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1. ATSDR > Public Health Assessments & Consultations

PETITIONED PUBLIC HEALTH ASSESSMENT

KELLY AIR FORCE BASE
(a/k/a EAST KELLY AIR FORCE BASE)
SAN ANTONIO, BEXAR COUNTY, TEXAS

APPENDIX A: Site Maps

Figure 1. Intro Map

Figure 2. Private Well Locations

Figure 3. Soil Gas Well Locations

APPENDIX B: Quality Assurance and ATSDR Methodology

Quality Assurance

In preparing this report, ATSDR relied on the information provided in the referenced documents and by contacts with the Texas Natural Resources Conservation Commission, Texas Department of Health, San Antonio Metropolitan Health District, Environmental Protection Agency, United States Geological Survey, community members, and Kelly Air Force Base. ATSDR assumes that adequate quality assurance and control measures were taken during chain-of-custody, laboratory procedures, and data reporting. The validity of the analyses and conclusions drawn in this document are determined by the availability and reliability of the information.

Human Exposure Pathway Evaluation and the use of Comparison Values

ATSDR assesses a site by evaluating the level of exposure in potential or completed exposure pathways. An exposure pathway is the way chemicals may enter a person's body to cause a health effect. It includes all the steps between the release of a chemical and the population exposed: (1) a chemical release source, (2) chemical movement, (3) a place where people can come into contact with the chemical, (4) a route of human exposure, and (5) a population that could be exposed. In this assessment, ATSDR evaluates chemicals in the soil, air, and groundwater that people living in nearby residences may consume or come into contact with.

Data evaluators use comparison values (CVs), which are screening tools used to evaluate environmental data that is relevant to the exposure pathways. Comparison values are concentrations of contaminants that are considered to be safe levels of exposure. Comparison values used in this document include EPA's Region III risk-based concentration. Comparison values are derived from available health guidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor.

The derivation of a comparison value uses conservative exposure assumptions, resulting in values that are much lower than exposure concentrations observed to cause adverse health effects; thus, insuring the comparison values are protective of public health in essentially all exposure situations. That is, if the concentrations in the exposure medium are less than the CV, the exposures are not of health concern and no further analysis of the pathway is required. However, while concentrations below the comparison value are not expected to lead to any observable health effect, it should not be inferred that a concentration greater than the comparison value will necessarily lead to adverse effects. Depending on site-specific environmental exposure factors (for example, duration of exposure) and activities of people that result in exposure (time spent in area of contamination), exposure to levels above the comparison value may or may not lead to a health effect. Therefore, ATSDR's comparison values are not used to predict the occurrence of adverse health effects.

The comparison values used in this evaluation are defined as follows: The CREG is a concentration at which excess cancer risk is not likely to exceed one case of cancer in a million persons exposed over a lifetime. The CREG is a very conservative CV that is used to estimate cancer risk. Exposure to a concentration equal to or less than the CREG is defined as an insignificant risk and is an acceptable level of exposure over a lifetime. The risk from exposure is not considered as a significant risk unless the exposure concentration is approximately 10 times the CREG and exposure occurs over several years. The EMEG is a concentration at which daily exposure for a lifetime is unlikely to result in adverse noncancerous effects.

Selecting Contaminants of Concern

Contaminants of concern (COCs) are the site-specific chemical substances that the health assessor selects for further evaluation of potential health effects. Identifying contaminants of concern is a process that requires the assessor to examine contaminant concentrations at the site, the quality of environmental sampling data, and the potential for human exposure. A thorough review of each of these issues is required to accurately select COCs in the site-specific human exposure pathway. The following text describes the selection process.

In the first step of the COC selection process, the maximum contaminant concentrations are compared directly to health comparison values. ATSDR considers site-specific exposure factors to ensure selection of appropriate health comparison values. If the maximum concentration reported for a chemical was less than the health comparison value, ATSDR concluded that exposure to that chemical was not of public health concern; therefore, no further data review was required for that chemical. However, if the maximum concentration was greater than the health comparison value, the chemical was selected for additional data review. In addition, any chemicals detected that did not have relevant health comparison values were also selected for additional data review.

Comparison values have not been developed for some contaminants, and, based on new scientific information other comparison values may be determined to be inappropriate for the specific type of exposure. In those cases, the contaminants are included as contaminants of concern if current scientific information indicates exposure to those contaminants may be of public health concern.

The next step of the process requires a more in-depth review of data for each of the contaminants selected. Factors used in the selection of the COCs included the number of samples with detections above the minimum detection limit, the number of samples with detections above an acute or chronic health comparison value, and the potential for exposure at the monitoring location.

APPENDIX C: Estimated Exposure Dose and Cancer Risk for On-site Soil

• ATSDR selected an exposure scenario for incidental ingestion of soil at East Kelly as representing the greatest potential exposure to soil and its potential contaminant concentration if migration off-site occurs. Although ingestion of maximum concentrations of chemicals detected may be unlikely, it represents the greatest potential exposure to chemicals in the soil.



• ATSDR screened the maximum contaminant concentrations by comparison to the EPA's 1997 Region III Risk-Based Concentration (RBC) Tables for residential soil. All contaminants that exceeded this comparison value were selected for further evaluation. Maximum concentrations were used to calculate an exposure dose. Risk-based screening levels for carcinogens were based on combined childhood and adult exposure. Risk-based screening levels represent theoretical risks and should not be viewed as predictors of adverse health effects; the actual risk may be zero¹.



