MATHER AIR FORCE BASE
MATHER, SACRAMENTO COUNTY, CALIFORNIA
Mather Air Force Base is located in the Central Valley region of Northern California, approximately 10 miles east of Sacramento and immediately south of Rancho Cordova. The base ultimately encompassed approximately 5,850 acres and operated as a pilot and navigator training post from 1918 through 1993, when it was closed under the Department of Defense (DOD) Base Realignment and Closure (BRAC) Act of 1988. Currently, much of the base is undergoing commercial redevelopment and reuse.
While Mather was an active duty base, hazardous materials, such as fuel oils, lubricants, solvents, and protective coatings, were used in the operation and maintenance of aircraft. The U.S. Air Force (USAF) began to identify locations where these materials might have been released after the 1982 DOD Installation Restoration Program commenced. Mather was placed on the U.S. Environmental Protection Agency's (USEPA) National Priorities List on November 21, 1989, because of contamination released during past disposal practices and accidental spills of hazardous materials. The USAF has identified 89 sites and four groundwater contaminant plumes at Mather and has completed investigations of these areas. Site remediation and preparation of Records of Decision are underway.
Communities around Mather depend on groundwater as the primary drinking water source. Groundwater contamination on and off the base is the most important and widespread exposure situation at Mather. In preparing this public health assessment, the Agency for Toxic Substances and Disease Registry (ATSDR) reviewed available environmental sampling data from the USAF, the USEPA, the Regional Water Quality Control Board, and the California Department of Health Services. As a result of reviewing collected information and visiting the site, ATSDR identified additional ways that people may be exposed to environmental contamination, including contact with contaminated soils on base and contaminated surface water and sediments in on-base drainage areas. From this data review and site visits conducted in 1997 and 1999, ATSDR determined that the following exposure situations did not present a public health hazard.
Exposure Hazard Summary Table - Mather Air Force Base, CA
| Exposure Scenario | Time Frame |
Exposure | Public Health Hazard? |
Actions Taken/Recommended |
| Use of contaminated groundwater from on-base wells in the main base supply system | past current future |
yes no no |
no no no |
|
| Use of contaminated groundwater from the on-base AC&W water supply well | past current future |
yes no no |
no no no |
|
| Use of contaminated groundwater from off-base community supply wells operated by the Citizens Utilities company of California and Sacramento County | past current future |
yes no no |
no no no |
|
| Use of contaminated groundwater from off-base private wells west of Mather | past current future |
yes no no |
no no no |
|
| Contact with contaminated surface soils in various areas throughout Mather | past current future |
possible unlikely unlikely |
no no no |
|
| Contact with contaminated surface water/ sediment in streams and ditches throughout Mather | past current future |
possible unlikely unlikely |
no no no |
|
Exposure situations and public health hazards
ATSDR concluded that the three exposure situations (contact with contaminants in on- and off-base supply wells, on-base surface soil, and on-base surface water and sediment) would not present public health hazards (Table 1). For each of these situations, people were exposed to the contamination, but these exposures are not likely to produce adverse health effects because the contaminant concentrations people were exposed to were too low, and exposure was infrequent and of short duration. Actions have been taken by the Air Force to prevent current and future exposures (Appendix B).
Contamination in on- and off-base water supply wells poses no apparent public health hazard because contamination was below concentrations that are likely to produce adverse health effects to past area residents and workers who used the water. The USAF and public water suppliers closed their contaminated wells, treated water from the public wells prior to distribution, and connected homes with private wells to the public water supply to prevent future exposure to groundwater contamination.
The USAF and public water suppliers regularly monitor wells to ensure that wells in use meet state and federal safe drinking water standards. On-base supply systems and off-base community supply systems are monitored quarterly for volatile organic compounds (VOCs) and perchlorate. The USAF also conducts annual monitoring for VOCs at active private wells to the south. The USAF has a plan in place that outlines actions that will be taken to prevent exposures that may result in adverse health effects if contaminants are found in supply wells in the future.
