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L., <br /> Instructions <br /> Soil samples should be quantitatively analyzed for <br /> BTX&E using EPA Method 8020. Soil samples should also <br /> be quantitatively analyzed for TPH using the DHS method <br /> described in Appendix C. All results should be <br /> reported in parts per million, either milligrams of <br /> fuel constituents per kilogram of soil (mg/kg) or in <br /> micrograms of fuel constituents per gram of soil <br /> (µg/g) . Appendix C explains these analytical <br /> procedures and how to interpret results. <br /> 6. Do BTX&E or TPH Concentrations Exceed Allowable Levels? <br /> Explanation <br /> To estimate the levels of BTX&E and TPH that can be <br /> safely left in place or used as cleanup values without <br /> threatening water quality, a leaching potential <br /> analysis was developed (see Table 2-1, page 29) . This <br /> leaching potential analysis is based on modeling <br /> results and the best professional judgment of <br /> experienced field staff. <br /> The leaching potential analysis begins with four char- <br /> acteristics that heavily influence downward migration <br /> of fuel constituents: depth to ground water, subsurface <br /> fractures, precipitation, and man-made conduits. A <br /> fifth characteristic -- unique site features -- was <br /> added to account for special local conditions. Next, <br /> the analysis requires scoring each characteristic on a <br /> scale of low (10 pts. ) , medium (9 pts. ) or high (5 <br /> pts. ) potential for leaching. Finally, the leaching <br /> potential analysis sets allowable levels at three <br /> degrees of sensitivity, expressed in terms of ppm of <br /> BTX&E and TPH, that can be left in the soil without <br /> degrading ground water. If the concentration of <br /> benzene, toluene, xylene, ethylbenzene, or TPH is above <br /> the allowable level, then the site investigation should <br /> proceed to the General Risk Appraisal (page 37) . <br /> No BTX&E level is presented for the most sensitive <br /> sites (e.g. , 40 pts. or less) . BTX&E levels should be <br /> below detection limits if TPH levels are 10 ppm or <br /> lower, therefore no BTX&E levels are presented to avoid <br /> the impression that detection limits are recommended as <br /> cleanup levels. Thus, the leaching potential analysis <br /> for sensitive sites relies exclusively on TPH values. <br /> If BTX or E are detectable, even though TPH is below 10 <br /> ppm, the site investigation should proceed to the <br /> General Risk Appraisal . <br /> 27 <br />