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Review of the US Navy's Human Health Risk Assessment of the Naval Air Facility at Atsugi, Japan In Section 4.1 (Radian 1998c), the following objectives are stated for the soil sampling: The objectives of the soil sampling program are to: 1) provide data to help determine the risk from soil at each specified AOC; and 2) determine whether there has been any soil contamination at NAF Atsugi that can be attributed to emissions from the Jinkanpo Incineration Complex. Although those objectives qualitatively match the risk-assessment objectives, they do not indicate that the contribution of the incinerator will be quantified. Different objectives are also found in the Final Monitoring Report (Radian 2000a), whose executive summary states: A comprehensive health risk assessment has been conducted by the Navy at NAF Atsugi to evaluate potential health risks related to air quality and emissions from the Shinkampo Incineration Complex (SIC), a privately owned and operated facility. The risk assessment is being conducted to ensure the protection of the health of our military and civilian personnel and their families assigned to NAF Atsugi. But Section 2.1 (Radian 2000a; Objectives of Ambient Air Monitoring and Approach to Evaluate Data ) states: The two primary objectives of the ambient air monitoring are to assist in defining: The extent of chronic and acute risk to Naval Air Facility (NAF) Atsugi base personnel; and The contribution of the risk attributable by the Shinkampo Incineration Complex (SIC). Those different statements of objectives could imply substantially different approaches. NEHC should ensure that the objectives of each aspect of the risk-assessment project are consistent with the overall project objectives so that sampling is conducted to meet the overall objectives. APPENDIX B Air-Dispersion Modeling Air-dispersion modeling was performed to predict the concentrations of airborne contaminants at NAF Atsugi resulting from incinerator emissions. Although this is potentially an important aspect of the exposure assessment, the NEHC draft summary report provides few details of the modeling. The results are summarized in a single paragraph (p. 27) and a map (Fig. 2-2) (NEHC 2000). No information regarding the assumptions, data sources, methods, or intermediate results is presented. This subcommittee's evaluation of the dispersion modeling relies heavily on the Pioneer draft report (Pioneer 2000; p. 13, p. 92), a Radian International report (Radian 2000a), and Appendix I of the Radian report (2000d). Despite the limitations of air-dispersion modeling, in general the subcommittee concludes that the modeling as performed in this study is sophisticated and provides the best basis for determining the contribution of the incinerator facility to exposures at NAF Atsugi. General Comments Dispersion modeling was performed for the six contaminants whose measured concentrations showed a statistically significant correlation with the percentage of time that the monitoring site was downwind from
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Review of the US Navy's Human Health Risk Assessment of the Naval Air Facility at Atsugi, Japan the incinerator facility during the monitoring period (Radian 2000a). Those contaminants were [2,3,7,8-TCDD] toxicity equivalents (TEQ), hydrogen chloride, cadmium, lead, arsenic, and PM10. The modeling had two objectives. The first was to estimate incinerator emission rates by comparing the incinerator's impact on air quality at the monitoring sites (estimates were produced via modeling) with the measured concentrations, correcting for background contaminant levels. The second was to estimate the average ground-level concentrations at points across the entire NAF Atsugi. The impact of each incinerator stack on contaminant concentrations was estimated at each air-monitoring site, assuming a unit emission rate of 1 g/s. The emission rate was then determined on each day of monitoring by subtracting the measured background concentration from the measured downwind concentration and dividing the difference by the sum of the modeled unit-emission-rate concentrations for the three incinerator stacks. The measured concentrations were 24-h composites. Only data from sampling sites downwind of the incinerator facility for more than 25% of the sampling period were used to estimate the emission rate. The site that was downwind from the incinerator the lowest percentage of time (always 2 h or less) was used to estimate the background concentrations. Estimated emission rates were used to calculate the average concentrations at all grid points and receptor sites over the entire study period (April 21, 1998, through June 25, 1999). Lack of critical information increased the uncertainty of the estimates. The stack exit temperatures and velocities were estimated on the basis of the experience of the Navy's consultants, who had worked with waste incinerators presumably in the United States. To assess the impact of using different estimates, dispersion estimates were made for several stack exit velocities. The impact of the different estimates on overall concentration estimates was less than a factor of 2 at more than 90% of the modeled receptor sites. The uncertainty in those estimates, therefore, is within the range of error typically associated with Gaussian dispersion models—a factor of 2 or 3 under the best meteorologic conditions (Turner 1970). No upper-air data were available for determining the mixing height; therefore, Radian International developed an algorithm based on similarity theory and used two empirical equations from EPA for estimating mixing height (Radian 2000d). That seems appropriate under the circumstances, particularly because receptor sites are so close to the source that the mixing height would seldom affect the results. Despite those missing input data, the dispersion-modeling approach used in the NAF Atsugi study minimizes the uncertainties that can be encountered in dispersion modeling. Most dispersion-modeling applications are based on measured emission rates often determined over very brief periods that might not be representative of other operating conditions. In the NAF Atsugi study, the emission rates were estimated from ambient concentrations measured at intervals over the 14-mo study period. That should result in less error in the final concentration estimates because the emission rates used are “calibrated” to produce modeled estimates that are in agreement with measured concentrations. Therefore, this modeling approach has a substantial advantage over dispersion modeling as it is generally used for other purposes, such as determining compliance with ambient-air concentration limits. The dispersion-modeling approach used by Radian International (2000a,d) might be thought of as a relatively sophisticated means of interpolating and extrapolating, spatially and temporally, measured contaminant concentrations—one that adjusts concentration estimates to account for the impact of meteorologic variables on pollutant transport. For the six contaminants modeled, the estimated concentrations might be better estimates of the exposure potential than the average measured concentrations because modeling was able to take into account meteorologic variation over almost the entire study period. Specific Comments On pp. 27-28 of the NEHC draft summary report, the dispersion-modeling results are presented only briefly, and no discussion of the dispersion-modeling method is presented elsewhere in the NEHC draft
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