Perchlorate Contamination in the Mather Air Force Base Water Service Area
RANCHO CORDOVA, SACRAMENTO COUNTY, CALIFORNIA
The California Department of Health Services (CDHS), under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR), is conducting public health assessment activities on the Aerojet-General Corporation (Aerojet) Superfund site in Sacramento County, California (See Figure 1, in attachments). A preliminary public health assessment written in December 1988 recommended that when additional environmental information and data became available ATSDR would make another assessment (1). A site review and update written in March 1993 also recommended a public health assessment be conducted when more data became available (2).
This health consultation is one in a series that will be performed as part of the ATSDR public health assessment process at this site. During this process, data and information on the release of hazardous substances and their impact on public health will be evaluated. Four health consultations have recently been written as part of this series (3-6). In this health consultation, we will focus on describing the perchlorate contamination that has reached the Mather Air Force Base Water Service (Figure 1) and evaluate the health impact from the exposure that has occurred. We are also in the process of writing several other health consultations that focus on perchlorate exposure to consumers of water from other water purveyors in the area and from private wells in the area. In addition, we are also in the process of writing a health consultation that describes the perchlorate groundwater contamination west of the Aerojet Superfund site.
Aerojet began operation in 1951. Since that time, Aerojet has manufactured liquid and solid propellants for military and commercial rocket systems and has fabricated, assembled, tested and rehabilitated rocket engines (1). In addition, between 1974 and 1979, Cordova Chemical Company, a wholly-owned subsidiary of Aerojet, manufactured paint components, herbicides, and pharmaceutical products. Over the years, Aerojet and Cordova Chemical disposed of hazardous waste by burial, open burning, discharge into unlined ponds, and injection into deep underground wells (1). Some of these discharges, including perchlorate, have contaminated the environment and have moved off-site of the Aerojet facility boundary (Figure 1). Perchlorate in the groundwater arises from ammonium perchlorate being a main component of solid rocket fuel. In addition to the natural migration of perchlorate-contaminated groundwater from the site, Aerojet is reinjecting treated groundwater, contaminated with perchlorate, at the sites's western boundary. The Regional Water Quality Control Board (RWQCB), the California Department of Toxic Substances Control (DTSC) and the U.S. Environmental Protection Agency (USEPA), are the lead regulatory agencies overseeing groundwater investigation and cleanup at Aerojet, and are also investigating other sources of the perchlorate, such as the McDonnell Douglas (now Boeing) and Purity Oil Sales sites.
Mather Air Force Base is located to the southwest of the Aerojet site and it is listed on the National Priority List due to soil and groundwater contamination. As part of the Base Realignment and Closure Act, Mather Air Force Base was identified for closure and on September 30, 1993 the base closed (7). The base was and is essentially composed of several different land uses, served by two water systems, the Main Base and the Family Housing areas. Until the perchlorate contamination was discovered, the two water systems essentially operated independent of each other even though there was an interconnection (8).
The Main Base area is located to the north of the air fields (Figure 2) and this is where all the air force management operations were carried out. The Main Base Water System has 210 connections serving 413 buildings in the administrative and industrial area of the base including the aircraft hangers and the flight line adjacent to the base's runways (8). In 1988, when the base was in operation, approximately 6,200 people worked within the Main Base water System Area. A 29-bed hospital is located in the Main Base area; since the base closure, the hospital is being operated by McClellan Air Force Base. The Main Base area, now called Mather Field, is being used for air cargo service, light industrial and office businesses under the direction of a county redevelopment project. The redevelopment project has been increasingly successful in creating new businesses to relocate or locate at Mather Field. Currently, there are approximately 50-60 businesses employing approximately 1,900 employees. The Main Base water system also serves a transitional family housing unit, Mather Community Campus, that can accommodate several hundred people.
Prior to the discovery of the perchlorate contamination, the Main Base was served by four wells (MB Wells 1,2,3,4) located within the Main Base area (Figure 2) (8). The four wells rotate as the lead well to supply water to the system. The water from the four wells is pumped to a 650,000 gallon ground level reservoir, located near Main Base well #1 (9). As the water is needed in the Main Base area, it is pumped from the storage tank into the distribution system. A 300,000 gallon elevated storage tank is located midway in the distribution system and provides additional storage and pressure in the distribution system (9).
The 650,000 gallon ground level reservoir was taken out of service from December 1995 to June 1997 for repair of defects (9). For some of the time when the 650,000 gallon ground level reservoir was out of commission, the Main Base system was operated partially in manual mode. Specifically, from December 1995 to summer 1996, the well rotation was not automated so demand was often manipulated by hand. Since Main Base well #1 is located close to the Main Base Treatment Plant, this well may have been used more often (9).
The Family Housing area is composed of 414 two- and three-bedroom duplexes, 857 two-, three-, and four bedroom houses, and several common use facilities, including two schools (Mather Heights and Kittyhawk Schools), a teen/youth center, swimming pool, Little League fields, a convenience market, and a gas station (10). A golf course and riding stable are also serviced by the Family Housing water system. In 1988, before the base closed, approximately 4,500 people were serviced by the Family Housing Water System (8). The common use facilities are still in use even though the base has closed. Sacramento County Parks and Recreation operates the recreational and parks areas including the golf course for general use. The housing units are not currently occupied.
The Family Housing area is served by five wells (FH Wells 1, 3, 4, 5 and 6; however, wells 3 and 6 are temporarily out of operation) located within the Family Housing area (Figure 2). Water from the five wells is pumped to a central treatment facility before it is pumped to an elevated 500,000 gallon tank (8). The treatment facility chlorinates the water and removes iron and manganese to improve the esthetic quality of the water.
Even though there is a large plume containing volatile organic compounds (VOCs) such as tetrachloroethylene (PCE) and carbon tetrachloride coming from the contamination that originated from on-site sources, there has been very little VOC contamination detected in Mather wells. The Main Base well #1 had trace amounts of PCE (<0.95 ppb) detected in it. In February 1997 sampling, Main Base well #3 had a detectable amount of PCE (0.97 ppb) detected in it; a sample taken in April 1997 had not detection (<0.5 ppb).
Nitrate concentration in the Main Base wells ranged from 1.3 to 2.2 ppm in 1991 and 1.24 to 1.28 ppm in 1992 (9). Nitrate concentrations in the Family Housing wells ranged from 0.14 to 0.18 ppm in 1991 and <0.01 to 1.5 ppm in 1992. The drinking water standard for nitrate is 45 ppm.
The Main Base system is interconnected in two locations. Prior to the discovery of the perchlorate, there was a pipeline that interconnected the Main Base system with the Family Housing system that was in poor condition and was not used (8). Recently, this interconnection has been upgraded and is currently in use.
The Main Base system is also interconnected with Citizens Utility's Suburban System (8). Citizen Utility shut down one of its Suburban system wells (Citizens Utility well #29) because PCE (originating from Mather) was detected in a monitoring well located upgradient to well #29. Citizens Utilities wanted compensation for the water production loss. The Air Force constructed a one-way intertie leading from the Main Base system to Citizens Utilities' Suburban System which could provide 900 gallons per minute. The intertie was used to supply water to Citizens Utility's Suburban System from July to November 30, 1995 (8) and from July to October 1996 (10).