EPA Comment

ATSDR's Response

Evaluation of Current Exposures

122

Based on the limited information presented in the PHA, we agree with ATSDR's conclusion that the current uranium exposures at Scarboro are probably within acceptable limits. However, we recommend that ATSDR provide more detailed presentations and analyses, as discussed in Comment 6 [ATSDR note: the following comments].

Thank you for your comment. ATSDR concluded that current uranium exposure poses no apparent public health hazard to residents living near the Y-12 plant, including Scarboro residents. Current uranium exposure would not result in harmful health effects. The commenter's recommendations will be discussed in the following responses to public comments.

123

For current uranium exposures, ATSDR should present missing data sources, provide explicit calculations of intakes and doses, modify selected exposure parameter values, include additional exposure pathways, and present cancer risk estimates.

For the evaluations of current exposures, we found that, in many cases, the empirical data used in the dose calculations are incomplete or absent, exposure parameter values are not defined or explained, no equations are provided, and some relevant exposure pathways are omitted. For these reasons, we provide the following comments and suggestions: [ATSDR note: This comment is split into the following separate comments.]

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice.

The current exposure evaluation primarily relied on data supplied by OREIS, a centralized, standardized, quality-assured, and configuration-controlled environmental data management system. It is a public data source available at the following Web site http://www-oreis.bechteljacobs.org/oreis/help/oreishome.html .

ATSDR also supplemented the current exposure pathway with data from FAMU (1998) and EPA (2003). The FAMU data are available in OREIS. EPA Region IV's final report is available at the following Web site: http://www.epa.gov/Region4/waste/fedfac/doeorr.htm .

These data sources are also available at the DOE Information Center (475 Oak Ridge Turnpike, Oak Ridge TN 37830; phone: 865-241-4780; Web site: http://www.oakridge.doe.gov/info_cntr/index.html ).

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of EPA risk assessment and risk analysis to determine if levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements and to help regulatory officials make decisions in support of cleanup strategies that will ensure overall protection of human health and the environment. ATSDR acknowledges that conservative safety margins are built into EPA risk assessments and that these assessments do not measure the actual health effects that hazardous chemicals at a site have on people. For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

Any modified exposure scenarios are discussed within the document either in the main text or within the footnotes of the tables and figures, where the data are presented.

124

To assess radiological impacts via air pathways (pp. 78-80), ATSDR should show all uranium air concentration data used to calculate inhalation doses for Stations 1, 37, 38, 40, 46 (Scarboro), 51, and 52, along with a reference for the primary data source, and explain why doses are presented for the other monitoring stations.

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice. ATSDR evaluated over 500 air samples from OREIS to assess current exposures through the air pathway. OREIS is a centralized, standardized, quality-assured, and configuration-controlled environmental data management system that is publicly available at the following Web site http://www-oreis.bechteljacobs.org/oreis/help/oreishome.html . ATSDR added the source of the data to the legend in Figure 22.

ATSDR clarified the text to indicate why data from the other monitoring stations were presented.

125

To assess radiological impacts via air pathways (pp. 78-80), ATSDR should show the equation or equations, parameters, and parameter values used, including exposures frequencies, duration, and ICRP dose coefficients (which are currently not provided).

Exposure scenarios and equations are discussed within the document either in the main text or within the footnotes of the tables and figures, where the data are presented. The ICRP dose coefficients are copyrighted and can be obtained through many university and technical libraries. They are also available from the following Web site: http://www.icrp.org/ .

126

To assess radiological impacts via air pathways (pp. 78-80), ATSDR should explain whether average or 95^th percentile Scarboro uranium air concentrations were used in the calculations, and whether or not background uranium air concentrations were subtracted from site-specific concentrations.

As noted in the footnote to Table 15, ATSDR used the average air concentrations to calculate uranium doses. The doses were not corrected for background. However, ATSDR also calculated exposure to background locations (Stations 51 and 52) so the reader could compare the Scarboro doses to the background doses.

127

To assess radiological impacts via air pathways (pp. 78-80), ATSDR should calculate lifetime cumulative radiological doses and risks for all ages combined for all of the air pathway-dependent exposure pathways, such as the air-to-pasture grass-to-meat/milk pathways, included in the assessment of past exposures.

ATSDR should discuss why EPA's accepted risk range for CERCLA sites should or should not be used for risk comparisons of the data and exposures.

Discuss why ATSDR uses the dose criteria, and do not use, refer to, or at least compare this to EPA's risk range for CERCLA sites.

Livestock are only allowed within the city limits in limited zoning areas. Therefore, the air-to-pasture grass-to-meat/milk pathways are not realistic current exposure scenarios.

To determine the public health implications (potential health hazard) from current exposure to uranium released from the Y-12 plant, ATSDR scientists conducted a realistic site-specific assessment. The estimated doses are based on daily exposure, up to an age of 70 years (i.e., lifetime).

To understand why ATSDR scientists use doses in the public health assessment process (instead of the quantitative baseline risk assessments conducted by regulatory agencies, such as EPA) it is important to understand the deliberate differences between ATSDR's health assessments and EPA's risk assessments. The public health assessment is different from a risk assessment primarily in its purpose, goals, exposures evaluated, and the use of information.

ATSDR Public Health Assessment vs. EPA Baseline Risk Assessment Issue

As explained in ATSDR's Public Health Assessment Guidance Manual (http://www.atsdr.cdc.gov/HAC/HAGM/), EPA's Risk Assessment Guidance for Superfund – Human Health Evaluation Manual, and in A Citizen's Guide to Risk Assessments and Public Health Assessments at Contaminated Sites (written jointly by ATSDR and EPA Region IV; see Appendix J), there are deliberate differences between ATSDR's health assessments and EPA's risk assessments. The two agencies have distinct purposes that necessitate different goals for their assessments. An EPA baseline risk assessment is used to support the selection of a remedial measure at a site. An ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying those populations for which further health actions or studies are needed.

Public Health Assessment

The public health assessment process serves as a triage for evaluating the public health implications of exposure to environmental contamination and for identifying appropriate public health actions for particular communities. PHAs are used to identify populations off the site who are exposed to hazardous substances; to determine how and when they were exposed; to determine whether these past, present, or future exposures are likely to lead to illness; and to recommend follow-up public health actions to address the exposure and ensure the protection of public health. The public health assessment process is iterative and dynamic and may lead to a variety of public health actions. The process also serves as a mechanism through which the agency responds to site-specific community health concerns.

