PUBLIC HEALTH ASSESSMENT
MARCH AIR FORCE BASE
(a.k.a. MARCH AIR FORCE BASE)
MARCH AIR FORCE BASE, RIVERSIDE COUNTY, CALIFORNIA
ATSDR reviewed the environmental data generated from investigations at March AFB to determine if there are any associated past, current, or future public health hazards. ATSDR also evaluated other pertinent environmental data routinely collected such as production well monitoring data. From this review, ATSDR identified and evaluated the nine exposure situations listed below. Our overall general conclusion is that these exposure situations are not (apparent) public health hazards. These nine exposure situations are discussed in the following sections with justifications for our conclusions.
Green Acres Military Family Housing (No Apparent Public Health Hazard)
- Past, current, and future exposure to pesticides in indoor air and crawl spaces.
- Past, current, and future exposure to lead in paint and soils.
- Past, current, and future exposure to asbestos in building materials.
On- and Off-site Ground Water (No Apparent Public Health Hazard)
- Past exposure to volatile organic compounds and boron on-base
- Past and potential current and future exposure to volatile organic compounds off-base
Arnold Heights Military Family Housing (No Apparent Public Health Hazard)
- Past and potential future exposure to lead and oils.
Runoff from Site 40 (Landfill #8) near Arnold Heights (No Apparent Public Health Hazard)
- Past exposure to runoff
Mercury in Hospital Plumbing (No Apparent Public Health Hazard)
- Past and potential future exposure
Sampling for Potential Radioactive Contamination at the Weapons Storage Area or Other Basewide Areas (No Public Health Hazard)
- Potential building contamination
The Green Acres Military Family Housing Area consists of 130 multi-bedroom houses. Prior to 1996, the houses were used for the military and their families. The AFBCA has targeted 111 of the houses for transfer to the private sector. These houses are currently leased to the MJPA. In turn, MJPA is renting the houses to individuals and families. The remaining 19 houses have been retained by March Air Reserve Base for billeting, offices, and a museum.
At Green Acres Houses, the military used pesticides to reduce insect infestations, painted with lead-based paint and used asbestos containing building materials (ACM) in this housing complex. People living in Green Acres were potentially exposed to pesticides, apparently evaporating from the crawl space soils and migrating into the living space. This evaporation and presence in houses is not uncommon with houses treated with pesticides. People in these houses were also potentially exposed to pesticides in the crawl space soils, lead in soils outside of the houses, lead from paint, and asbestos from building materials. Based on average family sizes and the number of bedrooms, the 130 houses were occupied by approximately 300 to 500 residents.
ATSDR reviewed the pesticide, lead, and asbestos sampling data together with past, current, and future exposure scenarios, uses of the Green Acre Houses, and the toxicology of the chemicals. In each case, ATSDR has concluded that there are no apparent public health hazards for past, current, and future exposures because the estimated exposures were below levels of concern when evaluated with the toxicological properties of the chemicals.
Although we concluded that there is no apparent public health hazard, ATSDR recommends future exposure prevention through the following measures:
(1) The Air Force Base Conversion Agency (AFBCA) or March Joint Powers Authority (MJPA) should prevent and lower potential pesticide exposures in the crawl spaces by keeping crawl space doors locked to prevent access and installing vapor barriers in the crawl spaces to prevent or lower pesticide vapor migration into the houses.
(2) The AFBCA or MJPA should maintain lawns and shrubs adjacent to the houses including the roof driplines and all bare soils should be replanted to prevent access to the lead in the soils by children and gardens adjacent to the houses should be prohibited to limit contact with the lead in the soil. Children should not be allowed to play next to the homes because of lead contaminated soils identified in the drip soil samples. Playground equipment or fenced areas for children should not be located next to the homes.
(3) The AFBCA or MJPA should maintain and routinely inspect the asbestos in the houses.
Table 1 includes a summary of our evaluations of these exposure situations and the remainder of this section discusses these topics in more detail.
The Green Acres Military Family Housing Area (Green Acres) consists of 130 multi-bedroom houses. One hundred and eleven (111) of the houses are part of the realignment of March Air Force Base to civilian use. These houses have been leased to the MJPA. MJPA is handling the transition of the property from the military to civilian ownership. In turn, the MJPA has leased the houses to private individuals until final disposition of the property. The other 19 houses have been retained by March Air Reserve Base for billeting, offices, and a museum. A fence separates the leased houses from the 19 houses that have been retained and the March Air Reserve Base.
The Green Acres houses were constructed between 1928 and 1936 with steel reinforced, cast-in-place concrete and roofed with mission tiles. Crawl spaces were incorporated in the construction. The houses are part of the March Field Historic District that is on the National Registry of Historic Places. Because of this designation, modifications to these houses are restricted (March AFB 1996).
Beginning in 1992, March AFB sampled the Green Acres houses for pesticides and lead contamination and evaluated them for asbestos. Based on these sampling results, ATSDR evaluated the exposure to people using these houses. Our evaluation is discussed in the following sections for the following exposure situations.
- Breathing pesticides in indoor air.
- Breathing pesticides in the crawl space or contacting the pesticides in the crawl space soils.
- Ingesting lead contaminated paint from paint dust, paint chips, or soils outside the house.
- Breathing asbestos contaminated air.
For each pathway, we discuss the sampling history, data, human exposure routes, and public health implications.
As part of the Basewide Environmental Survey and Area of Concern Site Investigation (Tetra Tech 1996b), the AFBCA collected indoor air samples from six Green Acres Houses in 1996 and analyzed them for 10 pesticides listed in Table 3. Pesticides were detected in all six houses (Armstrong Labs 1997). Several of these pesticides concentrations found exceeded ATSDR's screening values and further evaluation was conducted.
In 1997, with the assistance of the Air Force's Armstrong Labs, AFBCA expanded the study and conducted sampling of indoor air at 121 of the 130 houses (93%) at Green Acres. They analyzed the samples for the 21 pesticides listed in Table 4. Of the 21 pesticides analyzed, 13 were detected. Of the 121 houses, 67 had one or more of the pesticides measured above the detection limits and 28 houses (23%) had indoor air concentrations exceeding the health based screening values. Table 4 lists the detection limits, the highest concentrations detected, and the health screening values. From the air concentrations, Armstrong Labs calculated the excess cancer risk from inhaling the contaminated indoor air and found the risk in three houses above EPA's acceptable excess cancer risk of one in 10,000. Additional information about this Risk Assessment is presented in Appendix I.
A contaminant exceeding a comparison value or acceptable excess cancer risk does not mean that it will cause adverse health effects. These comparison values and excess cancer risk are designed to be conservative (overly protective of public health) and are used to select chemicals for further evaluation. This selection process and evaluation are part of the ATSDR methods explained in the sidebar on Page 4.
ATSDR evaluated the exposure of adults, children and infants to pesticides in indoor air at the Green Acre Houses. The source of the pesticides is the crawl space soils from past applications to control insects. The pesticides move into the indoor air from the crawl space in two steps. In the first step, the pesticides move from the soils to the crawl space air either as a vapor (similar to the evaporation of water but at a much slower rate) or contained on airborne soil particles, if the crawl space soils become stirred up. ATSDR believes the predominant mechanism is through the vapor because there is no routine activity in the crawl space to stir up the soils and the pesticides in the living area were identified using a sampling method that is designed primarily for collecting vapors (particles may be collected but the sampling efficiency is unknown, EPA 1999). A flood in 1992 flooded about one-half of the crawl spaces (DeVenoge 2000) and could have been a conduit for soil particles moving closer to the living area.
The second step is the movement of the vapor in the crawl space air to the indoor air through the heating and air-conditioning duct work or through gaps in the flooring or walls.
Once the vapor enters the living space, people can come into contact with the pesticides in three ways: inhalation, ingestion, or dermal contact. Because the pesticides are likely moving from the crawl space to the indoor air as a vapor, ATSDR considered inhalation as the primary exposure route.
The exposed population includes adults, children, and infants. ATSDR focused on sensitive subpopulations which included women of childbearing age, children, and infants. Since pesticides like chlordane, dieldrin and DDT can be passed to infants though breast milk, we evaluated exposure to infants via breast feeding, in addition to inhalation (Sonawane 1995; Albers et al. 1996).
ATSDR reviewed all of the air sampling data and chose chlordane, dieldrin, and DDT for further evaluation. ATSDR made the following conservative (protective of public health) assumptions for our exposure evaluation:
- Exposure occurred to individuals sensitive to the effects of exposure to hazardous chemicals including adult females of reproductive age, young children less than six years of age, and breast-feeding infants.
