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PUBLIC HEALTH ASSESSMENT

CASTLE AIR FORCE BASE
ATWATER, MERCED COUNTY, CALIFORNIA


SUMMARY

Castle Air Force Base (AFB), an inactive military base, encompasses 2,777 acres of land in the San Joaquin Valley, California. Castle AFB is surrounded primarily by agricultural areas, but urban residential areas in several nearby cities are rapidly growing. The installation, which opened in 1941, provided basic flight training and military support for over 50 years. Prior to base closure in September 1995, Castle AFB employed up to 7,300 individuals on base.

Castle AFB was placed on the U.S. Environmental Protection Agency (EPA) National Priorities List in 1987 because of contamination detected in the base groundwater and soil (USAF, 1998). The primary contaminant of concern at this site is trichloroethylene (TCE), although cis-1,2-dichloroethylene, petroleum hydrocarbons, inorganics, and other volatile organic compounds have been detected at levels above the Agency for Toxic Substances and Disease Registry (ATSDR) health-based comparison values.

Community members have expressed concern about potential health effects associated with site contaminants in groundwater, soil, and locally-grown agricultural produce. ATSDR conducted a site visit in January 1998 and identified no immediate public health hazards.

ATSDR reviewed and evaluated groundwater data. TCE was detected in groundwater beneath Castle AFB and off site, particularly west and southwest of the base. Routine monitoring of the base drinking water wells, nearby public water supply wells, private wells in the area, and irrigation wells near Castle AFB, indicated that the water used by the public did contain low-level TCE concentrations in the past. Past exposures, however, were minimized by aggressive United States Air Force (USAF) efforts to provide bottled water and alternative drinking water sources to impacted individuals. In on- and off-site areas where people have ingested TCE-contaminated groundwater at levels above health-based guidelines, no public health hazard exists due to the short durations of exposure, the low exposure doses, and/or remediation efforts by USAF. Currently, all public water supplies meet EPA's drinking water standards. In addition, Castle AFB has several active systems in place to treat and capture the contaminated groundwater. To ensure continued delivery of safe drinking water on- and off-site, Castle AFB has agreed to supply alternate drinking water sources should it become necessary in the future. For these reasons, ATSDR concludes that TCE-contaminated groundwater from Castle AFB does not pose a public health hazard.

ATSDR also reviewed on-site soil data. Two hundred and nine sites were investigated, 31 of which were evaluated in detail by ATSDR due to their potential to impact underlying groundwater or to be accessed by the general public under the Final Environmental Impact Statement: Disposal and Reuse of Castle AFB. At all 209 sites, ATSDR concluded that soil contaminants do not pose a public health hazard because: 1) contaminants in on-site soil were detected at levels that do not pose a public health hazard; 2) contamination was located in areas where public exposure was infrequent or unlikely (e.g., subsurface soil, industrial areas, or areas surrounded by perimeter fencing); or 3) USAF remediation activities have lowered soil contaminant concentrations to levels that do not pose a health hazard. ATSDR concludes that no public health hazards are associated with exposure to on-site contaminated soil.

Lastly, ATSDR reviewed data on agricultural produce from the land surrounding Castle AFB. Locally-grown produce is not bioaccumulating TCE or other contaminants at levels of human health concern. Therefore, ATSDR concludes that no public health hazards are associated with the consumption of produce from farms in the vicinity of Castle AFB.

Based on review of available information on groundwater, soil, and locally-grown produce, ATSDR concludes that Castle AFB should be assigned to the No Public Health Hazard category.


BACKGROUND

Site Description and History

Castle Air Force Base (AFB) is a closed military base located in central California's San Joaquin Valley (Figure 1). The majority of Castle AFB lies in an unincorporated area of Merced County; a portion of the base is within Atwater city limits. The city of Atwater lies west of the base and the city of Merced is approximately 7 miles southeast of Castle AFB (Jacobs, 1995). With the exception of residential areas in the community of Atwater, the land surrounding Castle AFB is predominantly agricultural. Crops grown in the area consist mostly of almonds, peaches, and grapes. Several small dairies and a large chicken farm are located to the east of Castle AFB (USAF, 1994a, b).

The Main Base area of Castle AFB consists of a runway and airfield, industrial areas, recreational facilities, and housing units on 2,777 acres of relatively flat terrain. Public access to the Main Base is restricted by perimeter fencing. There are also three off-base Castle AFB properties: Castle Park (a recreation facility), Castle Gardens Family Housing Area (a mobile home park), and Castle Vista Housing Area (Jacobs, 1995) (Figure 2).

Castle AFB was established in December 1941 to provide basic flight training and military support. Beginning in 1957, Castle AFB added weapons storage and explosive ordinance disposal operations to base activities. Waste producing activities included painting and stripping operations, aircraft and vehicle maintenance, and pesticide application (Jacobs, 1997a). The base also contains several landfills, fuel/oil storage areas, wastewater treatment centers, and fire protection training areas. From 1941 to the mid-1970s, the majority of the waste oils, fuels, and solvents were disposed of in pits throughout the base. One on-base pit was used for burning waste oils, fuels, and solvents. Some of the chemical wastes were reported to have been discharged to the sanitary and storm sewers or allowed to run off onto surface soils directly adjacent to specific maintenance facilities (Jacobs, 1997b).

In the mid-1970s, waste oils and fuels began to be disposed of off-base. Solvents and other chemical wastes were often combined with waste oils and fuels or were discharged to the sanitary, industrial, or storm sewer systems. Up through the mid-1980s, some wastes were still allowed to run off into areas adjacent to specific facilities and contaminated fuel continued to be burned during fire protection training exercises. After 1988, solvents and other hazardous chemicals were collected at designated storage areas and contracts for off-base disposal were occasionally arranged (Jacobs, 1997b).

The principal site contaminant at Castle AFB is trichloroethylene (TCE), although fuel products, pesticides, and metals are also present. Most contamination is contained within the industrial areas of Castle AFB property, although some contamination has migrated off base via groundwater.

Remedial and Regulatory History

Environmental investigations at Castle AFB began in 1978 after trace amounts of TCE were detected in four base production wells (PW-1, PW-2, PW-3, and PW-4) used for drinking water. During 1980, routine well sampling detected trace levels of TCE in military drinking water supplied by the same four base wells where TCE was detected in 1978 (Jacobs, 1996a).

The Department of Defense's Installation Restoration Program (IRP) at Castle AFB began in 1981 when the United States Air Force (USAF) identified 35 contaminated sites that were potential sources of groundwater contamination (Jacobs, 1997a). Sampling results from both the upper and lower portions of the shallow aquifer indicated that TCE levels as high as 136 parts per billion (ppb) were present on base (Jacobs, 1996a). These high TCE levels, however, did not occur in drinking water production wells.

In October 1983, under Phase I of the IRP, USAF reviewed past and current waste generation and disposal methods to locate potential sources of TCE-contaminated groundwater. Most hazardous wastes at Castle AFB were associated with aircraft and vehicle maintenance, industrial operations, fire protection training, pesticide use, and fuels management. An additional seven potential sources were identified when USAF characterized waste disposal areas and delineated the extent of groundwater contamination (Jacobs, 1995).

In February 1984, TCE was detected in on-base production wells (PW-1, PW-2, PW-3, and PW-4) at levels exceeding the U.S. Environmental Protection Agency's (EPA) maximum contaminant level (MCL) of 5.0 ppb (Jacobs, 1996a). The following month, the California Regional Water Quality Control Board (RWQCB) Central Valley Region (CVR) ordered Castle AFB to provide users of the base water supply and any contaminated off-base wells with additional sources of potable water (Gutierrez-Palmenberg, 1997). Castle AFB was also required to implement remedial measures to correct identified and future groundwater degeneration from waste discharges. USAF complied with the RWQCB requirements and in February 1985 began operating a new, contaminant-free water production well (PW-10).

