well as the cleanup alternatives Hill officials are proposing:
- Berman Pond is a former evaporation pond for industrial wastewater which was operated from 1940 to 1956. It was eventually filled in, and in 1985 a clay cap was installed, but the cap covered only part of the pond.
Officials propose removing the old cap and installing a new one which will cover the entire pond. The new cap would prevent surface water from going through the ground and carrying the contaminants to the shallow groundwater about 75 feet below.
"The threat to groundwater in the area from this site is minimal," Gemperline said. "The contamination does not appear to be moving towards the groundwater. If we were to see that change, then we may have to go back and reassess our action."
The groundwater is not used for drinking or irrigation.
Since the contaminants are not being removed as part of the remedial action, the proposal recommends careful monitoring of the site.
- Two buildings near Berman Pond were used from the late 1950s to 1985 to service fuel trucks. Trucks were emptied into a floor drain prior to maintenance, and the fuel was then disposed of. Approximately 100 cubic yards of soil reaching a depth of five feet were contaminated with DCE.
Officials propose using vapor extraction to remove the DCE from the soil. That process would not effect operations at the buildings, which are currently being used as a hazardous waste control facility.
- Two underground tanks beneath Hill's wastewater treatment plant were used until 1992 to store sodium hydroxide. During their use, several hundred thousand gallons of the caustic liquid leaked out, raising the pH of the soil from 6.2 to over 12.
Hill officials placed an asphalt cap over the site in 1993 to prevent precipitation from moving the contaminant deeper into the groundwater. The proposed final solution is simply to maintain the cap and regulate digging in the area to prevent the contaminant's spread.