PUBLIC HEALTH ASSESSMENT
TUCSON INTERNATIONAL AIRPORT AREA
TUCSON, PIMA COUNTY, ARIZONA
This section presents the environmental data on private wells in the Plume B area. Section 5.0"Public Health Implications" presents a discussion of these data and their relevance to publichealth. For reference purposes and to provide the reader with a convenient frame of reference, thedata are presented here alongside the USEPA's maximum contaminant levels (MCLs), which arelegal standards for public drinking water supplies. The differences between MCLs and otherhealth guidelines is presented in the Comparison Values section of the Appendix.
The most recent monitoring well data suggest that a groundwater plume that has beencontaminated with TCE and chromium has migrated in a northwest direction from Valencia Roadnear the AANG to Drexel Road. The total size of the contaminated groundwater plume isapproximately 2 miles long and one-half mile wide. Since Plume B is migrating in anorthwesterly direction, it has the potential to affect private drinking water wells and irrigationwells in nearby residential areas. Figure 3 in the Appendix shows the approximate extent ofPlume B.
In 1994, a private well inventory was conducted by the PCDEQ to determine the extent ofcontamination in private wells throughout the larger TIAA Superfund Site and surroundingresidential areas that might have been affected by the larger groundwater plume. This studyincluded a portion of the residential area near Plume B with the exception of the far most westernand northwestern portions. In 1998, a second follow-up private well study was conducted byPCDEQ which extended beyond the 1994 study boundaries to include the area north andnorthwest of the Plume B area (PCDEQ 1998).
ADHS selected the private wells that are currently being used in the area east of 6th Avenue and north of Valencia Road to be evaluated. In total, 24 private wells were identified in the area east of 6th Avenue. Five of these wells, three of which are located near the corner of 6th Avenue and Valencia, have either been shut down or were not sampled at the request of the owners, leaving a total of 19 private wells to be evaluated in this health assessment.
Samples were analyzed at the USEPA Regional Laboratory in Richmond, California, usingUSEPA Method 524.2 for VOCs, and USEPA Method 200.7 for Total Chromium. TurnerLaboratories, located in Tucson, Arizona, was used to analyze the Hexavalent Chromium samplesusing Method SM 17-3500 CR (PCDEQ 1994, 1998).
In 1994, the highest concentrations of chromium and TCE were found in one well at 160.0 µg/L and 120 µg/L, respectively. This well has been shut down. In the 1998 study, the levels of chromium and TCE ranged from non-detect to 9.9 µg/L and 50 µg/L, respectively, for the private wells currently in operation in the Plume B area. Figure 4 in the Appendix shows the location of the private wells in the ADHS study area. Table 1, below, lists the private wells in the study area that are currently used for drinking, bathing, and cooking purposes, and the highest TCE and chromium contaminant levels that have been detected from either the 1994 or 1998 private well studies.
|Well ID #||Present Status||TCE† |
|12||Mobile Home Park||N.D.||6.3 **||NO|
|9||Private residence||N.D.||3.0 **||NO|
|18||Private residence||N.D.||5.6 **||NO|
|21||Private residence||N.D.||5.8 **||NO|
|17||Private residence||N.D.||1.2 **||NO|
|7||Private residence||4 **||N.D.||NO|
|13||Mobile Home Park||3.6||5||NO|
|15||Private residence||3 **||6.3 **||NO|
** Indicates an increase in contaminant level from 1994 samples to 1998 samples.
Table 2 lists the private wells that are used for irrigation purposes. The highest detected level is listed whether it was from the 1994 or 1998 private well studies.
MCL=5 µg/L ‡
|10||Private residence||ND||NO||2.8 **||NO|
|14||Private residence||50.0 **||YES||9.9 **||NO|
|2||Private residence||16.0 **||YES||ND||NO|
** Indicates an increase in contaminant level from 1994 to 1998.
As seen from Table 2, there are three private irrigation wells that had TCE levels above the MCL. Additionally, chromium and TCE concentrations both increased in one well, chromium increased in another well, and the TCE level increased in a third well from the 1994 sampling to the 1998 sampling. These changes indicate, as previously mentioned, that characterization of the plume is ongoing. Table 3, below, provides a summary of all the private wells in the ADHS Plume B study area.
|Chemical||Concentration Range (µg/L†)||Comparison Value||Exceed |
|# Wells Above MCL|
|TCE‡||ND§ - 50.0||5.0||MCL||YES||3|
|Chromium||ND - 9.9||100||MCL||NO||0|
TCE was detected in excess of the MCL in three irrigation wells. Concentrations of chromium inthe irrigation wells were below the MCL of 100 µg/L (PCDEQ 1994, 1998).
