Skip directly to search Skip directly to A to Z list Skip directly to site content




March 1999 Plume Outlines and Tucson International Airport Area (TIAA) Site. Map from: Arizona Department of Environmental Quality, Southern Region Office.
Figure 1. March 1999 Plume Outlines and Tucson International Airport Area (TIAA) Site. Map from: Arizona Department of Environmental Quality, Southern Region Office.

Contaminated Municipal Wells, Tucson, Arizona
Figure 2. Contaminated Municipal Wells, Tucson, Arizona

Results of 1994 & 1998 Private Well Studies Conducted by Pima County Department of Environmental Quality
Figure 3. Results of 1994 & 1998 Private Well Studies Conducted by Pima County Department of Environmental Quality

Indoor Air Concentrations: Jury Model

Soil gas exposures were evaluated using the Juror Indoor Air Model to estimate indoor air exposure concentrations. The model assumes that gas entering a structure is instantaneously mixed within the entire volume. VOC concentrations within a building are a function of the flux from the soil, the area and volume of the building, and the rate of air exchange for the structure. This is a common assumption for assessments of this type and is intended as an upper bound estimate. It should be recognized that anytime a model is used the uncertainty of the estimated quantities is greater than if an accurate measurement were taken. These estimates assume that each VOC detected in soil gas is uniformly present beneath each building at the maximum concentration detected during the investigation. Therefore, this screening level analysis very likely overestimates concentrations of soil gas contaminants in indoor air.

Data used for the soil gas exposure assessment included all results previously presented in this health assessment. Indoor air concentrations were estimated using the following model:

Jury Model
Jury et al. have developed an equation for estimating the flux of a contaminant from a finite source of contaminated soil (Jury et al. 1990). The model is applicable when contamination extends from the surface for a known fixed thickness in the soil column. The model is applicable when there is no clean soil layer above the contamination. The following assumptions were used to derive this simplified equation:

  • Uniform soil properties (homogeneity)
  • Instantaneous linear equilibrium adsorption
  • Linear equilibrium liquid-vapor partitioning
  • Uniform initial contaminant concentration
  • Contaminants present at less than saturation
  • No clean soil layer
  • No water evaporation or leaching
  • No biological or chemical degradation

Equation and symbol explanations

To estimate the average contaminant flux over 30 years, the time-dependent contaminant flux must be solved for various times and the results averaged. A simple computer program or spreadsheet can be used to calculate the instantaneous flux of contaminants at set intervals and numerically integrate the results to estimate the average contaminant flux. The time-step interval must be small enough (e.g., 1-day intervals) to ensure that the cumulative loss through volatilization is less than the total initial mass. Inadequate time steps can lead to mass-balance violations (USEPA 1996a).

Alternatively, the EMSOFT computer program developed by the USEPA Office of Research and Development National Center for Environmental Assessment (NCEA) may be used to estimate average flux. The computer program provides an average emission flux over time by using an analytical solution to the integral, thereby eliminating the problem of establishing adequate time steps for numerical integration. EMSOFT is available through the NCEA in Washington, D.C.

Public Comments and Responses

ADHS and ATSDR provided an opportunity for public comments in the final draft stage of this document from. November 7, 2000 to April 5, 2000. Comments were provided by The U.S. Air Force, the Air National Guard, Sustainable Borderlands Planning, the USEPA, and Pima County Department of Environmental Quality (PCDEQ). These comments and ADHS responses are summarized below.

Comment A:
The PCDEQ wrote several comments on the public health assessment as follows:

Comment A-1a:
The executive summary does not make it clear that the report is only summarizing and commenting on current and future exposures. It would be helpful to clarify this, as was done in the November 13, 2000 report.

Response A-1a:
While we do not attempt to quantify exposures prior to 1981, we do comment on past conditions, and conclude that due to lack of data, past groundwater conditions were an indeterminate public health hazard.

Comment A-1b:
In the summary only trichlorethylene (TCE) is identified as a pollutant. It should also be mentioned that additional pollutants of concern were found, including chromium.

Response A-1b:
We intentionally focused only on TCE as the primary pollutant in order to simplify the summary as much as possible.

