Closer to closure: McClellan’s Soil Vapor Extraction Systems working their way into extinction
By Scott Johnston, AFCEC Public Affairs
/ Published April 15, 2014
SACRAMENTO, Calif. -- Steadily chugging along since the early 1990s, the soil vapor extraction systems at the former McClellan Air Force Base here are progressively heading the way of the dinosaur - into extinction.
The majority of the soil cleanup systems at McClellan have already worked themselves out of a job. They've removed all of the contaminants they can reach and are shut down. Only four systems remain and the Air Force expects those to be closed within the next two years.
"It's definitely another good news story in the cleanup program here at McClellan," said Steve Mayer, base environmental cleanup coordinator for the Air Force Civil Engineer Center. "The systems have made great progress."
Soil vapor extraction, or SVE, is another tool in the environmental cleanup arsenal at McClellan, removing contaminants from the soil before they get carried down to groundwater.
SVE systems work by vacuuming volatile organic compounds, or VOCs, out of the spaces between particles of soil. Those compounds are the result of past activities at McClellan that involved the use of fuels, solvents, cleaners and other chemicals.
Sometimes, those chemicals escaped to the environment from leaking tanks or drains, spills or past standard industrial disposal practices. Left in place over time, the VOCs percolate down through the 100-plus feet of soil to the groundwater beneath the former base.
SVE, a key component of the overall groundwater cleanup program, removes contaminants from the soil quicker and is less costly compared to later removing them from the groundwater.
When ongoing monitoring shows that contaminants have been removed to a prescribed level, the system at a site is temporarily shut down for approximately six months, before the well is resampled.
In the event that contaminants in small, tight soil pockets have re-emerged (or rebounded) into the area, the system is restarted and operates until sampling results over several months to years consistently show that contaminants haven't rebounded. At that point, the system is no longer needed so it's permanently shut down and the wells removed.
To date, the closed base's SVE systems have removed more than 1.4 million pounds of contaminants.
"We started out with 26 areas, or plumes of VOCs in the soil, and now there's four," said Ken Smarkel, a groundwater remediation program manager contractor at the former McClellan. "We're hoping to close those four within the next couple years, so it's definitely made impressive progress."
The remaining systems are located throughout the former base, including the Operable Unit D landfill site at the north end of the base, the former fire training area, the old industrial waste water treatment plant and south of Dudley Boulevard near Bldg. 475.
The Air Force began installing a series of soil vapor extraction systems to remove the VOCs from the soil in 1993. At its peak operation, the SVE network on the former base included more than 100 extraction wells and 15 treatment systems removing contaminants from 26 plumes. The wells vacuum the air between the soil particles in the ground and pump it to a treatment system where the VOCs are removed and the clean air is then released back into the atmosphere.
"The plume at the Operable Unit D site has shrunk down to just two little spots," said Smarkel. "We're getting really close to closure at all of the sites."