PUBLIC HEALTH ASSESSMENT

MATHER AIR FORCE BASE
MATHER, SACRAMENTO COUNTY, CALIFORNIA

EVALUATION OF ENVIRONMENTAL CONTAMINATION AND EXPOSURE SITUATIONS

Introduction

What is meant by exposure?

ATSDR's PHAs are exposure, or contact, driven. Chemical contaminants disposed or released into the environment have the potential to cause adverse health effects. However, a release does not always result in exposure. People can only be exposed to a contaminant if they come in contact with that contaminant. Exposure may occur by breathing, eating, or drinking a substance containing the contaminant or by skin contact with a substance containing the contaminant.

How does ATSDR determine which exposure situations to evaluate?

ATSDR scientists evaluate site conditions to determine if people could have been (a past scenario), are (a current scenario), or could be (a future scenario) exposed to site-related contaminants. When evaluating exposure pathways, ATSDR identifies whether exposure to contaminated media (soil, water, air, waste, or biota) has occurred, is occurring, or will occur through ingestion, dermal (skin) contact, or inhalation.

If exposure was, is, or could be possible, ATSDR scientists then considers whether contamination is present at levels that might affect public health. ATSDR scientists select contaminants for further evaluation by comparing them against health-based comparison values. Comparison values are developed by ATSDR from scientific literature available on exposure and health effects. These comparison values are derived for each of the different media and reflect an estimated contaminant concentration that is not likely to cause adverse health effects for a given chemical, assuming a standard daily contact rate (e.g., amount of water or soil consumed or amount of air breathed) and body weight.

Comparison values are not thresholds for adverse health effects. ATSDR comparison values establish contaminant concentrations many times lower than levels at which no effects were observed in experimental animals or human epidemiologic studies. If contaminant concentrations are above comparison values, ATSDR further analyzes exposure variables (for example, duration and frequency), the toxicology of the contaminant, other epidemiology studies, and the weight of evidence for health effects.

Some of the comparison values used by ATSDR scientists include ATSDR's environmental media evaluation guides (EMEG), reference dose media guides (RMEG), and cancer risk evaluation guides (CREG) and EPA's maximum contaminant levels (MCL). MCLs are enforceable drinking water regulations developed to protect public health. CREGs, EMEGs, and RMEGs are non enforceable, health-based comparison values developed by ATSDR for screening environmental contamination for further evaluation.

More information about the ATSDR evaluation process can be found in ATSDR's Public Health Assessment Guidance Manual at http://www.atsdr.cdc.gov/HAC/HAGM/ or by contacting ATSDR at 1-888-42ATSDR.

If someone is exposed, will they get sick?

Exposure does not always result in harmful health effects. The type and severity of health effects that occur in an individual from contact with a contaminant depend on the exposure concentration (how much), the frequency and/or duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, lifestyle, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. Together, these factors and characteristics determine the health effects that may occur as a result of exposure to a contaminant in the environment.

There is considerable uncertainty about the true level of exposure to environmental contamination. To account for the uncertainty and to be protective of public health, ATSDR scientists typically use high-end, worst-case exposure level estimates as the basis for determining whether adverse health effects are possible. These estimated exposure levels usually are much higher than the levels that people are really exposed to. If the exposure levels indicate that adverse health effects are possible, then a more detailed review of exposure combined with scientific information from the toxicological and epidemiologic literature about the health effects from exposure to hazardous substances is performed.

Appendix A (Figures 4 and 6) and Appendix C provide an overview of ATSDR's exposure evaluation process. Appendix E defines some of the terms used in this report.

What exposure situations were evaluated for Mather?

ATSDR identified three exposure situations at and near Mather for further evaluation: consumption and domestic use of contaminated groundwater, contact with contaminated surface soil, and contact with contaminated surface water and sediment. Table 1 provides a summary of the exposure situations at Mather evaluated in this PHA. Appendix C provides a description of ATSDR's evaluation process used to identify exposure situations at Mather.

Table 1: Completed Exposure Situations at Mather AFB

	Exposure Pathway Elements
Pathway Name	Contaminant	Environmental Medium	Point of Exposure	Route of Exposure	Time of Exposure	Exposed Population	Comments
Drinking water	Tetrachloro- ethylene (PCE) and perchlorate	groundwater	on-base supply wells (Main Base supply system)	ingestion, inhalation, dermal (skin) contact	past	on-base workers, on-base residents in the transitional housing unit, and patients at the on-base hospital (An estimated 3,000 workers and 4,000 residents were present at Mather. Some workers may also be residents.)	Past: No apparent public health hazards were identified. Based on estimated exposure doses, the Agency for Toxic Substances and Disease Registry (ATSDR) determined that concentrations detected are unlikely to cause harmful effects. Current/Future: No current or future exposures are/will occur. The contaminated wells were closed. The U.S. Air Force (USAF) also monitors active supply wells and tracks groundwater plume migration to ensure that supply wells will not be impacted by contaminants at levels that may pose public health hazards in the future. Treatment systems are in operation to remove contaminants, except for perchlorate, from groundwater. A perchlorate treatment system is expected to be approved for construction in 2001.
Drinking water (continued)	Trichloro- ethylene (TCE)	groundwater	on-base Aircraft Control & Warning (AC&W) water supply well	ingestion, inhalation, dermal (skin) contact	past	on-base workers at the AC&W facility (It is estimated that less than 50 workers were at the AC&W facility.)	Past: No apparent public health hazards were identified. Based on estimated exposure doses, ATSDR determined that concentrations detected are unlikely to cause harmful effects. Current/Future: No current or future exposures are/will occur. The USAF closed the well, operates a treatment system to remove plume contaminants from groundwater, and monitors plume migration to ensure other supply wells are not impacted by contaminants at levels that may pose public health hazards.
Drinking water (continued)	carbon tetrachloride and TCE	groundwater	off-base community supply wells	ingestion, inhalation, dermal (skin) contact	past	off-base residents (adults and children) (An estimated 26,500 people live within 1-mile of Mather.)	Past: No apparent public health hazards were identified. ATSDR determined that concentrations detected are unlikely to cause harmful effects based on estimated exposure doses. Current/Future: No current or future exposures are/will occur. The contaminated wells were closed or water is treated prior to distribution. Active supply wells, guard wells, and monitoring wells are regularly sampled to ensure that wells will not be impacted in the future. Treatment systems are in operation to remove contaminants from groundwater.
Drinking water (continued)	benzene, carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1-dichloro-ethylene, 1,1-dichloropropane, TCE, and PCE	groundwater	off-base private wells	ingestion, inhalation, dermal (skin) contact	past	off-base residents (adults and children) and workers (An estimated 35 homes and businesses used private wells.)	Past: No apparent public health hazards were identified. ATSDR determined that concentrations detected are unlikely to cause harmful effects based on estimated exposure doses. Current/Future: No current or future exposures are/will occur. The USAF connected homes and businesses with private wells to the public water supply.
Surface soil	polyaromatic hydrocarbons (PAHs), Aroclor-1260, pesticides, arsenic, cadmium, chromium, iron, and lead	surface soil	sites throughout Mather	incidental ingestion, dermal (skin) contact	past	on-base workers and recreational users (An estimated 3,000 workers and 4,000 residents were present at Mather. Some workers may also be residents.)	Past: Infrequent exposure of short duration by on-base workers and recreational users is unlikely to pose a public health hazard. Current/Future: The USAF is conducting remedial actions to prevent current and future exposures to contaminants at levels that may pose a potential health hazard.
Surface water and sediment	bis(2-ethylhexyl) phthalate, PAHs, polychlorinated biphenyls, dieldrin, chlordane, antimony, arsenic, cadmium, chromium, lead, and manganese	surface water and sediment	streams and ditches throughout Mather	incidental ingestion, dermal (skin) contact	past	on-base workers, residents, and recreational users (An estimated 3,000 workers and 4,000 residents were present at Mather. Some workers may also be residents.)	Past: Infrequent exposure of short duration by on-base workers, residents, and recreational users is unlikely to pose a public health hazard. Current/Future: The USAF is conducting remedial actions to prevent current and future exposures to contaminants at levels that may pose a potential health hazard.

ATSDR	Agency for Toxic Substances and Disease Registry
PAH	polycyclic aromatic hydrocarbons
TCE	trichloroethylene
AC&W	Aircraft Control & Warning
PCE	tetrachloroethylene
USAF	U.S. Air Force

Exposure to Contaminants in Drinking Water

Communities at and surrounding Mather depend on groundwater as their primary drinking water source. However, past industrial and commercial activities at Mather, as well as Aerojet, Cordova Chemical, McDonnell-Douglas, and Purity Oil Company facilities northeast of the base, contaminated groundwater with VOCs, mainly TCE, and perchlorate. ATSDR, therefore, evaluated potential exposures to community members drinking water that may contain contamination.

In evaluating exposure to contaminants in drinking water, ATSDR identified three types of water supply systems: on-base supply systems, off-base community supply systems, and off-base private wells. These supply systems were or could be impacted by one or more of the five groundwater plumes found at and northeast of Mather, including: AC&W groundwater plume, Main Base and SAC Industrial Area groundwater plume, Site 7 groundwater plume, Northeast groundwater plume, and Perchlorate groundwater plume (Appendix A, Figures 2 and 5).

