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Mr Nuel Henderson, SJCEHD April 7,2006 . Well Installation Report ARCO Facility No 5469 Stockton,California Page 4 Additional soil from each sampled interval was placed and sealed in plastic bags to allow the accumulation of volatile organic compound (VOC) vapors within the airspace in the bags A portable photo-ionization detector (PID) was used to measure VOC concentrations from each sample, in parts per million by volume (ppmv) PID results are included on the boring logs presented in Appendix B PID results were also used to evaluate which soil samples should be sent to the laboratory for chemical analysis Groundwater Monitoring Well Installation Wells MW-11 through MW-13 were constructed using 4-inch diameter schedule 40 PVC well casing and 20 feet of 0 02-inch diameter factory slotted well screen Wells MW-11 and MW-13 were screened from approximately 33 to 53 feet bgs and well MW-12 was screened from approximately 32 to 52 feet bgs A filter pack of LonestarTM 43 sand was placed in the annular space around the well from the bottom of the casing to approximately 2 feet above the top of the well screen Approximately 3 feet of bentonite was placed on top of the filter pack and hydrated with clean water to provide a transition seal for the well The remaining annular space around the well casing was backfilled to surface grade with neat cement A traffic rated vault box was placed over the wells, and a watertight locking cap was placed on the top of the well casing Well details and DWR well completion reports for MW-11 through MW-13 are included in Appendix B Well Development and Sampling Wells MW-11 through MW-13 were developed on February 23, 2006, by surging and bailing with a bailer Groundwater pumping was also utilized to develop wells MW-12 and MW-13 Development continued, to the extent practical, until the groundwater discharge stream appeared free of suspended sediment Stratus returned to the site on March 6, 2006, to sample the newly installed wells The first quarter 2006 groundwater sampling event was also completed at this time Prior to sampling, approximately 3 well casing volumes (approximately 20 to 22 gallons) were purged from each monitoring well The groundwater samples were subsequently collected using a new, clean, disposable bailer Groundwater recovered in the bailer was transferred to properly preserved containers (voas) supplied by the laboratory Each sample was subsequently labeled, identified on a chain-of-custody form, and placed in an ice-chilled cooler Field data sheets from the well development and groundwater sampling events are presented in Appendix C The newly installed groundwater monitoring wells will be incorporated into the site quarterly monitoring program K IBp-Arco for URS\5469\Reports\ARC05469-wellreport2006 doc 5MAT[15