Contamination in surface soil poses no apparent public health hazard because contaminant concentrations were low and any exposure to on-base workers or recreational users would have been infrequent and of short duration, limiting the amount of exposure. Currently, the USAF is cleaning up contamination to prevent further exposures to contaminants in surface soil at levels that may present a public health hazard.
Contamination in surface water and sediment poses no apparent public health hazard because exposure to past on-base workers, residents, and recreational users were infrequent and of short duration. Currently, the USAF is cleaning up contamination to prevent future exposures to levels of contamination that may result in adverse health effects. No areas of contamination have been found adjacent to Mather Lake, a recreational area open to the public. Thus, no exposures are expected to occur during recreational use of Mather Lake.
Site Description and Operational History
Mather Air Force Base (Mather) is located in the Central Valley region of Northern California, approximately 10 miles east of Sacramento and immediately south of Rancho Cordova (Appendix A, Figures 1 and 2). The base encompassed approximately 5,850 acres at the time of closure in 1993 (USAF 1998). Residential housing and commercial businesses are located along the western and northwestern base boundaries. Gravel mining operations are located along the northeastern and southwestern property boundaries. Land to the east and southeast is largely undeveloped (USAF 1999). The Aerojet-General Corporation (Aerojet) National Priorities List (NPL) site is located northeast of Mather (ATSDR 1998).
Mather was first activated in 1918 as a combat pilot training school. The base was placed on inactive status from 1922 until 1930 and again from 1932 until 1941. Mather was reactivated in 1941 as a pilot and navigator training post. After World War II, Mather was the only aerial navigation school for the U. S. military and its allies. In addition to training conducted by the 323rd Flying Training Wing, Mather also hosted the Strategic Air Command (SAC) 320th Bombardment Wing from 1958 to 1989 and the 940th Air Refueling Group from 1976 until closure in 1993 (USAF 1994a).
After more than 50 years of active service, Mather was closed on September 30, 1993, under the Department of Defense (DOD) Base Realignment and Closure Act of 1988. Currently, much of the base is undergoing commercial redevelopment and reuse. Portions of the site are designated for reuse as a cargo airport, commercial businesses, residential housing, and parks and recreation areas (USAF 1994a, 1999).
While Mather was active, the operation and maintenance of aircraft, small arms, radar equipment, vehicles, and other equipment, as well as dry cleaning activities, required the use of toxic and hazardous materials. These materials included fuel, oils, lubricants, solvents, protective coatings, and weed and pest control mixtures. One solvent, trichloroethylene (TCE), was used from 1958 through 1974 by the U.S. Air Force (USAF) and until as late as 1992 by the Army National Guard, who have also been stationed at Mather. These materials may have been disposed or spilled onto the ground or into unlined ditches and may have resulted in contamination found throughout the base (USAF 1994a).
Remedial and Regulatory History
The USAF began to identify locations where these materials might have been released after the 1982 DOD Installation Restoration Program (IRP) commenced. Investigations conducted under the IRP confirmed the presence of volatile organic compounds (VOCs) and hydrocarbons at several locations throughout Mather. Based on these findings, Mather was placed on the NPL on November 21, 1989 (AFBCA 1999).
In July 1989, the USAF, the U.S. Environmental Protection Agency (USEPA), and the state of California Department of Toxic Substances Control signed a Federal Facility Agreement (FFA). The FFA was signed to ensure that environmental impacts from past operation and operation ongoing at that time were thoroughly investigated and appropriate remedial actions are taken to protect people and the environment. The FFA did this by establishing enforceable deadlines for investigation documents, defining the roles and responsibilities of the USAF, USEPA, and the state of California, and providing a means for dispute resolution if conflict arises (AFBCA 1999).
Currently, there are 89 IRP sites and four groundwater contaminant plumes at Mather. These sites and contaminant plumes have been grouped in six operable units (OUs) based on type of site and scheduled remediation. The IRP sites and plumes are grouped as follows:
- The Landfill OU (OU4) consists of six locations (sites one to six) where waste generated at Mather was buried.