ATSDR evaluated potential past, current, and future exposures for each population using the three different water supply systems and determined that, although people on and off base were exposed to groundwater contamination in the past, the amount of exposure was considered too low to result in health effects. ATSDR concluded that contaminants in groundwater pose no apparent public health hazards. This conclusion is based on information provided in Table 2, which lists the populations that may contact contaminants in the three water supply systems, the years when the water supply systems have operated, the plumes that may have impacted the water supply systems, and the actions taken to prevent exposures. The following text provides more detail about groundwater at and around Mather, the three water supply systems, the five groundwater plumes, and the assumptions used to draw conclusions about potential public health hazards.

Table 2: Summary of Exposures to Contaminants in Drinking Water

Potentially Exposed Populations	Water Supply Systems Used by Each Population	Time When Water Supply System Was Used	Groundwater Plume Potentially Impacting the Water Supply System	Date When Contamination Was First Detected	Detected Contaminants	Date When Exposure to Detected Contaminants Ceased	Actions Taken to Prevent Exposures
On-Base Water Supply Systems
On-base workers	AC&W supply well	Past (before 1979)	AC&W	1979 a	Trichlorethylene (TCE)	1979	The well was closed in 1979 and sealed in 1990.
	Main base supply system	Past, current, and future	Northeast and Perchlorate	1996 b	Tetrachloroethylene (PCE) and perchlorate	1997	Contaminated wells in this system were closed or only serve as standby or emergency supply wells. Standby wells are sampled regularly to ensure the safety of the water supply.
	Family housing supply system	Past, current, and future	None	Not applicable	None	Not applicable	Wells are sampled regularly to ensure the safety of the water supply.
On-base residents	Family housing supply system	Past, current, and future	None	Not applicable	None	Not applicable	Wells are sampled regularly to ensure the safety of the water supply.
Off-Base Community Water Supply Systems
Off-base residents and workers west of Mather who are connected to community water supplies	Citizens Utilities Company of California supply system	Past, current, and future	Main Base and SAC Industrial Area	1996 (Moonbeam well) and 1997 (Mars well) c	TCE and carbon tetrachloride	1996 (Moonbeam well) and 1997 (Mars Well)	A treatment system was installed at the Moonbeam well and the Mars well no longer serves as a supply well. Wells are sampled regularly to ensure the safety of the water supply.
	Sacramento County supply system	Past, current, and future	Main Base and SAC Industrial Area	1996 c	Carbon tetrachloride	1996	A treatment system was installed and wells are sampled regularly to ensure the safety of the water supply.
Off-Base Private Wells
Off-base residents and workers west of Mather with private wells	Private wells	Past (before 1984)	Main Base and SAC Industrial Area	1979 a	Benzene, carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1-dichloroethylene, 1,1-dichloropropane, TCE, and PCE	1984	Homes and businesses were connected to community supply systems. Private wells may be used for irrigation.
Off-base residents and workers south of Mather with private wells	Private wells	Past, current, and future	None	Not applicable	None	Not applicable	Monitoring wells and private wells are sampled regularly to ensure the safety of the water supply.

PCE	Tetrachloroethylene
TCE	Trichloroethyelene

^a The date when contaminants were first detected was also when the wells were first sampled. Exposures, therefore, could have been occurring for an unknown period before the first sampling event.
^b Water supply wells were monitored for VOCs before the date when PCE was first detected. Exposures to PCE , therefore, could have occurred only during the period between quarterly monitoring events. The date when perchlorate was first detected was also the date when the analysis for perchlorate was improved to meet the perchlorate action level. Exposures to perchlorate, therefore, could have been occurring for an unknown period before the improved analytical method was used.
^c Water supply wells were monitored prior to the date when contaminants were first detected above comparison values. Exposures to concentrations above comparison values, therefore, could have occurred only during the period between quarterly monitoring events.

Hydrogeology

Groundwater at Mather is first encountered approximately 85 feet below ground surface (bgs) and continues to at least 1,300 feet bgs. Aquifers in the region tend to dip gently and flow to the southwest. Aquifers consist of permeable unconsolidated sediments of fluvial and alluvial origin (meaning from past river flow). Two aquifers, located in soil in the Laguna Formation and the Mehrten Formation, underlie Mather.

The aquifer within the Laguna Formation is described as four hydrogeologic units (Units A through D) and extends from approximately 85 to between 220 and 430 feet bgs. Unit A, which contains the water table aquifer beneath the western portion of Mather, is the uppermost aquifer unit. In the eastern portion of Mather, the water table aquifer may be found in the deeper Units B or C. Unit B directly underlies Unit A and is composed of coarse sands and gravels, which means that groundwater can flow freely in the aquifer. Unit B, therefore, is important for groundwater transport of contamination. Unit C, which consists of a layer of silt and clay, is found underlying Unit B. The silt and clay in Unit C restrict groundwater movement and effectively acts as a barrier to impede groundwater and contaminant movement downward to the next hydrogeologic unit, Unit D. Unit D is located at the bottom of the Laguna Formation and at the top of the Mehrten Formation. Unit D is made up of silt and clay with deposits of coarser soils that act like confined aquifers (Montgomery-Watson 1999a).

The second aquifer is found within the Mehrten Formation. This aquifer underlies the Unit D portion of the Laguna Formation aquifer and is found at depths below 220 to 430 feet bgs. The Mehrten Formation aquifer is considered an excellent source of groundwater and is the primary source of potable water on and west of Mather. Migration of base contamination into this aquifer is limited by the silt and clay of Units C and D of the Laguna Formation (Montgomery-Watson 1999a).

Groundwater is recharged by infiltration of rainfall, stream flow, and irrigation in upland areas east of the base. Other local sources of groundwater recharge may include Morrison Creek, Mather Lake, precipitation captured in the former sewage treatment oxidation ponds (IRP site ST81), settling ponds at nearby quarries, storm and sanitary sewer lines, and possible leaks from Folsom South Canal (Montgomery Watson 1999a).

Groundwater Use and Drinking Water Supplies

Groundwater from the Mehrten Formation serves as the primary source of drinking water for most people in the area of Mather Air Force Base. People obtain groundwater pumped from on-base supply systems, off-base community supply systems, or off-base private wells.

On-base Supply Systems

The on-base water supply is or has been provided by three supply systems: the AC&W, family housing, and main base supply systems. In addition to these systems, individual wells served the golf course and a former military dog training facility. The wells serving the golf course may have provided potable water, but these wells have not been used for potable water for several decades. The well at the dog training facility was maintained as a potable supply well by the USAF, but has been inactive since the base closed in 1993. These wells are not located within areas identified as having groundwater contamination (Hughes 2000).

The AC&W water supply was composed of a single well that served workers at the AC&W facility. This well pumped groundwater from below 200 feet bgs, which means this well likely pumps water from Unit D of the Laguna Formation aquifer or the Mehrten Formation aquifer. The USAF stopped using this well in 1979 when contamination was found in the water, as described in the following section, and the wellhead was sealed in 1990 to prevent future use (CH2MHill 1982; USAF 1993; Hughes 1999).

The family housing supply system is an active supply system composed of five wells located in the former on-base housing area. These wells pump groundwater from a depth 250 to 560 bgs, which means they likely pump groundwater from the aquifer in the Mehrten Formation. These wells supplied water to the housing area when it was occupied and currently supply water to all of Mather and an off-base area east of Mather. This system will also be used to supply water to new housing units constructed at the Mather housing area as part of the base redevelopment. The five wells are pumped into a central treatment facility, which removes iron and manganese, before storage in an elevated 500,000 gallon storage tank. No contamination has been found in these wells since quarterly monitoring for VOCs began in 1993. Wells in the on-base family housing supply system were conveyed to Sacramento County in 1999. Therefore, Sacramento County monitors wells for contamination, including monitoring for VOCs every three years. Monthly monitoring for perchlorate, which has not been detected, began in August 1997 (AFBCA 1998; Hughes 2000; McDonald 2000; Taylor 1999; Fricke 2000).

The main base supply system served the operations areas of the base and is composed of four wells. These wells pump groundwater from a depth of 250 to 580 feet bgs, which means they likely pump groundwater from the aquifer in the Mehrten Formation. One well (main base well 2), however, pumps some groundwater from above 250 feet, which means this well may be drawing in groundwater from Unit D of the Laguna Formation aquifer. Historically, the USAF automatically rotated wells as the lead well and pumped water to a 650,000 gallon storage reservoir. Water from the reservoir was then distributed as needed. An additional 300,000 gallon storage tank is located within the distribution system. For a period from December 1994 through June 1997, the 650,000 gallon reservoir was taken out of service for repair. During that time, the wells were manually rotated and pumped directly into the distribution system (AFBCA, 1998). In March 1997, perchlorate contamination (discussed further in the following section), was found in two of the main base wells and the USAF closed these wells. To account for the loss of this water supply, the family housing supply system was connected to the main base distribution system and a 1,000,000 gallon storage tank was built (AFBCA 1998; ATSDR 1998). Wells in the main base supply system were conveyed to Sacramento County in 1999. Therefore, Sacramento County monitors wells for contamination, including monitoring for VOCs every three years. Monthly monitoring for perchlorate began in August 1997; none has been detected (Hughes 2000; Fricke 2000).

