SITE INFORMATION AND CORRESPONDENCE FILE 1

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Nov - 12 - 96 07 : 21P Sierra - Pacific Grnd water 916 933 - 3197 P . 02 Sierra-Pacific Groundwater Consultants, Inc. Geologists, Engineers, and Compliance Specialists November l2, 1996 Mr. Steve Sasson San Joaquin County Public Health Services Environmental Health Division P. O. Box 388 Stockton, California 96201A88 (Via Facsimile) Dear Mr. Sasson, As we discussed on the project site yesterday afternoon, this letter has been prepared to summarize our agreed-upon additional work at the California Tank. Lines Facility, located at 3105 South E1 Dorado Street in Stockton. We have completed two of the original three borings scheduled in our workplan dated August 28 , 1996 and amended by letter dated October 15, 1996, as approved by you. We deepened the second boring, in the center of the former UST excavation area, from 20 to 40 feet, as we were encountering continuing evidence of soil contamination based upon field evidence (odors and photoionization detector readings). On reaching groundwater at 40 feet below ground surface (bgs), we found evidence of contamination necessitating construction of a ground-water monitoring well (see attached revised figure3). The new scope of work will include construction of the monitoring well, and three additional soil borings at the locations indicated on the attached figure. The monitoring well will be constructed oft-inch PVC, screened from approximately 30 to 50 feet bgs with 0.010-slot PVC well screen. A 92112 Lonestar sand filter pack will be placed to a paint 28 feet bgs in the well, or 2 feet above the top of the well screen. A minimum oft feet of bentonite chips, hydrated in place, will be placed above the sand as a seal against descending waters in the annulus around the casing pipe, Blank PVC casing will be placed above the well screen to within 0. 5 feet of the ground surface. A flush-mounted traffic-rated well box will be set in concrete around the top of the casing. The well will subsequently be developed by surging and purging, and will be sampled in accordance with Tri-Regional Guidelines dated 10 August, 1990, published by the California Regional Water Quality Control Board . In each of the new soil borings, samples will be collected at five-foot intervals beginning at 15 feet bgs, continuing to approximately 40 feet bgs. At that paint, hydropunch equipment will be driven approximately 5 feet into the saturated zone, and a grab sample of groundwater will be retrieved using a small-diameter PVC well screen and a stainless steel bailer. All such equipment shall be pre-cleaned or decontaminated at the site in accordance with the procedures in the approved workplan. The groundwater samples obtained will be analyzed for total petroleum hydrocarbons (TPH) by EPA method 8015-modified, for benzene, toluene, ethylbenzene, total xylene (BTEX), and for MTBE by EPA method 8020 . Should the 8020 results indicate the presence of MTBE in any sample, an analysis of that sample for MTBE by EPA method 8270 will also be run. The (916) 913-1468 4911 Winlpl.r nriv Suite 4 Fa Dnesdn Hills, C.e11M1lnlln 95762 (916) 933-31W FAX