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Ronald Rowe, Sr. REHS <br /> San Joaquin County Public Health Services j <br /> August 10, 1999 <br /> Page 2 <br /> • A Recommendations section has been added to the report to present recommendations to <br /> the sampling plan for subsequent sampling events. A Groundwater Monitoring <br /> Frequency Decision Tree has been added to this section. The decision tree provides a <br /> guideline for determining the frequency of collecting groundwater samples for analysis. <br /> Table 6 has been added to the.report to summarize the third quarter 1999 sampling plan. <br /> In order to continue the accurate assessment of the groundwater flow, both water . <br /> level measurements and evaluation of the groundwater gradient will continue to be <br /> performed on a quarterly basis. Groundwater samples will also continue to be <br /> collected on aquarterly basis from those wells located. within the plume. The <br /> proposed changes to the monitoring plan are only to those wells that are located <br /> upgradient and cross-gradient to the plume and source area. The analytical results from <br /> the upgradient and cross-gradient wells have been consistently non-detect, and the <br /> groundwater flow direction has been extremely stable since 19995. In the opinion of Del <br /> Monte, continuing to sample those wells on a quarterly basis will not provide additional <br /> useful information. <br /> •We also propose to.continue to.sample for oxygenates on a quarterly basis through the end <br /> of 1999 in.the wells within the plume. If oxygenates are not.detected in the next two <br /> sampling events, we propose to discontinue testing for oxygenates. <br /> The third quarter monitoring event is scheduled for September 1999. In order to properly plan <br /> For this event, we request an approval of the recommended sampling plan (Table 6)by August <br /> 30, 1999. If you have any questions or comments, please feel free to call me at (415) 247- <br /> 3520. <br /> Best regards, <br /> i <br /> Steven P. Ronzo <br /> I <br /> cc: Margaret Lagorio/SJC-PHS <br /> Mark List/CVRWQCB <br /> Jim Munch/SWRCB/USTCF <br /> Richard Fish/Del Monte <br /> Susan Flieder/Del Monte <br /> Liz Dodge/CH2M HILL <br /> RE\Stockton#33\PHS Rowe Ltr—Monitoring Report <br />