In the public health assessment process, similar techniques to those of the quantitative risk assessment methods (i.e., generating quantitative "risk estimates") may be used primarily as a screening tool to clearly rule out the existence of public health hazards or as a way of understanding regulatory concerns. However, if exposure at a site exceeds one or more media-specific comparison values (dose-based comparison values or quantitative risk estimates), the public health assessment process proceeds with a more in-depth health effects evaluation. ATSDR scientists conduct a health effects evaluation by carefully examining site-specific exposure conditions about actual or likely exposures; conducting a critical review of available toxicological, medical, and epidemiologic information to ascertain the substance-specific toxicity characteristics (levels of significant human exposure); and comparing an estimate of the amount of chemical exposure (i.e., dose) to which people might frequently encounter at a site to situations that have been associated with disease and injury. This health effects evaluation involves a balanced review and integration of site-related environmental data, site-specific exposure factors, and toxicological, radiological, epidemiologic, medical, and health outcome data to help determine whether exposure to contaminant levels might result in harmful effects. The goal of the health effects evaluation is to decide whether or not harmful effects might be possible in the exposed population by weighing the scientific evidence and by keeping site-specific doses in perspective. The output is a qualitative description of whether site exposure doses are of sufficient nature and magnitude to trigger a public health action to limit, eliminate, or further study any potential harmful exposures.

The PHA report presents conclusions about the actual existence and level of the health threat (if any) posed by a site. It also recommends ways to stop or reduce exposures. The conclusions and recommendations are based on the professional knowledge and judgment of the health assessment team members. However, because of uncertainties regarding exposure conditions and adverse effects associated with environmental levels of exposures, definitive answers on whether health effects actually will or will not occur are not possible. However, providing a framework that puts site-specific exposures and the potential for harm in perspective is possible. It is one of the primary goals of the public health assessment process.

Baseline Risk Assessment

The quantitative baseline risk assessment (the framework of the EPA human health evaluation) is a numerical analysis used to determine if levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements. The risk assessment process is used by regulators as part of site remedial investigations to support risk management decisions and to define remedial actions involving hazardous site cleanup strategies (the determination of permit levels for the discharge, storage, or transport of hazardous waste; the establishment of clean-up levels; the determination of allowable levels of contamination) that ensure overall protection of human health and the environment. Remedial plans based on a quantitative risk assessment represent a prudent public health approach–that of prevention.

The EPA risk assessment provides an estimate of theoretical risk from possible current or future exposures and considers all contaminated media regardless of whether exposures are occurring or are likely to occur. For cancer effects, risks are expressed as probabilities. For noncancer effects, exposure levels are compared to pre-established levels deemed to be safe. The quantitative risk estimates are not intended, however, to predict the incidence of disease or measure the actual health effects that hazardous substances at a site have on people. The estimated predictions are based on statistical and biological models that include a number of protective assumptions about exposure and toxicity to ensure protection of the public. By design they are conservative predictions that generally overestimate risk. For this reason, the risk estimates are very useful in deciding the extent to which a site needs to be cleaned up (and to what levels) to adequately protect public health.

By design, risk assessment involves estimating exposure doses based on conservative (protective) standard (or default) exposure and toxicity assumptions (which often overestimate health risk) to ensure that remedial actions are amply safe and protective of health. Therefore, people will not necessarily be affected even if they are exposed to materials at dose levels higher than those estimated by the risk assessment. Therefore, EPA's quantitative risk assessment (which are used for regulatory purposes) do not provide perspective on what the risk estimates mean in the context of the site community and do not measure the actual health effects that hazardous substances have on people.

Thus, while a risk assessment conducted under EPA's Remedial Investigation/Feasibility Study (RI/FS) process is used to support the selection of a remedial measure at a site, an ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying those populations for which further health actions or studies are needed. The health assessment also makes recommendations for actions needed to protect public health, which may include issuing health advisories.

An interactive program that provides an overview of the public health assessment process ATSDR uses to evaluate whether people will be harmed by hazardous materials is available at: http://www.atsdr.cdc.gov/training/public-health-assessment-overview/html/index.html. A comprehensive guide to the Superfund risk assessment process is available from EPA on the Internet at: http://www.epa.gov/superfund/programs/risk/rsk_sf1.htm .

ATSDR Cancer Framework Policy

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of EPA risk assessment and risk analysis to determine if levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements and to help regulatory officials make decisions in support of cleanup strategies that will ensure overall protection of human health and the environment. ATSDR acknowledges that conservative safety margins are built into EPA risk assessments and that these assessments do not measure the actual health effects that hazardous chemicals at a site have on people. For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html.

128

EPA uses Preliminary Remediation Goals [PRGs] to screen radiation sites, not RBCs [old name].

Should add the PRGs for Uranium isotopes or discuss why EPA's PRGs are not appropriate for screening sites [soil, water samples]. See Web site: http://epa-prgs.ornl.gov/radionuclides/ .

ATSDR referenced EPA Region III's RBC for fish consumption. RBCs are health-based comparison values that are updated quarterly. From the October 15, 2003 Updated Risk Based Concentration Table Cover Memo:

"The RBC Table contains Reference Doses (RfDs) and Cancer Slope Factors (CSFs) for 400-500 chemicals. These toxicity factors have been combined with "standard" exposure scenarios to calculate RBCs--chemical concentrations corresponding to fixed levels of risk (i.e., a Hazard Quotient (HQ) of 1, or lifetime cancer risk of 1E-6, whichever occurs at a lower concentration) in water, air, fish tissue, and soil." (EPA Region III 2003)

The ATSDR radiogenic cancer comparison value of 5,000 mrem over 70 years was used by ATSDR to evaluate the carcinogenic effects of radiation from uranium exposure.

See the responses to comments 127 and 18 for additional information on the differences between an EPA risk assessment and an ATSDR health assessment and on ATSDR's radiogenic cancer comparison value.

129

To assess radiological impacts via air pathways (pp. 78-80), ATSDR should conduct a sensitivity and uncertainty analysis, assigning PDFs to all uncertain parameters, and present distributions of dose and risk estimates.

As stated in the title, the Task 6 report was a "Screening Evaluation of Potential Off-Site Exposure." It routinely and appropriately used several layers of conservatism and protective assumptions and approaches. (See the list of conservative aspects of the screening evaluation on pages 48 and 92 of the PHA.) Since the screening evaluation resulted in a total past uranium dose below levels of health concern, ATSDR does not believe the evaluation of Y-12 uranium releases requires a refined evaluation with uncertainty and sensitivity analyses.

