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1 Southland/Stockton 15 <br /> March 1991 <br /> Water Sampling and Analysts Water samples will be collected after sufficient well volumes <br />' have been purged to ensure that the samples are representative (See Appendix E for Standard <br /> Operating Procedures (SOP) 9 and 10 regarding well sampling) The samples will be transported on ice <br />' to a certified laboratory for analysis using EPA Method 602 <br />' The sampling of the three new wells will be scheduled to coincide with the regular quarterly <br /> sampling events <br />' SOIL VENT SYSTEM EVALUATION <br />' The analytical data from the sod samples collected during drilling for the on-site monitoring well <br /> will be evaluated to help confirm the effectiveness of the sod-vent system If the sod sampling confirms <br />' that levels of TPH-as-gasoline greater than 10 parts per million are present, then operation of the soil- <br /> vent system will continue If elevated concentrations of hydrocarbons are detected and it is necessary <br />' to continue operation of the soil-vent system, then additional sod sampling will be conducted at a later <br /> date The following section discusses the 10 ppm TPH clean-up criteria <br />' Soil Clean-uta Objective Discussion_ <br /> The maximum allowable concentration of TPH-as-gasoline in sod of 10 ppm is based upon a <br /> leaching potential analysis from the State Water Resources Control Board, Leaking Underground Fuel <br />' Tank (LOFT) Field Manual <br /> The leaching potential analysis uses a point system to rate site specific conditions including the <br /> following the minimum depth to groundwater, the presence of subsurface fractures, the average annual <br /> precipitation, the presence of man-made conduits, and the presence of unique site features such as <br /> Iwells Based on the leaching potential analysis the estimated maximum allowable TPH-as-gasoline level <br /> that can be left in place without threatening the groundwater is 10 ppm A copy of the leaching potential <br /> analysis is provided (Appendix F) <br /> I <br /> I <br /> C� GROUNDWATER <br /> TECHNOLOGY, INC <br />