In September 1984, field investigations revealed that soil at the majority of IRP sites had not been affected by past waste disposal practices (Jacobs, 1995). The highest TCE-concentrations were detected in the central portion of the Main Base. The investigations also indicated that the potential for contaminated soil to impact groundwater quality needed further evaluation. In 1987, EPA placed Castle AFB on the National Priorities List (NPL) under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA; also known as Superfund). Castle AFB was listed on the NPL primarily due to TCE contamination identified in the IRP investigation. Phase I of the remedial investigation (RI) began in August 1988, when USAF installed monitoring wells in the upper and lower zone of the shallow aquifer and in the confined aquifer.

On July 21, 1989, the Air Force entered into a Federal Facilities Agreement (FFA) with EPA Region IX and the state of California. The FFA established a procedural framework, schedule, and deadlines for developing, implementing, and monitoring appropriate environmental restoration efforts specific to designated IRP sites. Also in 1989, the Castle AFB Technical Review Committee (TRC) was formed with representatives from the Air Force, EPA Region IX, state and local agencies, and community members. The TRC has been transformed into the Restoration Advisory Board (RAB) which meets monthly. The RAB's primary mission is to develop partnerships between Castle AFB and the local community and to provide the community a voice in decision making. Specifically, Castle AFB's RAB has been active in reviewing technical issues associated with the site (Gutierrez-Palmenberg, 1997).

Phase II of RI, initiated in 1989, consisted of two rounds of quarterly groundwater sampling in 160 wells (including previously-installed base and Phase I wells, new RI base wells, and off-base private wells). Additionally, 77 soil borings were drilled and sampled to further characterize various sites. Investigations identified nine physically and hydraulically distinct TCE groundwater plumes originating on Castle AFB property. Additionally, a cis-1,2-dichloroethylene (cis-1,2-DCE) groundwater plume was identified in the vicinity of Castle Vista (Jacobs, 1994, 1995).

Phase III of RI field activities began in March 1990 and continued through May 1991. These activities included additional quarterly ground water sampling and analysis and a preliminary site assessment of the Castle Vista landfills. Also during Phase III, contaminated areas at Castle AFB were divided into three operable units (OU) to better define the extent of the groundwater contamination plumes and their related source areas (USAF, 1998):

  • OU 1 addresses the TCE contamination in the aquifer (specifically, the shallow groundwater zone) beneath the central portion of the Main Base and contiguous off-base areas to the south and southwest.


  • OU 2 addresses contaminated groundwater beneath an area on base known as Discharge Area Number 4 (DA-4) and a contiguous off-base area west of the Main Base (referred to as the Wallace Road area).


  • The Source Control OU (SCOU) addresses the problem of soil contaminants at a wide variety of sites across the base and their effect on groundwater plumes.

In 1996, the Castle AFB Comprehensive Basewide Program (CB) Part 1 Record of Decision (ROD) was finalized. It summarized the multiple sites at Castle AFB targeted for remediation activities. Because remediation efforts targeted multiple media, USAF divided the CB into two parts: Part 1 focuses on groundwater remediation by integrating OU 1 and OU 2 efforts, and Part 2 (entitled Castle AFB CB Part II ROD) combines information and results from all three OUs (groundwater and soil). The anticipated completion date for the Castle AFB CB Part II ROD is the year 2000.

Demographics and Land Use (Reuse Plan)

To characterize the population and identify the presence of sensitive subpopulations, such as young children, in the vicinity of an NPL site, ATSDR examines the demographics of the nearby communities. This information also provides detail on residential history in a particular area that helps ATSDR assess time frames of potential human exposure to contaminants. The demographic and housing data for Castle AFB and the surrounding areas, particularly the areas west and southwest of the site where groundwater contamination has migrated, are presented in this section. The demographics are based on census data from 1990.

Castle AFB and Site Area Population and Housing Data

The area surrounding Castle AFB supports a rapidly growing population with an estimated 1995 population of 202,789 for Merced County (CJPA, 1996). The county contains the largest number of Southeast Asian refugees per capita in the country. The largest minority group in Merced County is Hispanic. Approximately 20% of California's Hispanic migrant population lives in the San Joaquin Valley and Merced County lies in the San Joaquin Valley. Continuously high unemployment (13.1% to 18.4% depending on the season) and high poverty (28.4%) are problematic in Merced County, so much so that the federal government designated the county a Long Term Economic Deteriorated Area (CJPA, 1996). A large proportion of the population in the general surrounding area is relatively transient in nature.

In the past, over 10% of all employment was derived from Castle AFB activities (CJPA, 1996). Approximately 5,200 to 7,300 military and civilian jobs were based at Castle AFB, with an additional 1,500 jobs created off-site (USAF, 1994a). The closure of Castle AFB significantly impacted the local employment and economic structure of the area. Formerly-occupied off-base housing areas such as Castle Vista now stand vacant (ATSDR, 1998). These housing facilities, however, are expected to be occupied in the future as reuse plans are implemented. Currently, over 1,000 jobs are located on base (ATSDR, 1998).

Land Use in the Castle AFB Area

The area surrounding Castle AFB supports an economy strongly oriented towards agriculture and agricultural products. Agricultural areas and rural farm residences are located to the north of the base. Urban residential areas, consisting of former off-base housing, trailer parks, and recently-constructed residential suburban housing, is located west, south, and east of Castle AFB (USAF, 1994a,b).

The underlying groundwater supplies all military, municipal, and private production wells in the area (Jacobs, 1996a). Irrigation water also comes from underlying groundwater. Some irrigation water used by neighboring farms drains into Canal Creek which lies along the base's eastern boundary. There are also about 20 acres of shallow, seasonal wetlands (vernal pool wetlands) in the northeastern area and several man-made drainage ditches at Castle AFB. No one drinks area surface water (USAF, 1994a).

Castle AFB Reuse Plan

Castle AFB has certain restrictions regarding future activities (e.g., no digging without special health and safety precautions) in various areas of known contamination. If potential exposures at these areas of known contamination are not mitigated through the IRP, the restrictions will remain in place even after the Air Force vacates the property.

As outlined in the Final Environmental Impact Statement: Disposal and Reuse of Castle AFB (FEIS), most of the base's former properties will be re-designated for institutional, commercial, or industrial purposes (USAF, 1994b). Castle Airport, covering 1,606 acres, will use the main runway, taxiway, stub apron parking, operational apron, and aviation support. Other parcels are going to be transferred to the Federal Bureau of Prisons for the construction of two minimum security prisons (USAF, 1998).

Only a small portion of Castle AFB property has been designated for public sale and all these areas meet environmental health guidelines or are currently undergoing or will undergo remediation efforts (USAF, 1994b). Areas designated for reuse by the public include: Castle Gardens and Castle Vista for use as privately owned housing; Castle Park for public recreation; the Challenger Learning Center and Aviation Challenge Foundation for educational purposes; the Castle Aviation Museum Foundation for tourism purposes; several small buildings for use by a women's shelter; and a gym area and athletic facilities for use by local schools (USAF, 1998). Based on this future land use scenario, potential receptors for on-site soil contaminants include the on-base industrial workers (adult), on-base visitors (adult and child), and off-base residents (adult and child) living in Castle Vista or Castle Gardens.

ATSDR Activities

The Agency for Toxic Substances and Disease Registry (ATSDR) conducted its initial site visit of Castle AFB in April 1991. A follow-up site visit took place in January 1998. During the 1998 site visit, ATSDR viewed on-base sites and remediation efforts, as well as sites located in the off-base housing areas of Castle Gardens and Castle Vista. ATSDR also met with USAF, the California Department of Health Services (CADHS), interested media representatives, and a RAB member/community representative.

According to the community representative, no area residents have expressed any specific health concerns they attribute to Castle AFB. Most concerns appear to focus on the economic impacts of the base reuse plan. In general, the local community trusts that the Air Force is doing everything necessary to ensure the safety of human health (ATSDR, 1998).

Quality Assurance and Quality Control

In preparing this public health assessment, ATSDR relied on the information provided in the referenced documents. The environmental data presented in this public health assessment are from USAF and EPA reports; the remedial site investigations of the IRP sites; quarterly groundwater monitoring data; and drinking and irrigation water data from Castle AFB, municipal, and private wells.