- These people were exposed to maximum concentrations in air sixteen hours per day (based on the Exposure Factors Handbook, Tables 15-131, U.S. EPA 1997a), 365 days per year.
- Occupancy of the housing was assumed to be approximately nine years, likely longer than most military personnel and their families which occupied Green Acres Housing and slightly longer than the average time for nonmilitary people in the western United States (Exposure Factors Handbook Table 15-163, U.S. EPA 1997a). This length of residence is assumed for past, current, and future scenarios.
- ATSDR based the exposure evaluations on the maximum detected concentrations for all three pesticides in Green Acres Housing indoor air.
In summary, ATSDR considers that, under realistic, site-specific conditions of exposure at Green Acres Housing, that the levels of chlordane, dieldrin, DDT, DDD, and DDE in indoor air are too low to produce adverse health effects in humans, including young children and infants. We came to this conclusion by reviewing toxicological and epidemiological data for cancer and noncancer effects discussed in this section.
Health Implications Review Process
For the evaluation of noncancer health effects, we first compared the indoor air concentrations to ATSDR's minimal risk levels (MRLs) or U.S. EPA's reference air concentrations (RFCs). If the air concentrations exceeded the MRL or RFC, we evaluated the concentration against the health studies and safety factors that were used to create the MRL or RFC. This approach (also know as weight-of-evidence) includes the evaluation of all relevant data including case studies, epidemiologic studies, long-term animal bioassays, short-term tests, and structure-activity relationships.
The MRL and RFC are defined as an estimate of daily human exposure to a dose or concentration of chemical that is likely to be without an appreciable risk of adverse, noncancerous health effects over a specified duration of exposure. MRLs and RFCs are usually based on the most sensitive indicator of toxicity observed in animal studies and are reduced 100 to 1,000 times further to account for uncertainty in generalizing from the effects on animals to the effects on people. Human data are preferred, but are frequently not sufficient to derive an MRL or RFC.
ATSDR health assessors use MRLs and RFCs as screening tools. Environmental levels that result in hypothetical exposures below the MRL or RFC are considered not likely to cause adverse human health effects with respect to noncancer endpoints. Estimated exposures above the MRL or RFC require that the health assessor do a more detailed evaluation of site-specific and chemical specific factors than are provided by the MRL or RFC. Simply stated, MRLs and RFCs are used as screening levels. In lieu of missing information, default assumptions are used during their calculation. They should not be considered thresholds for noncancer health effects nor should they be viewed as regulatory or cleanup thresholds.
We discuss the indoor air concentrations for chlordane, dieldrin, and DDT (includes DDE and DDD) in the following sections along with their MRLs or RFCs, cancer risks, and other pertinent toxicological and epidemiological data.
ATSDR considers that the chlordane levels at Green Acres are too low to produce adverse noncancer health effects and excess cancer risks above acceptable levels in residents, even from exposure to maximum concentrations in indoor air.
The maximum detected level of chlordane in Green Acres indoor air was 0.00024 mg/m3. This level is approximately 12 times greater than the MRL of 0.00002 mg/m3. Because the air levels exceeded the MRL, ATSDR performed a more detailed study of the toxicology (cancer and noncancer) of chlordane with site-specific factors. This maximum value was compared to other screening values, air levels reported in epidemiologic studies, accidental human exposures, and relevant animal studies.
The maximum chlordane concentrations exceeded the ATSDR inhalation MRL, but were below the EPA reference concentration (RfC) of 0.0007 mg/m3 for chlordane. The MRL and RFC were based on the same study in rats but were interpreted differently (Khasawinah et al. 1989; ATSDR 1994a; EPA 1997b). The RfC was based upon data unavailable at the time ATSDR's MRL was established. Both values incorporate numerous safety factors and conservative assumptions in order to protect sensitive individuals. Using the RfC, we can conclude that the air concentrations at Green Acres do not pose an apparent public health hazard. However, because of the discrepancy between the MRL and RfC, we evaluated the concentration further against animal and epidemiological studies.
For chlordane, the chronic inhalation MRL is 5,000 times lower than the lowest dose where no adverse health effects were observed (NOAEL). The NOAEL of 0.1 mg/m3 for effects on the liver of rats exposed via inhalation to technical grade chlordane (a relatively impure form of chlordane with a mixture of different types (isomers) of chlordane) for 90 days was used as the basis of ATSDR's MRL (ATSDR 1994a). After making standard assumptions and assigning "uncertainty" factors to account for the difference in human sensitivity compared to animals, variability in responses between humans, and adjustments to long-term exposures at 24 hours per day, every day of the week, the MRL of 0.00002 mg/m3 was derived. Monkeys tested in a similar fashion to rats showed no effects at levels of exposure as great as 10 mg/m3 (ATSDR 1994a). This is important since available data suggest that monkeys and humans are less likely to be affected by chlordane than rats and mice (ATSDR 1994a).
Compared to levels in experimental studies, levels of chlordane in Green Acres were more than 400 times lower than levels of chlordane that were without health effects in animal studies. Additionally, the indoor air levels were below levels (0.002 mg/m3) that have not been associated with adverse health effects in humans chronically exposed to chlordane in occupational situations (ATSDR 1994a).
The indoor air levels of chlordane at Green Acres were below the levels identified in a study of indoor air levels of chlordane in an apartment complex where effects on neurological function were observed (Kilburn et al. 1995). In this study, chlordane levels above 0.0005 mg/m3 seemed to be associated with impairment of neurological function. The maximum concentration in Green Acres Housing was more than two times below the lowest air concentration identified in this study where no effects on the residents were observed.
No animal studies were located regarding cancer effects in animals after inhalation of chlordane. Long term oral exposure in rats and mice detected liver tumors, but these animals were exposed at higher levels and in a fashion that would increase exposure doses and is unlikely to occur in Green Acres residents (ATSDR 1994a). Occupational studies have generally failed to detect cancer or other chronic effects due specifically to chlordane (ATSDR 1994a).
Therefore, we concluded that the chlordane levels are too low to produce adverse health effects.
The indoor air concentrations for dieldrin slightly exceeded the air comparison values for children and infants. Based on our evaluation, we believe that it is unlikely that adverse health effects and unacceptable cancer risks would be experienced from breathing air containing the maximum concentration of dieldrin.
The maximum detected concentration of dieldrin in the indoor air at Green Acre Houses (0.00028 mg/m3) exceeded the ATSDR screening value of 0.0000002 mg/m3 for cancer. Therefore, ATSDR evaluated dieldrin further for cancer and noncancer health effects. Our evaluation included a review of the exposure assumptions and the toxicity of dieldrin.
The ATSDR screening value is overly protective of human health because it overestimates exposure based on exposure 24 hours a day, 365 days a year, and for 70 years. In realistic terms, average residency times are about 7 to 9 years and people on average, stay in their houses about 16 hours per day and are at the house about 350 days per year (U.S. EPA 1997a).
Based on more realistic exposure durations, the new noncancer comparison values are 0.00028 mg/m3 (adults), 0.00013 mg/m3 (children), and 0.0001 mg/m3 (infants). The cancer comparison values are 1.2 mg/m3 (adults), 0.85 mg/m3 (children), and 4.0 mg/m3 (infants). The maximum level of dieldrin measured in air of 0.00028 mg/m3 is equal to the estimated air noncancer comparison values for adults, and only slightly exceeded the level for children and infants. Therefore, we evaluated the noncancer toxicological studies further.
The noncancer screening values are overly protective of public health because they are based on overestimated values of dieldrin toxicity. The toxicity of dieldrin is identified through its minimum risk level (MRL) by ATSDR (referred to as a reference dose, RfD, in EPA literature) for noncancer effects. The MRL is derived from studies on animals or humans with additional safety factors.
In our previous discussion, we said that people at Green Acres have been exposed to pesticides by inhalation. A review of the scientific literature on dieldrin located no inhalation studies in animals or humans. We did identify human worker studies involving inhalation as an exposure route, but these studies were difficult to interpret because exposure through skin contact was also involved. Studies on the oral route of exposure in animals do exist, and ATSDR has derived MRLs for oral exposure to dieldrin based upon the NOAEL in animal studies. Based on the how dieldrin enters and distributes through the body, we have assumed that the animal ingestion studies can be applied to inhalation (See Appendix K for more information on the oral to inhalation assumption).
Most of the data on toxicity of dieldrin comes from animal studies. Animal studies involving long-term exposure at high levels show adverse health effects on the liver, nervous system, and immune system (ATSDR 1993). Studies in mice and rats show that chronic exposure at high levels can produce liver tumors (ATSDR 1993).
