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Mr. Marshall Cloud <br /> December 6, 2006 <br /> Page 2 <br /> respectively. Soil vapor samples were only collected from two of the three originally <br /> planned depths due to the higher than normal ground water table. Shallow soil vapor <br /> samples were collected at five feet below ground surface, with the deeper soil vapor <br /> samples being collected at least one-foot above the static ground water level. <br /> Fieldwork sampling results showed TCE concentrations in soil vapor at five of the 12 <br /> locations with concentrations ranging from 120 to 1,600 ppbv. Ground water analytical <br /> results identified TCE at nine of the 12 locations ranging in concentration from 0.856 <br /> to1,350 pg/L. The highest TCE concentrations in ground water were located west of the <br /> former Site P-5A runway and found in soil borings SBI 106 thru SB1109. <br /> Conclusion <br /> The presence of TCE in shallow soil vapor above the.cleanup level in conjunction with <br /> elevated TCE concentrations in ground water indicate former Site P-5A is a continuing <br /> source of TCE contamination to ground water. The lateral and vertical extent of TCE <br /> contamination in this area is unknown and should be delineated to better understand <br /> the distribution of contaminants. <br /> DTSC concurs with the Technical Memorandum's recommendations and conclusions to <br /> better define the lateral and vertical distribution of contamination through additional CPT <br /> fieldwork. The future anticipated fieldwork at Site P-5A would: verify a connection or <br /> disconnection between Site P-5A source area and MW437 TCE contamination; locate <br /> the center of mass of the dissolved TCE in ground water related to the Site P-5A source <br /> area; and locate the center of TCE mass in soil vapor related to Site P-5A source area. <br /> If you have any questions or comments regarding this letter, please feel free to contact <br /> me at (916) 255-3713, or e-mail me at pmacnich(cDdtsc ca qov. <br /> Sincerely, <br /> Wu <br /> Peter MacNicholl, P.E. <br /> Remedial Project Manager <br /> Office of Military Facilities <br /> cc: See DDJC-Sharpe Distribution List. <br />