EVALUATION OF ENVIRONMENTAL CONTAMINATION AND POTENTIAL EXPOSURE PATHWAYS

Introduction

In this section, exposure pathways are evaluated to determine whether people accessing or living near Castle AFB could have been (past scenario), are (current scenario), or will be (future scenario) exposed to site-related contaminants. In evaluating exposure pathways, ATSDR determines whether exposure to contaminated media has occurred, is occurring, or will occur through ingestion, dermal (skin) contact, or inhalation of contaminants. When exposure to contaminated media occurs, the exposure pathway is regarded as "complete." To determine whether completed pathways pose a potential health hazard, ATSDR compares contaminant concentrations to health-based comparison values. Comparison values are calculated from available scientific literature on exposure and health effects. These values, which are defined for each of the different media, reflect the estimated maximum contaminant concentration for a given chemical that is not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. If contaminant concentrations are above comparison values, ATSDR further analyzes exposure variables (for example, duration and frequency) and the toxicology of the contaminant. This exposure evaluation process is summarized in Figure 3.

ATSDR evaluated available information on all nine of the groundwater contamination plumes (Figure 4), 209 Castle AFB SCOU sites (Figure 5), and locally-grown agricultural produce to determine if they pose any past, current, or future public health hazards. ATSDR identified two groundwater plumes, the Main Plume (TCE) and the Castle Vista Plume (cis-1,2-DCE) as completed exposure pathways. Information on these plumes and associated exposure pathways is summarized in Table 1 and the following text. The public is not exposed to the other seven groundwater plumes because no production wells are located in the plumes' vicinities. An evaluation of potential public health hazards associated with all 209 SCOU sites is summarized in Appendix A. None of these 209 SCOU sites are associated with any known public health hazards because: 1) no site-related contaminants are present; 2) contaminant concentrations detected are too low to pose a health hazard; 3) past and current exposure to the general public has been prevented; and/or (4) remedial activities have reduced contaminant concentrations to levels that pose no public health threat. Similarly, the consumption of locally-grown agricultural produce is not associated with any known public health hazards because contaminant concentrations in the produce were not detected or were too low to pose a health hazard.

The following discussion evaluates community concerns about potential human exposure via contaminated groundwater, soil, and agricultural produce. This public health assessment will state each concern, present a brief summary of ATSDR's conclusions, and describe in more detail any identified exposure pathways and the basis for ATSDR conclusions. ATSDR's conclusions regarding the past, present, and potential future exposures to various environmental media on and in the vicinity of Castle AFB are based on evaluation of data gathered from remedial site investigations, groundwater monitoring data, on- and off-base drinking water wells data, irrigation wells data, and the observations compiled during site visits.

1. Concern: Groundwater

Could exposure to TCE or other contaminants in groundwater result in adverse human health effects for residents of neighboring communities or for former residents, employees, or visitors of Castle AFB?

Conclusions

After detailed review of the available data, ATSDR has drawn several conclusions regarding past, present, and possible future exposures to contaminated groundwater at Castle AFB.

Past Exposures

  • Past activities at Castle AFB affected groundwater underlying military property. TCE is the main contaminant of concern.


  • People living on or near Castle AFB were exposed to TCE-contaminated drinking water in the past. The initial date of contamination remains unknown, but trace amounts of TCE were first detected in drinking water in 1978. Contaminant concentrations did not exceed ATSDR comparison values for drinking water until 1984.


  • Adverse health effects from TCE contamination are unlikely due to the relatively low levels of TCE, the limited duration of exposure, and the aggressive remediation efforts by USAF.


  • ATSDR concludes that no public health hazards are associated with the past consumption of water from Castle AFB, the city of Atwater, or private wells in the surrounding area.

Present and Potential Future Exposures

  • Current and future exposures to contaminated groundwater are unlikely because the drinking water is monitored quarterly, treated at the wellhead, and several pump-and-treat systems actively control known TCE plumes.


  • ATSDR concludes that no public health hazards are associated with the present or potential future consumption of water from Castle AFB, the city of Atwater, or private wells in the surrounding area.

Discussion

Castle AFB's Hydrogeology

Groundwater beneath Castle AFB lies approximately 70 to 80 feet below ground surface (bgs), but the water table in the CVR is steadily dropping (USAF, 1996). Between 1985 and 1993, the water table underlying Castle AFB declined by approximately 25 to 30 feet (Jacobs, 1994). The groundwater is divided into five heterogenous groundwater zones or hydrostratigraphic zones (HSZ). Each HSZ is characterized by laterally discontinuous sediment layers; each layer consisting of finer sediments at the top and a predominant water-bearing lense at the bottom. The HSZs are not isolated aquifers, although water mixing between layers is extremely limited.

  • The shallow HSZ extends from about 70 feet below bgs to an average depth of 95 feet.


  • The upper-subshallow HSZ extends from the bottom of the shallow HSZ to an average depth of about 130 feet bgs.


  • The lower-subshallow HSZ extends from the upper-subshallow HSZ to an average depth of about 220 feet bgs.


  • The confined HSZ extends from the base of the lower-subshallow HSZ to an average depth of about 350 bgs.


  • The deep HSZ starts at the base of the confined HSZ and extends to an unknown depth.

Although water flow direction varies among the different HSZs, in general, the groundwater gradient is relatively flat (0.001 to 0.002 ft/ft) and water flows predominantly west-southwest towards the San Joaquin River (Jacobs, 1994).

Two regional pumping centers, located to the northwest and south-southwest of Castle AFB, influence local groundwater flow directions in the Atwater-Merced area. Because large volumes of groundwater are pumped for irrigation purposes during the late summer and fall, the water levels fluctuate greatly and observe cyclical seasonal patterns (especially in the confined HSZ). There is also a small, natural downward vertical gradient of groundwater flow (particularly between the shallow and upper subshallow HSZs) (Jacobs, 1994).

Groundwater is the major migration pathway for contaminants beneath Castle AFB. Monitoring wells, production wells, and irrigation wells are man-made vertical pathways, while natural HSZs layers act as horizontal pathways for contaminant plumes (Jacobs, 1996a). The migration and fate of dissolved contaminants in groundwater at Castle AFB, therefore, depends largely on the influence of local pumping centers as well as natural hydrogeologic conditions.

Groundwater Use

Castle AFB, the city of Atwater, and the Merced Irrigation District are the three principal users of groundwater on or near Castle AFB (Gutierrez-Palmenberg, 1997; Jacobs, 1996a). In addition to on-site production wells, there are more than 100 municipal, private, irrigation, and production wells within one mile of Castle AFB (USAF, 1994b). All five HSZs contribute water to the military, public, or private wells and/or water distribution systems. The deepest well (city of Atwater, AM-19) is 670 feet bgs, while the shallowest wells are less than 100 feet bgs. Most private wells located close to the base draw groundwater from the shallow HSZ (USAF, 1994b).

Castle AFB on-base production wells are capable of producing 4,900 gallons per minute (gpm) (Jacobs, 1996a). Based on data from the last year the base was open, approximately 2,000 gpm were used in the summer, while approximately 1,000 gpm were used in the winter. Currently, water usage is much less. The base's principal production wells are PW-10 and PW-12 which extract water from the confined and deep HSZs. The only other active production wells at Castle AFB (PW-6 and PW-11) are used on demand, usually only in the summer months. PW-6 extracts water from the shallow and upper subshallow HSZs to supply the weapons storage area (WSA) and on-base dog kennels. PW-11, drawing exclusively from the shallow HSZ, is used on demand to serve the rifle and skeet ranges (Jacobs, 1996a).

Water demands of the communities surrounding Castle continue to grow as the population increases (Jacobs, 1996a). Total groundwater pumping in the Atwater-Merced area ranged from about 47,000 to 120,000 acres-feet per year during the 10-year period between 1963 and 1973. In 1988, 11 wells belonging to the city of Atwater were in service and produced about 6,300 acre-feet of water, serving approximately 20,000 residents (Jacobs, 1996a).