The exposure levels in these animal studies are much higher than the exposure levels to dieldrin in Green Acres indoor air. In fact, the maximum exposure levels of indoor air at Green Acres were 166 times below the lowest exposure tested without adverse effects on a long term study in dogs (0.005 mg/kg/day, ATSDR 1993). Exposure at Green Acres is 100 times lower than the lowest oral exposure tested to human volunteers without adverse effects (0.003 mg/kg/day, Hunter and Robinson 1967).
The majority of studies in workers exposed to dieldrin in the workplace show no toxic effects from exposure. Human occupational studies have not detected an increase in cancer among exposed workers (ATSDR 1993). A study where human volunteers consumed doses of dieldrin as high as 0.003 mg/kg/day for 18 months showed no adverse health effects (Hunter and Robinson 1967). For the purposes of this evaluation it is assumed that there is no difference in the absorption and metabolism of dieldrin between the lungs and gastrointestinal tract, and that equivalent oral and inhalation exposure levels will result in the same absorbed dose of dieldrin. The levels of exposure in the study by Hunter and Robinson were more than 90 times higher than the highest dose estimated from exposure to dieldrin in indoor air at the maximum concentration. Additional information about dieldrin is provided in Appendix J.
Human occupational studies have not detected an increase in cancer among exposed workers (ATSDR 1993). The exposure levels in occupational settings are likely much higher than the exposure levels to dieldrin in Green Acres indoor air.
Therefore, we concluded that the dieldrin levels were to low to produce adverse health effects.
DDT, DDD, DDE
The maximum level of DDT detected in indoor air at Green Acres housing (0.00040 mg/m3; includes the sum of DDT, DDD, and DDE) was below the estimated air comparison values. DDT was chosen for further evaluation because the DDT levels in one or more houses reached one-third of their MRLs and when combined with chlordane and dieldrin exceeded screening levels.
A review of the scientific literature on DDT, DDE, and DDD located no inhalation studies in animals or humans. Human occupational studies include inhalation as an exposure route, but other routes such as skin contact were also involved. Studies on the oral route of exposure do exist, and ATSDR has derived MRLs for oral exposure to DDT and its breakdown products DDD and DDE.
Absorption of DDT by the lungs is considered to be a minor route of entry due to the particle size of DDT prevents inhalation deep into the respiratory tract (ATSDR 1994b). Metabolites of DDT have been detected in workers exposed to DDT by inhalation, but it is believed that the likely route of exposure from inhalation is due to swallowing material deposited in the respiratory tract and cleared by the mucocilliary apparatus in the lungs and swallowed (ATSDR 1994b). Additional information about DDT is provided in Appendix J.
Although experimental data on the inhalation route is limited, we assumed that there were no significant differences in metabolism between the inhalation and oral routes of exposure, and subsequent distribution in tissues. We assumed equivalent exposure levels by inhalation or ingestion would result in roughly equivalent internal doses. ATSDR estimated air comparison values based upon the oral MRLs for inhalation exposures to adults, children and infants that would be unlikely to produce adverse health effects.
Using conservative exposure estimates for residents of Green Acres housing at the maximum concentration of DDT/DDD/DDE in air, our calculated doses were 588 times lower than the NOAEL in animal studies involving oral exposure to rats, and more than 500 times lower than the lowest level where no effects were observed in humans exposed to DDT orally (ATSDR 1994b, see Appendix K for additional information about DDT toxicity). As a result, it is unlikely that adverse health effects in adults, children or infants would be experienced from breathing air containing the maximum concentrations of DDT in Green Acres housing.
Evaluation of pesticide exposure to children and infants
Since pesticides like chlordane, dieldrin and DDT can be passed to infants though breast milk, we evaluated exposure to infants via breast feeding and inhalation (Sonawane 1995; Albers et al. 1996). Pesticides such as chlordane, DDT and dieldrin accumulate in body fat, and have been measured in mothers' milk (Sonawane 1995; Albers et al. 1996). To evaluate this exposure pathway, we estimated levels of pesticides in human milk based upon maternal inhalation exposure of indoor air at the Green Acre Houses using the procedures described by Shelley et al. (1988) and Rogan et al. (1994). Our results show that the estimated chlordane and DDT levels are below the typical levels in human milk reported in the scientific literature, while dieldrin was slightly higher. For all three pesticides, the infant exposures to pesticides in breast milk from maternal exposure to pesticides in indoor air were well below the MRLs for ingestion of these pesticides. As a result, there are no apparent public health hazards to infants from the combined exposures of inhalation or indoor air and ingestion of breast milk from their mothers.
Evaluation of the effects of exposure to multiple pesticides
ATSDR recognizes that people may be exposed to multiple chemicals via several routes of exposure. Although exposures to individual pesticides in Green Acres indoor air are not likely to result in adverse health effects, to be protective, ATSDR researched the effects of multiple exposure to DDT, dieldrin and chlordane.
There is limited information available on the influence of exposure to multiple chemicals and on the effects of combined exposure to the pesticides detected in air at Green Acres housing. In long term animal studies, effects on the liver seem to be a common toxic endpoint from exposure to all these pesticides. Assuming an additive effect on liver toxicity, there still appears to be no significant contribution to the likelihood of adverse health effects from chronic (long-term) exposure to these pesticide concentrations.
Studies involving exposure to mixtures of pesticides indicate that these mixtures can affect the metabolism of these chemicals, but the impact on the toxicity of DDT, chlordane and aldrin is unknown (ATSDR 1994a, Chaturvedi 1993). A study in rats showed that the short term toxicity of high exposure levels to chlordane was increased up to four times by previous exposure to DDT and dieldrin (ATSDR 1994a). Prior exposure to DDT increased the elimination if dieldrin metabolites (ATSDR 1993). Exposure to these pesticides can influence the metabolism of other chemicals such as therapeutic drugs or hormones (ATSDR 1994b).
The exposure levels to chlordane in Green Acres housing were 400 times lower than the level where no adverse health effects were seen in animal studies, so a slight increase in potential chlordane toxicity would still be well below the levels of concern for health effects. Studies involving workers exposed to chlordane and other pesticides have not detected an increase in health effects (ATSDR 1994a). As a result of the rat and worker studies, ATSDR concludes that health effects from combined pesticide exposure at Green Acre Houses poses no (apparent) public health hazard.
ATSDR concludes that past pesticide exposure also probably posed no apparent public health hazard. We, however, had less information to base this conclusion on since past concentrations of pesticides in indoor air at Green Acres are not known. In looking for an answer, we reviewed past studies of indoor air. The ATSDR toxicological profile on chlordane lists 22 studies of indoor air chlordane concentrations in houses. Concentrations ranged from not detected to 0.055 mg/m3 compared to the maximum in Green Acre Houses of 0.00024 mg/m3. The highest concentrations were primarily in houses with misapplications. Studies also showed a tendency to have higher concentrations in house applications prior to 1983 presumably because chlordane use was restricted to certified applicators around this time (Fenske and Sternbach 1987). A study in 1992 in Kansas showed indoor air concentrations in a house increase after application from 0.00025 mg/m3 to 0.00121 mg/m3. Levels returned to 0.00029 mg/m3 (close to preapplication levels) after six months. Another study in twelve New Jersey houses showed a slight but not a statistically significant increase in mean concentrations after application but a 100 percent increase in houses with detectable levels (Louis and Kisselbach 1987). In short, concentrations of pesticides in indoor air at Green Acres may have been higher in the past after application for periods up to one year. However, the concentrations and lengths of exposure probably posed no (apparent) public health hazard to nonsensitive individuals.
The crawl space soils do not pose a (apparent) public health hazard for people contacting the soil or breathing the air in the crawl spaces at Green Acres Housing. ATSDR bases this conclusion on the concentrations in the soils and the assumption that people, in that past, would have gone into the crawl space on a very limited basis. Current and future exposure is limited by locked access doors. Access is only available by the property management company under contract to the March Joint Powers Authority.
In 1995, AFBCA sampled the crawl space soils in 20 of the 128 houses (16%) for seven pesticides (See Table 2). Of the seven pesticides, DDT was detected in the crawl space soils of all 20 houses ranging from <0.0017 to 440 mg/kg. Methoxychlor was detected in one house at 0.047 mg/kg (Tetra Tech 1996b).
