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a sampling plan that provides a high likelihood that any significant <br /> leakage into fill and earth materials will be identified. <br /> CLEAN-UP AND CLOSURE ACTIVITIES <br /> LLNL is proposing to permanently close the Bldg. 874 underground tank <br /> system by removing the tank, associated piping, and, if found, <br /> contaminated soil or fill. Closure activities will be performed in <br /> accordance with the requirements of Title 23 of the California <br /> ' Administrative Code, Chapter 3, Subchapter 16, "Underground Tank <br /> Regulations, " Article 7, Sec. 2672 (b) (State of Calif. , 1985) . The <br /> Leaking, Underground Fuel Tank (LUFT) Field Manual (State Water Resources <br /> Control Board, 1988) will be used as guidance for sample management and as <br /> a determinant of soil clean-up levels. The extent of contamination, if <br /> any, will be determined by the sampling and clean-up plan described below. <br /> To estimate the levels of total petroleum hydrocarbon (TPH) and <br /> benzene, toluene, xylene, and ethylbenzene (BTX&E) that can be safely left <br /> in place, a Leaching Potential Analysis has been performed according to <br /> the LUFT Field Manual. Five site characteristics were evaluated for their <br /> influence on the potential for leaching at a site._ Appendix B provides a <br /> tabular assessment of the leaching potential of the soil in the vicinity <br /> of Tank 874. The basis for the scored values is as follows: <br /> 1 The minimum g depth to groundwater from the soil sample site in the <br /> P P <br /> vicinity of Tank 874 is approximately 40 ft. A score of 5 is <br /> assigned to this site feature. <br /> 2) Subsurface fractures are known to exist in the bedrock that <br /> underlies the Tank_ 874 locale. A score of 5 is assigned to this <br /> ' site feature. <br /> ' 3) The average annual precipitation for the area is 10.73 in. A <br /> score of 9 is assigned to this site feature. <br /> 4 <br />