• ATSDR assumed the same ingestion rates as recommended for incidental soil ingestion of 200 milligrams (mg)/day for children and 100 mg/day for adults. ATSDR used standard body weights for children (15 kilograms[kg]) and adolescents/adults (70 kg).



• The exposure frequency was assumed to be constant since the scenario is targeting possible residential areas. Durations were assumed for children, 0-6 years and adolescents/adults, 7-30 years.



• The carcinogenic potency slope oral taken from RBC Tables were as follows:

The results are presented in Table 2.

APPENDIX D: Soil Gas and Estimated Risk

Table 3. East Kelly Soil Gas Sampling Results Compared to RBCs and Estimated Indoor Air Cancer Risk

Chemical	Maximum Soil Gas Concentration µg/m3	RBC µg/m3	Maximum Estimated Indoor Air Concentration1 µg/m3	J&E Estimated Cancer Risk2	ATSDR Estimated Cancer Risk3
1,1,2-Trichloro-1,1,2-trifluoroethane	275	31,000
cis-1,2-Dichloroethene	344	37	0.0059	Not classifiable4	Not classifiable4
1,1,1-Trichloroethane	9.3	1000
1,1-Dichloroethane	20.6	520
Benzene	7.3	0.22	0.00013	4.9E-10	1.08E-08
Ethylbenzene	10.4	1000
Methylene Chloride	286	3.8	0.0054	1.9E-8	2.54E-08
Tetrachloroethene (PCE)	14,230	3.1	0.23	5.8E-8	1.34E-06
Toluene	165	420
Trichloroethene (TCE)	618	1	0.011	7.9E-9	1.89E-07
Xylenes	29.9	310
1,2,4-Trichlorobenzene	179	210
Hexachlorobutadiene	265	0.081	0.0037	3.5E-8	8.17E-07
Styrene	8.1	1000
Vinyl Chloride	ND

¹ Indoor air concentrations were derived using EPA's Johnson & Ettinger model for subsurface vapor intrusion into buildings
^2,3Cancer risks were derived using both EPA's Johnson & Ettinger model and ATSDR's Public Health Assessment Guidance Manual for chemicals detected above RBC
⁴ Not classifiable as to human carcinogenicity based on no data on humans or animals
ppbv = parts per billion volume
g/m3 = micrograms per cubic meter
RBC = 1997 Risk-based concentration
ND = Not detected
Shading indicates 1997 RBC ambient air comparison value exceedence

Estimated Exposure Dose and Cancer Risk from Soil Gas to Indoor Air

Johnson and Ettinger Model Assumptions

• Cancer risk estimates were calculated using the Johnson and Ettinger model for carcinogenic chemicals that exceeded their comparison value. The default time for carcinogens is 70 years; the default residential exposure duration is 30 years; the default exposure frequency is 365 days per year; the default hazard quotient for noncarcinogens is 1. Default reference doses and carcinogenic potency factor slopes in the model are from the Integrated Risk Information System and Health Effects Assessment Summary Table [1].



• These assumptions for the Johnson and Ettinger model for subsurface vapor intrusion into buildings were used to calculate the cancer risk in the model. However, the groundwater to soil gas step was eliminated since soil gas concentrations were known.



• Non-carcinogen hazard quotients were tabulated for each chemical exceedence. The accumulative hazard quotient did not exceed 1.

ATSDR Exposure and Cancer Risk Assumptions

• ATSDR screened the maximum contaminant concentrations by comparison to the EPA's 1997 Region III Risk-Based Concentration (RBC) Tables for ambient air. All contaminants that exceeded this comparison value were selected for further evaluation. Maximum concentrations were used to calculate an exposure dose. Risk-based screening levels for carcinogens were based on combined infant, childhood, and adult exposure.



• ATSDR assumed the inhalation rates of 3.8 cubic meters (m³)/day for infants, 15 m³/day for children, and 23 m³/day for adults [2]. ATSDR used standard body weights for infants (15 kilograms[kg]), children (42.5 kg), and adults (70 kg).



• The exposure frequency was assumed to be constant at since the scenario is targeting possible residential areas. Durations were assumed for infants, 0-1 years; children, 1-10 years; adults, 11-30 years.

The carcinogenic potency slope inhalation taken from 1997 RBC Tables are as follows:

1. US Environmental Protection Agency. 1997. User's Guide for the Johnson and Ettinger (1991) Model for Subsurface Vapor Intrusion into Buildings. Washington, DC.



2. ATSDR. 1993. Public Health Guidance Manual. Lewis Publishers, Boca Raton, FL.

APPENDIX E: Exposure Pathway Table

TABLE 1. POTENTIAL EXPOSURE PATHWAY

Pathway Name	Source	Medium	Route of Exposure	Exposure Elements			Exposure Activities	Chemicals of Concern
				Point of Exposure	Receptor Population	Time
Off-site Soil Gas	Contaminated Shallow Groundwater	Soil Gas	Inhalation	Off-site	Residents	p, c, f	Indoor Activities	VOCs
Key: p = past; c = current; f = future;

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