- The Aircraft Control and Warning (AC&W) OU (OU1) consists of the AC&W groundwater plume, a disposal site (site 12), and three underground storage tank (UST) sites (sites 25, 30, and 47).
- The Soil OU (OU3) consists of contaminated soils associated with waste disposal pits, oil/water separators, gas stations, USTs, fire training areas, and miscellaneous sites. This OU includes sites 7, 9 to 11, 13 to 16, 21, 22, 24, 26 to 29, 31 to 46, 48 to 66, and 69 to 77.
- The Groundwater OU (OU2) consists of the Main Base and SAC Industrial Area groundwater plume, the Site 7 groundwater plume, and the Northeast groundwater plume.
- The Basewide OU (OU5) includes other IRP sites remaining at the base. These include sites 8, 10C, 17, 18, 19, 20, 23, 67, 68, 78, 79, 81 to 84, 86, and 87.
- The Supplemental Basewide OU (OU6) consists of sites that were removed from the Basewide OU to facilitate the completion of a record of decision (ROD) for the Basewide OU. The Supplemental Basewide OU includes sites 80, 85, 88, and 89.
The USAF has completed investigations and prepared RODs for each of the OUs, except the Supplemental Basewide OU (OU6). The RODs establish required remedial actions, if any, for each of the IRP sites and groundwater plumes. The USAF has completed or is in the process of implementing remedial actions selected under the RODs (AFBCA 1999; USAF 1998). Appendix B lists all the IRP sites, past investigations, and completed or planned remedial actions. This table also provides an evaluation of potential public health hazards associated with each site.
The 1997 Defense Authorization Act allows USEPA and the state governor to permit DOD to transfer ownership of contaminated property at a military facility prior to completion of remedial actions, provided that the military organization certifies that remediation will be completed. As part of the transfer process, a Finding of Suitability for Early Transfer (FOSET) is prepared and is open to regulatory and public comment. At Mather, two FOSETs were prepared in 1998 and allowed the transfer of a total of approximately 700 acres to Sacramento County and other recipients. Mather is the first military base in California to complete early property transfers (Gutierrez-Palmenberg, Inc. 1999).
The Agency of Toxic Substances and Disease Registry (ATSDR) completed a preliminary public health assessment (PHA) for Mather in April 1989. Under this preliminary PHA, ATSDR reviewed data for three disposal areas: 7100 Disposal Area (IRP site WP07), the AC&W Disposal Area (IRP site WP12), and the West Ditch (IRP site SD15). Contaminants were detected in site media at each disposal area. The preliminary PHA concluded that although health threats were possible, insufficient data were available to evaluate these threats. When additional data became available, ATSDR recommended further assessment of the base (ATSDR 1989).
ATSDR performed follow up site visits in April 1991 and May 1997 to collect additional information. During the site visits, ATSDR met with representatives of the USAF, the California Department of Health Services (CDHS), and community members to identify community concerns. ATSDR contacted representatives of the California Department of Toxic Substances Control and the Regional Water Quality Control Board by telephone to collect information about community concerns, site contamination, actions taken to protect public health and the history of regulatory involvement at Mather. In preparation of the final PHA, ATSDR visited the site in May 1999 to evaluate site conditions and hold a public availability session. The purpose of the public availability session was to provide an opportunity for community members to meet individually with ATSDR staff to discuss health concerns about site contamination, ask questions and obtain information about ATSDR activities at Mather Air Force Base. Concerns and comments raised during these site visits are discussed in the "Evaluation of Environmental Contamination and Potential Exposure Situations" section and the "Community Health Concerns" section of this PHA (USAF 1997, 1999).
In May 1998, in cooperation with ATSDR, CDHS completed a health consultation, summarized here, on perchlorate-contaminated groundwater in the Mather water service area (ATSDR 1998). The perchlorate contamination likely originates northeast of the base at Aerojet--a former rocket fuel manufacturer--and Cordova Chemical--a nearby chemical company. ATSDR evaluated four groups of people potentially exposed to groundwater contamination: on-base workers, temporary adult residents, base visitors, and patients at the on-base Hospital. Based on available information, ATSDR concluded that it was unlikely that exposure to perchlorate in drinking water would have caused any adverse health effects to on-base workers, residents in transitional housing, or visitors. ATSDR felt that potential health effects to hospital patients were uncertain because patients may represent a sensitive subpopulation (ATSDR 1998). Additional information about the perchlorate-contaminated groundwater, ATSDR's evaluation, and potential health effects is provided in the "Evaluation of Environmental Contamination and Potential Exposure Situations" section of this PHA and Appendices C and D.
