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leaking underground storage tank sites of $100,000, $1,000, 000, <br /> and $10, 000, 000 at 80%, 10%, and 10% of all sites, respectively, <br /> a total cost to investigate and remediate the identified sites in <br /> the United States would be approximately 210 billion dollars. <br /> This is on the order of the United States defense budget and <br /> exceeds the gross national product of many countries. It should <br /> be pointed out that these figures include only non-farm under- <br /> ground fuel storage tank leaks and not pipeline leakage, above <br /> ground spillage, or nonfuel contamination. In addition, this <br /> figure is only an estimate of currently leaking tanks and does . <br /> not include abandoned tanks, past leaks, or future leaks: <br /> Although the precise figures utilized to obtain this estimate are <br /> certainly disputable, even 10% of this figure represents an <br /> enormous sum. <br /> The RA process as applied to an underground tank site has six <br /> steps: site characterization, haa�:d identification, toxicity <br /> evaluation, fate and transport analysis, exposure assessment, and <br /> risk characterization. Its application to the Stockton site is <br /> described here: <br /> Site Characterization - This is the process of <br /> identifying the source and extent of contamination at the <br /> site in three dimensions, along with the physical <br /> features that may influence contaminant fate. The site <br /> characterization for the Stockton site is given in <br /> Chapter 2. <br /> Hazard Identification - Fuels are complex chemical <br /> mixtures. In the hazard identification step the com- <br /> ponents of greatest concern are identified on the basis <br /> of their concentration, toxicity, and mobility. <br /> Only the chemicals identified here are examined in <br /> later steps. <br /> • 5 <br />