Of the 20 houses sampled for pesticides in the crawl spaces soils, 14 houses had concentrations of one or more pesticides that exceeded ATSDR's Cancer Risk Evaluation Guide for 1 in 1,000,000 excess cancer risk (see Table 2) from incidental ingestion of the soils. These comparison values are default values assuming exposure of 365 days per year for 70 years. Since residents have limited access to these soils, ATSDR recalculated the risks assuming seven years of exposure (an average tour of duty), six years for children and assumed five days per year of exposure. Using the highest concentrations for each pesticide, the recalculated adult cancer risk is lower than 1E-6 and the noncarcinogenic doses are lower than the reference doses for children and adults indicating that health effects are not expected (See Appendix D for sample calculations).
These risk calculations have the following limitations:
- Only eight pesticides were analyzed for and other pesticides may be present that could increase the risk. ATSDR does not have a list of the pesticides used at Green Acres, but other pesticides were identified from the indoor air measurements. In addition, since most of these pesticides have been banned for use in houses, the use of other pesticides such as chlorpyrifos could be present. Chlorpyrifos is used in houses to control cockroaches, fleas, and termites.
- 20 (or 16%) of the houses were sampled. Some houses may have higher concentrations of pesticides.
- The pesticide concentrations in the crawl space air are unknown, but could add to the health risk when people entered the crawl space and contacted the soils. Although pesticides have relatively low volatility, their presence in the indoor air of the living quarters indicates that they are probably present in the crawl space air also.
- The exact exposure duration to crawl space soils is unknown, but we assumed five days/year to account for adults entering the crawl space for household maintenance or 12 days/year to account for children entering the crawl space during playing activities.
Although the analysis has some limitations, the most important factor is that the crawl space soils are not easily accessible and hence, exposure is unlikely. Therefore, ATSDR concludes that the crawl space soils pose no apparent public health hazard.
Public Health Action Plan
Actions Taken and Proposed:
AFBCA has analyzed air and soil samples from the Green Acre houses as described in the previous section. MJPA is currently leasing the property to private citizens.
The crawl spaces have been secured with locked doors preventing access by the tenants.
ATSDR places emphasis on the prevention of exposure and recommends actions, when possible to reduce exposure. Although we concluded that pesticides in the crawl space soils and indoor air poses no (apparent) public health hazard, we recommend the placement of barriers in the crawl space to prevent or lower pesticide migration into the houses.
March AFB has found leaded paint on the interior and exterior surfaces at the Green Acres Military Family Housing. In addition, soils collected at the roof dripline have been found to contain lead above levels of concern. Pediatric blood lead data shows no positive tests from the children that were living on base and tested but the blood lead data does not indicate which children were selected for testing at March AFB. There were approximately 772 children (0 to 6 years old, 1990 US Census, Geolytics 1998) living on-base in 1990 and 100 were tested from 1992 through 1996. With this limitation, ATSDR concludes that lead is not a public health hazard at the Green Acre Houses based on the blood lead data. However, future exposure should be prevented by prohibiting children from playing next to the homes because of lead contaminated soils identified in soil samples adjacent to the homes. Access to these soils should be prevented by the maintenance of lawns and shrubs adjacent to the homes and the prohibition of gardens in these same areas. ATSDR also recommends that MJPA and AFBCA follow the protective public health measures identified in 66 Federal Register 1206 for lead in residential soils.
The history of the sampling, sampling results and current activities are presented below.
History of Sampling and Sampling Results
In 1992, March AFB sampled the exterior surfaces of 51 randomly selected housing units at Green Acres for lead in the paint. The results ranged from 5.1 to 94,000 ppm (trace to 9.4% by weight). Sometime between 1992 and 1994, March AFB removed the lead-based paint from the exterior of all 51 houses except houses 141 and 176. (March AFB 1995).
In 1994, March AFB sampled the interior and exterior surfaces of 13 randomly selected Green Acres houses (March AFB 1995). Some of these houses had their exterior surface evaluated and abated in the 1992 study. In the 1994 study, lead-based paint was found in all 13 houses (interior and exterior). Lead-based paint was considered present when the reported lead level was equal to or greater than 1.3 mg/cm2 (These units are not convertible to ppm or percent listed above. The units differ because different analytical methods were used). Current U.S. Department of Housing and Urban Development guidelines specify that lead paint is present when the paint has lead concentrations of 1.0 mg/cm2 or 5,000 ppm (HUD 1997). As a result, additional surfaces measured by March AFB may contain lead paint according to this lower value.
In the 1994 study, the March AFB sampled the roof dripline soils of 7 houses at Green Acres. The soils from all 7 houses had lead concentrations greater than California's modified Preliminary Remediation goal of 400 mg/kg (See Table 5) and greater than the new Federal lead standards (effective March 6, 2001, 66 Federal Register 1206) of 400 parts per million (ppm) of lead in bare soil in children's play areas.
All seven of these houses had exterior lead-based paint removed in the 1992 to 1994 time period (March AFB 1995) so the concentrations of lead in the soil should not increase.
Although lead may be present in the environment, exposure, and uptake may or may not be occurring. Measurement of blood lead concentrations is the most widely used indicator of lead exposure. ATSDR was provided pediatric blood lead data from March AFB. Of the 272 samples taken, 100 samples were from children who lived in on-base housing. Of the 100 samples, there were no positive tests. Armstrong Labs (USAF) reported that a positive test was a value above the CDC public health standard of 10 micrograms per deciliter (g/dL) and that the blood lead sampling began in 1992.
MJPA has remodeled the Green Acre houses prior to tenants taking occupancy. Remodeling includes the removal of chipped and peeling paint followed by repainting.
People can be exposed to lead from multiple sources. At the March AFB, these sources include lead-contaminated paint, household dusts, and foundation soils (soils near the base of the buildings). Preschool-age children and fetuses are usually the most vulnerable segments of the population for exposures to lead (ATSDR 1988, 1992b, 1997b). Children can be exposed to lead from paint if the lead paint is on surfaces subject to abrasions (e.g., window frames), is on chewable surfaces like window sills, or on surfaces in poor condition (e.g., on walls that are chipping, peeling, or chalking). The March AFB lead-based paint study stated that the interior paint was in fair condition, in need of minor repair, and the exterior paint was peeling (the areal extent of the peeling was not reported, March AFB 1995). The interior paint is being repaired prior to occupancy. However, lead-based paint may still be abraded at windows and doors.
The blood lead data indicates no public health hazard in the past. Future exposure would not be a problem if people maintain the painted surfaces (no chipping, peeling, etc.)
ATSDR toured Green Acres October 19, 2000 and found one home with playground equipment next to the home and another home with a fenced-in yard next to the home with children's toys. Some of the homes had bare soils adjacent to the homes. The combination of bare soils and evidence of children playing next to the homes create a potential for lead exposure.
Public Health Action Plan for Lead at Green Acres
Actions Taken and Proposed:
AFBCA has sampled and analyzed lead-based paint and lead contaminated soils. MJPA has removed chipped and peeling paint and repainting prior to occupancy. Rental agreements contain notification of the lead-based paint and lead-based paint hazards. Tenants are also provided a pamphlet on lead poisoning prevention titled "Protect Your Family From Lead in Your Home."
ATSDR recommends that the lawns and shrubs be maintained adjacent to the houses including the roof driplines and all bare soils should be replanted to prevent access to the soils by children and gardens adjacent to the houses should be prohibited to limit contact with the soils. This recommendation also extends to prohibiting children from playing next to the homes because of lead contaminated soils identified in the drip soil samples. This means that playground equipment or fenced areas for children should not be located next to the homes.Gardens adjacent to the homes should be prohibited to prevent exposure. The MJPA and its property management contractor are responsible for maintenance and should implement this recommendation. ATSDR also recommends that MJPA and AFBCA follow the protective public health measures identified in 66 Federal Register 1206 for lead in residential soils.
March AFB has identified building materials in Green Acres that potentially contains asbestos. This identification was based on the generic type of building materials and the dates of manufacture. Asbestos may be present, but the specific forms of asbestos present and its availability for exposure is unknown. Asbestos containing materials (ACM) that were friable and a source of fiber to the indoor air were removed. ACM was left in place if it was in good condition and not damaged or deteriorated to the extent that it creates a potential source of fibers.
Public Health Action Plan
Actions Taken and Proposed:
AFBCA has removed friable asbestos from the houses. The remaining suspected asbestos containing materials have been inspected and found to be in good condition (not damaged or deteriorated to the extent that it creates a potential source of fibers). The rental agreement contains provisions for not renting the houses if ACM is found damaged or deteriorated and for monitoring the ACM. The rental agreements also include monetary penalties if the tenants damage the ACM (AFBCA no date). A recently completed Basewide Asbestos Survey Report found attic vent pipes in 56 houses wrapped in asbestos. The Air Force has agreed to repair or remove this asbestos. Repair work will take about six months. The repair dates have not been reported (CEDAR 1999).
