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Mather Cleanup Update

Mather Lake
Mather Lake
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Mather is in the final stages of environmental cleanup. All major decisions have been made, documented and overseen by the Air Force Real Property Agency, the U.S. EPA, Department of Toxic Substances Control, Regional Water Quality Control Board, and the Integrated Waste Management Board. Community members provided input through the Mather Restoration Advisory Board (RAB) beginning in 1994. The RAB was adjourned in 2011, after all cleanup decisions had been made and attendance at RAB meetings had dwindled.

The Air Force has spent more than $162 million on the cleanup and millions more will be spent for ongoing monitoring and operation of groundwater treatment and soil cleanup systems, and maintenance and monitoring of landfill sites. Of the 89 sites identified at Mather, 75 sites are clean. Fourteen of the remaining sites are being cleaned or awaiting official closure documentation.

Mather Air Force Base, earlier called Mather Field, operated from 1918 to 1993, although there were breaks in service prior to World War II. To perform its mission, Mather's military workforce used chemicals, including fuels, solvents and oils . Over the years while the base was open, some chemicals leaked into the ground from storage tanks. Some were washed down drains or spilled during transportation and use. Chemical disposal also contributed to soil and groundwater contamination. Such disposal practices, legal in the past, are now known to cause environmental contamination and are no longer used.
In 1979, contamination was detected in water supply wells near Mather. The primary source was solvents such as perchloroethylene (PCE), tetrachloroethene (TCE) and carbon tetrachloride. More extensive testing followed in the 1980s, and 89 sites were identified as needing further study or cleanup. These included former landfills and sites with contaminated soil, groundwater, or both. The biggest problem was from solvents such as PCE, TCE and carbon tetrachloride, and from petroleum hydrocarbons (fuels and oils).

Environmental cleanup began in the 1980s, years before Mather closed. The cleanup primarily involves removing contaminants from the soil and groundwater beneath the land surface. Part of Mather was added to the Environmental Protection Agency's National Priorities List in July of 1987 and the remainder was added in June of 1989. Adding Mather to the NPL ensures that many parties are involved in the cleanup effort, including the US EPA, the state and regional water board. The Air Force is financially and legally responsible for the cleanup to protect human health and the environment.

Various processes remediate the contamination. These include groundwater treatment systems, soil vapor extraction, and bioventing. To date, more than 12 billion gallons of groundwater have been pumped out of the ground and treated at Mather. Some 4,050 pounds of solvents have been removed from the water and the cleaned water is injected back into the ground or used to maintain the level of Mather Lake during the dry season.

Soil vapor extraction, which vacuums chemical vapors from the spaces between the grains of soil above the water table, has removed an estimated 1,118,195 pounds of petroleum products from the soil. Soil vapor extraction has also removed some 7,411 pounds of solvents from the soil.

Bioventing pumps air underground so oxygen moves through the soil to promote the destruction of contamination by microorganisms such as bacteria and fungi.
Of the 89 sites identified at Mather, cleanup has been completed at 75 sites. Fourteen of the sites are being cleaned or awaiting official closure documentation.
More than 600 testing and treatment wells are in use at Mather as part of the groundwater cleanup. Thirty-four wells extract water for treatment, eight are injection wells that return cleaned water back into the ground, and the rest are monitoring wells, used to track and measure contamination.

The contaminated water is not used for drinking water. Drinking water is supplied by the Sacramento County Water Agency. Wells providing drinking water are tested regularly, and annual water quality reports are provided to water customers as required by law. In addition, the Air Force samples the water from many drinking water wells to ensure that the contaminated water doesn't impact drinking water supplies.

Former landfills at several sites (2, 5 and 6) were dug up and their waste was placed in landfill 4. Landfill sites 3, 4 and 7 were then "capped," or covered with impervious barriers. Such barriers keep rainwater from percolating through the waste and transporting it into the groundwater. Landfills are monitored to make sure the waste is contained.

All cleanup systems are in place and operating properly. Most of the groundwater cleanup will be finished in about five years, while getting the last remaining amount out of groundwater could take approximately 50 years. The Air Force will continue managing the cleanup process until the cleanup is finished.

Mather Cleanup Update, 2011
·89 sites identified
·75 sites are clean
·Drinking water is strictly monitored and safe
·600 wells test and treat water
·Landfills are monitored