As discussed in the NCRP Commentary 14, A Guide For Uncertainty Analysis In Dose And Risk Assessments Related To Environmental Contamination (issued in 1996) if a conservatively based screening calculation is performed and this screening calculation indicates the risk is "clearly below regulatory or risk levels of concern," and the possible exposure is low, then a quantitative uncertainty analysis may not be necessary. By design, conservative screenings are "highly unlikely to underestimate the true dose or risk."

Based on this document, ATSDR agrees with the Task 6 authors that a quantitative uncertainty analysis is not needed for this portion of the Oak Ridge Dose Reconstruction Project. On page D-3, the Task 6 authors state "although an uncertainty analysis of the Task 6 air source term was not within the scope of Task 6, experts interviewed during the project consider release estimates for enriched uranium to be suitable for the Task 6 screening assessment and are within an order of magnitude of actual releases" (ChemRisk 1999). The response to comment 166 provides additional details about conducting uncertainty analyses.

130

To assess radiological impacts via surface water pathways (pp. 80-82), ATSDR should show all uranium surface water concentration data, in units of isotopic uranium activities and mass concentrations, not just the average total uranium mass concentrations, along with a reference for the primary data source, and explain when, where, how, and by whom the measurements were made and how many were made.

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice.

ATSDR evaluated over 10,000 surface water samples from OREIS to assess current exposures through the surface water pathway. OREIS is a centralized, standardized, quality-assured, and configuration-controlled environmental data management system that is publicly available at the following Web site http://www-oreis.bechteljacobs.org/oreis/help/oreishome.html . ATSDR added the source of the data to the legend in Figure 23 and Table 16.

As noted on page 70 in the PHA, the surface water samples were collected from 1995 to 2002 at the two off-site locations and the three on-site locations depicted in Figure 23. Information about how and by whom the testing was conducted can be obtained from the primary reports available in OREIS.

131

To assess radiological impacts via surface water pathways (pp. 80-82), ATSDR should calculate age-dependent radiological and chemically-toxic doses for all of the surface pathway-dependent exposure pathways included in assessment of past exposures, and add an irrigation pathway.

ATSDR's current evaluation is based on site-specific assessment of realistic exposures.

Human exposures via livestock, dairy cattle, and irrigation exposure pathways are not realistic current exposure routes for the EFPC surface water pathway.

As noted on pages 70–72 and 86–87 of the PHA, the total uranium mean concentration in surface water from Scarboro ditches and Lower EFPC is below ATSDR's EMEG and EPA's MCL. ATSDR EMEGS are health-based comparison values developed for screening environmental contamination for further evaluation. EMEGS are protective of public health in essentially all exposure situations. Exposure to concentrations at or below ATSDR's EMEG is considered safe and not considered to warrant health concern. The MCL is a regulatory level of a contaminant that is allowed in drinking water. Therefore, the concentrations of uranium to which people might be exposed via incidental ingestion and immersion during recreation in the EFPC surface water are not a public health hazard.

132

To assess radiological impacts via surface water pathways (pp. 80-82), ATSDR should show the equation or equations, parameters, and parameter values used, including exposures frequencies, duration, and ICRP dose coefficients.

As a first step in the public health assessment process, ATSDR compared the surface water concentrations to the ATSDR EMEG of 20 µg/L for highly soluble uranium salts (see page 71 in the PHA). As described in the Evaluating Exposure section (Section III.A.2.), the EMEG is a nonenforceable, health-based comparison value developed for screening environmental contaminants for further evaluation. The EMEG is a concentration that is much lower than those that have been observed to cause adverse health effects and is protective of public health in essentially all exposure situations. As a result, concentrations detected at or below the EMEG are not considered to warrant health concern. As shown in Table 16, the off-site surface water concentrations were below the EMEG. Therefore, no further evaluation was required; ATSDR did not calculate doses. No equations, parameters, and parameter values need to be presented.

More information about the development of ATSDR's EMEGs can be found in Section 5.6 and Appendix A of the Public Health Assessment Guidance Manual at the following Web site: http://www.atsdr.cdc.gov/HAC/HAGM/.

133

To assess radiological impacts via surface water pathways (pp. 80-82), ATSDR should calculate lifetime cancer risks using EPA's radionuclide slope factors.

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of risk assessment and risk analysis. For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

Additionally, as noted on page 71 of the PHA, the mean total uranium concentrations in the off-site locations are below EPA's MCL for uranium of 30 µg/L. This MCL, according to the Final Rule, is "protective of kidney toxicity and carcinogenicity with an adequate margin of safety" (Federal Register 2000).

134

To assess radiological impacts via surface water pathways (pp. 80-82), ATSDR should conduct a sensitivity and uncertainty analysis, assigning PDFs to all uncertain parameters, and present distributions of dose and risk estimates.

As stated in ATSDR's response to comment 131, 132, and 133, the mean total uranium concentrations in the off-site locations of the EFPC are below ATSDR's EMEG and EPA's MCL for uranium and are not considered to warrant public health concern or further evaluation.

In addition, based on the ORHASP decision guides, the estimated Task 6 Level II screening risk from off-site exposure to Y-12 uranium is so low that further detailed study of exposures is not warranted. The Level II screening index (8.3 x 10^-5) is 1.2 times less than the ORHASP decision guide (1 x 10^-4). Therefore, it is below the threshold for consideration of more extensive health effects studies. (See the Level II screening index on page 4-12 of the Task 6 report and the ORHASP Decision Guides on page 57 of the ORHASP report.)

As discussed in the NCRP Commentary 14, A Guide For Uncertainty Analysis In Dose And Risk Assessments Related To Environmental Contamination, issued in 1996, if a conservatively based screening calculation is performed and this screening calculation indicates the risk is "clearly below regulatory or risk levels of concern" and the possible exposure is low, then a quantitative uncertainty analysis may not be necessary. By design, conservative screenings are "highly unlikely to underestimate the true dose or risk."

The response to comment 166 provides additional details about conducting uncertainty analyses.

135

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should show all uranium soil concentration data from DOE (1993), FAMU (1998), EPA (2002), studies of U.S. national background, and any other sources (e.g., data collected from off-site areas along the EFPC floodplain). These data should be presented as isotopic uranium activities and mass concentrations, and ATSDR should explain when, where, how, and by whom the measurements were made and how many were made.

