SITE INFORMATION AND CORRESPONDENCE_1

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Del Monte Foods One Market � P.O. Box 193575 San Francisco,CA 94119-3575 Steven P.Ronzone Telephone: (415)247-3000 Director/Real Estate&Facilities (415)247-3520(Direct) (415)247-3540(Facsimile) October 1, 1999 E Ronald Rowe R C@ V E U San Joaquin County Public Health Services OCT 0 5 1999 LOP/Site Mitigation Unit Environmental Health Division E=NVIRONMENTAL HEALTH 304 E. Weber Ave., Third Floor PERMIT / SERVICES Stockton, CA 95202 Re: July 1999 Groundwater Monitoring Results for Disco Site, 110 Filbert Street, Stockton, CA Dear Mr. Rowe: Enclosed please find the July 1999 groundwater monitoring report for the Disco site. The groundwater sample results and the groundwater flow direction continue to be consistent with previous sampling events. Oxygenates were not detected during this event. Oxygenates have not been detected in any well at the site in the past four, or more, consecutive sampling events. Monitoring wells at the Disco site containing petroleum hydrocarbons have either stable or reducing concentrations. Monitoring wells outside of the dissolved hydrocarbon plume continue to be consistently non-detect. Given the demonstrated stability of the groundwater flow direction (consistently towards the southeast since 1995) and the consistent analytical sample results of existing monitoring wells, we recommend that the frequency of sampling be reduced for select monitoring wells at the Disco site. Continuing to sample all wells on a quarterly basis will not provide additional useful information. A request to reduce the frequency of sampling to biannually and eliminate oxygenate testing was proposed in a letter from Del Monte to your office dated June 16, 1999. The request to reduce the frequency of sampling was denied, as stated in your July 7, 1999 letter: Quarterly Monitoring Report Review, Response to Request to Discontinue Oxygenate Analyses and Quarterly Sampling. Your letter stated that oxygenate testing may be eliminated from monitoring wells MW-DIS-3, -4, -5, -6, -7S, -7D, -8S, -8D, and —10, but must be continued for monitoring wells MW-DIS-1, -2, -9,NP-1-70', -80', -90', SVE-South, and SVE-North. In the revised February 1999 Groundwater Monitoring Report, submitted to your office on August 9, 1999, we presented a Groundwater Monitoring Frequency Decision Tree (Figure 3 in the February 1999 report, Figure 4 in the attached July 1999 report), to provide a guideline for determining the frequency of collecting groundwater samples for analysis. In the attached cover letter to the report, dated August 9, 1999, we requested a response to the recommended sampling plan (Table 6 in the monitoring report) by August 30, 1999, in order to plan for the