RIVERDALE -- A decades-old contamination problem is on the mend, say Hill Air Force Base representatives.
Alan Jones, a project manager for cleanup of TCE (trichloroethene) plumes originating on the base, said 119 Riverdale homes sit on top of two plumes. Over the years, technicians have tested the air in 84 of those homes and installed vapor removal systems in six.
Jones said the TCE contamination happened when Hill Air Force Base disposed of degreasers before 1980, when contamination was first discovered in Riverdale.
"The disposal methods weren't the greatest," Jones said.
TCE has recently been categorized as a carcinogen, or cancer-causing agent.
To clean up the contaminated groundwater, a groundwater extraction system on base delivered water to a nearby treatment plant. Once chemicals were removed from the water, treated water was allowed to infiltrate back into the ground in a drain field on base.
Since 1996, two groundwater extraction systems have removed at least 110 pounds of TCE.
Another remedy includes collecting groundwater in wells and drains before it is discharged directly into the storm sewer. Efforts also are being made to prevent precipitation from spreading contamination at the dump and off-base burn landfill.
The methods seem to have worked, because one plume affecting Riverdale has stabilized and the other is shrinking, Jones said.
Base representatives plan to discharge extracted and treated water into the sewer system because contamination levels are below discharge limits.
Also, base representatives plan to remove a carbon treatment system from the spring south of the Riverdale Craigdale subdivision. Filtration is now unnecessary because detection levels are below "action levels," Jones said. The spring will be monitored regularly.
One groundwater extraction well has been turned off, and initial results show cleanup levels are being maintained. The energy cost savings associated with shutting down the pumps in the system will be considerable, Jones said.
Jones said Riverdale residents' drinking water is not contaminated and that base officials are cleaning up the groundwater to meet drinking water quality as set by the Environmental Protection Agency.
"We're moving in the right direction," said Riverdale Councilman Norm Searle.