Off-base Community Supply Systems

Off-base community supply systems are operated by the Citizens Utilities Company of California (CUCC) and Sacramento County.

The CUCC Suburban supply system pumps groundwater from a series of wells located west and north of Mather to supply water to homes and businesses west and north of Mather (Table 3). Water from each well, except the Moonbeam well, is pumped directly into the distribution system. The Moonbeam well was closed because of contamination in 1996, and was reactivated in 1997 with a treatment system to remove contamination prior to distribution. To operate properly, the Moonbeam well must continuously pump water through the treatment system and into the distribution system, therefore, the Moonbeam wells is considered one of the primary supply wells. Another primary supply well is the Oaken Bucket well, which has not had any detected contaminants. These two wells may be the only wells contributing to the local distribution system during low demand periods. Operation of other wells is triggered when water pressure within the system drops. The Explorer well historically served as a primary well, but was closed in 1994 because of the potential for Mather contaminants to enter the water supply.

Sacramento County operates two wells to supply water to their office complex located on Branch Center Drive west of Mather. These wells were closed in October 1996 because of contamination, but were reopened in September 1997 with a treatment system to remove contamination before distribution. CUCC supplied water to the Sacramento building complex when the county wells were closed (AFBCA 1998; Taylor 1999).

Table 3: Description of Community Supply Wells

Well Name	Description
Citizens Utilities Company of California (CUCC) Wells
Moonbeam	In 1996, carbon tetrachloride (0.4 parts per billion [ppb]) was detected and CUCC ceased operation of this well. A water treatment system composed of granular activated carbon filtration was installed in April 1997 and the well resumed operation. Water from this well is tested regularly to ensure protection of public health.
Explorer	In 1994, CUCC opted to stop pumping from the Explorer Drive well due to its proximity of the Main Base and SAC Industrial Area groundwater plume. The Explorer well was destroyed in October 1998.
Mars	CUCC stopped using the Mars well when trichloroethylene (TCE) (5 ppb) was detected in a single sample in July 1997. TCE and tetrachloroethylene have been detected below comparison values since September 1997. A single detected of carbon tetrachloride (0.57 ppb) slightly above its comparison value (0.3 ppb) was found in September 1999. This well is available for use as fire protection, but is not currently operating as a drinking water supply well.
Oaken Bucket	The Oaken Bucket well is located near the Main Base groundwater plume and therefore is monitored carefully. No contamination has been detected in this well according to monitoring data from 1989 to present.
Nut Plains Drive	The Nut Plains Drive well is monitored closely because of its proximity to the Main Base and SAC Industrial Area groundwater plume. No contamination has been detected in this well according to monitoring data from 1993 to present.
Gould Way	No contamination has been detected in the Gould Way well according to monitoring from 1994 to present. The Gould Way well is located north of the Main Base and SAC Industrial Area groundwater plume.
Rosemont Area	The Rosemont Area includes several wells located west of Mather, proximate to the Main Base and SAC Industrial Area groundwater plume. No contaminants have been detected in these wells above comparison values.
Sacramento County Wells
Juvenile 1 and 2	In 1996, Sacramento County closed Juvenile 1 and 2 wells because of detection of carbon tetrachloride (0.54 ppb). A water treatment system composed of granular activated carbon filtration was installed in September 1997 and the wells resumed operation. Water from this well is tested regularly to ensure protection of public health.

Sources: AFBCA 1998; Gutierrez-Palmenberg, Inc. 1999

CUCC	Citizens Utilities Company of California
ppb	parts per billion
TCE	trichloroethylene

Off-base Private Wells

A small number of homes and businesses west and south of Mather use private wells for drinking water. Private wells located west of Mather and impacted by Mather contamination have been closed or are used for non-potable purposes only, such as irrigation. Some active private wells south of Mather are used as drinking water supplies. The USAF compiled an inventory of these private wells and monitors them, as well as the known areas of groundwater contamination, to confirm that off-base private wells are not impacted by Mather contamination (AFBCA 1998).

Nature and Extent of Contamination

During site investigations and sampling, the USAF discovered four groundwater plumes containing VOCs originating at Mather: the AC&W plume, the Main Base and SAC Industrial Area plume, the Site 7 plume, and the Northeast plume. The Main Base and SAC Industrial Area and the Site 7 plumes have both migrated beyond Mather's boundaries. A fifth groundwater plume--the perchlorate groundwater plume--originates at facilities upgradient of Mather, but has migrated beneath base boundaries. Potential sources include Aerojet and Cordova Chemical to the northeast, a site east of the base formerly owned by McDonnell-Douglas, and a site northeast of the base formerly owned by Purity Oil Company (Gutierrez-Palmenberg, Inc. 1997). Recent investigations indicate that the facility formerly owned and operated by McDonnell-Douglas is the most likely source (Fricke 2000). These five plumes are discussed in greater detail below.

AC&W Groundwater Plume

The AC&W site, located in the central portion of the base, supported a radar station operated by the AC&W Squadron and the Federal Aviation Administration. From 1958 to 1966, an estimated 1,200 gallons of TCE and 1,400 gallons of transformer oil were used at the AC&W site. Waste TCE was reportedly disposed of down a pipe at this site. Although investigations have not located this pipe, a TCE plume was identified in the upper 60 feet of the water table portion of the Laguna Formation aquifer, which is found in the hydrogeologic Unit C in this area. Sampling during the feasibility study found TCE at a maximum concentration of 800 parts per billion (ppb) (USAF 1993). Ongoing monitoring conducted from 1996 through 1999 has detected only TCE (to 200 ppb) and tetrachloroethylene (PCE) (to 10 ppb) above comparison values (Montgomery Watson 1997, 1998a, 1999a, 1999b).

This plume extends approximately 1 mile from the AC&W site to the southwest and underlies a small portion of the on-base housing area (Appendix A, Figures 2 and 5). A ROD addressing AC&W groundwater plume remediation was signed in December 1993. A pump and treat system was installed at the site and began operation in January 1995 (AFBCA 1999; USAF 1993, 1999).

Only the former AC&W site supply well has been impacted by this plume. Use of this well ceased in October 1979 and the well was sealed in 1990. The active wells in the on-base family housing supply system are located in the path of the AC&W plume. These wells, however, have not been impacted nor are they expected to be impacted by this plume because they draw water from Unit D of the Laguna Formation aquifer and the Mehrten Formation aquifer. The plume is located in Units B and C of the Laguna Formation aquifer and is prevented from migrating by the treatment system and extraction wells operated by the USAF. Wells in the on-base family housing supply system were conveyed to Sacramento County in 1999. Therefore, Sacramento County monitors wells for contamination. Monitoring includes sampling for perchlorate monthly and VOCs every three years (AFBCA 1999; Hughes 1999, 2000).

Main Base and SAC Industrial Area Groundwater Plume

The Main Base and SAC Industrial Area groundwater plume consists of several plumes commingled in Units A and B of the Laguna Formation aquifer underlying the northwestern portion of the base. Between 1918 and 1993, industrial and commercial operations conducted in the northwestern portion of the base generated plumes of VOC contamination in the underlying aquifer (USAF 1996). This plume was first identified in 1979 by the Central Valley Regional Water Control Board when private well sampling detected contamination; the reason private well sampling began in 1979 is unknown (AFBCA 1998, 1999; USAF 1994b).

Ongoing investigations of the groundwater contamination have detected VOCs in excess of drinking water standards. Sampling of groundwater monitoring wells conducted from 1996 through 1999 detected benzene (to 5 ppb), carbon tetrachloride (to 12 ppb), chloromethane (to 6.8 ppb), 1,2-dichloroethane (to 6.7 ppb), 1,1-dichloroethylene (180 ppb), methylene chloride (to 41 ppb), PCE (to 1,100 ppb), TCE (to 1,100 ppb), and lead (to 47.4 ppb) all above USEPA's MCLs. Most of these contaminants were found at their maximum concentrations in the water table (Unit A) and Unit B portions of the Laguna Formation aquifer (Montgomery Watson 1997, 1998a, 1999a, 1999b).

The Main Base and SAC Industrial Area plume currently extends off base approximately 1 mile to the west. The ROD signed in June 1996 selected groundwater treatment as the most appropriate remedial action. Treatment consists of operating several groundwater extraction wells and air strippers with reinjection of the treated water underground. The extraction system will be installed in four phases. Phase I treats on-base hot spots and began operation in April 1999. Phase II treats off-base hot spots and Phase III augments Phase I capture zones. Phase II and III began operation December 1999. Phase IV will augment off-base capture of groundwater contamination. Funding for Phase IV activities has been requested for implementation in 2001 (AFBCA 1999; USAF 1996, 2000; Hughes 2000).

Contaminants from the Main Base and SAC Industrial Area plume have been detected in off-base community supply systems and off-base private wells. Use of wells that have been impacted by this plume has ceased.

