ing hourly weather data(3) for the years 1989, 1990 and 1991 produced essentially identical results for both short term (hourly and daily) and long term (annual) nickel dispersion. All of the above maximum air concentrations occurred at areas within the DOE property.
The estimated nickel air concentrations at areas of potential off-site exposure (Table I-1) includeseveral notable trends. First, short term concentrations are much higher than long termconcentrations. This trend reflects how short term meteorological conditions control transport andhow averaging time affects concentration. One hour maxima are significantly greater than eight hourmaxima and much greater than annual average concentrations. Second, overall concentrations dropvery rapidly with distance away from the stack. At 1000 m, which is the distance to the closestresidence, all concentrations are about an order of magnitude lower than concentrations at 500 m.Third, the similarity between concentrations and distributions for different weather years indicatesthese data adequately capture the range of potential meteorological conditions.
The dispersion modeling indicates that most nickel deposition will occur within 500 m of the smelterbuilding. Measured soil nickel concentrations support the model results. Average soil concentrationsat locations within the security fence average 25 ppm. Areas within the buffer zone and off-site areashave statistically similar averages of ~12 ppm. These results indicate that onsite soils have elevatednickel concentrations relative to off-site areas but that there is no significant difference betweenbuffer area and off-site concentrations. Local nickel air concentrations and deposition to soil fromthe TVA plant may have been higher prior to the increase in stack height in the early 1970's .
The highest average annual nickel concentration at 1000 m from the smelter building is 0.004 µg/m3 which is about 50 times lower than the ATSDR comparison value of 0.2 µg/m3. Estimated long term exposures at 1000 m also represent no potential cancer risk(4). Similarly, the maximum short term nickel concentration of 1.1 µg/m3 (at 500 m from source; maximum one hour average) is more than 10 times lower than the worker exposure limit of 15 µg/m3 (which includes consideration of potential occupational cancer risk). The estimated maximum hourly, daily, and annual nickel air concentrations from PGDP smelter operations, with potential contributions from the PGDP steam plant and TVA facility, are below levels of health concern.
These estimated off-site nickel concentrations in air include potential contributions from the PGDPnickel smelter emissions, the PGDP steam plant nickel emissions, and the TVA Shawnee coal plantnickel emissions. Modeled emission rates from the PGDP steam plant were based on healthprotective assumptions concerning fuel usage, operating schedules, and emission factors. Actualemission rates are probably lower than modeled rates. All estimated nickel air concentrations,calculated using health protective model assumptions, in areas of potential off-site exposure aremore than 10 times lower than relevant health comparison values.
|500 m||1000 m||1500 m|
|1989 Annual Average||0.018||0.003||0.001|
|1990 Annual Average||0.022||0.004||0.002|
|1991 Annual Average||0.018||0.003||0.001|
|1989 1 hour maximum||1.0||0.12||0.05|
|1990 1 hour maximum||1.0||0.15||0.07|
|1991 1 hour maximum||1.1||0.17||0.06|
|1989 8 hour maximum||0.25||0.05||0.02|
|1990 8 hour maximum||0.23||0.05||0.02|
|1991 8 hour maximum||0.25||0.05||0.02|
Table I-2 lists the metals smelted at PGDP along with the estimated total amount of each metal andthe relevant inhalation health comparison values for each metal. The health comparison values forresidential and occupational exposure are a measure of the toxicity of each metal. The most toxicmetals have the lowest health comparison values because it takes a lower amount of the substance tocause sickness or adverse health effects. This evaluation focuses on nickel because it is relativelytoxic and very large quantities of t