Comment A-1c:
The summary makes the comment "There is currently no exposure of public health concern." Although this is technically true since no one is currently drinking water contaminated above an MCL, I recommend further clarification that an aquifer is a dynamic system and that pollution levels can and do vary over time. Indications from private well sampling study show TCE and chromium levels rising over time in some areas.

Response A-1c:
See revised text in the final document.

Comment A-2
ADEQ should be referenced as the source of information for the "General Hydrogeology" section rather than PCDEQ.

Response A-2
See revised text in the final document.

Comment A-3
Under the heading of "Water" on page 10 of the report this statement is made: "However, there have been no significant exposures since site monitoring and remedial activities began in 1981." This may be true for regulated public water systems, however, EPA Region 9 and PDEQ identified a private well in 1994, within the TIAASS, that was being used for drinking purposes. This well had TCE and Chromium contamination levels significantly above the respective MCL's.

A similar comment is made under "Past Conditions" on page 15 of the report, "Groundwater represented no apparent public health hazard after the contaminated municipal wells were closed." Again, a clarification should be made that this may only apply to water from a public water system and not water from private wells.

Response A-3
The "South side TCE Private Well Investigation, Tucson International Airport Area Superfund Site (PDEQ, 1994) page 5-3, contains the statement, "None of the fourteen wells used for drinking water exceeded the EPA's designated safe levels, which are known as Maximum Contaminant Levels (MCL).... For the wells that exceeded an MCL, none are being used for drinking or other household purposes."

Comment B:
Environmental Resources Management (ERM) wrote with several comments on behalf of the Air National Guard (ANG) as follows:

Comment B-1:
The General Electric facility was not named as a potential source of contamination in the Plume B Area in this report, while the facility was named as a potential source for this plume in the public health assessment report for the Plume B.

Response B-1:
See revised text in final document.

Comment B-2:
A supporting figure would be useful to display the locations of municipal supply and private drinking water wells listed in Tables 3 and 4 in addition to the private irrigation wells sampled by the PDEQ.

Response B-2:
Please see Figures 2 and 3 in the Appendix of the final document.

Comment B-3
Chromium: It is recommended that additional information be included regarding the presence of chromium. Specifically, the Assessment should include discussion of background levels of chromium in regional soil and groundwater... should clarify whether the concentrations of chromium reported in groundwater were associated with filtered or unfiltered samples....should describe the results of any hexavalent chromium analyses that have been performed.

Response B-3
Detected levels of Chromium were not above MCL's, so chromium was screened out as a chemical of concern, and additional information regarding chromium was not considered necessary. Chromium levels in private drinking wells are listed in Table 4.

Comment B-4
Data quality: It is recommended that additional information should be provided regarding sample collection and sample quality assurance/ quality control procedures. From this information, the document should briefly evaluate usability of the analytical data for the purposes of this Assessment.

Response B-4
Please see revised text in the final document.

Comment B-5
Detection limits should be provided for all analytical data reported in the document.

Response B-5
Although detection limits are not listed in the document, verification of appropriate detection limits was included in data review.

Comment B-6
Soil gas: It is agreed that the reported concentrations of constituents in soil gas are unlikely to pose an unacceptable risk. However, additional information should be provided regarding the calculation of modeled air concentrations and the comparison values (CVs) used to screen the modeled concentrations. The term EMEG should be defined, and a source provided for the EMEG values. Cited CVs seem quite high, and it is recommended that the units of the CVs be verified.

Response B-6
Thank you for notifying us of our mistake in conversion of the ATSDR air comparison values and our omission of supporting information. See revised text and Table 1 in the final document.

Comment B-7
Soil: The Assessment includes soil data for poly-chlorinated biphenyls (PCB's). The primary focus of the health assessment is TCE-contaminated groundwater. PCB's are not identified as contaminants of concern. Text should be revised to explain the inclusion of this data. Additional soil data should also be presented to allow a more detailed evaluation of current soil conditions.

Response B-7
As noted in the document, soil contamination was evaluated in greater detail in the previous environmental health investigations referenced in the text. Readers are referred to the former investigations for more detailed evaluation of soil contamination. PCB contamination of soils is not emphasized further in this summary document, since no current or potential future exposures to levels of public health concern were identified.

Comment B-8
Soil: It is recognized that access to the site is restricted. However, even under such conditions, certain populations may still have the opportunity to be exposed to site soil (e.g., workers). It is recommended that the potential for exposure to soil be more fully discussed.

