PUBLIC HEALTH ASSESSMENT
TUCSON INTERNATIONAL AIRPORT AREA
TUCSON, PIMA COUNTY, ARIZONA
3.0 ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS
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 public health. For reference purposes and to provide the reader with a convenient frame of reference, the data are presented here alongside the USEPA's maximum contaminant levels (MCLs), which are legal standards for public drinking water supplies. The differences between MCLs and other health guidelines is presented in the Comparison Values section of the Appendix.
3.1 Contamination of Private Wells
The most recent monitoring well data suggest that a groundwater plume that has been contaminated with TCE and chromium has migrated in a northwest direction from Valencia Road near the AANG to Drexel Road. The total size of the contaminated groundwater plume is approximately 2 miles long and one-half mile wide. Since Plume B is migrating in a northwesterly direction, it has the potential to affect private drinking water wells and irrigation wells in nearby residential areas. Figure 3 in the Appendix shows the approximate extent of Plume B.
In 1994, a private well inventory was conducted by the PCDEQ to determine the extent of contamination in private wells throughout the larger TIAA Superfund Site and surrounding residential areas that might have been affected by the larger groundwater plume. This study included a portion of the residential area near Plume B with the exception of the far most western and northwestern portions. In 1998, a second follow-up private well study was conducted by PCDEQ which extended beyond the 1994 study boundaries to include the area north and northwest 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, using USEPA Method 524.2 for VOCs, and USEPA Method 200.7 for Total Chromium. Turner Laboratories, located in Tucson, Arizona, was used to analyze the Hexavalent Chromium samples using 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.
Table 1: Maximum Contaminant Concentrations of the 12 Private Drinking Wells and Comparison to Corresponding MCLs*.
| Well ID # | Present Status | TCE† MCL=5 µg/L‡ |
Chromium MCL=100 µg/L |
Above MCL? |
| 25 | Cemetery | N.D.§ | N.D. | NO |
| 28 | Private residence | N.D. | N.D. | NO |
| 29 | Private residence | N.D. | N.D. | NO |
| 3 | Private residence | N.D. | 2.2 | NO |
| 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 |
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.
Table 2: Maximum Contaminant Concentrations of the 7 Private Irrigation Wells and Comparison to Corresponding MCLs*.
| Well ID | Location | TCE† MCL=5 µg/L ‡ |
Above MCL | Chromium MCL=100 µg/L |
Above MCL |
| 26 | Cemetery | ND§ | NO | 17.5 | NO |
| 24 | Private residence | ND | NO | ND | NO |
| 27 | Elementary school | ND | NO | ND | NO |
| 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 |
| 23 | Private residence | 7.0 | YES | 4.8 | NO |
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.
Table 3: Summary of the Maximum Contaminant Concentrations of Trichloroethylene (TCE) and Chromium, and Comparison to Corresponding MCLs*.
| Chemical | Concentration Range (µg/L†) | Comparison Value | Exceed MCL |
# Wells Above MCL | |
| µg/L | Source | ||||
| 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 in the 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 number of monitoring wells installed by USEPA while characterizing the extent of Plume B. Thirteen monitoring wells have been installed and sampled between 1997 and 1999. Monitoring well sample results available to ADHS indicate a scenario quite similar to that displayed by the private well data. As discussed previously, sampling data results from the 19 private wells show most wells have TCE concentrations below the MCL of 5.0 µg/L and three of the 19 wells exceed the MCL. 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 USEPA show that five of the 13 wells had maximum TCE levels that exceeded the MCL (ERMWest 2000). The maximum TCE levels in these five wells ranged from 8 µg/L to 30 µg/L, very similar to the levels observed in the private wells.
ADHS has not yet thoroughly evaluated the data from these monitoring wells; however, it seems appropriate for the purposes of this document to confirm the consistency with the private well data reviewed in this report. ADHS notes that the 13 monitoring wells are open to the aquifer at depths ranging from about 70 to 125 feet below the ground surface. Although ADHS does not have detailed information about the construction of the private wells, ADHS believes it is likely that those wells would be less than 200 feet deep and would most likely be open to the aquifer at depths ranging from about 70 feet below ground surface (roughly the depth to water in the aquifer) to the total depth of each well. In summary, the 13 monitoring wells appear to be encountering very similar portions of the aquifer as the 19 private wells, with the 13 monitoring wells providing more specific information on discrete screen-opening zones and lengths. The chemical results of TCE concentrations also support this conclusion, with the results from the 13 monitoring wells being very similar to the data from the 19 private wells. Together, this data indicates an aquifer contaminated over a sizable area with TCE, but with only a limited number of wells which contain more than 5 µg/L of TCE.
3.2 Physical and Other Hazards
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 seen around the neighborhoods.
In order to determine if residents are being exposed to TCE or chromium at levels of public health concern in drinking or irrigation wells near the TIAA site, exposure pathways are identified to determine if and how residents might be exposed to the contaminants. This health assessment reviews the current and future potential pathways from the private wells in the Plume B area. The lack of past environmental sampling data precludes evaluation of potential past exposures.
4.1 Completed Current Exposure Pathways
The currently completed exposure pathway identified is residential exposure to contaminated groundwater by use of private wells for irrigation purposes. This includes inhalation, limited ingestion, and dermal exposures from irrigation wells.
Current exposure pathways may result from people using the water from their wells either for irrigation or drinking purposes or both. Typical residential well exposures to TCE include dermal and inhalation exposures from bathing and showering, and ingestion exposures from drinking and using 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 the contaminated water. This would include exposures to adults while they are watering the lawn or gardens, children playing in yards that are irrigated with contaminated private well water, or anyone who eats garden vegetables that are irrigated with contaminated water and which accumulate 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.
Table 4: Summary of Complete Current Exposure Pathways
| Type of Private Well | EXPOSURE PATHWAY ELEMENTS | Time | ||||
| Media | Point of Exposure | Route of Exposure | Exposed Pop.* | COC† | ||
| Irrigation Well | Groundwater | yards, gardens | Ingestion Dermal Inhalation |
9 Residents |
TCE | Current |
4.2 Potential Future Exposure Pathways
ADEQ is still in the process of characterizing the boundaries of the plume due to the difficult hydrology of the area. Since the plume is slowly migrating northward, and has not been completely delineated, it is possible that uncontaminated wells could become contaminated in the future. In addition, exposure could occur in the future if abandoned wells are repaired and used for drinking or irrigation purposes, if a citizen decides to drill a private well in the area, or if an irrigation well is changed into a drinking water well. Because there are currently no ordinances in place in the site area to prevent this, these are all possibilities for potential future exposure pathways to occur.
ADEQ and PCDEQ are currently investigating the area to identify additional private wells that have been abandoned or were not previously identified in the 1998 Private Well study. There are 3 private drinking water wells and 2 irrigation wells that currently have no detection of chromium or TCE. Since these wells are close to other private wells that have detection of chromium or TCE, they are considered in this health assessment to have a slight potential of being contaminated in the future. These include drinking water wells at a cemetery and 2 private residences, and irrigation wells at a private residence and an elementary school. The elementary school 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.
Table 5: Summary of Future Potential Exposure Pathways.
| 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 Dermal Inhalation |
130 residents | TCE ‡ | Future |
| Irrigation Wells | Groundwater | Residences: yards, gardens | Ingestion Dermal Inhalation |
9 residents |
TCE | Future |
There are approximately 145 residents whose private wells have levels of TCE and/or chromium below the corresponding MCL. If the contamination increases in these wells to above the respective MCLs, these people are at risk of being exposed to elevated levels of TCE and/or chromium.
5.0 PUBLIC HEALTH IMPLICATIONS
This section reviews the potential for adverse health effects in persons exposed to specific contaminants through current or future exposure pathways. ADHS has analyzed the exposure scenarios to determine what, if any, public health hazard exists from exposure to contaminated groundwater in Plume B through the use of private wells. The analysis determined that some residents are currently being exposed to TCE and chromium through ingestion, inhalation, and dermal 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 above the chromium MCL. Three private irrigation wells had concentrations of TCE (at 50 µg/L, 16 µg/L, and 7 µg/L) which are above the MCL of 5 µg/L. The highest concentration of TCE (50 ug/l) was detected in a private well (rather than one of the 13 monitoring wells in the Plume B area), so ADHS focused our evaluation on these private wells. Therefore, TCE is considered the only chemical of concern (COC) in the ADHS study area.