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice. ATSDR evaluated soil samples from DOE (1993), FAMU (1998), and EPA (2003) to assess current exposures through the soil pathway. Page 29 in the PHA provides short summaries of the FAMU and EPA sampling. To expand the information presented, ATSDR added summary briefs of the EPA and FAMU reports in Appendix I of the final PHA.

136

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should move the entire discussion on the question of uranium enrichment in soil to an appendix.

The comment is noted. Since the issue of enrichment is a community health concern, ATSDR has decided to keep the organization of the PHA in its current form.

137

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should explain that only a limited number (i.e., 40 samples by FAMU, plus 7 samples and 1 duplicate by EPA) of surface (i.e., zero to 3-inch deep (top 5 cm) soil samples from disturbed areas in Scarboro were collected and analyzed.

Auxier & Associates stated on page 1 of their report that "for the stated scope of the study [FAMU 1998], the number of samples met or exceeded the number recommended in the EPA Region IV guidance (USEPA, Region 4, Science and Ecosystem Support Division, Environmental Investigations Standard Operating Procedures and Quality Assurance Manual, May 1996)" (Prichard 1998).

The FAMU soil sampling consisted of biased and random sampling throughout the Scarboro community in areas where potential airborne deposition could occur. The biased sampling included collecting samples in undisturbed areas along the perimeter of the Scarboro community near the ORR boundary (FAMU 1998).

In 2001, EPA Region IV collected uranium core samples from two locations in Scarboro "to determine if uranium isotopes could be found at depth" (page 4). The report stated that "none of the analytical values for the uranium cores were elevated above the PRG or background...There is no evidence that the substance is present at levels 12 inches below ground surface" (pages 7 and 17). From page 19 of their report: EPA Region IV "does not propose to conduct any further environmental sampling in the Scarboro community" and from page 26: "based on EPA's results, the Scarboro community is safe. Therefore, additional sampling to determine current exposure is not warranted" (EPA 2003). Page 29 in the PHA provides a short summary of the EPA sampling. To expand the information presented, ATSDR added a summary brief of the EPA report in Appendix I of the final PHA.

138

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should explain that the FAMU study did not measure U 234 and the EPA samples show that the combined U 234/235 activity concentrations do show enrichment over the U 238 concentrations [Note: Both U 234 and U 235 are enriched during the production of weapons-grade and reactor fuel materials.].

Figure 21, 24, and 25 in the PHA show that FAMU did not measure for U 234.

As stated on pages 73 to 77 of the PHA, ATSDR disagrees that there is evidence of significant enrichment. The sample that would suggest enrichment is SS EPA 1, a sample with a duplicate, which does not show this trend. The other samples do not show a significant difference once the uncertainties are taken into account. Furthermore, the method used to determine isotopic ratios has significant variability.

Additionally, EPA Region IV concluded on page 11 of their report that "the uranium results showed uncertainty of uranium enrichment due to the level of the uranium isotopes being at background levels and/or detection limits and uncertainty. The uranium-235 measurements, in particular, had results where the uncertainty was greater than the value measured. Therefore, determining uranium enrichment is uncertain as well. If there is some uranium enrichment potentially in the uranium isotopes in the Scarboro soil and sediment, the actual levels of uranium isotopes are still within the U.S. and Oak Ridge background ranges" (EPA 2003).

139

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should explain that the analytical method used, i.e., alpha spectrometry, is not sensitive enough to determine U 235 activities reliably near background concentrations, and that Inductively-Coupled Plasma (ICP)-mass spectrometry would have been a more precise and reliable method to ascertain uranium isotopic soil concentrations.

ATSDR agrees that the methods used by both FAMU and the EPA Region IV would not necessarily be sufficiently sensitive to determine U 235 activities near background. Nonetheless, from a public health perspective, the amount of uranium present in the community is below levels known to cause adverse health outcomes.

FAMU determined uranium isotopic content using alpha spectroscopy (FAMU 1998). EPA Region IV verified their results using gamma spectroscopy (EPA 2003). The EPA Region IV report states (on page vi): "EPA's study results are in agreement with similar, more extensive, studies done in 1998 by FAMU." They further explain on pages 7 and 9 that "gamma spectroscopy was used as a screen. It was chosen to analyze gamma-emitting isotopes which indicate radioactive decay... The analysis of the information reveals that all results for gamma emitters were within their predicted background ranges for the United States and Oak Ridge-wide. None of the analytical values were elevated above background. Uranium is both naturally occurring and site related... none of the EPA values were above the PRG or background" (EPA 2003).

EPA Region IV states on page 19 of their report: "The results of both the EPA and DOE sampling effort are consistent in their findings. There is not an elevation of chemical, metal, or radionuclides above a regulatory health level of concern. The EPA sample analysis supports that the Scarboro community is not currently being exposed to substances from the Y-12 facility in quantities that pose an unreasonable risk to health or the environment. The EPA does not propose to conduct any further environmental sampling in the Scarboro Community" (EPA 2003).

140

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should explain that that due to the potential migration of uranium into soil and the high uranium release estimates for the first half of the operation of the Y-12 complex... soil concentrations would have been higher before 1974 than when they were taken in Scarboro recently. Because subsurface soil samples may show elevated uranium soil concentrations, added surface samples and subsurface (core) soil samples in undisturbed areas in and around Scarboro are necessary before conclusions concerning the assessment of potential adverse health effects of are made.

The FAMU soil sampling consisted of biased and random sampling throughout the Scarboro community in areas where potential airborne deposition could occur. The biased sampling included collecting samples in undisturbed areas along the perimeter of the Scarboro community near the ORR boundary (FAMU 1998).

In addition, EPA Region IV stated on page 5 of their Scarboro sampling report that "because of the large amount of soil needed for each sample, the EPA samples were collected from 0-6 inches" (EPA 2003). Uranium is not expected to migrate to a great degree. The predominant chemical form of uranium released into the air from the Y-12 plant was highly insoluble uranium oxide (ChemRisk 1999). Leaching is not expected to be a major loss mechanism for insoluble materials, which bind tightly to clay soil particles (Prichard 1998). Therefore, this sampling procedure would have detected elevated uranium in surficial soils from undisturbed areas.

In 2001, EPA Region IV collected uranium core samples from two locations in Scarboro "to determine if uranium isotopes could be found at depth." (page 5, EPA 2003). The report stated that "none of the analytical values for the uranium cores were elevated above the PRG or background... There is no evidence that the substance is present at levels 12 inches below ground surface" (pages 7 and 17). From page 19 of their report: EPA Region IV "does not propose to conduct any further environmental sampling in the Scarboro community" and from page 26: "based on EPA's results, the Scarboro community is safe. Therefore, additional sampling to determine current exposure is not warranted" (EPA 2003). Page 29 in the PHA provides a short summary of the EPA sampling. To expand the information presented, ATSDR added a summary brief of the EPA report in Appendix I of the final PHA.