Site 7 Groundwater Plume

The Site 7 groundwater plume originates at a waste disposal pit site in the southwestern portion of the base (IRP site WP07). WP07 was used as a disposal pit for petroleum, oil, and lubricant (POL) wastes and other wastes that may have included solvents, waste paint, and thinners. At least one load of transformer oil disposed of at WP07 contained polychlorinated biphenyls (PCBs). Initial groundwater investigations at WP07 found TCE (to 180 ppb) and PCE (to 35 ppb) above drinking water standards in groundwater. Beginning in July 1996, vinyl chloride (to 19 ppb) has also been detected in monitoring wells (AFBCA, 1999). In addition to vinyl chloride, 1,2-dichloroethane (to 14 ppb), 1,1-dichloroethylene (to 3.2 ppb), PCE (to 21 ppb), TCE (to 130 ppb) have also been found in groundwater monitoring well samples collected from 1996 through 1999. The maximum detected concentrations of most of these contaminants were found in Unit B of the Laguna Formation aquifer; TCE and lead were found in Unit D of the Laguna Formation aquifer, but at concentrations below comparison values (Montgomery Watson 1997, 1998a, 1999a, 1999b).

The Site 7 groundwater plume currently extends approximately 1 mile off base to the southwest . The ROD signed in June 1996 called for installation of a groundwater treatment system consisting of extraction wells, an air stripper, and reinjection wells. Remediation began in December 1998 with one extraction well. Additional extraction wells are planned to be installed in 2000 after gravel mining to the south is complete (AFBCA 1999; USAF 1996, 2000).

The Site 7 groundwater plume has not impacted on-base or off-base supply wells. Several private wells are located along Jackson Road downgradient of the Site 7 groundwater plume. VOCs were detected in one well sampled in May 1996, however, the reported detections are believed to be erroneous. Sampling of the same well prior to and after May 1996 has found no VOCs. The USAF regularly monitors wells downgradient of the Site 7 groundwater plume for VOCs to ensure that the wells remain free of contaminants (AFBCA 1998).

Northeast Groundwater Plume

The Northeast groundwater plume apparently originates from sources within IRP sites Landfill 4 (LF04) and 5 (LF05). LF04 and LF05 were used for base waste disposal and may have received POL waste, solvents, waste paint and thinners, discarded pesticide containers, and hospital wastes. The Northeast groundwater plume flows west-southwest and converges with the Main Base and SAC Industrial Area plume in the north-central portion of the base. During investigations of groundwater at these landfills conducted before 1994, the USAF found cis-1,2-dichloroethylene (to 35 ppb), PCE (to 35 ppb), TCE (to 7.5 ppb), benzene (to 1.3 ppb), and lead (to 85 ppb) above drinking water standards in groundwater monitoring wells (USAF, 1995). Monitoring data from 1996 through 1999 reports that carbon tetrachloride (to 4.7 ppb), 1,2-dichloroethane (to 1.1 ppb), methylene chloride (to 14 ppb), PCE (to 17 ppb), TCE (to 8.5 ppb), 1,1,2,2-tetrachloroethane (to 0.56 ppb), and vanadium (to 30.1 ppb) have been found above drinking water standards in groundwater. The maximum detected concentrations of these contaminants were found in the water table (Unit A) and Unit B portions of the Laguna Formation (Montgomery Watson 1997, 1998a, 1999a, 1999b).

The portion of the Northeast groundwater plume that has not mingled with the Main Base and SAC Industrial Area is mostly contained within base boundaries. Contaminants within this plume may extend a short distance off base to the north at concentrations below drinking water standards. This plume may also have impacted on-base wells, which are currently inactive (main base well 1) or on emergency back-up status (main base well 3), within the main base supply system. These two wells, however, pump groundwater from a depth of 250 to 510 feet bgs, which means they likely pump groundwater from the aquifer in the Mehrten Formation. Long-term groundwater monitoring and institutional controls were selected as the most appropriate remedial action in the ROD signed in June 1996. These remedial actions were selected because contaminant concentrations only slightly exceed enforceable drinking water standards, and contaminant concentrations are expected to decrease over time. Actions were implemented at LF04 and LF05 to control the source of the contamination originating from these areas. These actions included excavating materials from LF05 and adding this material to LF04 and capping LF04 to prevent rainwater infiltration (AFBCA 1999; USAF 1996; Hughes 2000).

Perchlorate Groundwater Plume

Mather is not known to have used perchlorate, however, this contaminant has been found in groundwater beneath the base. Perchlorate likely entered groundwater as ammonium perchlorate, a main component of solid rocket fuel. Potential sources include Aerojet and Cordova Chemical to the northeast, a site east of the base formerly owned by McDonnell-Douglas, and a site northeast of the base formerly owned by Purity Oil Company (Gutierrez-Palmenberg, Inc. 1997). Recent investigations indicate that the perchlorate plume originates from the former aerospace facility owned and operated by McDonnell-Douglas and later sold to Aerojet (Fricke 2000).

In March 1997, perchlorate was found in three of the four wells within the main base supply system at 14, 120, and 67 ppb (wells 3, 2, and 1, respectively). This was the first time perchlorate was detected in on-base drinking water supply wells. Before 1997, the analytical methods used could only detect perchlorate in water samples at concentrations greater than 400 ppb. In 1997, CDHS established a provisional action level of 18 ppb for perchlorate in drinking water. Resampling of main base well 3 found perchlorate at up to 19 ppb. The wells within the family housing supply system are free of perchlorate contamination (ATSDR 1998; Spath 1997).

In March 1997, the USAF closed the main base wells 1 and 2 because of detected perchlorate concentrations. At that time no action level was available for perchlorate. Main base well 3 was placed on backup status in March 1997 and has only been used periodically since then (ATSDR 1998). Main base well 4 is free of contamination and is used as a backup well. Appendix D provides detailed information about the toxicology and regulatory standards for perchlorate.

An Engineering Evaluation/Cost Analysis was completed in August 2000 and a ROD is scheduled for completion in spring 2001. These documents address treatment of perchlorate in the groundwater. Extraction and biological degradation of perchlorate-contaminated water is proposed as the most appropriate remedy (Fricke 2000).

Evaluation of Potential Public Health Hazards

Groundwater, primarily pumped from the aquifer in the Mehrten Formation, serves as the primary drinking water source for Mather and the surrounding areas. In evaluating potential public health hazards from contaminants in groundwater, ATSDR identified three types of water supply systems: on-base supply systems, off-base community supply systems, and off-base private wells. ATSDR evaluated exposures to workers and residents that may use these systems as their drinking water supply. Overall, ATSDR concluded that use of these water supply systems is unlikely to result in adverse health effects and, therefore, poses no apparent public health hazards. Past exposures were below levels of health concern and the USAF and community water suppliers have completed measures, as described below, to prevent current and future exposures.

The following text provides information about each of the water supply systems, the potentially exposed populations, and potential exposure parameters used to reach the conclusion of no apparent public health hazards. Table 4 summarizes the maximum detected contaminant concentrations found in each water supply system. Appendix A (Figures 4 and 6) and Appendix C provide more detail about ATSDR's exposure evaluation process.

Table 4: Contaminants Detected Above Comparison Values in Drinking Water Supply Wells

Well	Contaminant	Plume Impacting the Well	Maximum Detected Concentration* (ppb)	Comparison Values
				Value (ppb)	Source
On-Base Supply Wells
AC&W Supply Well	Trichloroethylene (TCE)	AC&W plume	112	3	CREG
Main Base Well 1	Tetrachloroethylene (PCE)	Main Base/SAC or Northeast	0.95	0.7	CREG
	Perchlorate	Perchlorate	67	18	CDHS
Main Base Well 2	Perchlorate	Perchlorate	120	18	CDHS
Main Base Well 3	PCE	Main Base/SAC or Northeast	0.97	0.7	CREG
Off-Base Community Supply Wells
Moonbeam	Carbon tetrachloride	Main Base/SAC	0.4	0.3	CREG
Mars	TCE	Main Base/SAC	5	3	CREG
Juvenile 1 and 2	Carbon tetrachloride	Main Base/SAC	0.54	0.3	CREG
Off-Base Private Wells
Off-base private wells	Benzene	Main Base/SAC	2	1	CREG
	Carbon tetrachloride	Main Base/SAC	10	0.3	CREG
	Chloroform	Main Base/SAC	10	6	CREG
	1,2-Dichloroethane	Main Base/SAC	2.9	0.4	CREG
	1,1-Dichloroethylene	Main Base/SAC	9	0.06	CREG
	1,1-Dichloropropane	Main Base/SAC	2.5	0.16	RBC
	TCE	Main Base/SAC	44	3	CREG
	PCE	Main Base/SAC	17	0.7	CREG

Sources: AFBCA 1998; ATSDR 1998; Gutierrez-Palmenberg, Inc. 1999; Houston 1985; Smith 1993a, 1993b, 1994; USAF 1999

CDHS	California Department of Health Services Action Level
CREG	Cancer risk evaluation guide
ppb	parts per billion
PCE	Tetrachloroethylene
RBC	U.S. Environmental Protection Agency Region III risk-based concentration
TCE	Trichloroethylene

* The listed concentrations are the maximum detected concentrations found when the water supply wells were active and used for drinking water without treatment to remove contaminants.

