McClellan Cleanup: What's been done? What's left to do?
During operation of McClellan Air Force Base, the Air Force used a wide range of toxic and hazardous chemicals. These chemicals were mostly industrial solvents and cleaners, aviation fuels, electroplating chemicals, a variety of oils and lubricants, and some low-level radioactive materials. Past disposal practices, spills, releases, and leaking tanks and pipelines resulted in soil and groundwater contamination at the former base. The Air Force also put chemical wastes in disposal pits at McClellan from the 1940s through the 1970s. This was a commonplace industrial practice before more stringent modern environmental laws and regulations went into effect.
Groundwater contamination was discovered at McClellan in 1979 after extensive investigation. The Air Force installed a series of extraction wells and a groundwater treatment plant in 1987 to begin cleanup. In 1986, to eliminate potential exposure to contamination from private drinking wells in the vicinity of the groundwater contamination, the Air Force paid to transfer the onbase drinking water supply and 550 offbase residents to municipal water supplies. The Air Force installed a series of extraction wells and a groundwater treatment plant in 1987 to begin cleanup.
In 1987 the U.S. Environmental Protection Agency listed the entire base on its National Priorities List as a "Superfund" site. This listing requires the Air Force to follow the EPA-regulated cleanup process.
The Air Force assumes full responsibility for the contamination and cleanup actions at McClellan. To that end, the cleanup program at McClellan has two main goals:
Protect human health and the environment
Clean up contamination from past military operations to allow property transfer
Today, the Air Force is working aggressively to complete cleanup at the former base, which encompasses some 3,000 acres approximately 7 miles northeast of downtown Sacramento, California.
The cleanup program at McClellan is the largest such effort in the Air Force with some $500 million spent so far and another $400 million anticipated to be spent before the cleanup is complete. The Air Force is committed to ensuring that the former base is safe for the environment and the people who live, work, and play there. Remedies to achieve that goal are tailored to the specific site, contaminants, and intended use. They may include any of the following:
Groundwater pump and treat
Soil vapor extraction
Dig and haul (of contaminated soil)
Institutional controls (land use restrictions)
Groundwater Pump & Treat
In 1979, contaminants were discovered in the groundwater at McClellan and the Air Force began an intensive investigation of the extent of that contamination. The primary contaminants at McClellan are volatile organic compounds (VOCs) found in the cleaners and solvents used in the daily operations at the base. The mid-1980s brought a flurry of groundwater cleanup activities, including constructing protective caps over landfills to prevent rainfall from percolating through and carrying additional contaminants to the groundwater, providing municipal drinking water hookups on and off base, and designing and constructing of the first phase of the groundwater treatment system.
The groundwater at McClellan is not used for drinking water. City and County ordinances prohibit such use in the immediate area. The Air Force has ensured that all area residents are supplied with safe drinking water from the local suppliers.
Today, the McClellan groundwater cleanup program includes a network of 100 extraction wells across the base. The extraction wells supply some 1500 gallons per minute of contaminated water to the groundwater treatment plant, which cleans and then discharges the clean water into Magpie Creek. There are also more than 500 monitoring wells on and off the former base.
More than 65,000 pounds of VOCs have been removed from the groundwater at McClellan. Non-volatile organic compounds, such as hexavalent chromium, are also present in a few areas of the groundwater at McClellan and the treatment plant removes those contaminants as well. While the majority of contaminants have been removed, it is anticipated that the pump and treat system will run for another 50 years at McClellan.
Soil Vapor Extraction
The groundwater treatment program received a big boost with the implementation of soil vapor extraction systems (SVE) in 1993. The systems remove the VOCs that are in the soil above the groundwater. This layer of soil, between the surface where the contaminants were originally located and the groundwater is called the vadose zone. Because the VOCs move relatively slowly through the vadose zone, much of those contaminants are still there. The SVE system essentially "vacuums" the vaporized contaminants out of the soil and pumps them to a treatment plant where the contaminants are filtered and the clean air is released. Removing VOCs from the vadose zone by SVE is generally quicker and less costly than later removing them from the groundwater. To date, approximately 1.3 million pounds of contaminants have been removed from McClellan through SVE.
Dig & Haul
Depending on the type of contaminants present and the anticipated future use of the site, the Air Force and state and federal regulatory agencies may decide the best treatment is to remove the contaminants and the associated soil and dispose of it in an approved disposal facility. Frequently, this remediation method is employed at old landfill sites that may contain a variety of waste materials ranging from fuel drums to laboratory glassware.
An engineered cap over a contaminated area protects human health and the environment from future exposure while leaving the contaminants in place. In some cases, caps are accompanied by an engineered liner under the contaminant to prevent migration of the contaminant either into the atmosphere or down to the groundwater. This alternative is only used if it is compatible with the nature of the contaminants and future use of the area. Institutional Controls Institutional controls eliminate or limit exposure to humans by restricting land use and activities that can occur on the site. These restrictions, including permitting, zoning, deed restrictions, fencing, inspections, and enforcement, remain with the land indefinitely. These measures not only protect human health and the environment, but they are also tools to protect the other cleanup systems on site as well.
Monitoring & Review
An important component of all the cleanup programs at McClellan is ongoing monitoring and a comprehensive 5-year review. The monitoring provides verification on a regular basis (the frequency ranges from weekly to annual) that the program is working as intended. The 5-year review is a comprehensive "audit" of all the cleanup programs at the former base. It not only reviews the effectiveness of the cleanup action, but it also reviews the current knowledge about the contaminants and cleanup treatments to ensure the remedy remains protective of human health and the environment. Lastly, the review provides recommendations for ongoing operations of the remedy.
Community involvement and acceptance is a key part of the McClellan cleanup program. In addition to newsletters, mailers, and numerous speaking engagements, tours, and community events, the Air Force works with the McClellan Restoration Advisory Board to provide a two-way exchange of information with the community. The RAB is composed of representatives from various stakeholder groups within the local community as well as regulatory agencies. The group meets quarterly to advise the Air Force and regulatory agencies about community concerns and provide comments on McClellan cleanup documents.