The data collected by FAMU (1998) and EPA Region IV (2003) were evaluated for the current exposure pathway (1990 to 2002). The assertion that "soil concentrations would have been higher before 1974 than when they were taken in Scarboro recently" is not relevant to the current pathway evaluation. Please see the response to comments 105 and 121 regarding soil data used to evaluate the past soil exposure pathway.

141

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should show the equation or equations, parameters, and parameter values used to calculate the soil ingestion pathway, including exposures frequencies, duration, and ICRP dose coefficients, and calculate lifetime intakes, doses, and risks for all ages combined, not just the average radiological dose for a 1 yr old based on the ingestion of 100 milligrams of soil daily for the course of one year with a committed effective dose calculated to 70 years of age (PHA, p. 90, footnote to Table 19).

The ICRP dose coefficients are copyrighted and can be obtained through many university and technical libraries. They are also available from the following Web site: http://www.icrp.org/ .

The doses that ATSDR calculated were based on daily exposures, up to an age of 70 years (i.e., a lifetime). ATSDR primarily focused on two age groups: adults and 1-year-olds. The reasoning was that these would be the most likely impacted groups who might come in contact with potentially contaminated surface soils. Table 19 lists doses to a 1-year-old and Table 23 gives soil ingestion doses to adult males, females, 12-year-olds and 6-year-olds. During the evaluation of other intake pathways (taking into consideration ingestion rates and body weights) ATSDR determined that there were no significant differences between adults and other age groups.

As explained in Section 2 of ATSDR's Public Health Assessment Guidance Manual (http://www.atsdr.cdc.gov/HAC/HAGM/) and in A Citizen's Guide to Risk Assessments and Public Health Assessments at Contaminated Sites (written jointly by ATSDR and EPA Region IV) there are deliberate differences between ATSDR's health assessments and EPA's baseline risk assessments. The two agencies have distinct purposes that necessitate different goals for their assessments. A risk assessment is used to support the selection of a remedial measure at a site. An ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying those populations for which further health actions or studies are needed. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of EPA risk assessment and risk analysis to determine if levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements and to help regulatory officials make decisions in support of cleanup strategies that will ensure overall protection of human health and the environment. ATSDR acknowledges that conservative safety margins are built into EPA risk assessments and that these assessments do not measure the actual health effects that hazardous chemicals at a site have on people. For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html.

142

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should show the DOE data on levels of uranium isotopes in homegrown vegetables collected from a resident of Scarboro from 1998 to 2000 and show the equation or equations, parameters, and parameter values used to calculate the vegetable ingestion pathway, including exposures frequencies, duration, and ICRP dose coefficients, and calculate lifetime intakes, doses, and risks for all ages combined for fruits and vegetables combined, not just the average radiological dose for vegetable ingestion "based on 80-kilogram adult eating 2.27 grams of produce per kilogram of body weight per day (EPA 1997)."

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice.

ATSDR evaluated over 450 vegetable samples from OREIS to assess current exposures through the ingestion of garden vegetables. OREIS is a centralized, standardized, quality-assured, and configuration-controlled environmental data management system that is publicly available at the following Web site http://www-oreis.bechteljacobs.org/oreis/help/oreishome.html .

With regard to ingestion parameters, based on the EPA Exposure Factors Handbook (EPA 1997) and taking into account ingestion rates and body weights, the vegetable ingestion rate for adults was used as the most conservative scenario. During the evaluation of other intake pathways (and taking into consideration ingestion rates and body weights) we determined there were no significant differences between adults and other age groups.

Scarboro is known to have private vegetable gardens. The community has not expressed any concern over consumption of homegrown fruits.

As explained in Section 2 of ATSDR's Public Health Assessment Guidance Manual (http://www.atsdr.cdc.gov/HAC/HAGM/) and in A Citizen's Guide to Risk Assessments and Public Health Assessments at Contaminated Sites (written jointly by ATSDR and EPA Region IV) there are deliberate differences between ATSDR's health assessments and EPA's risk assessments. The two agencies have distinct purposes that necessitate different goals for their assessments. A risk assessment is used to support the selection of a remedial measure at a site. An ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying those populations for which further health actions or studies are needed. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of risk assessment and risk analysis. For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html.

143

To assess radiological impacts via soil pathways (pp. 84-94), ATSDR should show and use the external exposure rate measurement data (in units of micro-rem per hr) presented in EPA's Radiation Dose Survey Results report, rather than simply state for the external exposure pathway that: "Uranium is a very weak emitter of radiation and is considered a health problem if internalized within the body. A comparison of dose factors using Federal Guidance documents (EPA 1988, 1993) indicates that the uranium in [the external exposure] soil pathway can be removed from any additional evaluation" (PHA, p. 94, lines 3-5).

The comment is noted. In a true dose reconstruction, this would be an appropriate approach. However, the PHA was used as a screening tool to determine if additional actions would be necessary. As shown in the document, the estimated doses are sufficiently low that even if one were to add the external exposures and resulting doses to the internal doses, the result of the screening would still be that the doses were below levels of public health hazard.

144

To assess chemical impacts via air pathways (pp. 94-96), ATSDR should show all uranium air concentration data, not just the average values, for Stations 1, 37, 38, 40, 46 (Scarboro), 51, and 52.

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice.

ATSDR evaluated over 500 air samples from OREIS to assess current exposures through the air pathway. OREIS is a centralized, standardized, quality-assured, and configuration-controlled environmental data management system that is publicly available at the following Web site http://www-oreis.bechteljacobs.org/oreis/help/oreishome.html . ATSDR added the source of the data to Figure 27.

145

To assess chemical impacts via air pathways (pp. 94-96), ATSDR should show the equation or equations, parameters, and parameter values used, including exposures frequencies, and duration.

ATSDR's inhalation MRLs are expressed as air concentrations (milligrams per cubic meter) rather than as a dose per unit of bodyweight. As discussed on page 37 of the PHA, the MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure. It has built-in uncertainty or safety factors, making it considerably lower than levels at which health effects have been observed. Estimated doses that are less than the MRL are not considered to be of health concern. As shown in Figure 27, the average uranium air concentrations were well below the MRL. Therefore, no further evaluation was required; ATSDR did not calculate doses. No equations, parameters, and parameter values need to be presented.