On-base Water Supply Systems

Mather has historically provided on-base workers and on-base residents with water from three different on-base supply systems, as described in the earlier "Groundwater Use and Drinking Water Supplies" section of this PHA. These systems include the AC&W supply well, the family housing supply system, and the main base supply system.

AC&W Supply Well

The AC&W supply well provided drinking water to on-base workers at the AC&W site until 1979. Between 1979 and 1980, TCE from the AC&W groundwater plume was found above its comparison values in 15 of 19 samples collected from the facility's water supply well (concentrations ranged from 3.6 to 112 ppb). Use of this well ceased in 1979 and the well was sealed in 1990 (CH2MHill 1982; Hughes 1999).

ATSDR evaluated past exposures to on-base workers at this site. Current and future exposures were not considered because the well has been sealed and can no longer be used to supply water. Using conservative exposure assumptions, ATSDR concluded that past exposures to TCE in the AC&W well posed no apparent public health hazards.

The conservative assumptions used by ATSDR were chosen to overestimate the actual amount of contaminants to which on-base workers were exposed. ATSDR assumed that on-base workers drank 1 liter of water from this well for 250 workdays each year (accounts for a 5 day work week for 50 weeks per year). ATSDR also assumed that workers were employed at the site for 20 years (the period from 1958 when TCE use began at the base until 1979 when the well was closed). Each liter of water consumed by the on-base worker was also assumed to contain the maximum detected TCE concentration (112 ppb). Actual TCE concentrations ranged from 3.6 to 112 ppb. We do not know for certain when TCE first entered the well or what the highest TCE levels were in the well before sampling began in 1979. What we know about plume characteristics, groundwater flow, and supply well location, suggests, however, that it is unlikely that the portion of the plume with the highest TCE concentrations passed by the supply wells before 1979. Based on this information, we expect that historical TCE concentrations were lower than the maximum detected value of 112 ppb reached in 1979.

Family Housing Supply System

The family housing supply system is an active supply system composed of five wells located in the former on-base housing area. These wells supplied water to the housing area when it was occupied and currently supply water to all of Mather and an off-base area east of Mather. This system will also be used to supply water to new housing areas constructed at Mather as part of the base redevelopment. No contamination has been detected in these wells since quarterly monitoring for VOCs began in 1993 and monthly monitoring for perchlorate began in August 1997. Prior to 1993, the wells were sampled based on state regulatory requirements. Sacramento County currently operates and monitors this water supply system. Wells are sampled for VOCs every three years and perchlorate monthly.

ATSDR concluded that past, current, and future use of wells within the family housing area supply system posed no public health hazards. No contaminants have been detected in this supply system. Groundwater monitoring and remediation is underway to prevent future exposure to groundwater contamination that may pose a potential public health hazard.

Main Base Supply System

The main base supply system is composed of four wells which historically provided water to the operations area north of the airfield. Two of the wells in the main base supply system were impacted to a limited extent by PCE from the Northeast groundwater plumes. PCE was found slightly above its comparison value (0.7 ppb) in one sample from well 1 (0.95 ppb) collected in October 1996 and one sample from well 3 (0.97 ppb) collected in February 1997. Monitoring before these detections and since has not found any PCE above its comparison values. In addition to PCE, three wells in the main base supply system have been impacted by the perchlorate plume that originates off base to the northeast. Sampling in March 1997 found perchlorate in two of the four supply wells (to 120 ppb) above the CDHS established action level of 18 ppb. As a result, wells 1 and 2 were permanently closed in 1997 and wells 3 and 4 are used as backup wells (AFBCA 1998; ATSDR 1998).

ATSDR evaluated past exposures to on-base workers, residents in the transitional housing units, and patients at the on-base hospital. Using conservative exposure assumptions, ATSDR concluded that past exposures to PCE and perchlorate in the main base supply wells were too low to produce adverse health effects. Wells contaminated with PCE and perchlorate are closed or used only as backup supply wells. Sacramento County currently operates and monitors this water supply system. Wells are sampled for VOCs every three years and perchlorate monthly.

The conservative assumptions used by ATSDR were selected to overestimate the actual amount of contaminants to which people were exposed. Adults were assumed to drink 2 liters and children 1 liter of water from the supply system each day they were present at the base. ATSDR assumed workers were at the base 5 days a week, 50 weeks a year, for a period of 30 years. Families, both adults and children, in the transitional housing were assumed to live in the facility for 1.25 years, which is the maximum time the facility was open before the contaminated wells were closed. Both adult and children patients were assumed to stay in the hospital for 14 days. Each liter of water consumed from the main base supply system was also assumed to contain the maximum detected PCE (0.97 ppb) and perchlorate (120 ppb) concentrations. Actual PCE concentrations were likely much lower, regular monitoring of the wells before and after the PCE was detected found no contamination. We do not know for certain when perchlorate first entered the main base supply wells or what the highest levels were before 1997. What we know about plume characteristics, groundwater flow, and supply well location, suggests, however, that it is unlikely that the portion of the plume with the highest perchlorate concentrations passed by the supply wells before 1997.

Off-base Community Water Supply Systems

Two community water suppliers, CUCC and Sacramento County, provide drinking water to off-base residents. CUCC operates seven wells and Sacramento County operates two wells that have been impacted, or have the potential to be impacted by contamination in the Main Base and SAC Industrial Area groundwater plumes. Only carbon tetrachloride and TCE have been detected in off-base community wells above comparison values. Carbon tetrachloride was detected above its comparison value (0.3 ppb) in the CUCC Moonbeam well (0.4 ppb) and Sacramento County Juvenile wells 1 and 2 (0.54 ppb) while these wells were active supply wells. TCE was detected above its comparison value (3 ppb) in only one sample from the CUCC Mars well (5 ppb).

ATSDR evaluated exposures to off-base residents receiving water from community supply systems. Even using conservative exposure assumptions, ATSDR concluded that past exposures to carbon tetrachloride and TCE in off-base community supply wells posed no apparent public health hazards. Worker exposures were not evaluated separately because workers are exposed less frequently than residents. Contaminant levels below health concerns for residents, therefore, would be below health concerns for workers as well. To prevent current and future exposures, contaminated wells have been closed or treatment systems have been installed. Active supply wells are monitored quarterly to ensure that contaminants remain below regulatory standards set by USEPA and the state. Quarterly monitoring includes sampling wells for VOCs. Perchlorate sampling is proposed, but has not been regularly conducted to date (McDonald 2000).

To evaluate whether health hazards were associated with past exposures from use of off-base community supply systems, ATSDR used conservative assumptions to estimate the potential doses for off-base residents. Adults were assumed to drink 2 liters of water every day for a 30 year period. Children were assumed to drink 1 liter of water every day for 6 years, which accounts for ages 0 to 6 when children are most sensitive. Each liter of water was considered to contain the maximum contaminant concentrations detected before wells were closed or water was treated prior to distribution (0.54 ppb carbon tetrachloride and 5 ppb TCE). Actual concentrations were likely much lower; TCE in the Mars well and carbon tetrachloride in the Moonbeam well were only detected once during monitoring. Carbon tetrachloride in Juvenile wells 1 and 2 was detected in seven of the eight monitoring samples collected from these wells, but only twice did concentrations exceed the comparison value.

Off-base Private Water Supply Well Users

In the past, homes and businesses west of Mather operated private wells for their water supply. Sampling of private wells initiated in 1979 identified contamination in some of these private wells. Contaminants detected above comparison values in these private wells between 1979 and 1984 included benzene (to 2 ppb), carbon tetrachloride (to 12 ppb), chloroform (to 10 ppb), 1,2-dichloroethane (to 2.9 ppb), 1,1-dichloropropane (to 2.5 ppb), and PCE (to 18.4 ppb). In 1984, when it was suspected that contamination originated from the Main Base and SAC Industrial Area groundwater plume, the USAF began providing people with bottled water. All homes and businesses were connected to public water supplies in 1987, however, the USAF continues to monitor the closed private wells to track the plume migration. Private wells are also located to the south of Mather, but no contamination has been identified in these wells. The USAF monitors these wells to ensure that they remain free of contamination (AFBCA 1998, 1999; Gutierrez-Palmenberg, Inc. 1999; Houston 1985; Smith 1993a, 1993b, 1994).

ATSDR evaluated past exposures to off-base residents drinking from private wells. Current and future exposures are not occurring because homes and businesses have been connected to the municipal water supply and private wells are no longer used for drinking. Using conservative exposure assumptions, ATSDR concluded that past exposures to contaminants in off-base private wells posed no apparent public health hazards. Worker exposures were not evaluated separately because workers are exposed less frequently than residents. Contaminant levels below health concerns for residents, therefore, would be below health concerns for workers as well.