Mather is located in northern California in Sacramento County, approximately 10 miles east of downtown Sacramento (Appendix A, Figure 3). The unincorporated towns surrounding Mather have a population of approximately 90,000 residents, with the population anticipated growing to approximately 105,000 by 2005 (Gutierrez-Palmenberg, Inc. 1997, 1999). Residential housing and commercial businesses are located along the western and northwestern base boundaries. Gravel mining operations are located along the northeast and southwest property boundaries. Land to the east and southeast is largely undeveloped (USAF 1999). At least 18 schools or preschool programs, five day care centers, five medical centers, one senior center, one community center, and seven parks are located within a 2-mile radius of Mather; all of these facilities are to the west or northwest (Gutierrez-Palmenberg, Inc. 1999).
Before closure, Mather employed approximately 2,000 military personnel and 1,000 civilian personnel (CEDAR 1999). At peak operations, approximately 5,000 military personnel and 2,000 civilian personnel worked at Mather. When Mather was an active military base, access was limited to military and civilian personnel by gate guards, security patrols, and fencing. Additional access restrictions, such as barbed wire and guard towers, were in place around the SAC alert area (near IRP sites LF02 and ST46) and the weapons storage area (near IRP site WP17) (Hughes 1999, 2000).
On-base housing at Mather consisted of 18 dormitories and approximately 1,300 single family housing units located in the central portion of the base. Approximately 4,000 people, including military personnel and their families, resided in on-base housing. The on-base housing units were vacated in 1993 when the base closed. The on-base housing area is undergoing redevelopment and residents are beginning to occupy the new homes. The Kitty Hawk Elementary School and the Mather Heights Elementary School (kindergarten through grade 6) were located within the on-base housing area and, each year, provided schooling for approximately 700 children from military families stationed at the base (Hughes 1999, 2000). These schools are still operated by the local school district. An on-base hospital, currently operated by the Veterans Administration, is located in the northwestern portion of the base. This hospital provided medical care to military families with a capacity for approximately 100 in-patients. This hospital has been transferred to the Veteran's Administration for outpatient care with future inpatient care proposed after renovations and improvements. Transitional housing units for homeless families and individuals are located in the northwestern portion of Mather. These housing units previously served as dormitories for unmarried officers at Mather. Family units opened in January 1996 and individual units opened in 1997. Residents are permitted to remain in these housing units for no longer than two years (ATSDR 1998; CEDAR 1999; Hughes 1999, 2000).
Mather was closed in September 1993 and is currently undergoing redevelopment and property transfer for reuse as a civilian commercial area, an industrial center, residential neighborhood, and a parks and recreation area. After closure, access to the base was monitored by a private security firm to prevent vandalism. Currently, access is unrestricted except for the airfield; IRP sites Landfill 3, 4, and 7 (LF03, LF04, and WP07), and construction areas in the former on-base miliary housing are in the central portion of the base. Fencing, and in some cases gate guards, restrict access to these areas. The USAF is in the process of conducting remedial actions at several sites throughout Mather. Treatment systems are operating to remove contamination associated with groundwater plumes. Soil vapor extraction, bioventing systems, and other soil treatment systems are also in place at IRP sites LF03, LF04, WP07, FT11, FT10C, LF18, WP19, OT23, ST29, ST34, ST37, ST39, SS54, SD56, SD57, SD59, ST68, and ST71. Remedial actions have yet to be determined for IRP sites SD80, SD85, DD88, and OT89. At sites where contamination may be present or treatment systems are in place, the USAF has not installed fences to restrict access to the contaminated surface soil, surface water, and/or sediment. To limit injury, however, the USAF has implemented controls to prevent access to remediation equipment (e.g., drill rigs, soil processing systems, groundwater treatment systems) and physical hazards (e.g., excavations). These controls may include locking equipment to prevent operation and installing fences to prevent access to treatment systems or open excavations (Hughes 1999).