More information about the development of ATSDR's MRL can be found in Appendix A of the Uranium Toxicological Profile at the following Web site: http://www.atsdr.cdc.gov/toxprofiles/tp150.pdf.

146

To assess chemical impacts via air pathways (pp. 94-96), ATSDR should calculate lifetime cumulative intake of uranium for all ages combined for all of the air pathway-dependent exposure pathways included in assessment of past exposures.

As noted in comment 145, the average uranium air concentrations were well below the MRL, which have built-in uncertainty or safety factors, making them considerably lower than levels at which health effects have been observed. Estimated doses that are less than the MRL are not considered to be of health concern. Therefore, no further evaluation is required.

ATSDR's current evaluation is a site-specific assessment of realistic exposure. Table 7 in the PHA identifies the air pathways considered by the Task 6 team. Livestock are only allowed within the city limits in limited zoning areas. Most cattle were intended for the beef market. Therefore, the air-to-pasture grass-to-meat/milk pathways are not realistic exposure scenarios. Exposures through inhalation of air and consumption of vegetables are evaluated.

147

To assess chemical impacts via air pathways (pp. 94-96), ATSDR should conduct a sensitivity and uncertainty analysis, assigning PDFs to all uncertain parameters, and present distributions of intakes.

As stated in ATSDR's response to comments 145 and 146, the average air concentrations are well below ATSDR's MRL for uranium and are not considered to warrant public health concern or further evaluation.

In addition, based on the ORHASP decision guides, the estimated Task 6 Level II screening risk from off-site exposure to Y-12 uranium is so low that further detailed study of exposures is not warranted. The Level II screening index (8.3 x 10^-5) is 1.2 times less than the ORHASP decision guide (1 x 10^-4). Therefore, it is below the threshold for consideration of more extensive health effects studies. (See the Level II screening index on page 4-12 of the Task 6 report and the ORHASP Decision Guides on page 57 of the ORHASP report.)

As discussed in the NCRP Commentary 14, A Guide For Uncertainty Analysis In Dose And Risk Assessments Related To Environmental Contamination, issued in 1996, if a conservatively based screening calculation is performed and this screening calculation indicates the risk is "clearly below regulatory or risk levels of concern," and the possible exposure is low, then a quantitative uncertainty analysis may not be necessary. By design, conservative screenings are "highly unlikely to underestimate the true dose or risk."

148

To assess chemical impacts via soil pathways (pp. 96-99), ATSDR should show all uranium soil concentration data.

It is not ATSDR's policy to provide raw data from primary sources that are publicly available. But ATSDR does supply references to the data used; which is good technical practice. ATSDR evaluated soil samples from DOE (1993), FAMU (1998), and EPA Region IV (2003) to assess current exposures through the soil pathway. Page 29 in the PHA provides short summaries of the FAMU and EPA sampling. To expand the information presented, ATSDR added summary briefs of the EPA and FAMU reports in Appendix I of the final PHA.

149

To assess chemical impacts via soil pathways (pp. 96-99), ATSDR should calculate lifetime cumulative intake of uranium for all ages combined for all of the soil pathway-dependent exposure pathways, including the soil and vegetable ingestion pathways.

To determine the public health implications (potential health hazard) from current exposure to uranium released from the Y-12 plant, ATSDR scientists conducted a realistic site-specific assessment. The estimated doses are based on daily exposure, up to an age of 70 years (i.e., lifetime).

The uranium doses following ingestion of soils and vegetables from a private garden in Scarboro are so low that even if the exposures from the two pathways are combined, the resulting dose is still lower than the MRL. As discussed on page 37 of the PHA, estimated doses that are less than the MRL are not considered to be of health concern and do not require further evaluation. For example, if the highest dose following ingestion of soil (1.4 ×10^-5 mg/kg/day for a 6-year-old child) is added to the total intake from ingestion of vegetables grown in Scarboro (3.9 ×10^-5 mg/kg/day from Plot 46), the total ingestion dose is 5.3 ×10^-5 mg/kg/day, which is about two orders of magnitude below the MRL of 2.0 ×10^-3 mg/kg/day. Therefore, the combined exposure from both pathways would not result in harmful health effects.

150

To assess chemical impacts via soil pathways (pp. 96-99), ATSDR should conduct a sensitivity and uncertainty analysis, assigning PDFs to all uncertain parameters, and present distributions of intakes.

As stated in ATSDR's response to comment 149, the combined uranium dose from ingestion of soil and vegetables grown in Scarboro is about two orders of magnitude below ATSDR's MRL. The MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure. It has built-in uncertainty or safety factors, making it considerably lower than levels at which health effects have been observed. Estimated doses that are less than the MRL are not considered to be of health concern and do not require any further evaluation. As shown in Figures 28 and 29, the uranium doses from ingestion of soil and vegetables are well below the MRL. Therefore, no further evaluation was required.

More information about the development of ATSDR's MRL can be found in Appendix A of the Uranium Toxicological Profile at the following Web site: http://www.atsdr.cdc.gov/toxprofiles/tp150.pdf.

Scarboro

151

ATSDR's concluding categorization of the health impact of Y-12 uranium releases on the Scarboro community as posing no apparent public health hazard is misleading. It is clear that significant amounts of uranium have been released from Y-12 from 1944 to the present day, and that some portion of these releases have impacted and continue to impact the Scarboro community.

ATSDR agrees that significant amounts of uranium have been released from the Y-12 plant (see Figure 13 and Table 5) and that exposures are likely to have occurred. Table 25 summarizes the public health implications from exposures to Y-12 uranium. ATSDR concluded that exposures to uranium released from the Y-12 plant in the past and currently would not result in harmful health effects for either adults or children living near the Y-12 plant and assigned the site as having no apparent public health hazard. Therefore, the Y-12 uranium releases are not a public health hazard to the people living near the Y-12 plant. As described on page 117 and in Appendix A of the PHA, ATSDR's category of no apparent public health hazard means that people could be or were exposed, but the level of exposure would not likely result in adverse health effects. More information about ATSDR's conclusion categories can be found in Section 8 of the Public Health Assessment Guidance Manual at the following Web site: http://www.atsdr.cdc.gov/HAC/HAGM/.

152

Given the very small population size of this community, it is extremely unlikely that any associated excess radiation-induced cancer rates or chemically-induced toxic effects would be detectable; that is, there would be no apparent public effects. However, this is not same as concluding the levels of uranium released from the Y-12 plant in the past would not result in harmful health effects for either adults or children living near the Y-12 plant.

