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26056/26080 Thornton Road <br />September 1997 <br />Page 2 <br />well. The three vapor extraction wells will be drilled to 15 feet below ground surface and the air sparge <br />well will be drilled to 30 feet below ground surface. The sentinel monitoring well will be nested to <br />evaluate the vertical migration of contaminants. <br />PHS/EHD concurs which the recommendation to perform a feasibility study of vapor extraction and air <br />sparging. Feasibility studies are a necessary component of corrective action plans pursuant to the Health <br />and Safety Code and the Underground Storage Tank Regulations. PHS/EHD believes it imperative that <br />the nested well be installed in an intermediate location between the MW4 and the Supply Well to <br />confirm the extent of the shallower groundwater contamination and to investigate the vertical transport <br />of the contaminants, particularly since sandy soils have been encountered to 45 feet bgs which is the <br />maximum depth of investigation conducted thus far. <br />Please submit no later than November 3, 1997, a work plan to implement the feasibility study and to <br />complete the groundwater investigation. <br />PHS/EHD has requested that the groundwater samples which were collected on September 18, 1997, <br />additionally undergo EPA Method 8260 analysis for gasoline additives and oxygenate blending <br />compounds. While the tanks were removed prior to the time of this more recent gasoline reformation, <br />additives were likely in use during the time that the tanks were in operation. It is necessary that the <br />presence of these more recalcitrant compounds are investigated. <br />Please proceed with efforts to obtain pre-approval from the State Water Resources Control Board <br />Cleanup Fund for these activities. <br />If you have any questions or comments, please contact me at (209) 468-0337. <br />Donna Heran, REHS, Director <br />Environmental Health Division <br />MargareLLagorio, RE S <br />Supervisor <br />Mary Meays, Senior REHS <br />Site Mitigation Unit <br />cc: Elizabeth Thayer, CVRWQCB <br />cc: Steve Marquez, SWRCB <br />cc: Tom Lutterman, Smith Environmental <br />cc: Al Hoslett, Esq. <br />cc: Ron Rail, SJC Utilities Maintenance District <br />a