Response B-8
Please see revised text in the final document.

Comment B-9
Groundwater: The assessment states that contaminated groundwater is not being used for potable supply. However, the text does not discuss other possible uses of groundwater (industrial supply, fire suppression, etc.). It is recommended that the Assessment include discussion of this issue before concluding that site groundwater poses "no apparent public health concern."

Response B-9
We contacted the South Tucson fire department and verified the use of Tucson Water municipal supplies for fire suppression. For discussion of other uses of groundwater, please see revised text in the final document.

Comment B-10
Health studies: Section 4.3 states that several of the studies were suggestive for various outcomes. Extreme caution must be used when interpreting the results of these studies, since ecological studies ...may lead to either an underestimation or an overestimation of outcome effect. The principal utility of such studies lies not in suggesting a relationship between exposure and outcome, but in identifying avenues for further study. It is recommended that the text be revised to emphasize the uncertainties associated with the health studies cited.

Response B-10
See revised text in the final document.

Comment B-11
The recommendations from the health studies contained in the Appendix to the Public Health Assessment for Plume B should be included in the body of this Public Health Assessment.

Response B-11
See revised text in the final document.

Comment C
The U.S. Air Force provided several comments as follows:

Comment C-1
The Executive Summary reads, "There is currently no exposure of public health concern." Recommend this sentence be rewritten as, "Currently the levels of contamination in private drinking wells are not of public health concern." The concern....about people converting their irrigation wells should be expressed in this Executive Summary paragraph. Exposure to TCE in groundwater does exist via private wells, but at a level that is not of public health concern.

Response C-1
See revised text in final document.

Comment C-2
The site boundaries described in the Introduction do not match the boundaries shown in Figures 1 & 2. Figure 3 airport boundary does not match Figures 1 & 2. It is necessary to clarify what is meant by site boundary and ensure that the text description matches the boundaries shown in the figures.

Response C-2
See revised text in the final document.

Comment C-3
Why is Plume B referred to as West Plume B even though it is on the east side of the site?

Response C-3
Plume B is located on the east side of the site, but Plume B is composed of discrete areas of contamination, designated West Plume B, and East Plume B. West Plume B is located north of Valencia Road, extending westward toward the larger Plume A (Figure 1).

Comment C-4
Page 11, Section 4.1. Present Groundwater Conditions: The first sentence reads, "Current groundwater data indicate that contaminated groundwater from the site is not being used as a drinking water source (ATSDR 2000c)." This sentence should be revised since contaminated groundwater from the site is extracted, treated and placed into the Tucson drinking water distribution system at the Tucson Aquifer Remediation Project (TARP) plant.

Response C-4
See revised text in the final document.

Comment C-5
This document does not include the ATSDR future health study activities in the Public Health Action Plan (PHAP). It appears that any health study efforts by ATSDR are totally disconnected from the local efforts by the ADHS or Pima County and it is not clear that ADHS and Pima County are actively pursuing health study initiatives on their own. How are ATSDR studies being communicated to the public and does ADHS act as an advocate for these studies? Section 4.3 of the draft PHA discusses the TCE Subregistry to the National Health Interview Survey and ATSDR's intention to continue the registry and follow-up evaluation. This information should be included in the PHAP.

Response C-5
Please see revised text in the final document.

Comment D
The USEPA provided comments recommending inclusion of more recent data in the PHA as summarized below:

Comment D-1
Table 1: Additional soil gas samples have been collected at the former West Cap property since the 1997 data cited in this table. A summary of this recent data is attached (table 1). The recent data should be incorporated into the report since concentrations in some wells have increased since 1997.

Response D-1
See revisions to Table 1 in the final document.

Comment D-2
Table 4: Additional private well sampling was performed by PDEQ in 2000. Please see the attached table 2 for a summary of the recent data. The recent data should be incorporated as appropriate.

Response D-2
See revisions to Table 4 in the final document.

Comment E
Sustainable Borderlands Planning provided comments as summarized below:

Comment E-1
The literature reviewed appears to be a selection of articles that are unavailable to the general public, and the selection excludes many scientific articles which address the public health effects of contaminants being released from this facility. To our knowledge there has never been any serious epidemiological study of health effects directly related to this CERCLA site. The studies you cite pick very limited populations to examine. They do not reflect the population which live and have lived in the contamination area. For example, there are reports of a testicular cancer cluster among the faculty who taught college classes at the Three Hangars location of this site.

