PUBLIC HEALTH ASSESSMENT
WAHIAWA, HONOLULU COUNTY, HAWAII
The Schofield Army Barracks (Schofield) comprises two sections -- the East Range and the Main Post -- covering 17,725 acres on the island of Oahu in Hawaii, 22 miles northwest of the city of Honolulu. Most of the area surrounding the installation is rain forest or land used for pineapple production. Wheeler Army Airfield lies adjacent to the installation to the south and the town of Wahiawa lies to the north. Schofield serves as headquarters for the 25th Infantry Division and 45th Support Group. As an active military installation and a residential community, Schofield's mission is to provide administration, training, and housing facilities.
In April 1985, trichloroethylene (TCE) was detected in drinking water supply wells at the installation at concentrations up to 30 parts per billion (ppb). After this discovery, the Environmental Protection Agency (EPA) placed Schofield on its National Priorities List (NPL) in August 1990. A remedial investigation of the facility characterized the extent of groundwater contamination and revealed that several other environmental media, including soil, surface water, and sediment, were contaminated. Potential contaminants of concern at this site include volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), pesticides, polychlorinated biphenyls (PCBs), and inorganic chemicals. The Agency for Toxic Substances and Disease Registry (ATSDR) conducted an initial site visit in 1991 and a second site visit in 1995 (ATSDR 1991; ATSDR 1995). During these visits, ATSDR identified drinking water contaminated with TCE in the past as the only potential completed exposure pathway that may have posed a public health hazard.
Since ATSDR's initial site visit, potential groundwater, soil, surface water, and sediment exposure pathways have been more fully characterized. The groundwater beneath Schofield was found to contain levels of TCE and carbon tetrachloride that exceeded EPA's maximum contaminant levels (MCLs) for drinking water. Four on-site wells supply drinking water to the employees and residents of Schofield. Contamination of these wells is limited to TCE and the wells' water has been treated with an air stripper since September 1986. Drinking water supply wells are monitored to ensure federal drinking water standards are met, and a system of monitoring wells throughout Schofield and nearby communities is routinely monitored to ensure that contamination is detected and drinking water supplies are protected. On the basis of available data, ATSDR concludes that employees and residents of Schofield were exposed to contaminated drinking water in the past but that this exposure is not likely to have posed a health hazard. Further, ATSDR concludes that contaminated groundwater under Schofield does not pose a current or potential future threat to public health because drinking water is treated and monitored at the wellhead.
ATSDR also reviewed on-site soil, surface water, and sediment data. Although levels of VOCs, SVOCs, pesticides, PCBs, and inorganic chemicals were detected above comparison values in some samples taken in these media, ATSDR determined that they do not pose a public health threat because these detections occurred in areas of limited access (industrial areas), were detected in subsurface soil and are therefore inaccessible, or were detected sporadically and at levels that do not pose a health hazard. On the basis of available data, ATSDR concludes that exposure to contaminants in soil, surface water, and sediment at Schofield does not pose a health hazard.
Schofield Army Barracks (Schofield) is located on the north central plateau (Schofield Plateau) of the island of Oahu in the state of Hawaii, approximately 22 miles northwest of the city of Honolulu (see Figure 1). It covers approximately 27.7 square miles (17,725 acres) and is divided into two sections: the East Range and the Main Post. The closest municipality is Wahiawa, which is adjacent to and immediately north of the East Range. Wheeler Army Airfield is located between and south of the Main Post and East Range areas.
Schofield is an active military installation and a residential community where light industrial activities are performed. The facility was established in 1908 to provide a base for the Army's mobile defense of Pearl Harbor and Oahu. The installation has been in operation since that time, providing a military operational and residential base of varying capacity.
Following the attack on Pearl Harbor by the Japanese in 1941, Schofield became a supply base and command center for the war in the Pacific and established training camps. As many as 100,000 soldiers at a time may have been housed at Schofield during the war. Following World War II, the population at Schofield declined sharply, but increased again in 1951 when a basic training center for troops bound for the Korean War was established. During the mid-1950s, another resurgence occurred when the 25th Infantry Division was headquartered there. Troops were again deployed from Schofield during the Vietnam War. After the Vietnam War, many facilities at the site were renovated, and the civilian population of surrounding communities grew as roads were built. Throughout its history, Schofield's industrial operations involved vehicle and aircraft maintenance and repair, including painting and degreasing. These types of operations required using various types of organic solvents, including trichloroethylene (TCE) (HLA 1996a).
Schofield is the Army's largest installation outside the continental United States. Currently, the 25th Infantry Division and the 45th Support Group are headquartered at Schofield. The 25th Infantry Division's mission is to be prepared to respond to an emergency at a moment's notice. According to the 1990 U.S. Census, approximately 20,000 people reside at Schofield. No major industrial operations exist at the site. Current operations performed at Schofield are administration, firing and nonfiring training, and small-scale industrial operations, including vehicle and building repair and maintenance, weapons refinishing, electrical equipment service, and sewage treatment.