ADHS assesses a site by evaluating the level of exposure in potential or completed pathways. An exposure 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 with environmental data relevant to the exposure pathways. Comparison values are concentrations of chemicals that can reasonably and conservatively be regarded as harmless to public health based on the available scientific data. These comparison values are used for screening contaminants at a site to select which substances warrant more detailed evaluation by health assessors. The development of a comparison value includes conservative exposure assumptions which typically result in values much lower than those concentrations which have been observed to cause adverse health effects. If public exposure concentrations related to a site are below the appropriate comparison value, then the exposures are not of public health concern and no further analysis of the pathway is conducted. However, while concentrations below the comparison value are not expected to lead to any observable adverse health effect, it should not be inferred that a concentration greater than the comparison value will necessarily lead to adverse health effects. Depending on site-specific environmental exposure factors (for example, duration and amount of exposure) 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 and related 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 through various exposure pathways. Much of the toxicological information is based on dose-response relationships observed, primarily, in experimental animals, and typically extrapolated from high chemical 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 are present. ADHS has considered these variables in the development and application of comparison values.
For the West Plume B area of the Tucson International Airport Area Superfund site, ADHS has used Human Health Based Guidance Levels (HBGLs) as the appropriate comparison values with which to evaluate the available environmental data on potential exposures to TCE.
To further evaluate the human exposures that could occur from someone using a contaminated irrigation well, the ADHS developed and used a model that analyzes a chronic daily intake from multiple exposure pathways when using contaminated water for irrigation purposes. The ADHS calculated Human Health-based Guidance Levels (HBGLs) as comparison values that would incorporate all the various exposure pathways to the contaminated water via incidental ingestion and dermal contact, and inhalation pathways under irrigation scenarios.
HBGLs are used to help evaluate the health hazard from the cumulative inhalation, ingestion, and dermal contact with contaminants in groundwater. They are calculated using a human health-based approach that is generally consistent with risk assessment methodologies recommended by ATSDR, USEPA, and the ADHS. They use standard assumptions regarding daily intake of drinking water, air breathed, etc. when possible. Where standard assumptions were not available, the ADHS has made conservative assumptions based upon research of the particular exposure scenario and professional judgement. Equations used to quantify exposures were based upon generally 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 standard assumptions used, are presented in the Appendix (Tables A1 - A19).
A residential exposure scenario for flood irrigation was calculated which consists of residents who periodically irrigate their lawn with contaminated irrigation water or come in contact with water that is used to maintain neighborhood parks. This exposure scenario conservatively assumes 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 irrigation water for 4 hours per day, 350 days per year (COP 1998), for six years. Finally, an occupational exposure scenario was calculated for an adult maintenance worker exposed via inhalation of contaminants escaping from the flood irrigation waters for the 4 hours that the water is assumed to be standing in the property. The adult maintenance worker involved in flood irrigation duties is assumed to have incidental ingestion, inhalation and dermal contact with the flood irrigation water 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.
Table 6: Comparison of TCE* Concentrations to the HBGLs†.
| Chemical Found in Private Well | Exposure Pathway | Usage of Private Well | Comparison of Exposure Intake to HBGL | ||
| Values | HBGL | Exceeds HBGL? | |||
| TCE | 3 Private Wells | Irrigation | 7 µg/L‡ 16 µg/L 50 µg/L |
Adult: 397 µg/L Child: 87 µg/L Occupational:100 µg/L |
NO |
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 not represent a current public health hazard. However, owners of the wells have been notified that their wells have levels of TCE above the MCL, and have been given the option to change over to Tucson Water.
