aluatewithout such access.
ATSDR Response: We have reconfigured the ISC air dispersion model to include potentialcontributions from both PGDP steam plant and the TVA facility. Based on 1998 and 1999Toxic Release Inventory data for the TVA facility , the instantaneous nickel air emissionsaverage ~0.0025 g/sec. Assuming that those later years are similar to the years of PGDPnickel smelter emissions, the instantaneous TVA release is about 20 times lower than thePGDP smelter release (0.05 g/sec) and is dispersed from an 800+ foot stack. Similarly,using standard emission factors for coal and oil combustion and annual fuel usage rates,instantaneous nickel emissions from the PGDP steam plant averaged 0.00009 g/sec(dispersed from two adjacent 110 foot stacks), which is 500 times lower than the smelteremissions. The results of the revised air dispersion models indicate no differences in the shortterm or annual distributions of nickel. All estimated concentrations are still well below levels of health concern.
While the revised air model does not include potential re-suspension from roadways,particulates from road dust are relatively large particles with limited capacity for widespreaddispersion. Additionally, exposure to road dust within the non-residential WKWMAroadways would be a relatively infrequent type of exposure. As a result of the limitedcapacity for significant dispersion and the infrequent exposure, nickel in road dust alongWKWMA roadways is not an important contributor to the total airborne nickel load.
ATSDR Response: While this comment is theoretically true, based on availabledocumentation, particulates from the smelter are much larger than those from the PGDPsteam plant and TVA facilities and much more likely to settle out in a short distance fromthe release point. Conversely, the smaller particle sizes from the fossil fuel facilities andmuch higher release points (stack heights), which leads to longer suspension times, meansthat nickel from those sources is dispersed over a much larger area and does not significantlycontribute to localized air concentrations. The models include appropriate parameters forparticle size that largely determine settling rates and travel times. The modeled dispersionalso conservatively neglects wet deposition. Wet deposition occurs during precipitation (rain,snow events) and serves to limit dispersion. Neglecting this term increases the range andconcentration of potential dispersion.
ATSDR Response: The above factors have all been considered in the development of the healthcomparison values, the Public Health Assessment, and by reference, in this health consultation.
- Once again it is apparent that the ATSDR, while recognizing the variety andconcentration of contaminants at PGDP, has failed to address their combined effectwhen concluding "...estimated concentrations of all metal particulates from PGDPsmelter operations are below levels of health concern, (and that) no adverse healtheffects are likely...." In fact, inhaling a mixture of pollutants , individually or incombined form, can magnify the effect several times over the effect of inhaling anyone pollutant individually.
- The Health Consultation did not include specific mailing instructions for individualssending comments. Since a telephone inquiry seeking those instructions was notreturned I have sent our comments to the same address as comments for the PGDPHealth Assessment.
ATSDR Response: See above for response to assessing cumulative effects to differentcontaminants. ATSDR considered cumulative, additive, synergistic, and antagonistic effectsof exposure to the extent of scientific knowledge in this area. Information and referencesrelated to ATSDR's process of evaluation have been added to the consultation (and to thisappendix).
ATSDR Response: Instructions for mailing of written comments will be added to futureATSDR consultation cover pages (Health Consultation: A Note of Explanation) for healthconsultations. Thank you for bringing this to our attention.
- US Department of Energy. Report on the Paducah Gaseous Diffusion Plant