ATSDR recommends maintaining the asbestos containing materials by not disturbing asbestos containing materials and inspecting it once a year to see that it is not disintegrating with age and in need of encapsulation or removal.
ATSDR evaluated past uses of on-base and off-base contaminated ground water as a drinking water source. Our evaluation is presented in the next two sections.
Contaminated groundwater below March AFB has polluted the on-base water supply wells. These wells were used for drinking water until 1984. As part of the base water supply system, March AFB mixed water from these wells with a treated surface water source before distribution to the base. The wells supplied approximately 44% of the water used by the base. Contaminants we evaluated included volatile organic compounds (VOCs) and boron. Although boron is naturally occurring, it was a concern because of its high concentrations in the on-base water supply wells compared to most water sources.
The on-base water supply wells are no longer used. Therefore, ATSDR evaluated past exposures to adults and children and concluded that noncancerous and cancerous health effects are unlikely from exposure to VOCs and boron. During the operation of the wells, U.S. EPA drinking water standards were not in effect for organics. However, the mixed water in the distribution system would have met the current standards. Table 6 summaries our evaluation of this situation.
In this section, ATSDR presents an overview of the water supply system at March AFB including sampling history and data on the ground water, treated surface water, and tapwater. In the next section, ATSDR evaluates the human exposure routes and public health implications from the contaminated ground water.
Water Supply at March AFB
Before 1984, March AFB obtained its water from both surface water and ground water sources. The source of the surface water was Lake Mathews, approximately 10 miles west of the base. March AFB treated the water (including chlorination) from this lake at the on-base water treatment plant before distribution (Wall 1997). The Colorado aqueduct fed Lake Mathews, a branch of the California aqueduct system.
The ground water produced by March AFB was generated from six base wells: BPW-1, BPW-2, BPW-3, BPW-4, BPW-5, and BPW-6. Wells BPW-1, 2, 3, and 4 are on the main base and BPW-5 and 6 are at a satellite property approximately 3000 feet southeast of the main base (see Figure 2). The wells operated at various times from 1927 to 1988 as listed in Table 7.
Before distribution, water from the wells and water treatment plant were mixed. Figure 3 presents a schematic of the two systems and their connection to each other. From 1964 to 1984, base records show that the relative amount of water obtained from the wells averaged about 44% (see Appendix E) with the remainder coming from the water treatment plant (Wall 1997). As a result, the total water supplied by each individual well to the total water supply was significantly lower as shown in Table 7.
In mid 1984, Eastern and Western Municipal Water Districts of California began supplying water to March AFB (Wall 1997). These "Districts" are part of the Metropolitan Water District of the State of California's regional water agency that imports water from Northern California and the Colorado River, and delivers it on a wholesale basis to Southern California. Although March AFB had this new source of water, they maintained the off-base production wells (BPW-5 and BPW-6) for emergency supplies up to 1988.
Sampling History and Data
ATSDR compiled information on the sampling results from the ground water production wells, water treatment plant and taps in the distribution system for the years 1978 to 1984. Data after 1984 is not a concern because the use of the contaminated ground water ceased then.
From the available records, ATSDR ascertained that March AFB began sampling the production wells in 1978. This first analysis included trichloroethene, metals, boron, chloride, fluoride, cyanide, and other anions, and cations. In 1982, March AFB added eight additional volatile organic compounds to the analyte list (we included a list of these compounds in Appendix F). Also in 1982, March AFB began sampling the water from the water treatment plant and taps in the distribution system for the same constituents in the wells. In 1983, March AFB added pesticides and PCBs to the suite of compounds analyzed for in all the drinking water sources.
We summarized the analytical results for VOCs and boron in Appendix G. Analytical data pertinent to the public health evaluation is summarized in Table 8. Pesticides and PCBs were not detected in the water samples and are not discussed further. Although boron is naturally occurring, we discuss it here because of its high concentrations in the ground water compared to most water sources and the measured concentrations in the distribution line exceeded ATSDR's comparison values.
The tables and appendices show that from 1978 to 1984 (last sampling date is September 1983), the highest concentration of trichloroethene (TCE) detected in a production well was 66 g/L (BPW-1, June 1983). However, TCE was below detection limits in the blended water in a tap in the distribution system (<0.2 g/L). The second highest concentration of TCE in well water was 57.6 g/L (BPW-3) in February 1978. March AFB did not have a sample of the water in the distribution system during this sampling event. However, ATSDR assumes the levels were below concern because of the blending of the well with other wells and treated surface water.
The highest concentration of TCE ever detected in a tap water sample from the distribution system was 2.6 g/L in August 1983. During this sampling event, water from well BPW-1 was also sampled and found to contain TCE at 33.0 g/L. The reduced concentration in the distribution system showed that dilution was occurring from the other wells and treated surface water.
The other VOCs detected in the water supply system and distribution system included bromodichloromethane, bromoform, carbon tetrachloride, chloroform, dibromochloromethane, methylene chloride, and tetrachloroethene (PCE). The highest concentrations of carbon tetrachloride, methylene chloride, and PCE detected in a tap water sample from the distribution system were not detected, 0.5 g/L and 0.4 g/L, respectively (see Table 8). These concentrations are below EPA's maximum contaminant levels (MCLs).
The other VOCs, bromodichloromethane, bromoform, chloroform, and dibromochloromethane, belong to a group of compounds called trihalomethanes. The sum of the concentrations of each of these compounds equals the concentration of trihalomethanes. The highest concentrations for trihalomethanes in a tap water sample from the distribution system water were 79.5 g/L in September 1992. This concentration is below the trihalomethane MCL of 100 g/L.
ATSDR was concerned with boron concentrations in on-base tap water because of high concentrations found in the base production wells coupled with only a few boron samples from the distribution line. ATSDR has three data points from the distribution line for boron: <500 g/L, August 1979; 500 g/L, September 1982, and 900 g/L, September 1983. During this time, boron concentrations in the wells measured 4,600 g/L (BPW 3, August 1979), 1,800 g/L (BPW-6, August 1979), and 1,300 g/L (BPW-6, September 1983). The California drinking water action level is 1,000 g/L while ATSDR's Environmental Media Evaluation Guide (EMEG) is 100 g/L for children. We evaluated boron further in the Human Exposure and Public Health Implication Section.
Sources of Contamination and Clean up Activities
Sources of ground water contamination contributing to the chemicals in the base production wells probably originated from several locations because the wells pumped water from a wide area. Based on modeling by Tetra Tech (1995a), BPW-1 pulled water from a radius (radius of influence) of 2,500 to 3000 feet (using 1980 ground water levels and a production rate of 248 gallons per minute). Based on well pumping rates, BPW-3 and BPW-4 probably pulled from smaller radii because they had lower pumping rates. Nonetheless, the impact of the radius of influence from these three wells would have reversed the natural ground water flow direction for 2,500 feet or more downgradient. As a result, laterally adjacent and currently downgradient sources of contamination and the upgradient sources could have contributed to the ground water contamination. Therefore, the sites presented in Table 9 could have contributed to the ground water contamination that impacted the on-base production wells. Table 9 also shows the activities AFBCA has conducted and is planning to conduct, to address the sources of contamination.
ATSDR reviewed the existing data to determine human exposure and evaluated the impact on public health. Exposure was based on three factors: 1) the use of the contaminated ground water that determined the human exposure route(s), 2) the length of time the ground water was used (period of exposure), and 3) the types and amounts of volatile organic compounds and boron in the water during the exposure period. Since these factors have not previously been determined and are not precisely known, we developed a conservative scenario with assumptions based on the existing data discussed below.
The water at March AFB was used for residential, commercial and industrial purposes. Residential and commercial uses would have included drinking, bathing, cooking, and cleaning. Water would have been used in the industrial processes to operate and maintain the airplanes and support equipment.
Although data are available for total water usage at March AFB, ATSDR does not have an exact list of water uses or quantities of water used for each specific purpose. For residential use, ATSDR used national averages. For total residential tapwater intake including foods and beverages derived from tapwater, children are assumed to ingest 1 liter (L) of water per day and adults 2 L/day. To account for the inhalation and dermal contact with the volatile organic compounds while showering, bathing and other water uses, the U.S. EPA Supplemental Guidance to the Risk Assessment Guidance Document (1995) recommends using an additional 2 L/day ingestion rate as an additional equivalent amount to the amount inhaled or absorbed through the skin. Therefore, an adult is assumed to ingest water at a rate of 4 L/day and children 3 L/day.