Edible Plants
After conducting an extensive literature search, ADHS has concluded that there are insufficient
data to identify the possible health hazard related to the ingestion of edible plants grown with the
use of contaminated groundwater. While much of the present research has focused on the uptake
of pesticides into plants, the research on the uptake of industrial pollutants by plants and food
crops is rudimentary. Available data suggest that the uptake of organic contaminants by plants is
dependent on the various properties of the compound, the plant, and its environment. Until these
variables can be determined and identified, any health hazard to humans due to the consumption
of 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 the
Appendix for reference. Each chemical is summarized with regard to use, interactions with other
chemicals, exposure routes, toxicokinetics, toxic (health) effects, carcinogenicity, and regulatory
status. Much of this information is available in greater detail in the Toxicological Profiles
published by ATSDR. A copy of ATSDR's Toxicological Profile for TCE can be viewed at the
TCE Library at 101 W. Irvington in Tucson.
5.2 Health Outcome Data Evaluation
ATSDR has reviewed eight of the ten studies presented in Section 1.4. The comments are provided in the "Review of Health Studies Related to TCE Contamination at Tucson Superfund Site, Tucson Arizona," presented in the Appendix. Numerous and significant limitations exist in the eight studies. These limitations prevent definitive conclusions on the causal relationship between exposure and health outcomes. Almost no exposure information is available besides that of residence in the contaminated census tract or work. This is a poor surrogate for exposure, since the contamination plume does not occupy the whole census tract. Using the tract level for analysis rather than block level is likely to lead to exposure misclassification resulting in an underestimation of the outcome effect. It is recommended that any further studies use block level analysis of morbidity and mortality data.
No statistically significant results were found for the following outcomes studied: a) homebound program admission rates in the Tucson Unified and Sunnyside school districts, b) mortality rates of Hughes aircraft employees and, c) childhood leukemia and testicular cancer incidence in Pima County.
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) mortality due to asthma, d) neuro-behavioral performance and, e) prevalence of systemic lupus erythematosus.
Although a number of serious limitations exist in the above studies, it is recommended that the outcomes for which results were suggestive be included in any future studies of the Tucson TCE contamination problem when possible. It is also recommended that a trend analysis be done to determine if the elevations in specific birth defects or other outcomes were persistent after public water supply sources were used.
5.3 Community Health Concerns Evaluation
Water issues have been a concern of community residents in South Tucson for many years. The community 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 property and 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 the area may be motivated to use private wells since it appears less expensive than being hooked up to Tucson Water.
In 1988, ATSDR conducted a health assessment for the larger Main Plume at the TIAA site to address the community concerns. The assessment indicated that soil and groundwater in the Main Plume had been contaminated by chromium and volatile organic compounds such as TCE and DCE. The findings of the public health assessment for the Main Plume found that it is unlikely that exposure to the concentrations of TCE detected in the Tucson public water supply would result 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 result from exposures to water from the public water supply.
Sampling of private wells for TCE from 1981 through 1994 identified both drinking and irrigation private wells in and near the TIAA (primarily the larger groundwater plume known as the Main Plume) with the contaminant levels ranging from non-detect to 120 µg/L. One of the private irrigation wells (#14) had concentrations of TCE of 49 µg/L which has subsequently increased to 50 µg/L. ATSDR determined that the exposure to the TCE in irrigation well #14 was not a public health concern. However, some of the private drinking water wells presented a health concern, since the concentrations were high and durations of exposure were greater than 10 years. It was also determined that the cancer risk from exposures to water from contaminated private drinking water wells was slightly increased. More information on TCE is provided in the Appendix.
5.4 ATSDR's Child Health Initiative
ADHS has prepared this public health assessment under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). ADHS has included the following information in accordance with ATSDR's Child Health Initiative.
Sub-populations of concern are sensitive receptor populations who may be particularly susceptible to chemical exposure. This can include infants, the elderly, or individuals with respiratory 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 they breathe dust, soil, and heavy vapors close to the ground which can result in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Child- specific HBGLs were calculated in this health assessment to identify any health hazard that may exist for children near the Plume B area. The following results were found:
In summary, the concentrations of TCE detected in the monitoring, drinking, and irrigation wells do not pose a public health hazard to sensitive populations in the area, such as children and older adults.
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