PUBLIC HEALTH ASSESSMENT
PADUCAH GASEOUS DIFFUSION PLANT (U.S. DOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY
In this appendix air dispersion modeling and measured emissions are used to evaluate the off-siteconcentrations and potential health effects of airborne metal particulates emitted from secondarymetal smelting operations in the C-746A facility at the Paducah Gaseous Diffusion Plant (PGDP).Between 1952 and 1986, PGDP operated several smelters to recycle scrap metals. These metalsincluded steel, nickel, aluminum, copper, monel (a copper-nickel alloy), cobalt, gold, and silver .Of these metals, only nickel and aluminum were smelted in large quantities (more than 11 millionpounds of aluminum and about 37 million pounds of nickel) [1,2]. Because nickel is more toxicthan aluminum, this evaluation initially focuses on nickel emissions and potential exposures. Giventhat the dispersion and transport of the other recycled metals is basically the same as for nickel, theconcentrations of the recycled metals will be evaluated relative to the toxicity and estimatedconcentrations of nickel (airborne uranium emissions have been previously evaluated in this PublicHealth Assessment).
Nickel has a relatively high melting temperature (1455oC) such that it is very unlikely to occur ingaseous (vapor) form at normal atmospheric temperatures . Nickel (and other smelted metals) ismost likely to have been released from the smelter stack in a solid or particulate form. The PGDPpermit application states that nickel particulate emissions occurred as nickel oxides .
Approximately 17 million pounds of non-radiologically contaminated nickel were smelted from1977 to 1982. From late 1983 to 1986, an additional 20 million pounds of radiologicallycontaminated nickel were smelted. No off-site nickel air concentration data were collected by PGDPor by the Kentucky Department of Environmental Protection . Potential off-site exposures tonickel particulates released from the smelting operation are estimated using the Breeze Version ofthe US Environmental Protection Agency (EPA) Industrial Source Complex (ISC) air dispersionmodel . This model uses meteorological data from the Paducah-Barkley Airport (1989-91), andparticulate emission and source data from the PGDP air discharge permit application .
The smelter emission rate (nickel particulates) used in the air dispersion model is based on measuredemission rates described in the air discharge permit application . Three trial runs provide anaverage emission rate of 160 g/hr (0.044 g/sec) based on an average smelter charging load of 1520kg/hr (3350 lbs/hr). Modeled emission rates were rounded up to 0.05 g/sec. The 20 million poundsof nickel smelted from late 1983 to 1986 is equal to an average of ~6.7 million pounds/year. This 3-year time frame represents the period of highest annual nickel output and will be used to evaluatepotential air concentrations.
Although the specific operating schedule of the smelter is not known, an average annual productionof 6.7 million lbs/yr divided by the loading rate of 3350 lbs/hr equates to an operating schedule of 8hrs/day for ~250 days/yr. Variation in the operating schedule, such as 16 hrs/day for 125 days/yr,will not change the instantaneous emission rate nor significantly change the annual dispersedconcentrations. Some variation in short term concentrations may occur as a result of specific weatherconditions during smelter operation. However, multiple model runs were conducted usingmeteorological data from three years (1989, 1990, and 1991) to ensure that the range of weatherconditions were evaluated for both short term (one and eight hour maximum averages) and longterm (annual average) concentrations. Meteorological data from the 1984 to 1986 years are notavailable on the EPA website .
In addition to emissions from the PGDP smelters, nickel and other metal particulates were (and arestill) released from combustion of fossil fuels at the PGDP steam plant and the Tennessee ValleyAuthority (TVA) Shawnee facility. Instantaneous emission rates from the TVA facility are estimatedfr