3.1.1 Monitoring Well Data
In addition to the available data from private wells, ADHS located data collected from a numberof monitoring wells installed by USEPA while characterizing the extent of Plume B. Thirteenmonitoring wells have been installed and sampled between 1997 and 1999. Monitoring wellsample results available to ADHS indicate a scenario quite similar to that displayed by the privatewell data. As discussed previously, sampling data results from the 19 private wells show mostwells have TCE concentrations below the MCL of 5.0 µg/L and three of the 19 wells exceed theMCL. The three wells that exceeded the 5.0 µg/L MCL had maximum TCE concentrations of 7,16, and 50 µg/L. The results of TCE analyses on the 13 monitoring wells installed by USEPAshow that five of the 13 wells had maximum TCE levels that exceeded the MCL (ERMWest2000). The maximum TCE levels in these five wells ranged from 8 µg/L to 30 µg/L, very similarto the levels observed in the private wells.
ADHS has not yet thoroughly evaluated the data from these monitoring wells; however, it seemsappropriate for the purposes of this document to confirm the consistency with the private welldata reviewed in this report. ADHS notes that the 13 monitoring wells are open to the aquifer atdepths ranging from about 70 to 125 feet below the ground surface. Although ADHS does nothave detailed information about the construction of the private wells, ADHS believes it is likelythat those wells would be less than 200 feet deep and would most likely be open to the aquifer atdepths ranging from about 70 feet below ground surface (roughly the depth to water in theaquifer) to the total depth of each well. In summary, the 13 monitoring wells appear to beencountering very similar portions of the aquifer as the 19 private wells, with the 13 monitoringwells providing more specific information on discrete screen-opening zones and lengths. Thechemical results of TCE concentrations also support this conclusion, with the results from the 13monitoring wells being very similar to the data from the 19 private wells. Together, this dataindicates an aquifer contaminated over a sizable area with TCE, but with only a limited numberof wells which contain more than 5 µg/L of TCE.
No physical hazards that would be considered unusual were identified during the site visits. Children's toys were seen in the streets throughout the trailer park areas. Old cars were also seenaround the neighborhoods.
In order to determine if residents are being exposed to TCE or chromium at levels of publichealth concern in drinking or irrigation wells near the TIAA site, exposure pathways areidentified to determine if and how residents might be exposed to the contaminants. This healthassessment reviews the current and future potential pathways from the private wells in the PlumeB area. The lack of past environmental sampling data precludes evaluation of potential pastexposures.
The currently completed exposure pathway identified is residential exposure to contaminatedgroundwater by use of private wells for irrigation purposes. This includes inhalation, limitedingestion, and dermal exposures from irrigation wells.
Current exposure pathways may result from people using the water from their wells either forirrigation or drinking purposes or both. Typical residential well exposures to TCE include dermaland inhalation exposures from bathing and showering, and ingestion exposures from drinking andusing water for cooking. Since the wells of concern are irrigation wells, only limited dermal,inhalation, and ingestion exposures could occur to anyone who comes in contact with thecontaminated water. This would include exposures to adults while they are watering the lawn orgardens, children playing in yards that are irrigated with contaminated private well water, oranyone who eats garden vegetables that are irrigated with contaminated water and whichaccumulate the contaminants.
Table 4 identifies the estimated population that currently is being exposed to chromium or TCE through the use of contaminated private irrigation wells.
|Type of Private Well||EXPOSURE PATHWAY ELEMENTS||Time|
|Media||Point of Exposure||Route of Exposure||Exposed Pop.*||COC†|
|Irrigation Well||Groundwater||yards, gardens||Ingestion |
ADEQ is still in the process of characterizing the boundaries of the plume due to the difficulthydrology of the area. Since the plume is slowly migrating northward, and has not beencompletely delineated, it is possible that uncontaminated wells could become contaminated inthe future. In addition, exposure could occur in the future if abandoned wells are repaired andused for drinking or irrigation purposes, if a citizen decides to drill a private well in the area, or ifan irrigation well is changed into a drinking water well. Because there are currently no ordinancesin place in the site area to prevent this, these are all possibilities for potential future exposurepathways to occur.
