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California Regional Water Quality Control Board ', <br />Tm <br />• Central Valley Region . <br />Karl E. Longley, ScD, P.E., Chair <br />Linda S. Adams Arnold <br />Secreta or Sacramento Main Office <br />rJen 11020 Sun Center Drive #200, Rancho Cordova, California 95670 6114 Schwarzenegger <br />Environmental Governor <br />Protection Phone (916) 464-3291 • FAX (916) 464-4645 <br />http:// w b ��.ca.gov/centralvalley <br />IL�LU <br />18 June 2007 <br />JUN 2 7 2007 <br />Mr. Kyle Christie, LPR6-161 ENVIRONMENT FiEALTH <br />Environmental Project Manager PERMIT/SERVICES <br />Atlantic Richfield Company <br />6 Centerpointe Drive <br />La Palma, CA 90623 <br />OFFSITE CPT GROUNDWATER INVESTIGATION, APPLIED AEROSPACE STRUCTURES <br />CORPORATION, STOCKTON, SAN JOAQUIN COUNTY <br />Staff of the Central Valley Regional Water Quality Control Board (Regional Water Board) have <br />reviewed the 22 February 2007 Offsite CPT Groundwater Investigation (Report). The Report <br />provides the results of an investigation completed in December to define the downgradient <br />extent of migration of volatile organic compounds (VOCs), including trichloroethylene (TCE), <br />from the Applied Aerospace Structures facility. The investigation consisted of six cone - <br />penetrometer borings with grab -groundwater samples from several depths in each boring. <br />Three additional borings were planned but not installed due to access problems. <br />The two southern -most borings did not detect VOCs in any of the samples taken from three <br />depths, therefore the southern -most limit of the contamination is defined. Of the remaining <br />borings, P-101 contained 8.77 ug/I and 5.52 ug/I of TCE at 85 feet and 102 feet below ground <br />surface (bgs), respectively. Boring P-106, downgradient of P-101, contained only 1.38 ug/I <br />and 0.56 ug/I of TCE at 85 feet and 102 feet bgs, respectively, therefore the downgradient <br />extent of TCE migration is fairly well defined. Boring P-103 is about 200 feet south of P-101 <br />and contained 2.25 ug/I TCE at 107 feet bgs. <br />The Report recommends installing two wells to monitor VOCs near P-106 and P-103. MW -16 <br />is proposed near P-106, and will be screened from 85 to 100 feet bgs. Monitoring well MW -17 <br />will be installed about 50 feet east of P-103 and screened from 100 to 110 feet bgs. <br />The proposed wells are acceptable to Regional Water Board staff. You may proceed to <br />schedule installation. If you have any questions regarding this letter, you may contact me at <br />(916) 464-4677 or by email at gdjuth@waterboards.ca.gov. <br />GERALD J. DJUTH, P.E., C.E.G. <br />Site Cleanup Program <br />cc: Ms. Margaret Lagorio, San Joaquin County Public Health Services, Stockton <br />Mr. Fred Kintzer, Parsons Engineering Science, Inc., Walnut Creek <br />California Environmental Protection Agency <br />C3 Recycled Paper <br />