On April 30, 1985, the Hawaii Department of Health announced that TCE had been detected at 30 parts per billion (ppb) in one of the four on-site wells supplying drinking water to residents and personnel at Schofield (U.S. Army 1985a). The Army suspended use of the wells on May 2, 1985, and drinking water was supplied from off-site wells in Wahiawa (U.S. Army 1985b). To meet demand, intermittent pumping of the least contaminated Schofield wells was approved, and the water was blended with uncontaminated water from Wahiawa. Water was blended from Wahiawa and Schofield wells until September 1986, when an air stripper treatment system was installed in Schofield's water supply wells. Blending of water from Wahiawa supply wells was discontinued at that time. Water from the Schofield wells continues to be treated at the wellhead by air stripper technology and is the source of drinking water for the installation.
As a result of the 1985 TCE discovery, the U.S. Environmental Protection Agency (EPA) evaluated the installation in July 1989 and proposed Schofield for the National Priorities List (NPL). Schofield was listed on the NPL in August 1990. EPA, the State of Hawaii, and the Army negotiated a Federal Facilities Agreement authorizing a remedial investigation (RI). A total of four operable units (OUs) were designated to facilitate orderly investigation of the source(s), nature, and extent of contamination at the installation, and to enable the design of necessary and appropriate cleanup measures, if any (HLA 1996a).
After a thorough review of Army records of historical operations, old photographs of the installation, and discussions with post employees, OU 1 was designated to include 10 sites, located throughout the Main Post and East Range, that were considered possible sources of the TCE groundwater contamination (HLA 1995a). The RI did not identify the source of the TCE groundwater contamination, however. Furthermore, the record of decision (ROD) for OU 1, issued in April 1995, states that no remedial action is necessary for any of the sites "because no contaminants were found at the ten OU 1 sites investigated that presented an unacceptable risk to human health or the environment based on EPA risk guidelines" (HLA 1995b). Table 1 summarizes the waste disposal history, investigation results, current status, and evaluation of public health hazards at all sites in OU 1.
OU 2 covers the TCE-contaminated groundwater. Investigations at OU 2 were designed to determine the level and geographical extent of contamination. Although TCE, carbon tetrachloride, pentachlorophenol, antimony, chromium, cadmium, and nickel were detected above maximum contaminant levels (MCLs) in groundwater samples, TCE was the only contaminant that exceeded an MCL in Schofield water supply wells (HLA 1996a). Two TCE-contaminated groundwater plumes were identified under Schofield: one at the water supply wells and one under the Former Schofield Barracks Landfill (Former Landfill). TCE levels did not exceed the MCL at any off-site municipal drinking water or irrigation wells downgradient of Schofield, and the RI determined that migration would not occur to these wells for at least 100 years (HLA 1996a).
The ROD for OU 2, issued in August 1996, calls for long-term monitoring of groundwater at Schofield but no remediation beyond the air stripper treatment system that has been in operation at the drinking water supply wells since September 1986 (HLA 1996c). Table 1 summarizes the RI investigation results, current status, and evaluation of public health hazards for OU 2. Table 2 summarizes the TCE concentrations detected in the groundwater at Schofield during the RI and the first two rounds of sampling performed as part of the long-term monitoring.
During the review of historical operation records from Schofield, several other potentially contaminated sites were also identified. A total of 34 of these sites were located throughout the Main Post and the East Range and were designated as OU 3 (Uribe 1996a). The ROD, issued in August 1996, concluded that no remedial activities were required at any of the sites in OU 3 "because no contaminants found at OU 3 were present at concentrations that pose an unacceptable risk to human health or the environment based on U.S. EPA risk guidelines" (Uribe 1996b). Table 1 summarizes the waste disposal history, investigation results, current status, and evaluation of public health hazards at all sites located in OU 3.
The RI determined that the Former Landfill was the source of one of the plumes of TCE contamination in the groundwater. This plume emanates from under the landfill, lies within the Main Post, and is separate from the plume contaminating the drinking water wells (HLA 1996a). The Former Landfill was designated as OU 4. The investigation for OU 4 was conducted in accordance with EPA's guidance for municipal landfills (HLA 1995c). The ROD, issued in July 1996, calls for regrading and recapping the landfill, which was originally capped in 1983 (HLA 1996b). Table 1 summarizes the waste disposal history, investigation results, current status, and evaluation of public health hazards at the Former Landfill.
The Schofield Plateau is bounded on the east by the Koolau Mountain Range, which rises to an elevation of 2,800 feet above sea level, and on the west by the Waianae Mountain Range, which rises to an elevation of 4,000 feet above sea level. The central portion of Schofield Army Barracks is nearly flat but slopes upward to the east and west toward the mountain ranges. The surface soil at the site is in-situ weathered volcanic basalt (saprolite) to about 75 to 200 feet deep, and overlies basaltic bedrock.