Past water usage for commercial and industrial purposes is unknown. For this evaluation, ATSDR assumed that workers were consuming the water and exposed to contaminants in the water from dermal contact and inhalation. ATSDR assumed the same exposure rate as residential users (4 L/day).
Different populations at March AFB were exposed to different amounts of contaminated ground water based on how much time spent at the base. These populations could have included:
- Military personnel who lived and worked at the base and their families that lived, worked, and went to school at the base. Due to troop rotations, these people would have been exposed for five to nine years.
- Military personnel who worked on the base but lived off base. As in the first case, exposure would have occurred for five to nine years but exposure would have been less than the full 4 L/day of water since they consumed water off-base.
- Civilians who worked on base but lived off base. These people could have been exposed for the number of years employed by the base, but since they lived off base, would have been exposed to less than the full 4 L/day of water.
- Other people including visitors or other military personnel on shorter tours of duty.
For the purposes of our evaluation, we selected the worst case scenario of a person living and working on base exposed to the full 4 L/day (based on military personnel living on base) for 30 years (based on civilian personnel working on base).
Types and Amounts of Volatile Organic Compounds in the Production Wells and Water Supply System
The types and amounts of volatile organic compounds found in samples collected from the production wells and water distribution system were discussed in the previous section. However, to have less uncertainty about exposure, it would be desirable to have ground water data from the onset of contamination and have ground water data for a complete set of VOCs in the production wells. These historical data gaps cannot be filled, but we reviewed the ground water monitoring well data to develop a reasonable worst case scenario and ensure that higher concentrations or other contaminants did not occur in the production wells. The monitoring well system consists of more than 400 wells. These wells have been sampled at least 18 times since 1992 for metals, volatile organics, and semi-volatile organics. Some of these wells were sampled starting in 1985.
Based on the spatial and temporal distribution of the ground water contaminants from the sampling database and the groundwater hydrology, ATSDR has made the following assumptions:
- The production wells were not impacted by concentrations greater than the values documented in the limited historical data set.
- The production wells were not impacted by contaminants that were not analyzed for.
- Water from BPW-4 was not contaminated.
- Water from BPW-5 and 6 did not contribute contamination to the distribution system although they had one VOC detected before 1983 (chloroform 1.8 g/L, see Appendix G) and these wells were not analyzed for volatile organics besides TCE until 1982. In other words, we assumed that the chloroform was not an indicator of continuous contamination in the wells.
To simplify the risk calculations further and select a conservative exposure scenario, ATSDR selected the highest VOC concentrations detected as representative of the well water from BPW-1 and BPW-3 dating to the onset of contamination. In all cases, BPW-1 had the highest concentrations. Values from BPW-1 are presented in Table 10 with the concentrations in the water well system and water distribution system. The water distribution system values were calculated based on the amount of mixing with other sources of water. We have assumed the onset of exposure to have occurred in the 1940s with exposure ceasing at the end of 1983, a period of 44 years. We calculated the health risks from the mixed water.
Risk Calculation and Health Impact
The risk calculation and health impact is discussed separately for VOCs and boron.
• Volatile Organic Compounds
ATSDR quantified the cancer and noncancer health risk from exposure to VOCs. We present our results in Table 10. Based on the assumptions and calculations, the sum of the cancer risks from each compound were less than 1E-5 and greater than 1E-6, indicating that only one additional case of cancer in a population of 100,000 to 1,000,000 people may occur. This risk a range that is considered acceptable by the EPA and is considered a low risk (safe) by ATSDR.
For the noncancer risk, the sums of the hazard quotients are below one for children and adults indicating that noncancer health impacts from VOCs are not likely. Therefore, ATSDR does not expect to find any health effects from the past use of ground water at the base from VOCs.
• Boron - Noncancer
March AFB measured concentrations ranging from non-detect (usually <500 g/L) to 4,600 g/L in the water supply system (production wells, water treatment system, and distribution system). The highest concentrations in the production wells, water treatment plant, and taps in the distribution system were 4,600 g/L, 2,300 g/L, and 900 g/L, respectively. In August 1979, the boron concentrations in water from the production wells were 4,600 g/L in BPW-1 900 g/L in BPW-5, 1,800 g/L in BPW-6. A sample drawn from the tap water in August 1979, was non-detect for boron. The water treatment plant was not sampled for boron at this time. The reduction of boron in the distribution system was probably the result of dilution from blending the groundwater with treated surface waters before distribution.
Unlike VOCs, boron is naturally occurring in groundwater and surface water. The highest concentration of boron in March AFB monitoring wells was 1,600 g/L. The background monitoring wells at March AFB had boron level ups to 660 g/L. However, these wells are not screened as deep as the production wells. A production well operated by the Eastern Municipal Water District (unknown depth) is 1000 feet south of BPW-5. In 1996, AFBCA measured boron in this well at 400 g/L. Surface water supplies in the Metropolitan Waste District of Southern California had boron levels of up to 340 g/L boron in 1990 (CA DHS, 1990).
A study completed in 1992 (from data collected in 1992) by Armstrong Labs investigated the occurrence of boron in the wastewater treatment plant (WTP) effluent because they were exceeding their effluent limitations. In the study, Armstrong Labs sampled various WTP influent to determine the source of the boron. Their sampling included drinking water as a source. Levels of boron in these samples averaged 225 g/L (Armstrong Labs 1992).
Although high levels of boron appeared in the production wells, tap water had concentrations up to 900 g/L boron (for time periods other than the 1992 study). Although the past history of boron concentrations prior to 1978 is not documented, ATSDR evaluated the health impact using the highest reported value of 900 g/L boron in the tap water. ATSDR believes this is reasonable since a sampling event in 1979 found boron at 4,600 g/L in BPW-1, 1,800 g/L in BPW-6, and <500 g/L in tap water. Therefore, 900 g/L boron measured during a different sampling episode is considered a conservative value.
Based on this concentration and assuming 1 L/day and 2 L/day ingestion (dermal contact was not considered a health threat at these concentrations and inhalation is not an issue because boron is not volatile) of tap water for children and adults, the exposure dose for boron is 0.058 mg/kg/day and 0.037 mg/kg/day, respectively. ATSDR compared these values with EPA's reference dose (RfD) of 0.09 mg/kg/day and ATSDR's Minimum Risk Level (MRL) of 0.01 mg/kg/day. When an exposure dose is lower than a RfD or MRL, no adverse health effects are likely. Here, the exposure doses fall between the RfD and MRL. Since ATSDR devised the MRL with a safety factor of 1,000, we conclude that sufficient safety exists with actual doses midway below the RfD and MRL. Therefore, ATSDR concludes that boron in the past drinking water was not a public health hazard.
Public Health Action Plan
Past uses of drinking water contaminated with VOCs and boron at March AFB posed no (apparent) public health hazard.
Actions Taken and Planned
March AFB began monitoring the on-base production wells in 1978 and ceased using the wells in 1984. Before using municipal water, March AFB's water supply system blended surface water with ground water. Therefore, the contamination in water from the base production wells appears to have been sufficiently diluted to concentrations below health concerns before distribution to the base. AFBCA has installed more than 400 monitoring wells to determine the nature and extent of ground water contamination and to monitor the ground water regularly.
AFRC abandoned BPW-1, 2, 3, and 4 in accordance with State of California Regulations in 1997.
No recommendations to protect public health are necessary since no current exposure exists and past exposure was not a problem.
Contaminated ground water from March AFB has migrated approximately 3/4 miles east off base toward the City of Perris (See Figure 4) People who used wells in this area were exposed to two volatile organic compounds: trichloroethene (TCE) and tetrachloroethene (PCE). According to March AFB, private wells for drinking water are not currently used in this area. Therefore, we evaluated probable past exposure dose levels for adults and children and concluded that noncancerous and cancerous health effects are unlikely. The results, summarized in Table 11, indicate that consumption of the contaminated water poses no apparent public health hazard.
To confirm the presence or absence of used private wells in the OU1 area, ATSDR recommends that AFBCA or AFRC send all parcel owners in the OU1 area letters asking about the presence of wells and their use. ATSDR recommends that AFBCA or AFRC sample previously unknown private wells if they are still in use. These wells should be sampled quarterly for one year. With the results of the first sample and each subsequent sample, AFBCA or AFRC should evaluate whether the sampled wells should be closed because of public health. AFBCA or AFRC should also provide information on the status of the investigated wells to the State Department of Water Resources, Santa Ana Regional Water Quality Control Board, State Department of Health Services (Division of Drinking Water and Environmental Management), and the Riverside County Health Department.