Approximately 700 acres of land located in the northwestern portion of the base have been transferred to Sacramento County under an early transfer program. This land was designated as part of an economic development conveyance. Sacramento County will lease or sell the land to state agencies or private businesses for reuse (CEDAR 1999; Gutierrez-Palmenberg, Inc. 1999; USAF 1999). In addition to Sacramento County, proposed reuse includes additional property transfers to the Federal Aviation Administration, Rancho Cordova Parks and Recreation, Folsom Cordova Unified School District, Sacramento County Office of Education, the U.S. Army, two churches, and private business owners (USAF 1999). Proposed reuses include operation of a cargo airport and commercial businesses, development for residential housing, and maintenance of park and recreation areas.
Of the approximately 5,850 acres that comprise Mather, the airfield, buildings, and base infrastructure occupy approximately 975 acres with an additional 665 acres maintained as landscaped grounds. Approximately 1,175 acres are defined as semi-improved and are periodically maintained. The remaining 3,035 acres are unimproved and portions of this area are mowed annually. Grasslands dominate the semi-improved and unimproved portions of the base. Vernal pools, which often support unique flora and fauna, are scattered throughout the grasslands (USAF 1994a).
Natural drainage patterns at Mather were altered by construction of the airfield and base buildings. Man-made drainage channels that collect surface water runoff are located throughout the base. The two largest ditches are the West Ditch (IRP site SD15) and the South Ditch (IRP site SD85) located adjacent to the airfield. Drainage channels at Mather generally flow intermittently to the southwest and discharge to Morrison Creek. Morrison Creek is an intermittent stream that flows from Mather Lake southwesterly through the base. Mather Lake is located in the northeastern corner of the base and is a 64-acre artificial lake that was created by damming Morrison Creek. In addition, the Folsom South Canal is located along the eastern base boundary. This canal is an artificial, concrete-lined aqueduct that transports water from the Nimbus Dam located on the American River northeast of Mather to the inactive Rancho Seco power plant located south of Mather (USAF 1994a; Gutierrez-Palmenberg, Inc. 1999).
When Mather was active, Mather Lake was used as a recreational area by military personnel and their families. Currently, the lake is open to the general public. Signs posted at the lake state that swimming and boating are prohibited. Fishing from the shore, however, is allowed with catch limits posted. Mather Lake was historically stocked annually with rainbow trout for sport fishing. The lake does not provide suitable habitat for trout, which limits the survival of the stocked fish. Catfish were also stocked to augment the natural population. Fish that have established breeding populations in Mather Lake include largemouth bass, bluegill, red ear sunfish, black crappie, and green sunfish, which are considered game fish and may be caught for human consumption. Golden shiner and mosquito fish, which are considered bait fish, are also present in Mather Lake.
During operation, playgrounds within the on-base housing area, the USAF golf course (including IRP sites MY82 and DD88), a firing range (IRP site FR86), and two trap and skeet ranges (IRP sites OT87 and OT89) were used as recreational areas in addition to Mather Lake. Sacramento County has continued operation of the golf course since 1993. The eastern portion of the base, including Mather Lake, is proposed for transfer to the Sacramento County Parks and Recreation for public use (USAF 1994a, 1999).
Quality Assurance and Quality Control
In preparing this PHA, ATSDR reviewed and evaluated information provided in the referenced documents. Documents prepared for the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA) programs must meet specific standards for adequate quality assurance and control measures for chain-of-custody procedures, laboratory procedures, and data reporting. The environmental data presented in this PHA are from site characterization, remedial investigation, and groundwater monitoring reports prepared by the USAF under CERCLA and RCRA. Based on our evaluation, ATSDR determined that the quality of environmental data available in site-related documents is adequate to make public health decisions.
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