ATSDR evaluates the potential for public health effects by comparing an estimate of the amount of uranium exposure (i.e., dose) that people might frequently encounter to conservative screening values and health effects levels documented in the scientific literature. A PHA factors in information from the adjacent community about actual or likely exposures and information from the community about their health concerns. ATSDR's determination that exposure to the levels of uranium released from the Y-12 plant would not result in harmful health effects is based on the amount, frequency, and duration of exposure, not on the number of people exposed. ATSDR concluded that the Y-12 uranium releases are not a public health hazard. The size of the community is irrelevant to the conclusions that past and current exposures to uranium were too low to be of health concern. ATSDR's PHA is based on health effects data from radiation and chemical exposures to uranium. It is not an epidemiologic study that is impacted by a small population size.

153

Based on our review, we conclude that Scarboro may not be the most heavily impacted off-site area nor the most suitable reference location, even though it is the nearest community to the Y-12 plant. The air dispersion modeling which provided the primary reason for selecting Scarboro as the reference location was based on overly simplified and unrealistic assumptions, such as flat terrain between Y-12 releases and receptor locations. It could not account for the complex geography, release heights, and unique meteorological conditions surrounding the Y-12 plant and Oak Ridge, and was consequently rejected by the Task 6 team (ChemRisk 1999) as the method used to reconstruct historical uranium air concentrations for Scarboro. For these reasons, and the fact that the predominant wind direction at the Y-12 facility has been stated as being generally from the southwest or northeast (i.e., up- or down-valley, away from Scarboro and Oak Ridge), we are concerned that the atmospheric transport and environmental fate of the bulk of uranium released from Y-12 has not been adequately accounted for. If the intent of the PHA is to assess the off-site impact of Y-12 uranium releases, we believe that ATSDR, or others, should expand the scope of the assessment to include additional communities surrounding the Oak Ridge Reservation.

Since Scarboro community is the sole focus of ATSDR's public health assessment, we suggest renaming the document to reflect this fact. However, it appears that the primary reason for selecting Scarboro as the reference location (and for rejecting all other nearby Oak Ridge communities) is based on the results of the air dispersion modeling conducted by the Task 6 team that included overly simplified and unrealistic assumptions. According to the Task 6 report (ChemRisk 1999, page 3-3), the modeling assumed flat terrain between Y-12 and Oak Ridge (i.e., no Pine Ridge). Such an assumption would understandably and predictably lead to the highest estimated air concentrations in the closest community, Scarboro. The Task 6 team was aware that the flat terrain approach would not account for the attenuation and redirection of wind flow away from Scarboro, and that the predominant wind direction at Y-12 is generally from the southwest or northeast (i.e., up-valley or down-valley). Moreover, the Task 6 team speculated that, even with additional algorithms, the air dispersion model would probably not adequately handle the majority of Y-12 release points, which were (are) at a lower altitude than Pine Ridge, and would also likely not account for the fact that the relative altitude of the Scarboro community is below the top of Pine Ridge, which further complicates the dispersion characteristics. Given these limitations, the Task 6 team concluded that modeling these characteristics would require substantially more effort, that was beyond the scope of their screening assessment, and that their air dispersion modeling approach was not appropriate for use at Y-12 and would overestimate air concentrations at the Scarboro. Therefore, to estimate historical air concentrations at Scarboro for all years for which release estimates were determined, the Task 6 team developed an empirical c/Q model based on the relationship between recent measured air concentrations at the Scarboro monitoring station and Y-12 uranium release estimates.

For these reasons, we are concerned that the atmospheric transport and environmental fate of the bulk of uranium released from Y-12 has not been adequately accounted for. If the intent of the PHA is to assess the off-site impact of Y-12 uranium releases, we believe that ATSDR, or others, should expand the scope of the assessment to include additional communities surrounding the Oak Ridge Reservation.

However, the representativeness of Scarboro data for releases to other areas should be more thoroughly described, including the uncertainty of the conclusions for any communities that may be more directly down-wind from the plant's air discharges.

The representativeness of the Scarboro Community for offsite impact of past uranium releases is highly questionable. Approximately 85 stacks have emitted uranium particulates over the past 50 years. The prevailing down-wind direction parallels the valley and is not due north over the ridge. The offsite impacts to areas that fall in line with the prevailing wind directions should be more thoroughly considered and the uncertainties in the reports conclusions described.

More explanation is needed in the document to explain why Scarboro is the reference location for assessing the impact of Uranium offsite form Y-12, and why other communities that may be more down-wind are not. Does air dispersion modeling indicate that the Scarboro area is in the prevailing down-wind direction? Any uncertainties in the conclusions regarding down-wind past and current exposures should be thoroughly discussed.

ATSDR believes the city of Oak Ridge is the only established community adjacent to ORR that could have been impacted by Y-12 uranium releases and that Scarboro is a representative community for the city of Oak Ridge. Therefore, the conclusions are valid for the people living near the Y-12 Plant, including the city of Oak Ridge.

As noted on page 43 of the PHA, the Task 6 team identified Scarboro as the reference location using the air dispersion modeling (USEPA 1995 as cited in ChemRisk 1999). The Task 6 team used the results of the flat terrain ISC dispersion model to identify the off-site housing area with the highest estimated uranium air concentrations. The Task 6 team understood the limitations of applying the flat terrain ISC dispersion model in the complex terrain surrounding the Y-12 facility and that the flat terrain model overestimated the air concentrations in Scarboro and other locations outside Bear Creek Valley (ChemRisk 1999, ORHASP 1997). However, when estimated results of air dispersion models were compared to the actual uranium air concentrations measured in Scarboro, the flat terrain model was the best predictor of estimated uranium air concentrations in Scarboro. The Task 6 report stated that "while other potentially exposed communities were considered in the selection process, the reference locations [Scarboro] represent residents who lived closest to the ORR facilities and would have received the highest exposures from past uranium releases...Scarboro is the most suitable for screening both a maximally and typically exposed individual" (ChemRisk 1999).