The conservative assumptions used by ATSDR were chosen to overestimate the actual amount of contaminants to which off-base residents were exposed. Adults were assumed to drink 2 liters of water every day for a 30 year period. Children were assumed to drink 1 liter of water every day for 6 years, which accounts for ages 0 to 6 when children are most sensitive. Each liter of water was considered to contain the maximum detected contaminant concentrations, as listed above.

We do not know for certain when these contaminants first entered private wells or what the levels were in the well before sampling began in 1979. What we know about plume characteristics, groundwater flow, and supply well location, suggests, however, that it is unlikely that the portion of the plume with the highest contaminant concentrations passed through the residential areas before 1979. ATSDR also assumed that people continued to use private wells for drinking water until 1984, when bottled water was provided.

Exposure to Contaminants in Surface Soil

Past activities and operations at Mather resulted in areas of surface soil contamination throughout the base. Based on land uses, ATSDR identified three populations that may come into contact with surface soil contamination at Mather: on-base workers, on-base residents, and recreational users. On-base workers may be exposed to surface soil contamination throughout the site. On-base residents and recreational users may be exposed to surface soil contamination in areas near their homes or recreational areas, such as the golf course and skeet and trap ranges.

ATSDR evaluated potential past, current, and future exposures for on-base workers, on-base residents, and recreational users who may contact contaminated soil and determined that the amount of exposure was considered too low to result in adverse health effects. ATSDR concluded that contaminants in surface soil pose no apparent public health hazard. Past exposures to on-base workers, on-base residents, and recreational users would have been infrequent and of short duration. The USAF is conducting remedial actions to prevent current and future exposures to contaminants in surface soil. The following text provides more information about surface soil contamination at Mather, land use and Mather, and assumptions used to draw conclusions about potential public health hazards.

Nature and Extent of Contamination

Surface soil sampling at sites located throughout Mather has found PAHs, Aroclor-1260, pesticides, arsenic, cadmium, chromium, iron, and lead at concentrations above soil comparison values. Oil and grease, diesel, and gasoline have also been detected, however, no comparison values have been established for these substances (USAF 1996). Most of the surface soil contamination was found at sites located in the operational areas of the base, near the runways, or in other areas with restricted access.

Nine IRP sites are located in areas frequented by on-base residents or on-base recreational users. Two sites (IRP sites ST28 and ST34) containing releases of petroleum products from USTs to subsurface soil are located within the on-base military housing area. No surface soil contamination was found at either site during investigations (USAF 1996). Two sites (SD14 and ST42) were located near the transitional housing units, however, no contamination requiring remediation was found at theses sites. ST42 consisted of a UST, which was removed in 1988, before the housing units were opened (USAF 1996). The other five sites are located near or within recreational areas at Mather. IRP sites SD80 and MY82 are located near the golf course in the eastern portion of the base. Only arsenic (9.8 parts per million [ppm]) was found above its comparison value in surface soil samples from SD80. No contaminants were found above comparison values in surface soil samples from MY82 (AFBCA 1997; Montgomery Watson 1998b). IRP sites FR86, OT87, and OT89 consist of a former firing range and two skeet and trap ranges that were used for recreational activities while Mather was active. Only lead (to 1,660 ppm) was found above its comparison value in surface soil samples from FR86 and OT89. Surface soil sampling at OT87 found benzo(a)pyrene (to 3.7 ppm), benzo(b)fluoranthene (to 92.8 ppb), dibenz(a,h)anthracene (to 0.97 ppm), indeno(1,2,3-c,d)pyrene (to 2.5 ppm), and lead (to 1,330 ppm) above comparison values. Table 5 summarizes the contaminants detected above their comparison values (AFBCA 1997; IT Corporation 1997; Wong 1999).

Table 5: Summary of Surface Soil Sampling Data That Exceed Comparison Values

Chemical	Maximum Detected Concentration (ppm)	Comparison Value (ppm)	Source
SD80
Arsenic	9.8	0.5	CREG
FR86 and OT89
Lead	1,660	400	SSL
OT87
Benzo(a)pyrene	3.7	0.1	CREG
Benzo(b)fluoranthene	92.8	0.87	RBC
Dibenz(a,h)anthracene	0.97	0.087	RBC
Indeno(1,2,3-c,d)pyrene	2.5	0.87	RBC
Lead	1,330	400	SSL

Source: AFBCA 1997; IT Corporation 1997; Wong 1999

CREG	Cancer risk evaluation guide
ppm	parts per million
RBC	U.S. Environmental Protection Agency Region III risk-based concentration
SSL	U.S. Environmental Protection Agency soil screening level

Evaluation of Potential Public Health Hazards

Based on a review of potential exposures and site data, ATSDR concluded that past, current, and future site use poses no apparent public health hazards because the exposure levels were too low to produce adverse health effects.

To evaluate whether past, current, or future public health hazards may be associated with surface soil contamination throughout Mather, ATSDR considered who may be exposed, how often and how long this exposure may occur, and what contaminant concentrations are present in the soil. People that may come into contact with contaminants in surface soil include on-base workers, residents, and users of recreational areas. The conclusion that there are no apparent public health hazards is based on the following information.

• Past, current, and future worker exposure was or is assumed to be infrequent and of short duration; workers were or are not expected to remain in an area of contamination over their entire workday or employment at Mather. In addition, workers were and are expected to wear personal protective equipment, such as work gloves, boots, and long pants, to prevent exposures.



• Although past recreational users may have contacted surface soil contaminants found at sites near recreational areas of Mather above comparison values, comparison values are derived assuming daily contact with contaminants in soil. Recreational use is expected to occur less frequently than assumed by the comparison values, resulting in exposure levels that are unlikely to produce adverse health effects.



• Exposure to past on-base residents in the military housing would have occurred in the on- base housing areas. Two sites were located in the on-base housing area and surface soil sampling at these sites found no contaminants above comparison values. Residents in the on-base housing, therefore, were not exposed to contaminants in surface soil at levels that would produce adverse health effects. The on-base military housing was vacated in 1993 when the base closed.



• Past officers in the former dormitories and current temporary residents in the current transitional housing are not exposed to contaminants in surface soil. The two sites located near the housing units did not contain contaminants at levels requiring remediation. One of the two sites consisted of a UST that was removed before the housing units were opened in 1996.



• To prevent current and future exposures as the base undergoes redevelopment and reuse, the USAF has completed or is conducting remedial actions. These actions are detailed in the RODs prepared by the base and may include institutional controls and deed restrictions. Institutional controls and deed restrictions can place limits on future uses of the site or can list requirements for developing the site. Remedial actions are conducted with oversight by USEPA and the California Environmental Protection Agency (CALEPA) to ensure protection of human health and the environment.

Exposure to Contaminants in Surface Water and Sediment

In the past, drainage ditches received wastewater, which may have contained contamination, from Mather activities. Contaminants could also be transported to waterbodies at Mather in stormwater runoff. Based on land uses, ATSDR identified three populations that may come into contact with contamination in on-base surface water bodies: on-base workers, on-base residents, and recreational users. On-base workers may be exposed to surface water and sediment contamination in drainage ditches located throughout the site. On-base residents and recreational users may be exposed to surface water and sediment contamination in areas near their homes or recreational areas, Morrison Creek or Mather Lake.

ATSDR evaluated potential past, current, and future exposures for on-base workers, on-base residents, and recreational users who may contact contaminated surface water and sediment and determined that the amount of exposure was considered too low to result in adverse health effects. ATSDR concluded that contaminants in surface water and sediment pose no apparent public health hazard. Past exposures to on-base workers, on-base residents, and recreational users would have been infrequent and of short duration. At Mather Lake, no contamination is expected, therefore, no exposures are occurring to recreational users of the lake. In addition, the USAF is conducting remedial actions to prevent current and future exposures to contaminants in surface water and sediment. The following text provides more information about surface water and sediment contamination at Mather, land use and Mather, and assumptions used to draw conclusions about potential public health hazards.

Nature and Extent of Contamination

Site investigations have found bis(2-ethylhexyl)phthalate, dieldrin, arsenic, and manganese above drinking water comparison values in surface water collected from sites throughout Mather. PAHs, PCBs, chlordane, dieldrin, antimony, arsenic, cadmium, chromium, and lead have been detected above soil comparison values in sediment from these sites. Sediment samples have also contained oil and grease, diesel, and gasoline, however, no comparison values are available for these substances (USAF 1996). Most of the sites with contaminants above comparison values in surface water and sediment are drainage ditches located along the runways and within the operational areas of Mather.

Three sites, however, are located adjacent to the on-base housing area and recreational areas of the base. IRP site SD80 is a drainage ditch that extends immediately south of the on-base housing area. Site investigations found dieldrin (to 0.029 ppb) and arsenic (to 2.5 ppb) above comparison values in surface water and chlordane (to 1.56 ppm), dieldrin (to 0.055 ppm), and arsenic (to 10.3 ppm) above comparison values in sediment. Surface water and sediment sampling locations were located well upstream of the on-base housing area (AFBCA 1997; Montgomery Watson 1998b). IRP site OT87 is a skeet and trap range located along Morrison Creek northeast of the on-base housing area. No contaminants were found above comparison values in surface water. Sediment sampling found arsenic (to 52 ppm) and lead (to 6,800 ppm) above comparison values (AFBCA 1997; IT Corporation 1997). Surface water and sediment samples were also collected at IRP site DD88, which is a drainage ditch located adjacent to the golf course in the eastern portion of the base. This drainage ditch is also part of the upper reaches of Morrison Creek as it drains from Mather Lake. Only manganese (to 147 ppb) was detected above its comparison value in surface water and dieldrin (to 0.1 ppm), antimony (to 10,500 ppm) and arsenic (to 12.1 ppm) were detected above comparison values in sediment from this site (Wong 1999). Tables 6 and 7 summarize the contaminants detected above their comparison values.

