om annual releases submitted to the Environmental Protection Agency Toxic Release Inventory(TRI) . The 1999 TRI indicates that 159 pounds of nickel compounds were released to air, the1998 release amount was 137 pounds. In order to account for yearly variations, this evaluationestimates an annual release of 170 pounds which, distributed over the course of an entire year,equals an emission rate of 0.0025 g/sec (released from a 244 m stack).
Airborne emissions released from the PGDP steam plant occur from two 34 m stacks that are inclose proximity to the each other and are modeled as a single source. Nickel emissions from thePGDP steam plant are estimated from maximum monthly coal and fuel oil usage (3300 tons/monthcoal and 400,000 gallons/year for fuel oil)  and standard emission factors . The estimatedinstantaneous maximum nickel emission rate from the steam plant (0.00009 g/sec) is more than 500times lower than smelter emissions. However, the steam plant was assumed to operate 24 hours/day,7 days/week for an annual emission rate about 100 times lower than the smelter emission rate.
The nickel releases from all sources are predominantly in a nickel oxide form [3;10]. Particulatereleases from the smelter are predominately about 30 microns in diameter with small fractions in the10 and 20 micron diameter size ranges . Nickel particulates from the PGDP steam plant andTVA facilities are predominately less than 5 microns in diameter [3,10].
The distance of the C-746A smelter building to the closest residence is more than 1000 meters (0.6 miles). Estimated air concentrations 1000 m from the source are used to evaluate potential residential exposures. Results of the air dispersion modeling are compared with the ATSDR health-based, non-cancer, comparison value (0.2µg/m3 chronic inhalation EMEG/MRL) [3,11] to determine if estimated long term air concentrations are at levels of health concern for residents. Potential cancer effects are evaluated by multiplication of the EPA unit risk for nickel subsulfide(1) of 4.8E-4 per µg/m3  and the maximum off-site nickel concentration (and an exposure factor based on duration of exposure of nine years).
WKWMA workers may have been present in buffer areas from 500 to 1000 m from building C-746A. Concentrations at points 500 m from C-746A will be used to evaluate potential worker exposures. WKWMA worker exposures are evaluated using the National Institute of Occupational Safety and Health (NIOSH) Recommended Exposure Limit of 15µg/m3 for soluble or insoluble nickel (8 hour time weighted average(2) ) . Nickel soil concentrations are compared with estimated air concentrations to determine if estimated nickel dispersion and deposition are reflected in nearby soils.
Activities of radiological contaminants from nickel samples (Th 230, Th 232, U 235 and Tc 99) and stack emission monitoring (U234, U235, and U238)  are used to determine the quantity ofradionuclides released during nickel smelting. Calculated quantities and rates of radionuclideemissions from nickel smelting are about 10,000 times lower than airborne radionuclide emissionsfrom other PGDP process operations used in Appendix E. Consequently, radiological emissionsfrom the smelting operations did not constitute a significant radionuclide source and will not changepreviously estimated releases or exposures.
The estimated average annual concentrations of nickel particulates (based on 1984-1986 emission data and hourly weather data for 1990) are shown in Figure I-1. The highest estimated annual average nickel concentration of 0.18µg/m3 occurred approximately 200 m north of the C-746A building which reflects prevailing southerly winds. The maximum one hour average concentration is estimated to be 15µg/m3 and the maximum eight hour average is estimated to be 3.0µg/m3 with both maxima about 200 m north of the stack. Distribution of short term nickel concentrations, although higher to the north, are more uniformly distributed around the C-746A building and reflect short term weather conditions which may have winds from any direction. Model runs us