ADEQ and PCDEQ are currently investigating the area to identify additional private wells thathave been abandoned or were not previously identified in the 1998 Private Well study. There are3 private drinking water wells and 2 irrigation wells that currently have no detection ofchromium or TCE. Since these wells are close to other private wells that have detection ofchromium or TCE, they are considered in this health assessment to have a slight potential ofbeing contaminated in the future. These include drinking water wells at a cemetery and 2 privateresidences, and irrigation wells at a private residence and an elementary school. The elementaryschool well is located directly east of the known Plume B boundaries.
Some of the wells that are furthest away from the known boundaries of Plume B have low detections of chromium. Because other plumes exist in the area, this contamination may not be directly related to Plume B. However, since traces of chromium and/or TCE have been detected in these wells, the wells are considered to be at risk for further contamination. Table 5 below provides a description of the potential future exposure pathways that have been identified for the ADHS Plume B study area and the estimated population that could be affected. It includes only those wells with current detections of TCE and/or chromium. Because chromium has generally been detected at levels well below the MCL, potential increases in levels of TCE are considered to pose the greatest potential future risk. The wells that have no detection of TCE and/or chromium should be re-evaluated as work continues at the site to determine if the wells remain outside the plume.
|Type of Private Well||EXPOSURE PATHWAY ELEMENTS||Time|
|Media||Point of Exposure||Route of Exposure||Exposed Pop.*||COC†|
|Drinking Water Wells||Groundwater||Residences: tap||Ingestion |
|130 residents||TCE ‡||Future|
|Irrigation Wells||Groundwater||Residences: yards, gardens||Ingestion |
‡ TCE = trichloroethylene.
There are approximately 145 residents whose private wells have levels of TCE and/or chromiumbelow the corresponding MCL. If the contamination increases in these wells to above therespective MCLs, these people are at risk of being exposed to elevated levels of TCE and/orchromium.
This section reviews the potential for adverse health effects in persons exposed to specificcontaminants through current or future exposure pathways. ADHS has analyzed the exposurescenarios to determine what, if any, public health hazard exists from exposure to contaminatedgroundwater in Plume B through the use of private wells. The analysis determined that someresidents are currently being exposed to TCE and chromium through ingestion, inhalation, anddermal exposures from the use of contaminated private wells for irrigation purposes.Concentrations of chromium were found in both irrigation and drinking wells but were not abovethe chromium MCL. Three private irrigation wells had concentrations of TCE (at 50 µg/L, 16µg/L, and 7 µg/L) which are above the MCL of 5 µg/L. The highest concentration of TCE (50ug/l) was detected in a private well (rather than one of the 13 monitoring wells in the Plume Barea), so ADHS focused our evaluation on these private wells. Therefore, TCE is considered theonly chemical of concern (COC) in the ADHS study area.
ADHS assesses a site by evaluating the level of exposure in potential or completed pathways. Anexposure pathway is the way chemicals may enter a person's body to cause a health effect.
The evaluation includes use of comparison values, which are screening tools used withenvironmental data relevant to the exposure pathways. Comparison values are concentrations ofchemicals that can reasonably and conservatively be regarded as harmless to public health basedon the available scientific data. These comparison values are used for screening contaminants at asite to select which substances warrant more detailed evaluation by health assessors. Thedevelopment of a comparison value includes conservative exposure assumptions which typicallyresult in values much lower than those concentrations which have been observed to cause adversehealth effects. If public exposure concentrations related to a site are below the appropriatecomparison value, then the exposures are not of public health concern and no further analysis ofthe pathway is conducted. However, while concentrations below the comparison value are notexpected to lead to any observable adverse health effect, it should not be inferred that aconcentration greater than the comparison value will necessarily lead to adverse health effects.Depending on site-specific environmental exposure factors (for example, duration and amount ofexposure) and individual human factors (such as: personal habits, occupation, overall health),exposure to levels above the comparison value may or may not lead to a health effect. Therefore,ADHS' comparison values should not be used to predict the occurrence of adverse health effects.Further information on comparison values and a description of some of the scientific terms andrelated health risk terminology (such as EPA's MCLs) is located in the Appendix section titled "Comparison Values."
ADHS acknowledges uncertainty exists in characterizing health effects from chemicals throughvarious exposure pathways. Much of the toxicological information is based on dose-responserelationships observed, primarily, in experimental animals, and typically extrapolated from highchemical doses in small animal populations to estimate low-dose responses. There often are also differences between animals and humans in metabolic response to a chemical, and chemical toxicity values are usually developed singly and responses may differ when complex mixtures arepresent. ADHS has considered these variables in the development and application of comparisonvalues.