The East Range is drained by the south fork of the Kaukonahua Stream, which empties into Wahiawa Reservoir 3 miles downstream of Schofield. The Main Post is drained mostly by the Kaukonahua Stream. The Kaukonahua Stream is located downstream from the Wahiawa Reservoir and eventually empties into Kaiaka Bay. The southern portion of the Main Post is drained by the Waikele Stream, which eventually empties into the West Loch of Pearl Harbor.
Three surface water reservoirs are located on the East Range of Schofield, none of which are used for drinking water. Other surface water bodies on site include intermittent and perennial streams, springs, and manufactured water conveyance tunnels.
Schofield is primarily surrounded by undeveloped forest scrub land, developed land used for the production of pineapple crops, and residential areas. In recent years, land use in Oahu has shifted more toward residential properties and tourism activities and away from pineapple production. Although land use within the installation has changed and will continue to change over the years, the Army has no plans to close Schofield.
Located in central Oahu, Schofield Barracks and Wheeler Army Airfield are removed from the island's major population centers. The demographic and housing data of this military complex and adjacent towns and community areas, based on 1990 census data, are presented in this section and summarized in Tables 3 and 4, respectively.
Schofield Barracks and Wahiawa Area
A total of over 39,000 people lived in the Schofield, Wheeler Army Airfield, and Wahiawa area in 1990 (see Table 3). Population density was highest in Wahiawa and Schofield. Nearly 70% of the population of Wahiawa was of Asian or Pacific Islander origin, but the majority of the population of the military installations was white. Both locations housed high percentages of children under the age of 10--a trend typical of military posts, which have high numbers of young couples in their childbearing years. There were also large average numbers of persons per household in all three areas.
Nearly half of the households in Wahiawa were owner-occupied. About one-third of the persons at Schofield lived in military group quarters (see Table 4).
Kunia and Rural Block Group 9
The area directly south of Schofield Barracks includes the small town of Kunia and a fairly large rural block group (BG 9) in Census Tract 86.03. Kunia is a rather densely populated area covering just over one-tenth of a square mile, but only 246 persons lived in BG 9 (see Table 3). In 1990, the majority of persons in both areas were male, which may be due to the close proximity of the military installations. Most persons in BG 9--and virtually all (95.5%) in Kunia--are of Asian or Pacific Islander origin. Both areas have relatively high percentages of children and low percentages of the elderly. The average number of persons per household is very high in both areas (see Table 4).
The vast majority of households in both areas were renter-occupied, again suggesting the presence of a large military population. Over 15% of persons in BG 9 lived in group quarters. The median value of owner-occupied housing in BG 9 was high (see Table 4).
Mililani Town and Waipio Acres
Mililani Town and Waipio Acres are located south of Wheeler Army Airfield and Schofield. Both areas were densely populated in 1990 (see Table 3). Over 60% of persons in Mililani Town were Asians or Pacific Islanders, and about half were in that racial category in Waipio Acres. As with other areas near Schofield, both towns housed high percentages of children under the age of 10 and low percentages of persons aged 65 and older. Both towns had high average numbers of persons per household (see Table 4).
Mililani Town had a high percentage of owner-occupied households, in spite of a relatively high median cost for owner-occupied units. Median rent was also high in both places (see Table 4).
In preparing this public health assessment, ATSDR relied on the information provided in the referenced documents. The environmental data presented in the public health assessment are from the 1995 Final RI Report for OU 1 (HLA 1995a), the 1996 Draft Final RI Report for OU 2 (HLA 1996a), the 1996 Final RI report for OU 3 (Uribe 1996a), the 1995 Final Feasibility Study (FS) Report for OU 4 (HLA 1995c), and the 1997 Final Interim Long-Term Groundwater Monitoring Report for OUs 2 and 4 (HLA 1997b). The limits of these data have been identified in the associated reports.
As part of the public health assessment process, ATSDR conducted an initial site visit on July 1, 1991, and a second site visit on January 23, 1995 (ATSDR 1991; ATSDR 1995). During these visits, ATSDR met with representatives from the installation and federal, state, and local agencies and gathered information regarding potential human exposure pathways at Schofield. From these meetings and a review of the available data, ATSDR identified a potential past completed human exposure pathway: consumption of TCE-contaminated drinking water by residents and employees at Schofield. No other completed human exposure pathways were identified. However, not enough data were available at that time to fully evaluate the following potential human exposure pathways:
- Potential off-site consumption of TCE-contaminated groundwater by residents of nearby communities.
- Contact with or consumption of contaminated surface soil.
- Contact with or consumption of contaminated surface water runoff to residential or recreational areas.
At the time of ATSDR's initial site visit in 1991, Schofield was in the preliminary stages of the NPL process, and the community did not express any specific health concerns. During the January 1995 visit, ATSDR met with community members who expressed concerns about groundwater and soil contamination.
