SITE INFORMATION AND CORRESPONDENCE_1994-1996

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I Shell Distribution Facility, Stockton -3- 23 March 1995 Hydrocarbon contaminants reported at Shell during 1994 include diesel, gasoline, the gasoline components benzene, toluene, ethylbenzene, and xylenes (BTEX), and dissolved lead. The analytical methods used by Shell's laboratories are in accord with the recommendations of the Tri- Regional Staff Guidelines. Some of the analytical detection limits that were reported seem high; perhaps due to high levels of concentrations and matrix interferences. The various analytes are non-uniformly distributed across the site, as shown in Figs 7-10 of the 1994 Annual Report. This suggests either(or both) differential migration of the plume components, or more than one plume/source. Several "hot spots" (points of higher than average concentration of one or more component in one or more sampling round) are shown. The "hot spots" do not coincide, further suggesting more than one source area. Some of the analytes are reported as "lighter than" or"heavier than" diesel, or"atypical" diesel. I do not know whether these reports mean that one or more additional, unspecified hydrocarbon components may be present, or that chemical alteration (weathering or degradation) of the diesel has occurred. Lastly, separate phase hydrocarbons are reported from several of the wells, in thicknesses up to .73 inches. Although all of the above information regarding contaminant distribution may be gleaned from examination of the text figures and the analytical reports in the 1994 Annual Report, it is not discussed in the narrative. Remedial Actions: Until April 1993, Shell was using three of the shallow monitoring wells (wells 1, 23, and 24) as extraction wells Extracted water was stored onsite in tanks and periodically trucked to the Shell refinery in Martinez for treatment. The extraction system was shut down when limitations were placed on the amount of water that could be handled by the refinery. Shell obtained a permit to discharge treated ground water to surface water in June 1994, and the ground water extraction was resumed November 29, 1994. Shell has submitted a Remedial Action Plan (RAP) which included initiation of a soil vapor extraction system(SVE). A pilot study for the SVE, completed in August 1994, found that SVE technology is appropriate for the site. An air discharge permit for the SVE, required from the San Joaquin County Air Pollution Control District, is pending. The SVE system was installed during the fourth quarter, 1994, but is not yet operating. Cleanup and Abatement Order 94-705 requires startup of the GWE and SVE systems by 1 December 1994. The Order also requires that Shell obtain all necessary local and state permits before beginning work, a requirement that they have violated in failing to obtain timely approval of the Air District permit for the SVE. The Order further requires that Shell ensure that the GWE completely capture the plumes (i.e., show zero lines of contamination in all water bearing zones). Sampling must show that the extraction is successful. If noncontainment is confirmed, Shell is required to submit, within 30 days of receiving the sample results, a Contingency Plan to mitigate the condition. In response to results of geoprobe studies conducted offsite in September, 1994, and in January 1995, Shell has proposed installation of two new ground water monitoring wells, MW-28 and