The AFBCA, AFRC, State, County, or private owners should close those wells that are no longer used or inadequately constructed within the plume or adjacent to the downgradient edge of the plume to prevent exposure and the spreading of contamination.
The AFBCA or AFRC should confirm with the County of Riverside that well permits should not be issued in the OU1 area.
In this section, ATSDR presents sampling history and data on the contaminated ground water that has migrated off base. In the next section, ATSDR evaluates the human exposure routes and public health implications from this contaminated ground water.
Sampling History and Data
As part of the installation restoration program (IRP), March AFB installed and sampled monitoring wells in 1985 and sampled private wells beginning in 1986. Six off-base private wells were part of this program: PPW-1, PPW-2, PPW-3, PPW-4, PPW-5, and PPW-6 (see Figure 4). Table 12 summarizes the sampling results for these wells from 1986 to 1990. We included detailed sampling results in Appendix H. As listed in the Appendix H, March AFB found TCE contamination in wells PPW-1 and PPW-3 at 3.9 and 0.8 g/L, respectively in the first round of sampling in March 1986. At that time, March AFB did not detect TCE in well PPW-2. Well PPW-4 was not sampled at this time. PCE was not detected in any of the wells.
March AFB sampled these five off-base wells almost monthly from 1986 through 1988. During this time, trichloroethene was detected consistently in wells PPW-1 and PPW-3 from 0.1 to 15 g/L and only one to two times in PPW-2 and PPW-4. The concentrations in these last three wells ranged from 0.2 to 6.2 g/L. Tetrachloroethene was detected in wells PPW-1, PPW-4 and PPW-3 one or two times from 0.2 to 0.8 g/L and was not detected in the other wells.
In 1988, March AFB began sampling two more private wells: PPW-5 and PPW-6. From 1988 to 1990, these wells were sampled three times and the concentrations of TCE ranged from 9.0 to 17 g/L. PCE was not detected.
Beginning in June 1986, March AFB initiated activities to provide alternative water supplies to the residents using wells PPW-1 and PPW-3. At first, bottled water was supplied followed by connections to the municipal water supply. When contamination was found in wells PPW-5 and PPW-6, March AFB provided alternative water supplies to those users and ingestion of contaminated groundwater ceased. However, exposure to vapors from the ground water continued during bathing, clothes washing, and dish washing.
ATSDR compared the levels detected in the private off-base wells to U.S. EPA's maximum contaminant limits (MCLs) set for public water supplies and to ATSDR's screening comparison values (CVs). As shown in Table 12, the levels detected exceeded the MCLs and CVs. Since the concentrations in the off-base drinking water supply exceeded these values, ATSDR investigated the exposure further.
Sources of Contamination and Clean up Activities
March AFB began investigating the ground water contamination with on- and off-base monitoring wells in 1985. Currently, March AFB has installed approximately 465 monitoring wells (some have been abandoned or damaged). Twenty-six of these wells have been installed east of the base (Figure 4) to determine the nature and extent of the off-base ground water contamination. From these off-base wells, AFBCA has determined that two different areas of contaminated ground water exist, a northern area plume and a southern area plume.
March AFB has determined that ground water contamination originated from fourteen different former disposal sites that had soil contamination. At eleven of those sites, the soil has been cleaned up. At the three remaining sites, the soil and water are currently being cleaned. Of the three remaining sites, March AFB has determined that IRP Site 31 is the major source of the off-base ground water contamination.
In 1992, March AFB initiated full operation of a ground water extraction and treatment system along its eastern boundary. This system was designed to prevent the further flow of contaminated ground water off-site from the source of the southern area plume. As an indirect benefit, the system may also treat some of the off-base ground water.
Human Exposure and Public Health Implications
ATSDR reviewed the existing data to determine human exposure and evaluated its impact on public health. Exposure was based on three factors: 1) the use of the contaminated ground water that determined the human exposure route(s), 2) the length of time the ground water was used (period of exposure), and 3) the types and amounts of volatile organic compounds in the water during the exposure period. Since these factors have not been previously determined and are not precisely known, we developed a conservative scenario with assumptions based on the existing data discussed below:
- Use of the ground water. The ground water east of the base was used for industrial, residential and agricultural purposes as suggested by the well inventory compiled by Earth Technology (July 1991). Figure 4 shows the off-base wells immediately east of the base that were registered with the State of California or identified by March AFB. Residents formerly using five of the contaminated wells discussed previously were supplied with municipal water.
- Amount of ground water used. The exact amount of ground water used is not known. However, residential use can be estimated from national averages. For total tap water intake, including foods and beverages derived from tap water, children are assumed to ingest 1 liter (L) of water per day and adults 2 L/day (U.S. EPA 1989a). To account for the inhalation and dermal contact of the volatile organic compounds while showering, bathing and other water uses, the U.S. EPA Supplemental Guidance to the Risk Assessment Guidance Document (1995) recommends using an additional 2 L/day ingestion rate as an additional equivalent amount to the amount inhaled or adsorbed through the skin. Therefore, we have assumed an adult to ingest 4 L/day and a child 3 L/day of water.
- Dates the ground water was used. The dates the ground water was used are important to determine how long exposure occurred. The start time would be the date the off-base private wells were first contaminated. The off-base private wells were installed in the early 1960s. ATSDR calculated that the ground water contamination migrated off base around 1970 and assumes that this is the date that off-base wells were contaminated. The 1970 date is based on the ground water velocity and distance the contamination has migrated off base. Using a ground water velocity of 0.5 feet/day (Tetra Tech 1994) with the current edge of contamination approximately 5000 feet east of the base boundary, it has taken the ground water contamination 27.4 years [5000 feet/(0.5 feet/day x 365 days/year)] to travel from the eastern edge of the base to its location in 1997. Therefore, 27.4 years ago from 1997, or approximately 1970, is when the contamination is estimated to have left the base and contaminated the first wells. This calculation assumes that the contamination travels as fast as the ground water. However, in some cases, the contamination may move slower (a process called retardation) than the ground water. This would result in the contamination migrating off base at a later time reducing the length of exposure. Since we did not have the data to determine if retardation is occurring, we will use the 1970 date that assumes a longer exposure time.
- Types and Amounts of Volatile Organic Compounds in the Ground Water.
From 1986 to 1990, March AFB sampled the off-base private wells for trichloroethene and tetrachloroethene (see Appendix H). The highest measured concentration of TCE and PCE was 17 and 0.8 g/L, respectively. To determine if other VOCs may have been present or if higher concentrations of VOCs could have contaminated the private wells from 1970 to 1990, ATSDR reviewed data from the off-base monitoring wells.
For the purposes of this evaluation, ATSDR evaluated the exposure from using the private off-base wells that have been identified and sampled. However, the complete history of all wells in this area is not known with complete certainty. In 1996, Tetra Tech (1996a) completed a parcel and well ownership study in this area with a thorough records search for wells followed by visual inspections. Some wells identified in the records were inspected in the field to determine current condition and use. This inspection, however, was limited because of two factors: (1) the records contained limited information on the location of wells and (2) the inspections were completed from the nearest street because of trespassing issues. As a result, not all wells identified in the records search were located in the field or positively identified as to condition and use. Examples of these wells include those numbered 3S/3W-E1/E2, 3S/3W-19D2, 3S/3W-19J1, 3S/3W-F1, 3S/3W-19(?) and wells 3S/3W-19E2, 3S/3W-3002, E9, E11, E12, and 3S/3W-30J1 shown in Figure 4. It is possible that wells identified in the records have been abandoned or never installed (applications for wells were submitted to the state and recorded in their database but the wells were not constructed, and the database records were not deleted). However, to confirm the presence or absence of these wells, ATSDR recommends that AFBCA or AFRC send all parcel owners in the OU1 area letters asking about the presence of wells and their use. (The 1996 Tetra Tech report recommends contacting owners of wells identified in the records but not in the field. ATSDR was not able to confirm if this recommendation was implemented). ATSDR recommends that AFBCA or AFRC sample previously unknown private wells if they are still in use. These wells should be sampled quarterly for one year. With the results of the first sample and each subsequent sample, AFBCA or AFRC should evaluate whether the sampled wells should be closed because of public health. AFBCA or AFRC should also provide information on the status of the investigated wells to the State Department of Water Resources, Santa Ana Regional Water Quality Control Board, State Department of Health Services (Division of Drinking Water and Environmental Management), and the Riverside County Health Department.