According to the Final Community Relations Plan prepared by the Army in 1997, the results of 20 community interviews conducted at Schofield in January 1992 identified the following concerns held by community members at that time (HLA 1997a):
- Groundwater and drinking water quality
- Long-term health effects of contaminated drinking water
- Sewage and wastewater treatment and disposal
- Toxic waste and hazardous material handling and disposal
- Vehicular and aircraft noise
- Unexploded ordnance and abandoned munitions
These health, environmental, and safety issues were evaluated throughout the RI process. ATSDR has gathered and reviewed RI data for all sites at Schofield. Table 1 summarizes site history, investigation results, current status, and evaluation of public health hazards for all sites evaluated during the RI.
The following discussion evaluates community concerns about potential human exposure via contaminated groundwater, soils, and surface water runoff. Tables and figures are provided at the end of this document. Table 1 provides evaluation of potential public health hazards for all sites. Table 2 lists TCE concentrations detected in Schofield's groundwater. Tables 3 and 4 provide population and housing data, respectively. Table 5 provides an evaluation of completed and potential completed exposure pathways. Table 6 lists all target analytes analyzed in the RI. Figure 1 is a location map; Figures 2 and 3 detail the groundwater system on Oahu. Figure 4 provides detail on ATSDR's exposure evaluation process.
Appendix A provides a glossary of environmental and health terms presented in the discussion. In evaluating environmental contamination, ATSDR uses several media-specific comparison values to select environmental contaminants for further evaluation, including environmental media evaluation guides, reference dose media evaluation guides, cancer risk evaluation guides, and EPA's MCLs. Appendix B describes the comparison values used in this evaluation. Appendix C provides the estimates of human exposure dose and determination of health effects from past consumption of TCE-contaminated groundwater.
Could contaminated groundwater result in adverse human health effects for residents or employees of Schofield or neighboring communities?
After detailed review of available data, ATSDR has drawn several conclusions regarding past, present, and future exposures to contaminated groundwater at Schofield:
- TCE contamination has affected Schofield's drinking water supply since at least 1985. The specific source of the contamination has not been identified; the initial date of contamination is unknown.
- Schofield's residents and employees were exposed to TCE-contaminated drinking water in the past. However, adverse health effects from this contamination are not likely due to the relatively low levels of TCE and the limited duration of exposure.
- Current and future exposures to TCE-contaminated groundwater are unlikely because drinking water is treated at the wellhead and monitored on a quarterly basis.
- Groundwater contamination from Schofield may have affected the drinking water supply and irrigation wells at the neighboring Kunia wells owned and operated by Del Monte Fresh Produce (Hawaii) Inc. (Del Monte). Past exposure to contaminants below MCLs in drinking water at these wells is not likely to be associated with adverse health effects. Current and future exposures are unlikely because the drinking water is treated at the wellhead. Groundwater contamination from Schofield has not affected and is not expected to affect any other drinking water wells in neighboring communities.
The principle source of groundwater recharge on Oahu is rainfall, and recharge is more predominant in the higher elevations (HLA 1996a). On Oahu, the fresh water percolating down through the ground into the saturated zone does not mix well with the denser salt water present in the subsurface environment, resulting in a lens-shaped fresh water body that rises where recharge occurs and thins where the fresh water discharges to the ocean.
The groundwater body that lies under the majority of Schofield is known as the Schofield High-Level Water Body (see Figure 2). It lies approximately 270 to 275 feet above mean sea level and 500 to 600 feet below ground surface at Schofield. Groundwater from the Schofield High-Level Water Body flows south to the Honolulu-Pearl Harbor Basal Water Body and north to the Waialua Basal Water Body, both of which are at lower elevations than the Schofield High-Level Water Body. The Schofield High-Level Water Body overlies sea water and is naturally bounded on the north and south by groundwater dams and on the east and west by dike-impounded water bodies within the mountain ranges (see Figure 3).
Groundwater is the primary source of drinking water on Oahu. Groundwater also supplies fresh water for other uses on the island, such as irrigation. Schofield's drinking water is drawn from the Schofield High-Level Water Body. Schofield's four drinking water supply wells, along with a monitoring well and water treatment plant, are located on the northwest corner of the East Range in chambers approximately 567 feet below ground surface at 287 feet above mean sea level. The original well chamber was constructed in 1938 to provide water for the growing military installations in the Wahiawa area. The wells pump 3.5 to 7 million gallons per day, depending on the season, to Schofield, and at times to parts of Wheeler Army Airfield, the Naval Computer and Telecommunications Area at Wahiawa (NCTAMS), and Helemano Military Reservation (Helemano), located north of NCTAMS (HLA 1996a).
Other wells that draw from the Schofield High-Level Water Body are the Wahiawa municipal wells and several irrigation wells. Directly south of Schofield, municipal wells in Mililani Town, Waipio, and Kunia as well as numerous irrigation wells draw from the Honolulu-Pearl Harbor Basal Water Body (see Figure 2).