Table 6: Summary of Surface Water Sampling Data That Exceed Comparison Values

Chemical	Maximum Detected Concentration (ppb)	Comparison Value (ppb)	Source
SD80
Dieldrin	0.029	0.002	CREG
Arsenic	2.5	0.02	CREG
DD88
Manganese	147	50	RMEG (child)

Source: AFBCA 1997; IT Corporation 1997; Montgomery Watson 1998b; Wong 1999

Table 7: Summary of Sediment Sampling Data That Exceed Comparison Values

Chemical	Maximum Detected Concentration (ppm)	Comparison Value (ppm)	Source
DD80
Chlordane	1.56	0.5	CREG
Dieldrin	0.055	0.04	CREG
Arsenic	10.3	0.5	CREG
OT87
Arsenic	52	0.5	CREG
Lead	6,800	400	SSL
DD88
Dieldrin	0.1	0.04	CREG
Antimony	10,500	20	RMEG (child)
Arsenic	12.1	0.5	CREG

Source: AFBCA 1997; IT Corporation 1997; Montgomery Watson 1998b; Wong 1999

CREG	Cancer risk evaluation guide
ppm	parts per million
RMEG	(child) Reference dose media evaluation guide for a child
SSL	U.S. Environmental Protection Agency soil screening level

No sampling has been conducted at Mather Lake, which is located in the northeastern corner of the base and is used for recreational activities, such as fishing and picnicking. However, there is no evidence that past site uses may have resulted in releases of hazardous substances to the lake and no IRP sites or groundwater plumes are located proximate to the lake (USAF 1999). It is unlikely, therefore, that contaminants may have migrated into the lake through surface water runoff or groundwater discharge to surface water.

Evaluation of Potential Public Health Hazards

To evaluate whether past, current, or future public health hazards may be associated with surface water and sediment contamination throughout Mather, ATSDR considered who may be exposed, how often and how long this exposure may occur, and what contaminant concentrations are present in the surface water and sediment. On-base workers, residents, and recreational users may contact contaminants in surface water and sediment.

Based on a review of potential exposures and site data, ATSDR concluded that past, current, and future site use poses no apparent public health hazards. This conclusion is based on the following information.

• Past on-base workers, including military and civilian personnel, may have contacted surface water and sediment containing the following contaminants above comparison values: bis(2-ethylhexyl)phthalate, PAHs, PCBs, chlordane, dieldrin, antimony, arsenic, cadmium, chromium, and/or lead. No surface water and sediment comparison values are available, therefore, contaminant concentrations detected in these media were compared to drinking water and surface soil comparison values, respectively. Drinking water and surface soil comparison values, however, assume daily intake and contact with water and soil. Worker exposures were expected to be much less frequent and of shorter duration than assumed by the comparison values. Workers were not expected to remain in an area of contamination over their entire workday or employment at Mather and surface water is not a source of drinking water for Mather. Past, current, and future workers were and are expected to wear personal protective equipment to prevent exposures.



• Exposure to past on-base residents, living in either on-base housing or transitional housing units occupied by homeless people and families, and recreational users may have occurred during recreational use of sites with dieldrin, arsenic, and manganese above drinking water comparison values in surface water and chlordane, dieldrin, antimony, arsenic, and lead above surface soil comparison values in sediment. Actual exposures are expected to be less frequent and of shorter duration than the daily exposure assumed for deriving the drinking water and surface soil comparison values. In addition, surface water is not used as a drinking water source by on-base residents or recreational users.



• To prevent current and future exposures as the base undergoes redevelopment and reuse, the USAF has completed or is conducting remedial actions. These actions are detailed in the RODs prepared by the base. Remedial actions are conducted with oversight by USEPA and CALEPA to ensure protection of human health and the environment.

HEALTH OUTCOME DATA

Health outcome data can provide information about the general health status of disease in communities living near sites with releases of hazardous materials. It can provide valuable information about the patterns of disease in the community, such as infant mortality or specific types of cancers. Health outcome data can also help address community concerns about the amount of certain diseases in their community compared with another. It is not meant to establish cause and effect between exposure to a hazardous substance and disease. When necessary, ATSDR reviews health outcome data to assist in determining the health implications of exposures to hazardous substances and identifying appropriate follow-up actions to protect the health of the community.

At this time, ATSDR is not planning a review of health outcome data for the communities surrounding Mather AFB. ATSDR believes that the levels of exposure to chemicals in groundwater, surface soil, and surface water and sediments, and the exposure durations were not sufficient to result in adverse health effects.

The May 1999 issue of the Journal of Occupational and Environmental Medicine contains a scientific paper that examines the association between perchlorate contamination in drinking water and an increase in congenital hypothyroidism (Lamm and Doemland 1999). Congenital hypothyroidism is a preventable cause of mental retardation detected at birth during newborn screening programs. This disease occurs when the maternal and fetal thyroid glands are not able to supply enough thyroid hormone to the fetus, resulting in mental retardation. Ingestion of sufficient concentrations of perchlorate in drinking water can block thyroid hormone formation, and may contribute to an increase in congenital hypothyroidism.

Lamm and Doemland obtained data from neonatal screening programs for the rates of congenital hypothyroidism in seven California and Nevada counties during 1996 and 1997. Sacramento County, California, was one of the areas in this study. The time period from 1996 to 1997 was relevant for the community at Mather AFB, since that was the time between when perchlorate was detected in drinking water and actions were taken to stop exposure. From an evaluation of the data, no increase in the amount of congenital hypothyroidism was observed in excess of the number of cases normally expected for Sacramento County. This indicates that the water supply in the Mather area did not appear to contribute to an excess number of cases of congenital hypothyroidism.

COMMUNITY HEALTH CONCERNS

ATSDR identified community health concerns through meetings with the community members, state and local officials, and USAF personnel and review of site documents, including RODs and Community Relations Plans. In preparing the Community Relations Plans, the USAF interviewed community members that are or potentially are affected by contamination at Mather. Concerns raised during these interviews are discussed and addressed in the following text. ATSDR also released this document for public comment in July 2000. The public comment period extended from July 14 to August 28, 2000. Comments and concerns submitted by community members have been addressed throughout this PHA. Appendix F also lists and discusses these comments.

• Are there any potential health threats posed by use of the contaminated water supply wells? Community members frequently discussed chronic stress experienced from perceived health threats and lack of knowledge about these health threats.

The aim of a PHA is to find out if people are being exposed to contamination released from a site and whether this exposure may lead to adverse health effects. At Mather, ATSDR reviewed information about base contamination and determined that people on and surrounding Mather were exposed to VOCs and perchlorate in on-base supply systems, off-base community supply systems, and off-base private wells. The "Evaluation of Environmental Contamination and Potential Exposure Situations" section of this PHA and Appendix C and D provide a detailed discussion of potential health effects to on-base workers, on-base residents, and off-base residents from exposure to these contaminants in drinking water. In no cases did ATSDR identify levels of past contamination in drinking water wells that may have posed potential adverse health effects from past use. The USAF and community water suppliers have discontinued use of contaminated wells or have installed water treatment systems and monitor wells regularly to ensure continued protection of public health. Regular monitoring includes collecting samples from on-base supply systems, off-base community supply systems, and private wells to the west and south and analyzing samples for VOCs and/or perchlorate. Homes with private wells located west of Mather and within the boundary of the Main Base and SAC Industrial plume were connected to public water supplies to prevent exposures.

To address community concerns about activities at Mather and potential health threats, the USAF runs a Community Relation Program. Under this program, the USAF produces and distributes newsletters, fact sheets, and press releases about base activities and contamination. The Administrative Record for Mather, which is a collection of the documents and correspondence produced during the investigation and cleanup of the base can be found at Mather and McClellan Air Force Bases. A copy of the Administrative Record is available for review by the public at the Rancho Cordova Community Library. The Restoration Advisory Board, which is composed of community members and USAF representatives, also meets regularly to discuss and review ongoing activities at Mather. Meeting dates are advertised in the Grapevine Independent (Gutierrez-Palmenberg, Inc. 1999). Community members that are concerned about base contamination can also direct questions to USAF and local regulatory agencies (such as CALEPA and CDHS).

• Have the groundwater plumes been accurately defined and how well are the drinking water supplies being protected?

During site investigations conducted since 1982, the USAF has installed and sampled hundreds of monitoring wells at and around Mather. Samples from these wells have served to define the extent of groundwater plumes, as shown in Appendix A, Figures 2 and 5, and ongoing monitoring of nearly 400 monitoring wells serves to track the movement of these plumes (Montgomery Watson 1999a). As a result, the USAF gained an understanding of the groundwater plume locations and movement at Mather.

