PUBLIC HEALTH ASSESSMENT
TUCSON INTERNATIONAL AIRPORT AREA
a/k/a EL VADO RESIDENTIAL PROPERTIES
TUCSON, PIMA COUNTY, ARIZONA
Public Health Assessments evaluate human exposure pathways, provide an assessment of the health implications of those pathways, and make recommendations for appropriate activities to mitigate exposures and provide appropriate follow-up activities.
This public health assessment evaluates whether a public health hazard still exists for off-site residents since the remediation activities were conducted in 1997. The discussion addresses the available data, the methodology used in the identification process, the criteria for selection and determination of the extent and levels of any residual off-site contamination.
At the time this investigation was conducted, the interim June 1995 Arizona residential Health-Based Guidance Levels (HBGLs) were used as comparison values to determine if all the contaminated soil had been removed. Remediation activities continued until all confirmatory samples were below 0.18 mg/kg. Since then, the HBGLs have been replaced by the Soil Remediation Levels (SRLs), which were promulgated in November 1997 and are currently used as comparison values. The HBGL for PCBs is more conservative than the current SRL, which indicates that all the confirmatory soil samples are below the residential SRL for PCBs of 0.66 mg/kg.
Site-specific soil contaminant concentrations are compared to SRLs to determine which soil contaminants will be evaluated further in a public health assessment. SRLs for soil ingestion were calculated by the Arizona Department of Health Services, Office of Environmental Health. SRLs are protective of human health, including sensitive groups, over a lifetime of exposure. Contaminant concentrations in soils that exceed SRLs may not necessarily represent a health risk. Rather, when contaminant concentrations in soil exceed these standards, further evaluation may be necessary to determine whether the site poses an unacceptable risk to human health (ADHS, 1997a).
The public health implications of exposure to groundwater contamination is not evaluated in this public health assessment because this exposure pathway was the focus of a USEPA private well study conducted in 1994 (USEPA, 1994).
This public health assessment does not evaluate the source contamination at the Three Hangars site. This subject will be reviewed in the final ATSDR Public Health Assessment for the complete TIAA site, for which a draft report has already been completed (ATSDR, 1996).
This section reviews the preremediation soil data and remediation confirmatory sample data to verify that remediation activities have eliminated any future health hazard.
In 1996, a total of 82 shallow soil samples were collected at grid locations placed throughout the drainage areas, the vacant lot, the backyards of four residential properties, and the area north and west of the church. Aroclor 1260 and 1254 were detected in concentrations exceeding of 0.18 mg/kg. In 1997, an additional 30 samples were taken and results identified Aroclor 1260 concentrations exceeding HBGL for PCBs.
As indicated in the final report of the remedial investigation, the overall pattern of the PCB distribution consisted of a decreasing width of contaminated soils and decreasing concentrations as one moved to the west from the Three Hangars site. This pattern suggested that, most of the PCBs had been deposited in the soils before reaching the property lines. The areas of highest PCB soil concentrations were east of the residential areas (Daniel, July 2, 1996).
Post-remediation activities occurred from March through May, 1997. It consisted of the removal of surface soils in the backyards of four residential properties, the vacant area north and west of the church, a vacant lot located west of Highway 89 between El Vado and East Corona Roads, and the associated drainages west of the Three Hangars site. The remediation area was divided into five separate sections. These sections are:
- Area A: Drainage area east of Highway 89
- Area B: Vacant lot west of Highway 89
- Area C: Backyard areas of the residences
- Area D1: Vacant area behind the church
- Area D2: Vacant area to the west of the church
A total of 31 confirmatory soil samples were taken in these five areas during the remediation activities. Remediation continued until samples indicated that the interim Arizona HBGL of 0.18 mg/kg PCBs had been achieved. For this public health assessment, the final confirmatory soil samples were compared with, and were found to be, below the PCB residential Arizona SRL of 0.66 mg/kg. Sample results are provided in Table 2 and corresponding diagrams are provided in the Appendix (Conestoga, 1997).