We ... urge the ATSDR to include information ...that documents adverse health effects rather than just publish information based on your small selection of studies that looks at only marginally related populations- and finds nothing to worry about.

Response E-1
All formal (health) studies conducted by county or state health department or university researchers in the contaminated area surrounding the Tucson International Airport were selected for review. The ADHS and a number of academic researchers familiar with the Tucson Airport problem were contacted to see if any additional studies had been conducted and were available for review. Only formal studies were selected in which either human subjects were studied or existing health data on morbidity/mortality was analyzed. Court affidavits, petitions, and opinions were not included in the review.

Limitations of these studies were cited in the draft PHA pg.17, including difficulties in accurately identifying exposed populations, due to use of the census tract level rather than the block level for analysis. Rather than "finding nothing to worry about," we concluded results of several of the studies were suggestive for several health outcomes, but limitations of the studies prevented establishing a relationship between exposure and effect. Recommendations were made for further study to investigate the suggestive outcomes.

Comment E-2
Your review begins assessment of data available since 1981. The statement "No sampling data were located which indicates groundwater chemical conditions prior to 1981," is grossly misleading. There is a wealth of information about this site going back to at least the 1950s, when several local lawsuits were filed regarding polluted private drinking wells.

Response E-2
As noted in the response to comment E-1, court affidavits, petitions, and opinions were not included as reference material in this Assessment.


a permeable rock stratum below the earth's surface through which groundwater moves; generally capable of producing water for a well.

chemicals of concern:
chemicals whose concentrations are above the appropriate screening level.

this word is used to describe water quality. This indicates that the water quality in question is in compliance with federal water quality standards developed by the United States Environmental Protection Agency.

detection limit:
the minimum concentrations that must be accurately and precisely measured by the laboratory and/or specified in the quality assurance plan.

the amount of contamination absorbed or deposited in the body of an exposed organism for an increment of time. A total dose is the sum of doses received by a person from a contaminant in a given interval resulting from interaction with all environmental media that contain the contaminant. Units of dose and total dose are often converted to units of mass per volume of physiological fluid or mass of tissue.

an event that occurs when there is contact at a boundary between a human being and the environment with a contaminant for a specific concentration for an interval of time: the units of exposure are concentration multiplied by time.

exposure pathway:
the process by which an individual is exposed to contaminants that originate from some source of contamination and are categorized as inhalation, dermal, and/or ingestion exposures.

gene mutation:
a persistent change in a single gene.

the period between stimulus application and response onset.

maximum contaminant levels:
enforceable drinking water standards that are protective of public health to the extent feasible with current technology.

minimal risk level:
an estimate of daily exposure of a human being to a chemical (in mg/kg/day) that is likely to be without an appreciable risk of adverse noncancerous effects over a specified duration of exposure.

small, discrete, solid or liquid bodies, especially those suspended in a liquid or gaseous medium.

parts per million:
one part per million (ppm) equals 1 pound chemical per million pounds of water.

public health assessment:
an evaluation of relevant environmental data, health outcome data, and community concerns associated with a site where hazardous substances have been released.

quality assurance:
a planned system of activities whose purpose is to provide assurance of the reliability and defensibility of the data.

quality control:
a routine application of procedures for controlling the monitoring process. QC is the responsibility of all those performing hands-on operations in the filed and in the laboratory.

route of exposure:
means by which the contaminant actually enters or contacts the body, such as ingestion, inhalation, dermal contact, and dermal absorption.

soil remediation levels (SRLs):
health-based soil screening levels. SRLs protect against toxic doses of systemic toxicants and limit excess lifetime cancer risk to one-in-one-million.

volatile compounds:
compounds amenable to analysis by the purge and trap techniques, also referred to as purgable compounds.

the conversion of a liquid or solid into vapors.


This Tucson International Airport Public Health Assessment was prepared by the Arizona Department of Health Services under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the public health assessment was begun.

Tammie McRae, MS
Technical Project Officer, SPS, SSAB, DHAC

The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health assessment and concurs with the findings.

Richard Gillig
Chief, State Program Section, DHAC, ATSDR

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #