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• PARSONS 2121 North California Boulevard, Suite 500 • Walnut Creek, California 94596 • (925) 941-3700 • Fax: (925) 979-9781 • www.parsons.com September 17, 2004 Ref: 440269 Gerald J. Djuth California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive 9200 Rancho Cordova, CA 95670 Subject: Installation of Offsite Monitoring Well MW -15 Lot Adjacent to Applied Aerospace Structures Corporation Stockton, California Dear Mr. Djuth: The purpose of this letter report is to document the successful installation and initial sampling of the new offsite monitoring well MW -15. Drilling, well construction, and initial sampling were completed in accordance with the Work Plan for Monitoring Well Installation, Offsite Southeast of MW -SR which was submitted to the RWQCB on October 23, 2003. The well was constructed on Wednesday July 21, 2004, and developed on Monday July 26. A dedicated low -flow sampling pump was set on July 28 with the intake approximately at mid -screen depth. The bottom depth of the 10 -foot screened interval was constructed at 64 R as compared to 63 ft bottom of the screened interval in well MW -5R. As indicated on the attached boring log, water -bearing fine-grained silty sand was encountered throughout most of the screened interval of MW -15 and a finer grained layer identified as sandy clay was encountered at the bottom of the hole. The installed location of the well is very close to the planned location shown on Figure 1. Final coordinates and elevation will be determined soon; surveying has been scheduled to be performed this week. The local groundwater gradient in the vicinity of the well will be determined when the elevation of the well has been calculated. The initial groundwater sample was collected from MW -15 on August 18th during the site annual groundwater monitoring event. As summarized in Table 6, the analytical results for the site as a whole were comparable to previous quarters and within historical concentration ranges. The sample from MW -15, yielded detections of TCE (4.4 µg/L) and l,l-DCE (0.9 µJL) which appears to be consistent with downgradient migration of contaminants from the vicinity of MW -5R. Concentrations at MW -5R were comparable to historical results for previous summer conditions: TCE (43 µg/L) and 1,1-DCE (3.9 µg/L).