SITE INFORMATION AND CORRESPONDENCE

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r o FORMER SAFEWAY PROPERTY 2 24 September 1996 1111 NAVY DRIVE,STOCKTON,SAN JOAQUIN COUNTY Water sample results were not submitted to us again until early 1994,when the three monitoring wells did not contain detectable contamination. Depth to water was approximately 30 feet. In July and November 1994, all three wells did contain diesel contamination at up to 670 and 510 ppb, respectively, while the depths to water were approximately 30 and 31 feet, respectively. We have received no reports, other than the closure report, since. In September 1995, a Phase I Audit of the site was conducted in preparation for sale of the property. Nine Hydropunch samples were collected. Six of the Hydropunch samples contained diesel at up to 1200 ppb. The Hydropunch samples containing diesel were widespread, indicating a very large plume. The consultants speculated that the diesel may have come from military activities or there may be offsite sources. At least one other nearby site also has diesel contamination. All samples contained various solvents,which appears to be part of a local solvent contamination plume detected at nearby sites as well. COMMENTS 1. Wells were first installed at the site in late 1987. However, quarterly monitoring reports were not submitted for all of 1988,three quarters of 1989, all of 1990,two quarters of 1991, all of 1992 and 1993, one quarter of 1994, all of 1995 and 1996. 2. Higher levels of contamination were generally detected in the Hydropunch samples than in the monitoring wells. Ground water contamination was not detected at this site until the water level dropped into the sandy layer. Perhaps, because the contamination resides primarily in the sandy layer, and the Hydropunch samplers have a small screen length/sample opening,the Hydropunch collects an undiluted and more accurate sample, unlike the monitoring wells with the longer screens. 3. The Hydropunch samples indicate that ground water contamination is more widespread than is indicated by the monitoring wells. 4. Ground water contamination is undefined and the investigation is incomplete. 5. The high levels of diesel contamination in ground water indicate that the source of the diesel has not been located and/or removed. REGIONAL BOARD STAFF RECOMMENDATIONS TO THE COMMITTEE 1. Quarterly ground water monitoring must be instituted, and reports sent both to the Regional Board and the County. 2. The ground water investigation must continue at this site so that contamination is more accurately defined and the source located. Ideally, adjacent and nearby sites,which also have diesel and solvent contamination would work with Safeway to investigate the problem. 3. Part of the investigation should focus on the sandy layer between approximately 25 and 32 feet with installation of several wells screened only in the sandy zone. 4. Careful analysis of chromatograms may give clues to the age and source of the diesel contamination.