Groundwater Quality and Source of Contamination
The April 1985 reporting of TCE contamination prompted the Army to assess and characterize the groundwater contamination at Schofield. Phase I of the RI for OU 2 was performed during 1993 and 1994. Phase II expanded on information collected in Phase I and determined that the TCE contamination consisted of two plumes: one under the East Range/Wheeler Army Airfield area and the second under the Former Landfill in the northeast section of the Main Post (see Figure 4) (HLA 1996a). Groundwater was sampled at all Schofield water supply wells, six monitoring wells surrounding the water supply wells, five monitoring wells on the Former Landfill, and several off-site municipal drinking water and irrigation wells.
No source of contamination for the plume that underlies the East Range and supports the Schofield water supply wells has been discovered. It is believed that TCE was not widely used by the Army until the 1950s; after 1980, federal environmental regulations required Schofield to transfer wastes such as TCE to the Petroleum, Oil, and Lubricant (POL) Area R (Site 20) for proper disposal (Turnbull 1997). It has been postulated that TCE was spilled or released upgradient of the supply wells in many locations throughout the East Range for many years before 1980 (Turnbull 1997; HLA 1996a).
The Former Landfill is the source for the second TCE plume. The Army used the Former Landfill as an open burn dump from 1942 to 1967, and then as a sanitary landfill until 1983. Solvents, unusable paints, and acids were reportedly dumped there. Disposal of these hazardous materials likely resulted in the TCE groundwater contamination located under the landfill. The landfill was closed and capped in 1983. To ensure that no further groundwater contamination occurs, the ROD for the Former Landfill calls for regrading and revegetating the cap (HLA 1996b).
Groundwater sampling conducted at Schofield during the RI detected TCE, carbon tetrachloride, pentachlorophenol, antimony, cadmium, chromium, and nickel above MCLs (see Table 1). TCE was the only contaminant detected above its MCL in the drinking water supply wells at Schofield (HLA 1996a). Specifically, the following contaminants were detected above MCLs in the drinking water supply wells, irrigation wells, or monitoring wells during the RI:
- TCE was detected above the MCL (5 ppb) in all samples collected from Schofield's drinking water supply wells (7.8-53 ppb). TCE was also detected above the MCL in samples from six monitoring wells (not detected [nd]-65 ppb) located on Schofield. TCE was detected below the MCL in three wells in the Kunia area, but was not reported above laboratory detection limits in any other off-site municipal drinking water or irrigation wells.
- Carbon tetrachloride (nd-8.2 ppb) was detected above the MCL (5 ppb) in one sample at a monitoring well located on the Former Landfill.
- Pentachlorophenol (nd-25 ppb) was detected above the MCL (1 ppb) in one sample at an off-site drinking water supply well in Waipio, located approximately 3 miles south of Schofield. Because this result was not reproduced during the second sampling event, it is considered doubtful. Further, because no pentachlorophenol was detected in samples at any other wells located between Schofield and the Waipio well, and because that well is located within the Honolulu-Pearl Harbor Basal Water Body, the detection is not believed to be related to activities at Schofield.
- Cadmium (maximum concentration of 11.2 ppb) was detected above the MCL (5 ppb) in one filtered sample from a monitoring well on the Former Landfill, but not in the corresponding unfiltered sample. This contaminant was therefore considered to be an anomaly.
- Antimony (maximum concentration of 55.1 ppb) was detected above the MCL (6 ppb) in eight wells: two Mililani drinking water supply wells, one Waipio drinking water supply well, three off-site irrigation wells, and two monitoring wells at the Former Landfill. Detected levels of antimony were inconsistent and considered anomalies.
- Chromium (maximum concentration of 364 ppb) was detected above the MCL (100 ppb) in four wells. These detections occurred at two off-site irrigation wells, and two off-site municipal drinking water wells, and were not confirmed during the second sampling event.
- Nickel (maximum concentration of 309 ppb) was detected above the MCL (100 ppb) in two off-site irrigation wells, and was not confirmed during the second sampling event.
In 1996 and 1997, two more rounds of groundwater sampling were performed as part of the Interim Long-Term Groundwater Monitoring program. During this sampling event, TCE was the only contaminant detected above MCLs. TCE concentrations were detected above the MCL in Schofield's drinking water supply and monitoring wells only; TCE was not detected above the MCL in any off-site municipal drinking water or irrigation wells during this sampling event. No other volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), or metals exceeded MCLs (HLA 1997b).
In 1986, TCE was detected below MCLs in the nearby Kunia drinking water supply wells owned and operated by Del Monte. The Kunia wells are located close to the southern boundary of the eastern edge of the Main Post of Schofield. In response to the TCE detections, Del Monte installed an air stripping tower treatment facility, which became operational in 1991. In accordance with the ROD for OU 2, the Army reimbursed Del Monte for capital costs of the treatment facility and funds the operation and maintenance of the facility. Since the treatment facility has been in operation, TCE has been detected above the MCL twice in water samples collected before the air stripper. TCE was detected at 7.7 ppb on October 5, 1993, and at 5.2 ppb on May 1, 1997 (Del Monte 1997). During the 1996 and 1997 rounds of groundwater sampling performed as part of the Interim Long-Term Groundwater Monitoring program, no TCE or any other contaminants from Schofield were detected above MCLs at off-site municipal drinking water or irrigation wells (HLA 1997b). Groundwater modeling performed during the RI indicates that TCE-contaminated groundwater plumes below Schofield will not reach other downgradient wells within 100 years (HLA 1996a). However, long-term monitoring of the off-site wells was established by the RODs for OU 2 and OU 4 and will continue to ensure that drinking water supplies off site are safe to drink into the future.