For the West Plume B area of the Tucson International Airport Area Superfund site, ADHS hasused Human Health Based Guidance Levels (HBGLs) as the appropriate comparison values withwhich to evaluate the available environmental data on potential exposures to TCE.
To further evaluate the human exposures that could occur from someone using a contaminatedirrigation well, the ADHS developed and used a model that analyzes a chronic daily intake frommultiple exposure pathways when using contaminated water for irrigation purposes. The ADHScalculated Human Health-based Guidance Levels (HBGLs) as comparison values that wouldincorporate all the various exposure pathways to the contaminated water via incidental ingestionand dermal contact, and inhalation pathways under irrigation scenarios.
HBGLs are used to help evaluate the health hazard from the cumulative inhalation, ingestion, anddermal contact with contaminants in groundwater. They are calculated using a human health-based approach that is generally consistent with risk assessment methodologies recommended byATSDR, USEPA, and the ADHS. They use standard assumptions regarding daily intake ofdrinking water, air breathed, etc. when possible. Where standard assumptions were not available,the ADHS has made conservative assumptions based upon research of the particular exposurescenario and professional judgement. Equations used to quantify exposures were based upongenerally accepted methods, models, toxicity values, and assumptions developed by the USEPA. The equations and assumptions used to calculate HBGLs are conservative and well documented(ADHS 1997a). The HBGL calculations for TCE in irrigation water, along with the standardassumptions used, are presented in the Appendix (Tables A1 - A19).
A residential exposure scenario for flood irrigation was calculated which consists of residentswho periodically irrigate their lawn with contaminated irrigation water or come in contact withwater that is used to maintain neighborhood parks. This exposure scenario conservativelyassumes that adults and children are exposed to the contaminated irrigation water via inhalation,ingestion, and dermal contact during periodic maintenance or play activities.
A child exposure scenario was also calculated for a child who is assumed to play in the irrigationwater for 4 hours per day, 350 days per year (COP 1998), for six years. Finally, an occupationalexposure scenario was calculated for an adult maintenance worker exposed via inhalation ofcontaminants escaping from the flood irrigation waters for the 4 hours that the water is assumedto be standing in the property. The adult maintenance worker involved in flood irrigation dutiesis assumed to have incidental ingestion, inhalation and dermal contact with the flood irrigationwater for eight hours per day, 250 days per year, for 25 years (ADHS 1997b).
The adult and child HBGL for residential use is 397 µg/L and 87 µg/L, respectively. The occupational HBGL is 100 µg/L. As seen in Table 7, estimated exposure doses from ingestion of contaminated private well water are below the respective HBGL.
|ChemicalFound inPrivateWell||ExposurePathway||Usage ofPrivateWell||Comparison of Exposure Intake to HBGL|
|TCE||3 PrivateWells||Irrigation|| 7 µg/L‡ |
|Adult: 397 µg/L |
Child: 87 µg/L
Table 7 shows that all three wells of concern had TCE levels below both the respective residential and occupational HBGLs. Therefore, the level of TCE in the irrigation wells does notrepresent a current public health hazard. However, owners of the wells have been notified thattheir wells have levels of TCE above the MCL, and have been given the option to change over toTucson Water.
After conducting an extensive literature search, ADHS has concluded that there are insufficientdata to identify the possible health hazard related to the ingestion of edible plants grown with theuse of contaminated groundwater. While much of the present research has focused on the uptakeof pesticides into plants, the research on the uptake of industrial pollutants by plants and foodcrops is rudimentary. Available data suggest that the uptake of organic contaminants by plants isdependent on the various properties of the compound, the plant, and its environment. Until thesevariables can be determined and identified, any health hazard to humans due to the consumptionof food grown with TCE contaminated groundwater cannot be determined.
Summary of Toxicological Data
A brief summary of toxicological information on TCE and chromium is provided in theAppendix for reference. Each chemical is summarized with regard to use, interactions with otherchemicals, exposure routes, toxicokinetics, toxic (health) effects, carcinogenicity, and regulatorystatus. Much of this information is available in greater detail in the Toxicological Profilespublished by ATSDR. A copy of ATSDR's Toxicological Profile for TCE can be viewed at theTCE Library at 101 W. Irvington in Tucson.