|Remediation Area||Number of Samples||Range of PCB* Concentrations (mg/kg)**||Mean (mg/kg)||SRL*** for PCBs (mg/kg)||Above SRL|
|AREA A: |
|12||<0.033 - 0.643||0.32||0.66||No|
|AREA B: |
|9||<0.033 - 0.182||0.100||0.66||No|
|AREA C: |
Backyards of Residences
|5||<0.033 - 0.122||0.076||0.66||No|
|AREA D1: |
Vacant Area North of the Church
|3||0.045 - 0.120||0.07||0.66||No|
|AREA D2: |
Vacant Area West of the Church
|2||0.035 - 0.039||0.037||0.66||No|
*PCB= polychlorinated biphenyls; **mg/kg= milligrams per kilograms; ***SRL= soil remediation level
The leaching rate of PCBs downward through the soil and into the groundwater does not pose a threat to human health and the environment. PCBs generally bind to surface soils and do not leach to groundwater. PCBs have not been detected in the groundwater and have not been detected in soils deeper than one foot below ground surface at the El Vado Road site.
To determine whether residents and transients are being, or could be exposed to any remaining soil contaminants, ADHS evaluated the environmental and human components that lead to human exposure. This pathway analysis consists of five elements:
- A source of contamination
- Transport through an environmental medium
- A point of exposure
- A route of exposure, and
- An exposed population
This public health assessment focuses on human populations living on El Vado Road. ADHS categorizes an exposure pathway as a completed, potential, or eliminated pathway. Completed pathways require that the five elements exist and indicate that exposure to a contaminant has occurred in the past, is currently occurring, or will occur in the future. Potential pathways, however, require that at least one of the five elements should be missing. Potential pathways indicate that exposure to a contaminant could have occurred in the past, could be occurring at the present time, or could occur in the future. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present.
Completed and potential exposure pathways and quality of the accompanying sampling data used to identify the exposure scenarios are discussed below.
Before remediation occurred, dermal, ingestion, and inhalation exposures to contaminated soil were identified for residents and transients. Children would have been exposed to the PCBs while playing in these areas via incidental soil ingestion, inhalation of fugitive soil dust, and dermal exposures. Transients may have been exposed via inhalation and dermal exposures while walking through these areas. The past exposure pathways are summarized in Table 3.
It is estimated that approximately 30 people could have been exposed to the post-remediated soil. This includes the residential families, and people who visited the church for weekly services and activities. A toxicological profile for PCBs is located in the Appendix.
The contaminated soil that was in the backyards and vacant lot has been removed and replaced with clean replacement soil. All the exposure pathways to the contaminated soil have been eliminated and residents are no longer exposed to the contaminated soil. Concentrations of PCBs in the clean replacement soil have been analyzed to assure that the health threat that was present before the remediation activities has been completely removed.
In 1996, 16 residents were sampled for blood PCB levels by the ADHS. Thirteen residents had serum blood levels below 3 µg/L, one resident had a level of 3.4 µg/L, and the remaining two residents had blood levels less than 6 g/L. According to population-based studies conducted by the Centers for Disease Control and Prevention (CDC), the average serum PCB levels in the United States range from 5 to 7 µg/L (ATSDR, 1999). Therefore, we can conclude that the PCB levels detected in these residents were not site-related.
ADHS has prepared this public health assessment under a cooperative agreement with 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 contaminant exposure. This may include infants, the elderly, or individuals with respiratory problems, depending on the COCs and the nature of the exposures. The exposure points for sensitive residents in this case include the backyards of the residences, the vacant areas north and to the west of the church, and the vacant lot. Because the contamination has been remediated, future exposure to PCBs by children who live and play in the area has been removed.
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances emitted from waste sites and emergency events. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of contaminant exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. SRLs are protective of human health, including sensitive groups, over a lifetime. Residential SRLs are specifically protective of childhood exposure for systemic toxicity. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.