In the past, residents and employees of Schofield were exposed to drinking water contaminated with TCE above the MCL. The initial date of contamination at the drinking water wells is unknown and, therefore, the date that exposure began is also unknown. No source for the TCE contamination was determined; it is believed that TCE may have been spilled or released to the land surface in many areas of the East Range upgradient from the water supply wells (Turnbull 1997; HLA 1996a). Because it is known that TCE was not widely used by the Army before the 1950s, contamination before that time is unlikely. Federal regulations promulgated in 1980 require the proper disposal of wastes such as TCE to preclude their release to the environment. Therefore, TCE may have been spilled or released to the environment during the 1950s, 1960s, or 1970s.
Although the precise date of contamination is unknown, the detailed information on the nature of groundwater movement that was gathered during the preparation of the RI for OU 2 makes it possible to estimate a range of the time during which TCE would have first appeared at the drinking water supply wells. Once the TCE was released to the land surface, it had to travel vertically through a 500- to 600-foot-thick vadose zone before it reached the groundwater. Travel time through the vadose zone in different areas of the installation is estimated to range from 7 to 10 years (Turnbull 1997). Finally, after the contamination reached the groundwater, it also had to travel horizontally in the Schofield High-Level Water Body before reaching the drinking water supply wells. Therefore, on the basis of the preceding factors, it has been estimated that the wells may have been contaminated as early as 1966 or as late as 1984 (Turnbull 1997). The earliest date of exposure to contaminated drinking water, therefore, may have been 1966.
No exposure to contaminated water would have occurred after the water supply was switched to the uncontaminated Wahiawa wells on May 2, 1985. During periods of peak demand, the Army blended drinking water from the Wahiawa wells and the least contaminated Schofield wells. In September 1986, the air stripper was installed at Schofield, and this practice of blending drinking water was discontinued. During the intervals of blending, TCE levels in the drinking water did not exceed the safe drinking water level established by the MCL.
No past exposure is expected offsite. Prior to the installation of the air stripping tower at the Kunia water supply wells, TCE was detected below the MCL. Beginning in 1991, drinking water has been effectively treated at the wellhead.
Current and Future Exposure
No current or future exposures are expected for employees or residents of Schofield. Residents and employees of Schofield continue to receive drinking water from the Schofield supply wells. Although the water in the supply wells is contaminated with TCE above the MCL, it is treated at the wellhead with air stripper technology, and TCE concentrations are reduced to safe drinking water levels before it is distributed for consumption.
No current or future exposure is expected off site. Groundwater at the Kunia drinking water supply wells is treated with an air stripper at the wellhead. Furthermore, the Army is monitoring wells that are located on and immediately downgradient of Schofield on a quarterly basis for 5 years. Remaining off-site wells and the monitoring wells at the Former Landfill also will be sampled on a semiannual basis for 5 years. The need for continued monitoring will be reevaluated during the 5-year site review.
Exposure Dose and Human Health
To determine the health significance of consuming TCE-contaminated water from Schofield supply wells, ATSDR estimated exposure doses for adults and children. In deriving the exposure doses, ATSDR incorporated information about exposure frequency and duration and contaminant concentration. For conditions at Schofield, ATSDR assumed that adults drink 2 liters of well water each day and weigh 70 kilograms (kg) and children drink 1 liter of water each day and weigh 16 kg.
Because the date that TCE first contaminated the groundwater is unknown, ATSDR used the longest possible exposure period (1966 to 1986) to calculate the most conservative exposure dose (20 years). ATSDR also assumed that drinking water contained the maximum concentration of TCE detected (30 ppb) at the time the wells were closed in 1985.
ATSDR believes that the estimated exposure dose is more conservative than the actual exposure dose for the following reasons:
- Military personnel and their dependents were usually stationed at Schofield for periods of about 2 years (ATSDR 1997).
- Civilian employees at Schofield would be exposed only during an 8-hour day, 5-day workweek (ATSDR 1997).
- Using the maximum TCE concentration detected in one of the four supply wells overestimates what could be delivered to the taps and consumed by Schofield well users. Actual concentrations would be lower due to the blending of water from two or more wells and the volatilization of organic chemicals during pumping and storing.
Applying these very conservative assumptions will most likely overestimate the health hazard associated with the past consumption of drinking water from the Schofield drinking water supply wells.
The method used by ATSDR to estimate exposure doses for past ingestion of Schofield's drinking water is described in Appendix C. The estimated doses were used to determine whether noncancer effects or cancer are a public health concern for this pathway.