Past residential use of the ground water is assumed to consist of drinking, cooking, and bathing. Therefore, residents were exposed to the ground water contaminants through ingestion, inhalation and dermal contact. Inhalation is assumed to occur as the volatile organic compounds evaporated during bathing, showering, cooking, and operation of the dishwasher or washing machine.
Past use of the water for agriculture would have consisted of inhalation during irrigation or through watering of livestock.
ATSDR also reviewed the ground water data to ensure that a previous volume of contaminated ground water, before the current contamination, had not contaminated the off-base wells and moved away, eluding detection. Previous contamination could have increased the length of time of exposure, exposed people to higher concentrations, or exposed more people further downgradient. ATSDR has determined that this has not occurred based on a review of maps showing the past and current areal extent and concentrations of TCE. These maps show an area of higher TCE concentrations on base and near the base boundary (50 to 100 g/L TCE) with decreasing concentrations as one moves further east. Furthermore, samples from two monitoring wells east of the ground water contamination have not shown detectable levels of PCE or TCE.
Exposure stopped when the local residents were supplied with bottled or municipal water. The exact dates are unknown, but memoranda from March AFB files suggested that the alternative water was supplied sometime between 1986 and 1990. To present a case of the longest exposure time (i.e., conservative evaluation), ATSDR selected 1990. Therefore, we estimate exposure to have occurred for 20 years from 1970 to 1990.
March AFB began sampling and analyzing off-base monitoring wells in 1985. From analysis of the data, March AFB identified two areas of ground water contamination east of the base, a northern plume area and a southern plume area. The northern area plume may have contaminated off-base private wells (see Figure 4), but March AFB determined that wells in this area have been abandoned or were never installed (applications for wells were submitted to the State and recorded in their database but the wells were not constructed, and the database records were not deleted).
The southern area plume has contaminated the private wells. March AFB began sampling and analyzing off-base monitoring wells in the southern area in 1987. Samples were analyzed for 33 volatile organic compounds including TCE and PCE. The highest concentration of TCE measured in the southern off-base wells was 42 g/L (monitoring well 5MW11 in May 1988). Before 1990 (the date exposure stopped), tetrachloroethene was not detected in any of the off-base monitoring wells in the southern area.
Other volatile organic compounds detected in off-base wells in the southern area before 1990 included carbon tetrachloride, chloroform, methylene chloride, 1,1- dichloroethene, and 1,1,1-trichloroethane, and vinyl chloride. Many sampling results were estimates and at very low concentrations because they were below or near the detection limit or present in the blank samples. In addition, a detected compound was often not detected in subsequent sampling events indicating that their presence is not confirmed or at levels well below detection limits.
ATSDR would have expected a higher frequency of other VOCs from the aerobic or anaerobic biodegradation of TCE (Mahaffey 1992). This process is apparently not occurring, perhaps because environmental conditions (such as a sufficient quantity of a primary metabolite) are not suitable in the water bearing geologic stratum.
Although it is possible that these other VOCs may have been present in the off-base private wells since the wells first became contaminated, based on the off-site monitoring and private well data, the concentrations would have been low (1 to 3 g/L) and below U.S. EPA's maximum contaminant levels for those chemicals in drinking water. Therefore, ATSDR did not evaluate these compounds further.
In conclusion, ATSDR has determined that it is unlikely that chemicals other than TCE and PCE were present in the off-site wells. Furthermore, it is unlikely that the water in the private wells had concentrations higher than measured; 17 g/L TCE and 0.8 g/L PCE.
Using the assumptions developed above, ATSDR calculated the carcinogenic and noncarcinogenic health risks for TCE and PCE. The results, summarized below, indicate that consumption of the contaminated water poses no apparent public health hazard (Calculations are shown in Appendix D-3).
Actions Taken and Planned
March AFB has taken the following actions in response to the off-base ground water contamination:
- Provided alternative drinking water supplies to the residents when March AFB discovered the contamination.
- Installed and sampled monitoring wells to determine nature and extent of the ground water contamination. Information on these wells was provided to the State.
- Installed and operated extraction wells along the eastern boundary of the base to prevent further migration of contaminated ground water off base.
- Requested the county of Riverside not to issue well permits on property with ground water contamination to prevent future exposure. However, when ATSDR discussed this with the county, some of the staff were unaware of this request.
- Conducted well surveys east and southeast of the base to identify all private wells and to ensure that the ground water is not being used.
March AFB is currently implementing a basewide ground water monitoring program to track the ground water contamination. Additional wells are being installed to better define the outer edges of the plume.
To confirm the presence or absence of wells in the OU1 area, ATSDR recommends that AFBCA or AFRC send all parcel owners in the OU1 area letters asking about the presence of wells and their use. ATSDR recommends that AFBCA or AFRC sample previously unknown private wells if they are still in use. These wells should be sampled quarterly for one year. With the results of the first sample and each subsequent sample, AFBCA or AFRC should evaluate whether the sampled wells should be closed because of public health. AFBCA or AFRC should also provide information on the status of the investigated wells to the State Department of Water Resources, Santa Ana Regional Water Quality Control Board, State Department of Health Services (Division of Drinking Water and Environmental Management), and the Riverside County Health Department.
The AFBCA, AFRC, State, County, or private owners should close those wells that are no longer used or inadequately constructed within the plume or adjacent to the downgradient edge of the plume to prevent exposure and the spreading of contamination.
The AFBCA should confirm with the County of Riverside that well permits should not be issued in the OU1 area.
Summary and Background
The Arnold Heights Family Housing Area consists of 542 multi-bedroom houses constructed in the early 1950s. These houses have been vacant since 1994 and the AFBCA has scheduled their demolition. Exact population of the houses during the period of their use is not available, but we estimated it to have been between 1,500 to 2,000 at any one time based on the number houses and their bedrooms.
Past residents (i.e., families) of Arnold Heights could have been exposed to contaminants present in the interior and exterior areas of these houses. Possible contaminants include lead in interior and exterior surfaces, pesticides and asbestos similar to those found in the Green Acres. ATSDR suspects these contaminants are present because maintenance procedures, such as pesticide application, were probably similar to Green Acres. Also, houses built during the early 1950s were typically constructed with materials containing lead and asbestos. Additionally, we suspect that oils, spread to control dust and weeds from 1941-1945, could be present in "oil mats" located in this housing area. PCB contamination could be present since PCBs were typical contaminants of oil in the past. One documented "oil mat," EBS Site P-2,7, is located at Arnold Heights. However, no data exists to confirm the presence of lead, pesticides, asbestos, or PCBs.
Although we do not have data on these houses, we are concluding that there is no apparent public health hazard for potential past exposure based on our review and conclusions at the Green Acres Houses. Although the houses are of different construction, we are assuming that maintenance, painting, and pesticide applications were similar to Green Acres (except oil mats were not identified at Green Acres). We are also assuming that the construction of the houses in the 1950s after the use of the oils (1941 to 1945) removed the exposure potential. Current and future use of these houses pose no public health hazard since they are not occupied and will be removed for future development under the reuse plan. The reuse plan specifies a mixed use including mostly commercial with recreational areas (March AFB Joint Powers Authority 1996).
To confirm our assumptions and prevent any exposures, ATSDR recommends that if the future land use includes a potential for contact with the soil such as the case of playgrounds or parks, the AFBCA, MJPA, or future owners should sample the soils for lead and PCBs after demolition and site preparation. The results of the soil samples should then be evaluated for health risks.
Human Exposure and Public Health Implications
For past exposure, ATSDR is concluding that there was no apparent public health hazard. We based this conclusion on the probable similarity in maintenance of the Arnold Heights houses with that of Green Acres Houses and the presence of the oil mats was prior to construction. These oil mats were identified in the Environmental Baseline Survey (EBS, Tetra Tech 1996b). For current exposure, ATSDR identified no public health hazards because the houses are vacant and access to the public is restricted by gates.
For future exposure, ATSDR concluded that there is no public health hazard since the houses will be removed, they were probably maintained like Green Acres, and the age of the oil mat. Sampling of the soils after razing the houses and prior to redevelopment would confirm our assumptions.
ATSDR concluded that there are no apparent public health hazards based on assumptions discussed above. To confirm our assumptions and prevent any exposures, ATSDR recommends that if the future land use includes greater potential for contact with the soil such as the case of playgrounds or parks, the AFBCA should sample the soils for lead and PCBs after demolition and site preparation. The results of the soil samples should then be evaluated for health risks.