ATSDR agrees with the commenters that the predominant wind direction at the Y-12 facility is southwest or northeast. According to the ORR meteorological monitoring, "prevailing winds are generally up-valley from the southwest and west-southwest or down-valley from the northeast and east-northeast... winds in the valleys tend to follow the ridge axes, with limited cross-ridge flow within local valley bottoms" (DOE 2002c). Therefore, most of the uranium would deposit up and down the valley in which the Y-12 plant is located. The Y-12 plant is located in Bear Creek valley, between Pine Ridge and Chestnut Ridge. These ridges extend to the northeast into Union valley. No one lives in Bear Creek valley or Union valley. The closest population living in the valley system between Pine Ridge and Chestnut Ridge is more than 3 miles away, across the Clinch River, in Wolf valley. The people living in Wolf valley would likely have been exposed to lower amounts of uranium than the people living in Scarboro because the majority of the uranium deposition would have been relatively close to the Y-12 plant.

Aerial surveys performed since 1959 are sufficiently sensitive to detect radiation sources. Those sources outside the confines of Y-12 have been verified by the state not to constitute a health hazard. By implication, the aerial surveys will readily detect sources that do constitute a hazard and except for a known few locations due to past or present operations within Y-12, the off-site areas such as the Bear Creek and Union valleys (including the residential areas of Oak Ridge) do not show any elevations of radiation above background. Thus, there is direct empirical evidence that the Oak Ridge neighborhoods have not been contaminated by Y-12 uranium releases.

ATSDR acknowledges that it is possible that the Woodland community, also located within the city of Oak Ridge near the gap in Pine Ridge, might have received higher uranium emissions than Scarboro. To evaluate this potential, ATSDR compared the ambient air monitoring data for Station 46 (Scarboro) to Station 40 (located on the Y-12 plant near the intersection of Bear Creek Road and Scarboro Road). While Station 40 is not located in Woodland, it is located in Bear Creek valley near the gap in Pine Ridge. ATSDR compared the average uranium air concentrations from 1986 to 2002 and found that the concentrations at Station 40 were, on average, 20% higher than those at Station 46. The average air concentrations at Station 40 ranged from being less than half those at Station 46 in 1997, to almost double those at Station 46 in 1990. For the years from 1986 to 1989, during higher production, the average uranium concentrations at Station 40 remained steady at 20% higher than those at Station 46.

Assuming, therefore, that the Woodland community was exposed to the uranium air concentration at Station 40 in Bear Creek valley, they could have potentially received up to twice the amount of uranium emissions as Scarboro. If ATSDR doubled the estimated exposure calculated for Scarboro, the Woodland community could have received a past uranium radiation dose of up to 310 mrem over 70 years (based on an air monitoring station located at the Y-12 plant), which is well below the radiogenic cancer comparison value of 5,000 mrem over 70 years. The current uranium radiation dose is estimated to be less than one mrem, also well below the radiogenic cancer comparison value. Therefore, even if the Woodland community were to have received double the emissions of Scarboro (which is unlikely), the exposures are still too low to be a public health hazard.

For perspective, ATSDR also compared the concentrations detected at Station 46 (Scarboro) to Station 41 (located in the city of Oak Ridge near the intersection of South Illinois Avenue and the Oak Ridge Turnpike) for the years in which both air monitors were in operation (1986 to 1991). The uranium air concentrations at Station 46 were, on average, 2.7 times higher than those at Station 41.

In addition, the past uranium radiation doses used in the public health assessment are from the Task 6 report which was a screening evaluation that routinely and appropriately used several layers of conservatism and protective assumptions and approaches in estimating concentrations and doses (see the list of conservative aspects of the screening evaluation on pages 48 and 92 of the PHA). The Task 6 report states that "some level of conservatism was maintained in the uranium concentration estimates used in Level II screening to ensure that hazards to a significant portion of the potentially exposed population were not underestimated" (ChemRisk 1999).

Also, the internationally recognized expert technical reviewers hired by ATSDR to review the Task 6 report pointed out that "the estimates made in the report tend to be on the conservative side–one expects, therefore, that (when in error) the report would tend to overestimate the extent to which exposure to uranium is a problem in the Oak Ridge area. Further refinements to the study are likely to reveal that uranium exposures are actually lower than those currently estimated" (see page G-7 of the PHA).

Therefore, the Scarboro community is used as a reference location because it represents an established community adjacent to ORR where residents resided during the years of uranium releases. Consequently, if the Scarboro community–the population likely to have received the highest uranium exposures from the Y-12 plant–was not in the past and is not currently being exposed to harmful levels of uranium from the Y-12 plant, then other residents living near the Y-12 plant, including those within the city of Oak Ridge, are also not being exposed to harmful levels of uranium.

154

ATSDR should change the title of the PHA to reflect the principal subject (i.e., Scarboro) or expand the scope of the assessment to include other Oak Ridge communities.

Can this be said of communities offsite other than Scarboro? Discuss any uncertainties in the report's conclusions regarding offsite areas in the prevailing own-wind direction from the past uranium air stack releases.

ATSDR's health assessment determined that people living near the Y-12 plant were not in the past and are not currently being exposed to harmful levels of uranium. Scarboro was chosen as a representative location and thus the conclusions are valid for the rest of Oak Ridge.

As noted on page 43 of the PHA, the Task 6 team identified Scarboro as the reference location using air dispersion modeling (USEPA 1995 as cited in ChemRisk 1999). The Task 6 team was able to identify the off-site locations with the highest estimated uranium air concentrations. The Task 6 report stated that "while other potentially exposed communities were considered in the selection process, the reference locations [Scarboro] represent residents who lived closest to the ORR facilities and would have received the highest exposures from past uranium releases... Scarboro is the most suitable for screening both a maximally and typically exposed individual" (ChemRisk 1999). Based on this, ATSDR believes that Scarboro represents an established community adjacent to the ORR where residents resided during the years of uranium releases. The city of Oak Ridge is the community that would have been impacted the most by Y-12 uranium releases. Based on this, ATSDR believes the city of Oak Ridge is the only established community adjacent to the ORR that could have been impacted by Y-12 uranium releases and that Scarboro is a representative community for the city of Oak Ridge.

The Scarboro community is used as a reference location because it represents an established community adjacent to ORR where residents resided during the years of uranium releases. Consequently, if the Scarboro community–the population likely to have received the highest uranium exposures from the Y-12 plant–was not in the past and is not currently being exposed to harmful levels of uranium from the Y-12 plant, then other residents living near the Y-12 plant, including those within the city of Oak Ridge, are also not being exposed to harmful levels of uranium.

ATSDR presented data from other locations, when available. For example, Figure 22 presents air concentrations for several monitoring stations, Table 15 presents total radiation doses from inhalation for these same monitoring stations, and Table 22 presents uranium doses from ingestion of garden vegetables grown on and off the ORR.