There is currently a system in place to ensure that active drinking water supply wells are protected. The USAF monitors wells within the groundwater plumes originating from Mather, guard wells, and drinking water supply wells. Guard wells are monitoring wells installed between a groundwater plume and a drinking water supply well at the same depth from which the drinking water supply well draws water. If contaminants are found in the guard well, this serves as an early warning that contaminants have migrated close to the supply well. In general, monitoring wells are sampled quarterly, as outlined in the Off-Base Water Supply Contingency Plan and the Groundwater Monitoring Program Evaluation Reports (AFBCA 1998; Montgomery Watson 1998c). Monitoring enables the USAF to track contaminant migration and anticipate and prevent use of public supply wells containing contamination at levels that may adversely affect public health. The USAF also installed and operates treatment systems to remove groundwater contaminants associated with plumes at Mather. Over time, groundwater contaminant concentrations will be reduced to levels that are safe to drink (AFBCA 1998; USAF 1996).

• Are the agreements between the CDHS, CUCC, and USAF sufficient to ensure safe drinking water? Citizens were especially concerned that the water supply be able to support new development and handle summer demand increases.

As required under the Groundwater OU ROD, the USAF prepared the Mather AFB Off-base Water Supply Contingency Plan. This plan describes the USAF strategy to mitigate adverse effects on drinking water supply wells if contamination is found in or near these wells in the future. The USAF identified supply wells that may be impacted by base plumes and monitors these wells and their guard wells. Guard wells are monitoring wells installed between a groundwater plume and a drinking water supply well at the same depth as the drinking water supply well. Contaminants detected in a guard well provide an early warning that contaminants have migrated close to the supply well. If contaminants are detected in the guard wells or supply wells at certain "trigger" concentrations, which are equal to one-half a contaminant's MCL and are listed in the contingency plan, actions will be taken to prevent public exposure to contaminants at levels that may adversely affect health. Actions may include installing water treatment systems or providing alternate water supplies. This plan will be reviewed annually and revised as needed to address contaminant migration, new contamination data, treatment contingencies, new regulatory standards, and the water suppliers' needs. Actions completed under a ROD are legally enforceable by USEPA and many of the treatment options outlined in the plan would require legal agreements to outline who is responsible for completing future remedial actions (AFBCA 1998). In this way, the contingency plan ensures that safe drinking water will be provided to the community.

• Will worker's health be impacted by site contamination and are site developers being adequately informed about deed restrictions and institutional controls?

Cleanup and construction workers employed at Mather during site redevelopment are required to follow Occupational Safety and Health Administration (OSHA) regulations to prevent exposures to base contaminants. These regulations outline requirements for use of site controls (e.g., dust suppression) and personal protective equipment (e.g., respirators). Any exposure that might occur during cleanup or construction despite OSHA controls is expected to be of short duration.

Currently, institutional controls and/or deed restrictions are in place at the landfill sites, which are in isolated areas of the base and surrounded by fences, and the Electron Tube Burial Site 16 (IRP site RW16). The Electron Tube Burial Site 16 was located underneath a building. Demolition of this building found no evidence of the reported electron tube burial area. Site developers are currently notified of land use restrictions at Mather through clauses in their leases and deed reviews conducted during property transfers. However, the USAF is scheduled to develop an institutional control implementation plan in 2000. This plan will detail how institutional controls and deed restrictions will be maintained and monitored in the future (Hughes 1999).

• Are current and future workers, residents, and site users at risk of injury from physical hazards, such as open pits or debris, located at Mather?

Currently, physical hazards, including open pits, debris, and heavy machinery, are present at Mather because of ongoing cleanup and redevelopment of the base. Workers are protected from injury through OSHA regulations that outline certain safety measures (e.g. fencing open pits) that must be followed at construction sites. Residents are beginning to move into homes built in the former Mather on-base housing area. Fencing around any remaining abandoned on-base housing units and construction areas prevents access by new residents and people at the schools and community centers near the former housing area. Temporary residents are living in the transitional housing area in the northwestern portion of the base. The USAF has taken measure to prevent injury by locking remediation equipment (e.g., drill rigs) and fencing areas (e.g., open pits and groundwater treatment systems). When the cleanup is completed, the USAF will conduct measures to eliminate physical hazards, such as disposing of debris and backfilling open pits, to prevent injury to future site users.

ATSDR CHILD HEALTH INITIATIVE

ATSDR recognizes that infants and children may be more sensitive to exposures than adults in communities with contamination in water, soil, air, or food. This sensitivity is a result of a number of factors. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. Children are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, potentially resulting in higher doses of chemical exposure per unit body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care. Therefore, ATSDR is committed to evaluating their special interests at sites such as Mather as part of the ATSDR Child Health Initiative.

ATSDR has attempted to identify populations of children in the vicinity of Mather. Approximately 4,700 children under the age of 10 years (approximately 18 percent of the total population) live within census tracts surrounding Mather (Bureau of Census 1991). At least 18 schools or preschool programs and five day care centers are located within a 2-mile radius of Mather; all of these facilities are to the west or northwest (Gutierrez-Palmenberg, Inc. 1999).

Like other people living or working at or in the vicinity of Mather, children may contact contaminated site media. As discussed in the "Evaluation of Environmental Contamination and Potential Exposure Situations" and the "Community Health Concerns" sections of this PHA, past, current, and future exposures for children include use of groundwater as a drinking water supply, contact with surface soil at recreational areas, and contact with surface water and sediment during recreational activities.

To evaluate whether children may experience adverse health effects through past, current, or future exposures to site contaminants, ATSDR estimated the potential doses for children. To estimate doses, ATSDR used very conservative assumptions that overestimate the levels of actual exposure. ATSDR concluded that exposure to site contamination does not pose unique health hazards for children. This conclusion is based on ATSDR's exposure evaluation and the following information:

• Comparison values are only used as screening values. Detection of chemicals above comparison values does not, of itself, necessarily imply that harmful exposure occurred.

• In the past, off-base children may have been exposed to VOCs above comparison values in groundwater pumped from off-base community supply systems and off-base private wells. On-base children in the transitional housing and on-base hospital may have been exposed to VOCs and perchlorate in the main base supply system. On-base children in the on-base housing were not exposed to contaminants in groundwater because no contamination above comparison values was detected in the family housing supply system. To evaluate exposures to children in the transitional housing units, the on-base hospital, and off-base homes, ATSDR assumed that children were exposed to the maximum detected contaminant concentration over the entire exposure period. ATSDR also used extremely conservative assumptions about how often and how long children are exposed to a chemical. Actual exposures are expected to be less frequent and over a shorter duration than assumed by ATSDR. A comparison of estimated exposure doses to ATSDR's minimal risk levels and the toxicology literature did not identify exposure levels for children that are likely to result in adverse health effects.

• Children may also have been exposed to contaminants in surface soil above comparison values during past use of recreational areas on base. Recreational areas with contaminants in surface soil above comparison values include one site near the golf course and three sites within former firing, trap, and skeet ranges. Although several contaminants were found above comparison values, these values are derived assuming daily contact with the contaminants in soil. Recreational use of the golf course and ranges is expected to occur much less frequently. In addition, the area of contamination near the golf course is located beyond the normal playing area, therefore, any exposure at this site would be infrequent and of short duration. Children may use the range areas with supervision by adults. Children remain near the firing points; they are not likely to enter the target area where contamination was found. Adverse health effects to children from contaminants in surface soil are not expected.

• During past recreational use of on-base streams, children may have been exposed to contaminants above comparison values in surface water and sediment. Streams near recreational areas with contaminants above comparison values in surface water and/or sediment includes one site by the golf course, one site near a trap range, and one site near the former on-base housing area. Children were unlikely to visit the golf course and trap range, therefore, any exposure would have been infrequent and of short duration. Moreover, the stream near the former housing area is not associated with any parks or established recreational areas. Only school-age children that may play without adult supervision would have used the stream for recreation, therefore, exposures would have been limited by the constraints of the school year and weather conditions. In addition, no surface water and sediment comparison values are available, therefore, contaminant concentrations detected in these media were compared to drinking water and surface soil comparison values, respectively. These comparison values are derived using conservative assumptions about daily exposures. Recreational use of the streams would have occurred significantly less frequently than assumed by the comparison values. Adverse health effects to children from contaminants in surface water and sediment, therefore, are not expected.

• To prevent current and future exposures to contaminants in groundwater, drinking water supply wells containing contaminants above comparison values have been closed or treatment systems have been installed. The USAF connected homes with private wells to the public water supply. Public water suppliers and the USAF regularly monitor wells to track contaminant migration and ensure continued protection of the drinking water supply. Regular monitoring includes collecting samples from on- and off-base public supply wells and analyzing samples for VOCs and/or perchlorate. To prevent current and future exposures to contaminants in surface soil, surface water, and sediment, the USAF has completed or is conducting remedial actions, such as excavating contaminated soil and sediment. Remedial actions for each site are designed to account for the future site use.

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