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Mr. Michael McAnulty lb - 2 - 41 21 April 2006 <br />possible. Staff believes that the first sample boring should be located adjacent to the <br />initial CPT log, from which permeable intervals can be chosen to sample. Additional <br />CPT logs can then be taken within the investigational area to determine if projection of <br />the permeable zones are possible from the logs. Sample borings should be advanced <br />as close as possible to the CPT locations. ARCO needs to obtain Regional Board staff <br />concurrence with the proposed sample intervals. <br />3. Staff review of available CPT and borehole logs indicate that in general, a permeable <br />sand zone exists between 45 and 60 feet bgs, near the water table. A lower permeable <br />zone is present somewhere between 80 and 95 feet bgs. ARCO needs to sample <br />these two permeable zones. A third sample should be taken at a secondary target <br />zone between these two, as identified from the CPT logs. <br />4. To facilitate the identification of the permeable zones, ARCO needs to obtain CPT logs <br />to a minimum of 100 to 110 feet bgs. <br />5. The Work Plan proposes analyzing water samples from P-102 and P-103 on an over- <br />night basis, to determine if it will be necessary to sample "optional" boring locations P- <br />106 to P-109, which are further downgradient. However, if any of the first five borings <br />detect VOCs above Water Quality Objectives, further downgradient sampling may be <br />required. Therefore, ARCO may be able to avoid a re -mobilization fee if the water <br />samples from each of the first five borings are analyzed on an overnight basis. <br />6. The current monitoring and reporting program for Applied Aerospace requires the use <br />of EPA Method 8021 B. The Work Plan proposes using EPA Method 8010, which is <br />equivalent and has a reporting limit of 0.5 ug/I, and is acceptable to Regional Board <br />staff. Also, EPA Method 8260 is acceptable to Regional Board staff as long as it is run <br />in a State -certified lab and has similar detection limits. <br />By 23 May 2006, please submit a revised work plan to address the above comments. If you <br />have any questions regarding this investigation, you may contact me at (916) 464-4677 or by <br />email at gdjuthCaD-waterboards.ca.gov. <br />l <br />GERALD J. DJUTH, P.E., C.E.G. <br />Associate Engineering Geologist <br />cc: Ms. Margaret Lagorio, San Joaquin County Public Health Services, Stockton <br />Mr. Fred Kintzer, Parsons Engineering Science, Inc., Walnut Creek <br />It .11'r,,, `� � . <br />PERM/ Th1E/�Lifj <br />j`,%goCES <br />