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Mr. Marshall Cloud <br /> September 22, 2003 <br /> Page 2 <br /> well as the deeper interval of 12 feet. This way if contamination was originally <br /> shown to exist in the upper interval it can be demonstrated that it did not migrate <br /> down into deeper soil and it can be inferred that no contamination would <br /> potentially exist in the intermediate soil interval between the two recommended <br /> sampling depths. <br /> 2.) After comparing the original baseline sample location figures from 1998 with <br /> those proposed in the Draft work plan it appears that many, if not all proposed <br /> locations are not taken in the vicinity of the baseline "hot spots." In a couple <br /> instances, placing the confirmation sample locations in the same location as the <br /> "hot spot" is not possible due to Vapor Extractions wells or Vapor Monitoring <br /> Wells currently occupying the location, but for many it is not. DTSC <br /> recommends that where possible, confirmation samples should be placed in the <br /> locations of the former "hot spots" in order for one to truly assess whether the <br /> cleanup goals have been achieved in soil vapor of 350 Parts Per Billion Volume <br /> (ppbv) and 780 ppbv for Trichloroethene and Tetrachloroethene, respectively. <br /> DTSC recommends the following locations be sampled in addition to the <br /> currently proposed closure/confirmations sample locations. <br /> SWMU 1/Area 2 — East-corner of square R32, east-corner (inside 350 ppbv <br /> isopleth line) square R22, and the east-corner of square P23. <br /> Area 1/Building 237 — North-east corner of square 115, south-east corner of H14, <br /> north-east corner of J13 (along edge of building), north-east corner of K13 (along <br /> edge of building), intersection point of squares K/L 11/12. <br /> Area 3 — Middle of square AF43, middle west-side of AJ41, middle west-side of <br /> AM42, south-west corner of AK42, north-east corner of AM44, north-west corner <br /> of AP47 and the bottom of the centerline between squares AI/AJ 45. <br /> If you have any questions of comments regarding this letter, please feel free to contact <br /> me at (916) 255-3713 or e-mail me at pmacnich(Ddtsc.ca.gov <br /> Sincerely, <br /> Peter MacNicholl <br /> Remedial Project Manager <br /> Office of Military Facilities <br />