ATSDR has reviewed eight of the ten studies presented in Section 1.4. The comments areprovided in the "Review of Health Studies Related to TCE Contamination at Tucson SuperfundSite, Tucson Arizona," presented in the Appendix. Numerous and significant limitations exist inthe eight studies. These limitations prevent definitive conclusions on the causal relationshipbetween exposure and health outcomes. Almost no exposure information is available besides thatof residence in the contaminated census tract or work. This is a poor surrogate for exposure, sincethe contamination plume does not occupy the whole census tract. Using the tract level for analysisrather than block level is likely to lead to exposure misclassification resulting in anunderestimation of the outcome effect. It is recommended that any further studies use block levelanalysis of morbidity and mortality data.
No statistically significant results were found for the following outcomes studied: a) homeboundprogram admission rates in the Tucson Unified and Sunnyside school districts, b) mortality ratesof Hughes aircraft employees and, c) childhood leukemia and testicular cancer incidence in PimaCounty.
In the reviewed studies, the reported results were suggestive for the following outcomes: a)congenital heart disease, b) musculoskeletal birth defects (county-year interactions) c) mortalitydue to asthma, d) neuro-behavioral performance and, e) prevalence of systemic lupuserythematosus.
Although a number of serious limitations exist in the above studies, it is recommended that theoutcomes for which results were suggestive be included in any future studies of the Tucson TCEcontamination problem when possible. It is also recommended that a trend analysis be done todetermine if the elevations in specific birth defects or other outcomes were persistent after publicwater supply sources were used.
Water issues have been a concern of community residents in South Tucson for many years. Thecommunity must be made more aware of the situation with the private wells in the Plume B area. For instance, managers of one mobile park were ready to fix the two private wells on the propertyand use them instead of being on Tucson Water, since it was cheaper. After speaking with them,they most likely will stay on Tucson Water. However, this indicates that other residents in thearea may be motivated to use private wells since it appears less expensive than being hooked upto Tucson Water.
In 1988, ATSDR conducted a health assessment for the larger Main Plume at the TIAA site toaddress the community concerns. The assessment indicated that soil and groundwater in the MainPlume had been contaminated by chromium and volatile organic compounds such as TCE andDCE. The findings of the public health assessment for the Main Plume found that it is unlikelythat exposure to the concentrations of TCE detected in the Tucson public water supply wouldresult in non-carcinogenic toxicity to the liver, central nervous system or other organs.Additionally, no congenital heart disease or other teratogenic effects would be expected to resultfrom exposures to water from the public water supply.
Sampling of private wells for TCE from 1981 through 1994 identified both drinking andirrigation private wells in and near the TIAA (primarily the larger groundwater plume known asthe Main Plume) with the contaminant levels ranging from non-detect to 120 µg/L. One of theprivate irrigation wells (#14) had concentrations of TCE of 49 µg/L which has subsequentlyincreased to 50 µg/L. ATSDR determined that the exposure to the TCE in irrigation well #14 wasnot a public health concern. However, some of the private drinking water wells presented ahealth concern, since the concentrations were high and durations of exposure were greater than 10years. It was also determined that the cancer risk from exposures to water from contaminatedprivate drinking water wells was slightly increased. More information on TCE is provided in theAppendix.
ADHS has prepared this public health assessment under a cooperative agreement with theAgency for Toxic Substances and Disease Registry (ATSDR). ADHS has included the followinginformation in accordance with ATSDR's Child Health Initiative.
Sub-populations of concern are sensitive receptor populations who may be particularlysusceptible to chemical exposure. This can include infants, the elderly, or individuals withrespiratory problems, depending on the chemicals of concern and the nature of the exposures. Children are more likely to be exposed because they are shorter than adults, which means theybreathe dust, soil, and heavy vapors close to the ground which can result in higher doses ofchemical exposure per body weight. The developing body systems of children can sustainpermanent damage if toxic exposures occur during critical growth stages. Child- specific HBGLswere calculated in this health assessment to identify any health hazard that may exist for childrennear the Plume B area. The following results were found:
- The level of the TCE in the private drinking water wells was below the MCL indicatingthe water to be safe to drink for children.
- The water in three of the irrigation wells was above the MCL. Further analysis wasconducted in the health assessment to determine if the detected TCE concentrations inthese wells could present a health hazard to children who might play in the irrigationwater. ADHS concludes that the level of TCE in the irrigation wells would not beconsidered a health hazard to children who would play with the water.
In summary, the concentrations of TCE detected in the monitoring, drinking, and irrigation wellsdo not pose a public health hazard to sensitive populations in the area, such as children and olderadults.