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Ronald Rowe October 1, 1999 Page 2 5 I October sampling event. We have not yet received your comments on the proposed sampling plan changes. We look forward to your response. The attached Groundwater Monitoring Report- July 1999, again recommends a sampling plan (Table 6) based on the Groundwater Monitoring Frequency Decision Tree. The proposed changes to the monitoring plan are only to those wells that are located upgradient and cross- gradient to the plume and source area. In order to continue the accurate assessment of the groundwater flow direction, water level measurements and evaluation of the groundwater gradient will continue to be performed on a quarterly basis. We will be performing one additional monitoring event for 1999, currently scheduled for late October to early November. Groundwater samples will be collected from all wells located within the plume and analyzed for TPH as gasoline, BTEX, and oxygenates. After the results of that monitoring event have been analyzed, the monitoring program shall be re-evaluated for the year 2000. If oxygenates are not detected in the next sampling event, we propose to discontinue testing for oxygenates in all wells. Any new wells installed at the site will be sampled with a frequency as outlined on the Groundwater Monitoring Frequency Decision Tree. We are proceeding with the recommended sampling plan (Table 6) in our preparation for the next sampling event. If you have any questions or comments please feel free to call me at (415) 247-3520. Reg s, Steven P. Ronzon cc: Margaret Lagorio / SFC-PHS Liz Dodge/CH2M HILL Mark List/CVRWQCB Keith Sheets /CH2M HILL Jim Munch/CVRWQCB David Irey/ SIC District Attorneys Office Richard Fish/Del Monte Nancy Bice Geosyntex Consultants Bill Sawyers/Del Monte Sara Flanagan /Pillsbury Madison & Sutro USTCF/SWRCB Disco Property/Stockton-UST Fund Manager WL Simmons c/o Sidney Rudy, Esq. 1 RE\Stockton#33THS Rowe Ltr CH2MHILL