Groundwater Quality

Groundwater in the upper four HSZs has been contaminated by TCE and other organic compounds from a variety of sources at Castle AFB. Trace amounts of TCE were first detected in base water production wells in February 1978. In 1984, TCE concentrations in on-base drinking water exceeded ATSDR's comparison value and EPA's MCL of 5.0 ppb. Subsequently, the contaminated wells were closed and PW-10 began operating in February 1985. Since the opening of PW-10, TCE levels have remained below 5.0 ppb. Unrelated to Castle AFB activities, groundwater also contains elevated levels of inorganic compounds (primarily nitrates). The inorganic compounds are likely coming from agricultural sources (Jacobs, 1994).

Nine physically and hydraulically distinct TCE plumes were identified during the RI (Figure 4). These nine plumes were divided into seven plume regions based on geographic location and source of contamination. These regions are defined as: Main Base Plume 1, Main Base Plume 2, East Base Plume, Castle Vista Plume, North Base Plume, Landfill 1 Plume, and Landfill 4 Plume. The Main Base Plume Regions 1 and 2 ( also known as the "Main Plume") account for approximately 98% (by weight) of the estimated 6,202 pounds of TCE in the groundwater (USAF, 1996). The Main Plume is much larger than the other plumes and covers a combined area of approximately 1,000 acres.

Although, the most significant contaminant of the Main Plume is TCE, cis-1,2-DCE, tetrachloroethylene (PCE), benzene, and carbon tetrachloride are also present. Major contaminants at the Castle Vista Plume are TCE, cis-1,2 DCE, and PCE. At the East Base Plume, TCE and bis(2-ethylhexyl)phyhalate (BEPH) are present. Contaminants at the North Base, Landfill 1, and Landfill 4 Plumes include TCE, PCE, BEPH, and antimony. Other contaminants detected at lower concentrations include benzene, toluene, ethylbenzene, and xylenes (BTEX), petroleum hydrocarbons, inorganics, and other volatile organic compounds (VOC) (USAF, 1994b, 1996). Most plumes contain low-level contaminant concentrations; only the Main Plume, Castle Vista Plume, and East Base Plume exceed ATSDR comparison values for drinking water.

Groundwater contamination in the various plume regions is primarily limited to the shallow HSZ. Main Plume contamination, however, is also present in the upper subshallow, lower subshallow, and confined HSZs (Jacobs, 1997c), and Castle Vista contamination extends into the upper-subshallow HSZ (Jacobs, 1997d). All contaminant plumes in the shallow HSZ appear stable (i.e., they are not increasing in size or concentration), although some downgradient migration may still be occurring (Jacobs, 1996a). There are not sufficient analytical data available to evaluate plume changes in the underlying HSZs, especially the lower sub-shallow and confined HSZs (Jacobs, 1996a).

Average TCE levels in the Main Plume (shallow and upper-subshallow HSZs) were approximately 150 ppb prior to USAF remediation activities (Jacobs, 1994). Recent sampling data indicates that average concentrations have dropped to 46 ppb (Hicks, 1998a), but levels as high as 740 ppb were recently detected in monitoring wells (Jacobs, 1996a). The maximum TCE concentrations ever detected in on-base production wells only slightly exceeded the EPA's MCL of 5.0 ppb. Greater TCE concentrations (up to 24 ppb) were detected in off-base private wells (formerly) used by Wallace Road residents (Gutierrez-Palmenberg, 1997; Jacobs, 1996a). TCE concentrations decline with depth and TCE has not been detected in the one well screened in the deep HSZ.

Impacted by the Castle Vista plume, the irrigation well (I2266) for the Thomas Oleata School contained elevated levels (approximately 10 ppb) of cis-1,2-DCE. This concentration slightly exceeded the state of California's MCL for drinking water (6.0 ppb), but it remained well below ATSDR's comparison value (and EPA's MCL) of 70 ppb (Jacobs, 1997d). The discrepancy between the state and federal MCL levels is because California derived its MCL from acute exposure studies (and therefore had to use additional safety factors) and EPA calculated its MCL using chronic exposure studies. The Thomas Oleata School irrigation well was never used for drinking water.

All major TCE plumes are currently being remediated and controlled by various systems installed by USAF (see the Completed Groundwater Actions section of the Public Health Action Plan). These remedial activities, planned to remove and contain TCE, also remediate other contaminants exceeding their respective MCLs (USAF, 1996). The smaller TCE plumes are closely monitored by USAF and unlikely to threaten public health because contaminant levels remain below their respective MCLs.

Exposure Evaluation and Potential Human Health Hazards

Public exposure to TCE-contaminated groundwater, both on- and off-base, has been extremely limited. The Main Plume and Castle Vista Plume are the only completed (past, present, or potential future) exposure pathways (see Table 1). Since no active production wells lie in the vicinity of the East Base Plume, no one is exposed to East Base Plume contaminants.

Past Exposure

On-base: After TCE was first detected above the MCL of 5.0 ppb in February 1984, USAF required on-base water to be boiled and/or required the use of bottled water at the base hospital, food-serving establishments, and residential facilities (Gutierrez-Palmenberg, 1997). Beginning in February 1985, a newly-constructed well (PW-10) began supplying the base's water. On-base drinking water contaminant concentrations have not been detected above MCLs since PW-10 began operating (Gutierrez-Palmenberg, 1997).

Off-base: Since the early 1980s, municipal water supply systems (including that of the city of Atwater) have been closely monitored by state and local governments. All municipal water supplies remain unaffected by Castle AFB-related contamination (Jacobs, 1997c).

In October 1984, TCE was first detected in trace amounts in off-base, private wells along Santa Fe Drive and Wallace Road, west of Castle AFB. In 1985, TCE contamination exceeded the MCL (5.0 ppb), with the maximum detected concentration reaching 24 ppb (Jacobs, 1996a). USAF immediately supplied all affected families (two families living on Santa Fe Drive and three families living along Wallace Road) with bottled water until activated carbon filtration systems could be installed on their private wells to remove the TCE. One Wallace Road resident was connected to the base water supply in February 1989; the other two Wallace Road residents were connected in October 1989. Additionally, an area resident whose house was located downgradient of AFB properties expressed concern about TCE in the groundwater from his private well. Although TCE did not exceed the MCL in his private well water, USAF installed an activated carbon filtration system on his well and supplied the resident with bottled water (Gutierrez-Palmenberg, 1997).

In November 1985, TCE contamination above the 5 ppb action limit was found in two of the three off-base wells at Castle Mobile Home Park. In response to this discovery, USAF began supplying bottled water to park residents until activated carbon filtration systems could be installed. Residents were connected to the city of Atwater water supply in March 1989 (Gutierrez-Palmenberg, 1997).

ATSDR Exposure Dose Estimates

In response to community concerns about exposure to TCE-contaminated groundwater, ATSDR estimated the potential exposure doses for adults and children who drank water from affected wells to determine if a health hazard existed. To estimate human exposure doses, ATSDR used very conservative assumptions believed to greatly overestimate the levels of actual exposure. These assumptions and ATSDR's methods are further described in Appendix B. ATSDR's estimated exposure doses were used to evaluate both potential noncancer and cancer effects.

Noncancer: The estimated exposure doses for ingestion of TCE-contaminated water are provided in Appendix B. The values for an adult and a child are less than the corresponding oral minimal risk level (MRL) for acute (14 days or less) ingestion of TCE; therefore, adverse noncancer effects are not expected to be associated with any short-term drinking water exposures. Intermediate or chronic MRLs for TCE do not currently exist, but the estimated exposure doses for adults and children are well below doses associated with noncancer health effects. ATSDR concludes that past exposure to the groundwater from Castle AFB, private drinking, and irrigation wells was not likely to have resulted in noncancer effects.

Cancer Effects: The link between oral exposure (ingestion) to TCE and increased cancer incidences in humans is controversial; some studies have shown that individuals drinking TCE-contaminated water with up to 220 ppb (a concentration approximately 10 times greater than the maximum level of TCE detected in drinking water in the Castle AFB area) suffered no increased incidence of cancer (ATSDR, 1997; Vartianinen et al., 1993). As described in Appendix B, residents of Castle AFB and the surrounding communities were not exposed to TCE concentrations associated with increased cancer incidences. Moreover, public exposure to TCE-contaminated drinking water occurred for an extremely limited time due to aggressive USAF remediation activities. ATSDR concludes that past exposures to the groundwater from Castle AFB, private drinking, and irrigation wells was not likely to have resulted in cancer effects.

Present and Potential Future Exposures

Current base drinking water comes from production wells in relatively uncontaminated areas, primarily the deep HSZ. Additionally, USAF filters and treats base drinking water to ensure that groundwater contaminants remain below levels mandated by federal and state drinking water standards. Because USAF will continue to filter and treat base drinking water and will continue its remediation activities, future exposure to contaminated groundwater via Castle AFB production wells is extremely unlikely. ATSDR concludes, therefore, that present and future exposures to contaminated groundwater from Castle AFB production wells are unlikely to pose any public health hazards.

No off-base residents are currently exposed to harmful levels of groundwater contaminants because: 1) municipal production and irrigation wells remain unaffected by contamination from Castle AFB, 2) private wells impacted by contamination are no longer in use, 3) private wells impacted by contamination have activated carbon filtration systems that reduce groundwater contaminants to levels below those mandated by federal and state drinking water standards (e.g., MCLs), or 4) contamination levels have been reduced (either naturally or by USAF remediation efforts) to levels below state and federal drinking water standards.

There is, however, the potential for future exposures to contaminants in downgradient Atwater municipal wells, specifically at AM-16 and AM-6. AM-16, located southwest of the Main Base, is considered a prime potential conduit/receptor for the Main Plume. AM-16 is screened from 330 to 660 feet bgs, within the confined and deep HSZs. It lies approximately 1,700 feet west (downgradient) of the estimated boundary of the TCE plume in the confined HSZ. Well AM-16 has a pumping capacity of approximately 2,000 gallons per minute and produces an average monthly volume of approximately 70 million gallons (Jacobs, 1996a). AM-6 lies at the leading edge of the Castle Vista Plume. It draws water primarily from the upper sub-shallow and lower sub-shallow HSZs. During 1997 investigations, trace amounts (less than 1 ppb) of cis-1,2-DCE and PCE were discovered in the municipal well (Jacobs, 1997d). Because both wells are closely monitored and USAF has devised remediation strategies (granular activated carbon pump-and-treat systems) in the event of contamination, future public exposure to contaminated drinking water from municipal wells is extremely unlikely. USAF, EPA, and the state of California continue to discuss the potential future installation and operation of wellhead treatment at AM-6 and the construction of a new water supply well to replace AM-6. ATSDR concludes that present and future exposures to contaminated groundwater from off-base production wells is unlikely to pose public health hazards.

2. Concern: Soil

Could exposure to soil contaminants in areas designated as "Residential" or "Public Facilities/Recreation" by the Castle AFB FEIS result in adverse health effects for employees, residents, or visitors of Castle AFB?

Conclusions

  • Castle AFB soils have been contaminated by routine military and industrial activities, including painting and stripping operations, aircraft and vehicle maintenance, and pesticide application.


  • The major sources of contamination at Castle AFB either have been or will be remediated (e.g., bioventing, soil vapor extraction, landfill consolidation, or capping).


  • ATSDR concludes that no public health hazards are associated with exposure (past, present, and future) to contaminated soil at Castle AFB because public access to contaminated sites is extremely limited, if it occurs at all.

Discussion

Soils in the Castle AFB area exhibit high variability in their permeability characteristics, but generally consist of course-textured, highly permeable surface soil and less permeable subsurface soil approximately 2 to 4 feet bgs (Jacobs, 1997a,b). The main sources of soil contamination at Castle AFB include underground storage tanks (UST), pipelines, and underground fuel lines; industrial waste lines; aircraft, vehicle, and equipment maintenance facilities; waste storage facilities; surface spills and releases; drains and sumps; fire training areas; and landfills and disposal pits. Almost all of the contaminated soil sites identified in the SCOU are either underground or located in industrial areas (e.g., the airport runways) where public exposure is unlikely (Jacobs, 1997b; USAF 1997a).

Solid Waste Assessment Tests were performed on all base landfills between 1990 and 1991. No leachate contamination was found to extend off site from any of the landfills and no evidence of hazardous waste was discovered. Castle AFB's SCOU addresses the problem of soil contaminants at a wide variety of sites across the base. From a total of 209 sites considered in the initial draft SCOU Remedial Investigation/Feasibility Study (RI/FS) (beginning in April 1993), soil at 28 sites or groups of sites was identified as having the potential to affect the quality of the underlying groundwater (Figure 5 and Appendix A) (Jacobs, 1997a,b).

ATSDR evaluated the data and information presented in the SCOU RI/FS, remediation reports, and work plans to assess potential exposure pathways via soil. ATSDR determined that human exposure to contaminated soil at Castle AFB does not comprise a past, present, or potential future pathway because contamination was: 1) detected at levels that did not pose a public health hazard; 2) detected at depths below the ground's surface that are inaccessible to the general public; or 3) in areas where site access was restricted, unlikely, or infrequent (e.g., industrial areas or areas surrounded by perimeter fencing). In addition, USAF has removed most contaminated soils and consolidated the debris into a restricted, on-base landfill and/or treated contaminated soils with remediation technologies in areas where future public exposure is a possibility (e.g., Castle Vista) (Gutierrez-Palmenberg, 1998a,b; USAF, 1998). Zoning restrictions are also in place to prevent future residential redevelopment in areas where contaminant levels were only reduced to industrial target cleanup goals (USAF, 1998). USAF and EPA are still considering alternatives at some installation sites. Appendix A and Appendix E provide the most current information about USAF remediaton efforts and the base reuse plan.

ATSDR concludes that soil contamination at Castle AFB does not pose a public health hazard.

3. Concern: Other Public Health Concerns

Has contamination from Castle AFB affected local agricultural products and potentially harmed those individuals consuming locally-grown produce?

Conclusions

  • ATSDR concludes that produce from farms surrounding Castle AFB is safe to eat; it does not pose a public health hazard.

Discussion

Prior to remedial investigations at Castle AFB, CADHS conducted a biological survey of the orchards bordering the Castle AFB area. Almonds trees irrigated with TCE-contaminated groundwater (10 to 12 ppb TCE) contained no detectable contaminant concentrations in the edible nut (CADHS, 1990; also see Hicks, 1998b; Jacobs, 1995; LABAT, 1995). Because the trees do not bioaccumulate TCE, the consumption of agricultural products from farms surrounding Castle AFB does not pose a public health hazard.


ATSDR CHILD HEALTH INITIATIVE

ATSDR recognizes that infants and children may be more sensitive to exposures than adults in communities with contamination in their water, soil, air, or food. This sensitivity is a result of a number of factors. Children are more likely to be exposed to soil or surface water contamination because they play outdoors and often bring food into contaminated areas. For example, children may come into contact with and ingest soil particles at higher rates than adults do; also, some children with a behavior trait known as "pica" are more likely than others to ingest soil and other nonfood items. Children are shorter than adults, which means they can breath dust, soil, and any vapors close to the ground. Also, they are smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Because children depend completely on adults for risk identification and management decisions, ATSDR is committed to evaluating their special interest at sites such as Castle AFB, as part of the ATSDR Child Health Initiative.

ATSDR has attempted to identify populations of children in the vicinity of Castle AFB and any completed exposure pathways to these children. In the past, Castle AFB maintained residences for base personnel and their families that were impacted by TCE-contaminated groundwater. Low-level TCE contamination also affected the drinking water sources of residential areas west (Santa Fe Drive and Wallace Road) and southwest (Castle Vista and Castle Gardens) of the Main Base. The estimated exposure doses for children, however, were below levels associated with adverse health effects (see Appendix B).

Children are not exposed to harmful levels of cis-1,2-DCE from the irrigation well at the Thomas Oleata School (I2266) because no one drinks from I2266. Cis-1,2-DCE concentrations are too low to be of health concern from inhalation or dermal contact. Moreover, due to USAF remediation activities, contaminant concentrations in the Castle Vista Plume are dropping. I2266 irrigation water currently meets all state and federal drinking water standards (cis-1,2-DCE concentrations range between 0.54 to 4.0 ppb). Additionally, I2266 is most frequently used during the summer months and is only operated at night when children are least likely to be present at the school.

Public recreation facilities located on Castle AFB property that are likely to attract children include Castle Park, the Challenger Learning Center and Aviation Challenge Foundation, the Castle Aviation Museum Foundation, and the gym and athletic facilities. None of these sites is associated with past hazardous waste activities (USAF, 1997b). Largely due to perimeter fencing and zoning restrictions, children do not have access to contaminated areas (e.g., industrial areas or subsurface soil). Exposure to on-site contamination is further limited because children visit on-base public recreation facilities infrequently and for only a few hours at a time. Visiting children will not remain on-site long enough to experience chronic exposure. In the few areas where surface soil contaminants exceed ATSDR comparison values for children (e.g., Castle Vista), USAF is remediating soil contamination to levels below state and federal guidelines.

Assuming that groundwater contamination in the vicinity of Castle AFB will continue to be closely monitored, that the base will continue to be used for the activities outlined in the FEIS reuse plan, and that children will continue to be restricted from industrial areas on the base, ATSDR concludes that past, present, and future exposures to on- and off-site groundwater and soil do not represent a public health hazard for children.


CONCLUSIONS

Based on a thorough evaluation of available environmental information, ATSDR has reached the following conclusions:

  1. TCE, cis-1,2-DCE, and other contaminants have been detected at levels above ATSDR comparison values in groundwater underlying Castle AFB property. Past and present exposure to most groundwater contamination has been avoided because seven of the nine identified plumes have not extended to active wells and/or contaminant concentrations remain below state and federal drinking water standards (e.g., MCLs). In on- and off-site areas where people have ingested TCE-contaminated groundwater at levels above health-based guidelines, no public health hazard exists due to the short durations of exposure, the low exposure doses, and/or remediation efforts by USAF.


  2. Future exposure to groundwater contaminants of concern (primarily TCE and cis-1,2-DCE) above health-based guidelines is unlikely. Castle AFB, municipal, private, irrigation, and production wells in the Merced-Atwater area will continue to be monitored closely.


  3. Some Castle AFB soils contain contaminants above ATSDR comparison values, but public exposure (past, present, and future) is not likely, largely because access to contaminated sites is limited and contamination occurs primarily in subsurface soils or industrial areas. In the few contaminated areas that the public may potentially access, USAF is in the process of remediating surface soil contamination as necessary to attain levels that do not pose a health hazard.


  4. No public health hazard exists (past, present, or future) from the consumption of agricultural products from the areas surrounding Castle AFB.

PUBLIC HEALTH ACTION PLAN

The Public Health Action Plan (PHAP) for Castle AFB contains a description of actions taken and those to be taken, as necessary, by ATSDR, USAF, EPA, and CADHS at and in the vicinity of the site subsequent to the completion of this public health assessment. The purpose of the PHAP is to ensure that the public health assessment not only identifies public health hazards, but provides a plan of action designated to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. The public health actions that are completed, being implemented, or planned are as follows (see Figure 6):

Completed Groundwater Actions

  • Beginning in 1994, OU 1 consisted of one extraction well and treatment system (air stripping technologies). In July of that year, the OU 1 remediation system was expanded and all extracted water was treated with air stripping technologies combined with the application of natural biological agents to enhance and accelerate the degradation of hazardous constituents. A repair and expansion phase was performed in 1996 to increase the flow rate of the remediation system and to optimize plume control. To date, OU 1 has treated approximately 550 million gallons of water, removing over 340 pounds of TCE. From July 1994 to April 1998, the average TCE concentration in OU 1 groundwater influent has declined from 150 ppb to 46 ppb (Hicks, 1998a; Stowe, 1998).


  • Beginning in 1996, groundwater extraction and treatment systems were installed to remove the highest contaminant concentrations in the shallow and upper subshallow groundwater zones within the OU 2 area of the Main Base Plume. As of early February 1998, OU 2 had treated a total of 672 million gallons of water and removed 226 pounds of TCE. From November 1996 to April 1998, the average TCE concentration in OU 2 groundwater influent has declined from 200 ppb to 25 ppb (Hicks, 1998a; Stowe, 1998).


  • Beginning in September 1997, the Phase 2 pump-and-treat system became operational. The Phase 2 system is designed to cover areas of the Main Base Plume not reached by OU 1 or OU 2 systems. Phase 2 has treated over 80 million gallons of water and removed approximately 23 pounds of TCE. The average TCE concentration in Phase 2 groundwater influent has not yet measurably declined; it is currently about 30 ppb (Hicks, 1998a; Stowe, 1998).


  • In October 1997, the Castle Vista treatment system became operational. It is designed to remediate the Castle Vista Plume. To date, it has treated 20.5 million gallons of water and removed 7.4 pounds of cis-1,2-DCE. From October 1997 to April 1998, the average cis-1,2-DCE concentration in Castle Vista groundwater influent declined from 26 ppb to 8 ppb (Hicks, 1998a; Stowe, 1998).

Completed Soil Actions

  • USAF completed investigations at the 209 RI/FS sites to identify potentially contaminated areas. Soil investigations, cleanup, and site restoration is completed at most of these targeted areas (see Appendix A).


  • As of 1996, USAF had removed or closed 142 of the 152 inactive USTs (ranging in size from 300 gallons to 25,000 gallons) and two above ground storage tanks at Castle AFB (USAF, 1997a).


  • USAF has implemented certain restrictions (e.g., no digging without health and safety precautions) regarding future land use and activities in various areas of known contamination. Areas not mitigated by IRP activities will continue to have restricted use after the Air Force has vacated the property. The health of workers at non-mitigated sites will be protected by Occupational Safety and Health Administration's regulations and restrictions.

Ongoing/Planned Actions

  • USAF will continue to monitor all regions of groundwater contamination and maintain or up-grade remedial equipment as needed.


  • USAF, EPA, CADHS, ATSDR, and local municipalities will continue to collect and analyze data from Castle AFB, municipal, private, irrigation, and production wells on- and off-base. Most importantly, ATSDR recommends on-going future monitoring of the city of Atwater's production well AM-6.


  • In order to prevent potential future exposure via AM-6, ATSDR recommends that the Air Force, EPA, and state of California develop a plan to install an AM-6 wellhead treatment system or to construct a new water supply well to replace AM-6. This plan should be implemented as needed, based on future drinking water quality conditions.


  • The two landfills located next to the Castle Vista residential housing area are in the final stages of remediation. Both Castle Vista Landfill A (CVLF-A) and Castle Vista Landfill B (CVLF-B) have been excavated and are in the process of being replaced with clean fill. The excavated landfill debris is being disposed of on-base in Landfill 4 (LF-4). LF-4, which is surrounded by perimeter fencing and inaccessible to the general public, will later be capped (Gutierrez-Palmenberg, 1998a,b).


  • Several landfills located on base property (in addition to the Castle Vista landfills previously mentioned) are being or will be consolidated into two on-base landfills (LF- 4 and LF-5). After consolidation efforts are completed, LF-4 and LF-5 will be capped. Both landfills are fenced so public exposure to contaminants within these landfills is highly unlikely (Gutierrez-Palmenberg, 1998a,b).


  • All areas where the potential exists for future public exposure (e.g., areas designated as "Residential" or "Public Facilities/Recreation" by the Castle AFB FEIS) and numerous industrial locations on base are being treated or will be treated with soil vapor extraction technologies to remove VOCs. Bioventing technologies are also being used (USAF, 1997a) (Appendix A).


  • CERCLA, as amended, requires ATSDR to conduct needed follow-up health actions in communities living near hazardous waste sites. To identify appropriate actions, ATSDR created the Health Activities Recommendation Panel (HARP). HARP has evaluated the data and information contained in the Castle AFB public health assessment for appropriate public health actions. At this time, no follow up health activities are recommended for Castle AFB because there is no know exposure at this site at levels that pose a public health threat.

PREPARERS OF REPORT

W. Mark Weber, Ph.D.
Environmental Health Scientist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

Gary Campbell, Ph.D.
Environmental Health Scientist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation


REFERENCES

ATSDR. 1997. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services. Toxicological Profile for Trichloroethylene. September 1997 (Update).

ATSDR. 1998. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services. Site visit. Castle Air Force Base, Merced County, California. January 21-22, 1998.

CADHS. 1990. California Department of Health Services. Ambient Air Monitoring Report: Castle Air Force Base, Merced County, California. October 1990.

CJPA. 1996. Castle Joint Powers Authority. Final Castle Air Force Base Reuse Plan. May 9, 1996.

EPA. 1989. U.S. Environmental Protection Agency Risk assessment guidance for superfund. Human health evaluation manual. Office of Solid Waste and Emergency Response. OHEA-E-451. 1989.

EPA. 1995. U.S. United States Environmental Protection Agency. Exposure Factors Handbook--Final Report. Office of Health and Environmental Assessment. 1995.

Gutierrez-Palmenberg, Inc. 1997. Community Relations Plan: Castle Airport Aviation and Development Center. July 1997.

Gutierrez-Palmenberg, Inc. 1998a. Castle Restoration Advisory Board Meeting Minutes and Question and Answer Summary: January 27, 1997, Atwater City Council Chambers.

Gutierrez-Palmenberg, Inc. 1998b. Castle Restoration Advisory Board Meeting Minutes and Question and Answer Summary: February 24, 1997, Atwater City Council Chambers.

Hicks, B. 1998a. Conversation between Brad Hicks, Remedial Project Manager, Castle Air Force Base, United States Air Force, and Kristen Honey, Eastern Research Group, Inc., regarding groundwater contamination at Castle Air Force Base. September 8, 1998.

Hicks, B. 1998b. Conversation between Brad Hicks, Remedial Project Manager, Castle Air Force Base, United States Air Force, and Kristen Honey, Eastern Research Group, Inc., regarding contamination in agricultural produce grown in the vicinity of Castle Air Force Base. April 24, 1998.

Jacobs. 1994. Jacobs Engineering Group, Inc. Operable Unit 2: Hydrogeological Technical Memorandum (Volume 1 of 2). United States Air Force Installation Restoration Program, Castle Air Force Base. Final, January 1994.

Jacobs. 1995. Jacobs Engineering Group, Inc. Installation Restoration Program, Castle Air Force Base Remedial Investigation/Feasibility Study, Scoping and Ecological Risk Assessment (ERA). Prepared for the Air Force Center for Environmental Excellence AFCEE, Brooks Air Force Base, Texas. December, 1995.

Jacobs. 1996a. Jacobs Engineering Group, Inc. Comprehensive Basewide Remedial Investigation/Feasibility Study - Part I (Volume 1 of 3; Groundwater Remedial Investigation Report). United States Air Force Installation Restoration Program, Castle Airport. June 1996.

Jacobs. 1996b. Jacobs Engineering Group, Inc. Comprehensive Basewide Remedial Investigation/Feasibility Study - Part 2 (Volume 1 of 1). United States Air Force Installation Restoration Program, Castle Airport. Draft, December 1996.

Jacobs. 1997a. Jacobs Engineering Group, Inc. Source Control Operable Unit Remedial Investigation/Feasibility Study Executive Summary. United States Air Force Installation Restoration Program, Castle Airport. Final, May 1997.

Jacobs. 1997b. Jacobs Engineering Group, Inc. Source Control Operable Unit Remedial Investigation/Feasibility Study - Part 2: Baseline Human Health Risk Assessment. United States Air Force Installation Restoration Program, Castle Airport. Final, May 1997.

Jacobs. 1997c. Jacobs Engineering Group, Inc. Long-Term Groundwater Sampling Plan 1997 Semi-Annual Report. United States Air Force Installation Restoration Program, Castle Airport. July 1997.

Jacobs. 1997d. Jacobs Engineering Group, Inc. Castle Vista Landfill B: Groundwater Remedial Action Work Plan Addendum. United States Air Force Remedial Action Contract, Castle Airport. Draft, September 1997.

LABAT. 1995. LABAT-ANDERSEN Inc. Sampling and Analysis Report for Chlorinated Dibenz Dioxins and Dibenz Furans in Wastewater and Sediments, Castle AFB California. May 25, 1995.

Stowe, R. (ed.). 1998. Castle Airport project update. In EnviroProgress (newsletter by Gutierrez-Palmenberg, Inc., for Castle Airport, Atwater, CA). Edition 23. July 1998.

USAF. 1994a. United States Air Force. Socioeconomic Impact Analysis Study: Disposal and Reuse of Castle Air Force Base, California. January 1994.

USAF. 1994b. United States Air Force. Final Environmental Impact Statement: Disposal and Reuse of Castle Air Force Base, California. November 1994.

USAF. 1996. United States Air Force. Record of Decision, CB-Part 1 Groundwater, Castle Air Force Base. September 15, 1996.

USAF. 1997a. United States Air Force. Record of Decision for Castle Source Control Operable Unit. Draft, November 15, 1997.

USAF. 1997b. United States Air Force. BRAC Cleanup Plan (BCP) Castle Air Force Base, Merced County, California: Implementing President Clinton's Decision to Promote Early Reuse of Closing Bases by Expediting Environmental Cleanup. May 1997.

USAF. 1998. United States Air Force. BRAC Cleanup Plan (BCP), Castle Air Force Base, Merced County, California: Implementing President Clinton's Decision to Promote Early Reuse of Closing Bases by Expediting Environmental Cleanup. Final, January 1998.

Vartianinen, T., E. Pukkala, T. Rienoja, et al. 1993. Population exposure to tri- and tetrachloroethylene and cancer risk: Two cases of drinking water pollution. Chemosphere. 27: 1171-1181.


Table 1: Summary of Exposure Pathways at Castle Air Force Base
PATHWAY NAME POTENTIAL SOURCE OF CONTAMINATION ENVIRON-MENTAL MEDIUM POINT OF EXPOSURE ROUTE OF EXPOSURE TIME OF EXPOSURE EXPOSED POPULATION COMMENTS
Drinking water
(On-base production wells)
Trichloroethylene (TCE)-- Castle AFB Main Base area.

Sites that are likely contributing to the Main Base Plume (Region 1 and Region 2) include: the Sanitary Sewer Line, Storm Drainage System, Petroleum, Oil and Lubricants Fuel Farm Area, Structure 61, underground fuel leaks, disposal area, and several buildings located in the Main Base area.

Groundwater Water supplied to on-base residents and employees of Castle AFB. Ingestion Past:
• TCE was first detected in trace amounts in on-base wells in February 1978. TCE was detected above the Maximum Contaminant Level (MCL) (5.0 parts per billion [ppb]) in on-base wells in 1984.

Present and Future:
• No contaminants (including TCE) have been detected above MCLs in on-base active production wells (PW) since February 1985 (when PW-10 began operating).

Past:
• Users of the Castle AFB water supply.

• Approximately 5,200 to 7,300 military and civilian jobs were based at Castle AFB.

Present and Future:
None

Past:
• After TCE was detected above the MCL in drinking water, the base commander notified workers and residents at Castle AFB to use an alternate water supply. The base commander also required the base hospital and all food-serving establishments to use bottled water.

Present and Future:
• The primary production wells for the base (PW-10 and PW-12) have been unaffected by contamination. The wells extract water from approximately 900 feet below ground surface. The water from PW-10 and PW-12 is chlorinated, fluoridated, and pumped directly into the water distribution system. The only other active production wells at Castle AFB (PW-6 and PW-11) operate on an as-needed basis for facilities in the northeast part of the base.
• All Castle AFB drinking water is filtered and treated, reducing groundwater contaminants to levels below state and federal drinking water standards.
• Remedial activities are reducing, and will continue to reduce, TCE concentrations in groundwater.
• Groundwater monitoring will continue on-base. If contamination of a drinking water well is detected in the future, the use of the affected well will be discontinued or further remediated as necessary.

Past, current, and future use of Castle AFB drinking water poses no public health hazards.

Drinking water
(Off-base private wells [west of Castle AFB along Santa Fe Drive and Wallace Road])
TCE-- Castle AFB Main Base area.

Sites that are likely contributing to the Main Base Plume (Region 1 and Region 2) include: the Sanitary Sewer Line, Storm Drainage System, Petroleum, Oil and Lubricants Fuel Farm Area, Structure 61, underground fuel leaks, disposal area, and several buildings located in the Main Base area.

Groundwater Water supplied to off-base residents living on Santa Fe Drive and Wallace Road. Ingestion Past:
TCE was first detected in trace amounts in off-base wells in October 1984. In 1985, TCE contamination exceeded the MCL (5 ppb).

Present and Future:
• No contaminants (including TCE) have been detected above MCLs since 1989 (when Santa Fe Drive and Wallace Road residents were connected to the Castle AFB water supply).

Past:
• Two families living on Santa Fe Drive.
• Three families living on Wallace Road.

Present and Future:
• None

Past:
• After TCE was first detected above the MCL in off-base drinking water, USAF supplied all affected residents with bottled water until activated carbon filtration systems could be installed on their private wells.
• One Wallace Road resident was connected to the base water supply in February 1989; the other two Wallace Road residences were connected in October 1989.

Present and Future:
• As of 1997, no residents were using bottled water and five families had carbon filter systems that are maintained by USAF. USAF will continue to change the carbon filters annually.
• All previously affected residents receive filtered and treated drinking water, either from their own private wells or from the Castle AFB water supply. All groundwater contaminant levels remain below state and federal drinking water standards.
• Groundwater monitoring will continue off-base. If contamination of a drinking water well is detected in the future, the use of the affected well will be discontinued or further remediated as necessary.
• USAF remedial activities are reducing, and will continue to reduce, TCE concentrations in groundwater.

Past, current, and future use of Santa Fe Drive and Wallace Road drinking water poses no public health hazards.

Drinking water
(Off-base wells at Castle Gardens [Castle Mobile Home Park])
TCE-- Castle AFB Main Base area.

Sites that are likely contributing to the Main Base Plume (Region 1 and Region 2) include: the Sanitary Sewer Line, Storm Drainage System, Petroleum, Oil and Lubricants Fuel Farm Area, Structure 61, underground fuel leaks, disposal area, and several buildings located in the Main Base area.

Groundwater Water supplied to Castle Gardens residents Ingestion Past:
TCE was first detected in trace amounts in October 1984. In November 1985, TCE contamination exceeded the MCL (5 ppb) in two of the three off-base wells supplying Castle Gardens.

Present and Future:
• No contaminants (including TCE) have been detected above MCLs since March 1989 (when Castle Gardens residents were connected to the city of Atwater water supply).

Past:
Approximately 120 residents of Castle Gardens.

Present and Future:
• None

Past:
• After TCE was first detected above the MCL in off-base drinking water, USAF supplied all affected residents with bottled water.
• Castle Gardens residents were connected to the city of Atwater water supply in March 1989.

Present and Future:
• All Castle Gardens residents are connected to the city of Atwater water supply which has remained unaffected by contamination. The city of Atwater drinking water has been screened since the early 1980s. No contaminant levels have exceeded state or federal drinking water standards.
• Groundwater monitoring of the city of Atwater drinking water will continue. If contamination is detected in the future, the use of the affected well will be discontinued or further remediated as necessary.
• USAF remedial activities are reducing, and will continue to reduce, TCE concentrations in groundwater.

Past, current, and future use of Castle Gardens drinking water poses no public health hazards.

Drinking water
(Municipal production and irrigation wells)
TCE-- Primarily the Castle AFB Main Base area, although other plumes could potentially migrate off-base and impact municipal well water.

cis-1,2-dichloroethylene (cis-1,2-DCE) and TCE-- Castle Vista area.

Sites that are likely contributing to the Main Base Plume (Region 1 and Region 2) include: the Sanitary Sewer Line, Storm Drainage System, Petroleum, Oil and Lubricants Fuel Farm Area, Structure 61, underground fuel leaks, disposal area, and several buildings located in the Main Base area.

The most likely source of contamination is Castle Vista Landfill B.

Groundwater Municipal water supplied to the city of Atwater and the Merced Irrigation District. Ingestion Past and Present:
• No contaminant levels in municipal production or irrigation wells have exceeded ATSDR comparison values for drinking water.

Future:
• Atwater municipal wells (AM) 16 and 6 could potentially become contaminated with TCE or cis-1,2-DCE, respectively.

Past and Present:
• None

Future:
• Atwater has a population of approximately 20,000. It has not been estimated how many of these residents are potential future receptors of contaminated municipal drinking water.

Past and Present:
• All city of Atwater drinking water has been screened since the early 1980s. No contaminant levels have exceeded state or federal drinking water standards.
• Approximately 12 irrigation wells are located within approximately 1 mile of Castle AFB, downgradient or crossgradient of the main plume regions. Only five of these wells are currently operational due to structural damages or lack of a power source. All operable irrigation wells remain unaffected by Castle AFB contamination. These wells are used on an as-needed basis, primarily in the summer months.

Future:
• AM-16 and AM-6 are considered a prime potential conduit/receptor for contamination from Castle AFB. AM-16 lies downgradient of the Main Plume. AM-16 was shut off in December 1996 at the USAF's request in order to minimize the potential for migration of the contaminant plume towards this well. AM-16 is periodically brought back on line to meet the city of Atwater's high water demands during the summer. AM-6 lies at the leading edge of the Castle Vista Plume. It is 1 of 10 operational production wells for the city of Atwater. Shutting off AM-6 could adversely affect the water pressure in the central part of the system. USAF, therefore, developed a pump-and-treat remediation strategy (wellhead granulated activated carbon treatment system) in the event that AM-6 becomes contaminated. USAF, EPA, and the state of California continue to discuss potential future installation and operation of wellhead treatment at AM-6 and potential future construction of a new water supply well to replace AM-6.
• Monitoring of the city of Atwater drinking water and the Merced Irrigation District irrigation water will continue. If contamination is detected in the future, the use of the affected well will be discontinued or further remediated as necessary.
• USAF remedial activities are reducing, and will continue to reduce, cis-1,2-DCE and TCE concentrations in groundwater.

Past, current, and future use of municipal drinking and irrigation water poses no public health hazards.

Drinking water
(Off-base wells at Castle Vista)
cis-1,2-DCE and TCE-- Castle Vista area.

The most likely source of contamination is Castle Vista Landfill B.

Groundwater Irrigation water supplied to Castle Vista residents Inhalation
Dermal Absorption
Past, Present and Future:
• One private irrigation well (I2266) at the Thomas Oleata School has low concentrations (0.54 ppb to 4 ppb) of cis-1,2-DCE and trace concentrations of TCE in its water. Past concentrations of cis-1,2-DCE were
slightly higher (approximately 10 ppb) and exceeded the state MCL of 6.0 ppb. No one, however, drinks from I2266. No Castle Vista drinking water has exceeded ATSDR comparison values or state and federal standards.
Past, Present and Future:
• Students and employees at the Thomas Oleata School.
Past, Present and Future:
• The only affected well (I2266) is a private irrigation well located at the Thomas Oleata School. I2266 is used solely for landscape irrigation at night when no children are present on school grounds. It is used on an as-needed basis, primarily in the summer months.
• No private drinking water wells have been impacted by the Castle Vista Plume.
• Groundwater monitoring of the Castle Vista irrigation and drinking water will continue. If contamination is detected in the future, the use of the affected well will be discontinued or further remediated as necessary.
• USAF remedial activities are reducing, and will continue to reduce, cis-1,2-DCE and TCE concentrations in groundwater.

Past, current, and future use of Castle Vista irrigation water poses no public health hazards.

Area Map - Castle AFB, California
Figure 1. Area Map - Castle AFB, California

Site Map - Castle AFB, California
Figure 2. Site Map - Castle AFB, California

ATSDR's Exposure Evaluation Process
Figure 3. ATSDR's Exposure Evaluation Process

Location of Suspected Groundwater Plumes
Figure 4. Location of Suspected Groundwater Plumes

Locations of the RI/FS Sites - Castle AFB, California
Figure 5. Locations of the RI/FS Sites - Castle AFB, California

Locations of Remediated Groundwater Plumes and SCOU Sites - Castle AFB, California
Figure 6. Locations of Remediated Groundwater Plumes and SCOU Sites - Castle AFB, California

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