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





In this section, exposure pathways are evaluated to determine whether people accessing or livingnear Williams Air Force Base (Williams AFB) could have been (past scenario), are (currentscenario), or will be (future scenario) exposed to site-related contaminants. In evaluatingexposure pathways, the Agency for Toxic Substances and Disease Registry (ATSDR) determineswhether exposure to contaminated media has occurred, is occurring, or will occur throughingestion, dermal (skin) contact, or inhalation of vapors. When exposure to contaminated mediaoccurs, the exposure pathway is regarded as "complete." To determine whether completedpathways pose a potential health hazard, ATSDR compares contaminant concentrations to health-based comparison values. Comparison values are calculated from scientific literatureavailable on exposure and health effects. These values, which are derived for each of the media,reflect the estimated contaminant concentration for a given chemical that is not likely to causeadverse health effects, given a standard daily ingestion rate and standard body weight. Ifcontaminant concentrations are above comparison values, ATSDR further analyzes exposurevariables (for example, duration and frequency) and the toxicology of the contaminant. Figure 4summarizes this exposure evaluation process.

ATSDR analyzed all 32 Installation Restoration Program (IRP) sites at Williams AFB todetermine whether there are past, current, or future public health hazards associated with them.ATSDR identified exposure to contaminated soil at the Former Skeet Range as the only pathwaythat could potentially cause a health hazard (ATSDR, 1997a). Information on the Former SkeetRange is summarized in Table 1, the text following, and Appendix A. An analysis of availableinformation for the other 31 sites, which is summarized in Appendix A, indicates that these sitesare not associated with public health hazards either because (1) no site-related contaminantswere present, (2) contaminant concentrations detected are too low to pose a health hazard, (3)past and current exposures have been prevented by strict security measures, or (4) affected areashave been or will be remediated (AFBCA, 1994, 1997a, 1997b; ATSDR 1996, 1997b, 1997c,1997d; EPA, 1992; IT 1996a, 1996b, 1996c).

Former Skeet Range

Approximately 33 acres of William AFB's property were used as a skeet range between 1942and 1952 (IT, 1996d). While the range was in operation, considerable lead shot was deposited onthe ground. In 1953, an on-base housing development, the South Desert Village, was built on topof the Former Skeet Range. The lead shot was mixed in with subsurface soils and buried duringdevelopment and landscaping activities (IT, 1996d). While residents lived in the housingdevelopment, the lead shot remained in subsurface soils, covered by lawns, foundations,roadways, and sidewalks. No records indicate that residents discovered or were affected by leadshot in soil (ATSDR, 1996; IT, 1996d).

The housing development was vacated in 1993 when the base closed. Neglect of the propertiescaused lawns to die and allowed rodents, such as ground squirrels, to establish dens in the area.These burrowing animals brought the lead shot to the surface and Williams AFB representativesdiscovered lead shot immediately outside the rodent dens, during the 1995 IRP fieldinvestigation (IT, 1996d). Once base personnel became aware of the lead shot problem, theyplaced a fence around the entire South Desert Village to limit the potential for exposure. In 1995and 1996, four thousand nine hundred twenty-four (4,924) soil samples were collected from onethousand two hundred twenty-six (1,226) boreholes to characterize the extent of leadcontamination. The number of intact lead pellets were counted for each of the soil samples. Anadditional twenty-two (22) samples were collected between 1993 and 1995 and analyzed fortotal lead to assess lead contamination and to evaluate the potential for lead leaching. Twelve(12) of these samples were analyzed in a treatability study via EPA Toxicity CharacteristicLeaching Procedure. No sample was found to exceed the lead EPA toxicity limit of five (5)mg/L. Total lead concentrations ranged from 360 to 70,000 milligrams (mg)/kilogram (kg) in the top 5 inches of soil (IT, 1996d).

According to Environmental Protection Agency (EPA) Region IX preliminary remediation goalsand Arizona's health-based guidance levels, areas containing less than and including 400 mg/kgof lead do not cause excessive health hazards and are acceptable for future residential use. Usingthis guideline, Williams AFB reduced the amount of fenced land so that it now includes onlythose areas with lead concentrations greater than 400 mg/kg. About 100 to 120 vacated housesare still within the fenced area (see Figure 5). Arizona State University plans to use these housesfor graduate student housing in the future.

On April 22, 1997, EPA Region IX, the Arizona Department of Environmental Quality(ADEQ), the Air Force Base Conversion Agency (AFBCA), and the Arizona Department ofWater Resources signed a consensus statement that addresses the planned remedial activities forthe portions of the Former Skeet Range with lead concentrations in excess of 400 mg/kg(AFBCA, 1997c, 1997d). The statement contains the following agreements:

  • The top 6 inches of accessible soil (soil that is not covered by foundations, roadways, and sidewalks) will be removed and replaced with clean fill. This will reduce the soil lead concentrations to below 400 mg/kg in the top six inches of soil.
  • Areas covered by foundations, roadways, and sidewalks will be considered capped. This cap prevents exposure to underlying soils. A Voluntary Environmental Mitigation Use Restriction (VEMUR) will be issued for these capped areas. The Arizona Amended Soil Remediation Rule requires that this property be classified as non residential however it can be inhabited provided that frequent and repeated contact with the soil has been limited through the use of a protective cap thereby eliminating unacceptable risk to the inhabitants.
  • Provisions will be made to ensure that the cap remains intact. An operation and maintenance plan will be drafted to address cap monitoring and cap repair. Additionally, future residents will be notified that they are not allowed to disturb the cap.
  • A plan will be drafted to identify clean-up measures that will be necessary if the cap is removed.

    Current Exposure

Soil at the Former Skeet Range does not pose a current public health hazard. There are nocurrent residents in the South Desert Village. Although non-residents could access unfencedportions of the site, contact with soil in these areas will not pose a health hazard because the leadconcentrations are too low (400 mg/kg and less). A fence prevents access to areas with higherlead concentrations, and warning signs are posted.

    Future Exposure

Soil at the Former Skeet Range will not pose a future health hazard. According to ADEQ andEPA Region IX standards, areas with lead concentrations less than and including 400 mg/kg donot pose a health hazard to future residents. Additionally, areas where concentrations currentlyexceed 400 mg/kg will not pose a health hazard to future residents because the activities outlinedin the consensus agreement will (1) reduce contaminant concentrations to safe levels and (2)ensure that exposures to areas contaminated with lead at levels greater than 400 mg/kg areprevented (AFBCA, 1997c, 1997d). An Operation and Maintenance plan will outline provisionsto ensure that the caps remain intact. To provide further insurance of the safety of futureresidents, ATSDR prepared an educational fact sheet that will inform residents of the area'sformer use and actions being taken to clean up the area.

    Past Exposure

Soil at the Former Skeet Range did not pose a health hazard in the past. Although residents hadaccess to the Former Skeet Range between 1953 and 1993, they were isolated from the leadcontaminated soil because the soil was covered by lawns, foundations, roadways, and sidewalks(ATSDR, 1996; IT, 1996d). As a result, residents were not continually and repeatedly exposedto lead shot. ATSDR can not conclusively state that no exposures occurred in the past. Ifexposures did occur when residents were digging or gardening in their yards, exposures wouldhave been infrequent and of short duration. Such intermittent exposures are unlikely to be associated with a health hazard.

Next Section          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. #