Noncancer Effects -- The estimated exposure doses are compared with standard toxicity values, such as ATSDR's intermediate oral minimal risk levels (MRLs), to determine the likelihood that adverse health effects, other than cancer, may occur. The MRL provides a conservative estimate of daily exposure to noncarcinogens that are not likely to result in adverse effects, even for the most sensitive members of the community (e.g., pregnant women, children). A more complete discussion of how toxicity values are derived and used to evaluated potential adverse human health hazards is presented in Appendix C.
The estimated exposure doses for an adult and a child are 0.000857 milligrams per kilogram per day (mg/kg/day) and 0.001875 mg/kg/day, respectively. These values are less than the corresponding MRL value of 0.002 for daily, lifetime ingestion of TCE. Therefore, human exposure to TCE at these levels is not likely to result in adverse noncancer effects. ATSDR concludes that past exposure to the Schofield water supply was not likely to have resulted in noncancer effects.
Cancer Effects -- When evaluating the potential for cancer to occur, ATSDR uses its estimated exposure doses and EPA's cancer potency factors (CPFs), which define the relationship between exposure doses and the likelihood of an increased risk of developing cancer over a 70-year lifetime. A more detailed discussion of CPFs and how they are used to determine whether concern for cancer effects exists is presented in Appendix C.
ATSDR's estimated cancer risk for past possible exposure to TCE-contaminated drinking water at Schofield is 2.69 x 10-6. ATSDR believes that exposure at this level does not contribute to excess cancer in a population. ATSDR concludes that past exposure to the Schofield water supply was not likely to have resulted in cancer.
Could soil contamination at Schofield result in adverse human health effects?
After detailed review of the available data, ATSDR concludes the following:
- Soil contamination as Schofield is not likely to result in adverse human health effects.
During the RI, soil gas, surface soil, subsurface soil, and sediment were sampled at the sites in OU 1 and OU 3 and at the Former Landfill. These samples were analyzed for VOCs, SVOCs, metals, pesticides/polychlorinated biphenyls (PCBs), explosives, polychlorinated dibenzodioxins (PCDDs), and/or polychlorinated dibenzofurans (PCDFs). A list of target analytes is presented in Table 6. Background soil samples were also taken to assess whether detected chemicals were representative of natural conditions.
During the RI, no sites at OU 1 or OU 3 were designated as requiring remedial action because "estimated risks are within ranges considered acceptable by EPA, ...chemical concentrations are representative of background conditions, and/or...a route of exposure does not exist" (HLA 1995a; Uribe 1996a). The Former Landfill was capped in 1983, and a fence was installed, limiting access. The ROD for the Former Landfill called for regrading the existing cap and instituting long-term maintenance (HLA 1996b). ATSDR performed a detailed review of the available data for all sites at OU 1 and OU 3 and for the Former Landfill, with particular attention to those sites at OU 3 that are currently residential or where future residential use is planned. Table 1 summarizes ATSDR's evaluation of the potential public health hazards for all sites. ATSDR concludes that exposure to contaminated soils in sites at OU 1 and OU 3 and at the Former Landfill are not likely to pose a public health hazard for the following reasons:
- All sites at Schofield have restricted access because it is an Army installation.
- The Former Landfill, all sites in OU 1, and multiple sites in OU 3 are industrial sites; therefore, access and exposure to soils are further limited at these sites.
- Contaminants detected above comparison values (CVs) in subsurface soils are inaccessible.
- Contaminants detected above CVs in surface soils were detected sporadically and/or at levels that do not pose a public health hazard.
Could surface water runoff from contaminated sites result in adverse human health effects for residential or recreational areas?
After detailed review of available data, ATSDR concludes the following:
- Surface water runoff from contaminated sites is not likely to result in adverse human health effects for residential or recreational areas at Schofield.
ATSDR performed a detailed analysis of sites in OU 3 where surface water runoff may flow to areas accessible to residential populations. Table 1 summarizes ATSDR's evaluation of the potential for public health hazards at each of the sites in OU 3. Surface water samples were taken from open drainage ditches. At some sites, no contaminants were detected above the MCLs, whereas at other sites, contaminants occurred sporadically or slightly above MCLs. The MCL is a drinking water standard, however, and water from open drainage ditches is not consumed. ATSDR concludes that surface water runoff to residential areas from contaminated sites at OU 3 is not likely to cause adverse human health effects.
ATSDR has drawn the following conclusions from current environmental data and information on the Schofield site:
- TCE concentrations in the drinking water wells at Schofield exceed the MCL; however, the TCE contamination does not pose a public health hazard. Exposure to contaminated drinking water at Schofield in the past is not likely to have resulted in noncancer effects or cancer because of the relatively low levels of TCE and the limited duration of exposure. Current and future exposures to contaminants in drinking water are unlikely to occur because air strippers operating at the wellhead effectively treat the water of the existing wells. Further, any wells drilled in the vicinity to develop water from the same groundwater source for drinking purposes in the future will be subjected to federal, state, and county regulations to meet safe drinking water standards (MCLs).
- Exposure to soil contamination is not likely to result in adverse human health effects because access to sites is limited; also, contamination is either restricted to subsurface soils and therefore is inaccessible or is sporadic and at levels that do not pose a health hazard.
- Exposure to surface water runoff from contaminated sites is not likely to result in adverse human health effects because contamination is at levels that do not pose a health hazard.
- On the basis of information available on contamination of groundwater and of the Schofield Barracks drinking water supply wells in the past and on localized contamination of soils and surface water, ATSDR concludes that the Schofield Barracks site should be assigned to the No Apparent Public Health Hazard category.
The Public Health Action Plan (PHAP) for Schofield contains a description of actions taken and those to be taken by ATSDR, the Army, EPA, and the Hawaii Department of Health at and in the vicinity of the site after the completion of this public health assessment. The purpose of the PHAP is to ensure that this public health assessment not only identifies public health hazards, but also provides a plan of action designed 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:
- The Army installed air stripper technology at the water supply wells in September 1986 to treat the contaminated water.
- The water supply will continue to be monitored and treated at the wellhead, ensuring that Schofield employees and residents have a clean drinking water supply.
- Long-term monitoring of groundwater contamination has been implemented at supply and monitoring wells both on and off site. This system will ensure that the migration of contaminated groundwater will be carefully tracked and, if necessary, corrective measures taken to ensure the safety of the area's drinking water.
- The Former Landfill will be recapped and revegetated and groundwater near the landfill will be monitored. This action will ensure that contaminants in the landfill will not continue to contaminate the groundwater.
- The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA; also known as Superfund), 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 Schofield Army Barracks Public Health Assessment for appropriate public health actions. No follow up health activities are recommended at Schofield because there is no known exposure at this site at levels that pose a public health hazard.
W. Mark Weber, Ph.D.
Geologist/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
ATSDR. 1991. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services. Trip report for site scoping visit, July 1-3, 1991, Schofield Barracks, Wahiawa, Honolulu, Hawaii (90Q6). July 11, 1991.
ATSDR. 1995. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services. Trip report: site visit; Schofield Barracks, Wahiawa, Hawaii, January 23-24, 1995. May 2, 1995.
ATSDR. 1997. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services. Record of Activity. Conversation on February 1, 1997, between W. Mark Weber, ATSDR, and Steve Turnbull, U.S. Army Corps of Engineers, Waterways Experiment Station, Hydro-Science Division, regarding groundwater investigations performed at Schofield. February 20, 1997.
Department of the Army. 1985a. Information paper: Trichloroethylene contamination of Schofield Barracks Wells. June 7, 1985.
Department of the Army. 1985b. Action plan for ensuring a continued safe drinking water supply for Schofield Barracks. May 17, 1985.
Del Monte. 1997. Letter to ATSDR regarding TCE contamination at Kunia wells. November 6, 1997.
Harding Lawson Associates. 1995a. Final remedial investigation report for Operable Unit 1, Schofield Army Barracks, Island of Oahu, Hawaii. Volumes I and II. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. April 1995.
Harding Lawson Associates. 1995b. Draft record of decision for Operable Unit 1, Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. April 1995.
Harding Lawson Associates. 1995c. Final feasibility study report for Operable Unit 4, Schofield Army Barracks, Island of Oahu, Hawaii. Volumes I and II. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. December 26, 1995.
Harding Lawson Associates. 1996a. Draft final Operable Unit 2 remedial investigation report, Schofield Army Barracks, Island of Oahu, Hawaii. Volumes I and II. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. April 2, 1996.
Harding Lawson Associates. 1996b. Final record of decision for Operable Unit 4, Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. July 12, 1996.
Harding Lawson Associates. 1996c. Final record of decision for Operable Unit 2, Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. August 12, 1996.
Harding Lawson Associates. 1997a. Final community relations plan for Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for U.S. Army Garrison, Hawaii and U.S. Army Environmental Center. January 31, 1997.
Harding Lawson Associates. 1997b. Final interim long-term groundwater monitoring report for Operable Units 2 and 4, Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for the U.S. Army Environmental Center, Aberdeen Proving Ground, MD. April 11, 1997.
HLA. See Harding Lawson Associates.
Turnbull, S. 1997. Correspondence with W. Mark Weber, ATSDR, regarding TCE conditions in groundwater prior to 1985 at Schofield Army Barracks. April 22, 1997.
Uribe & Associates. 1996a. Final remedial investigation report, Operable Unit 3, Schofield Army Barracks, Island of Oahu, Hawaii. Volumes 1 through 6. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. March 1996.
Uribe & Associates. 1996b. Final record of decision, Operable Unit 3, Schofield Army Barracks, Island of Oahu, Hawaii. Prepared for U.S. Army Environmental Center, Aberdeen Proving Ground, MD. August 1996.
Uribe. See Uribe & Associates.
U.S. Army. See Department of the Army.