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ti <br /> PUBLIC HEALTH SERVICES �O,.P�ut�;.•.C� <br /> I SAN JOAQUIN COUNTY <br /> JOGI KHANNA M.D.,M.P.H. <br /> Health Officer <br /> P.O. Box 2009 • (1601 East Hazelton Avenue) •Stockton, Oddomia 95201 cR f F o aP <br /> (209)46&3400 <br /> f <br /> SRIKANTH DASAPPA <br /> PO BOX 1839 = %~` APR 1 6 1993 <br /> SANTA MONICA CA 90406 r _ <br /> L_ U <br /> RE: USA Petroleum #65 SITE CODE: 1356 <br /> 2500 W. Lodi Avenue <br /> Lodi, Ca <br /> San Joaquin County Public Health Services,Environmental Health Division (PHS/EHD)has <br /> reviewed your letter, dated March 16, 1993, requesting semi-annual groundwater sampling <br /> at the above noted site and has the following comments. <br /> PHS/EHD agrees that a reduction in the frequency of the groundwater sampling for this site <br /> is warranted at this time. However, semi-annual groundwater sampling of the eight on-site <br /> wells would not provide adequate data to effectively monitor the subsurface conditions at <br /> this site. <br /> Monitoring wells #3, #4, and #6 have shown some degree of contamination during the past <br /> year of groundwater sampling. These results have been inconsistent in that the plume <br /> appears to be "jumping" from well to well, or, at times, is not there at all. The drop in the <br /> water table at this site from approximately 42 feet below ground surface (BGS) in 1987 to <br /> approximately 53 feet BGS in 1992 may be a contributing factor for these inconsistent <br /> results. <br /> Documentation from other sites in San Joaquin County has indicated a correlation between <br /> the drop in the water table and inconsistent fluctuations in the concentrations of <br /> contaminants in the groundwater. At sites where a drop in the water table has been <br /> documented, the hydrocarbons attenuate or become "hung up" in the soil, resulting in lower <br />! or nondetect concentrations of'contaminants in the groundwater. As the water table rises, <br /> the groundwater again becomes impacted by the hydrocarbons left behind in the soil. <br /> Data must be continually collected for this site to monitor the relationship between the <br /> vertical fluctuations of the water table and the contaminant concentrations in the <br /> groundwater. This data is needed so that an appropriate remediation alternative can be <br /> chosen for this site. It is also needed to effectively monitor and evaluate the remediation <br /> progress over time. <br /> Therefore, in order to monitor the above noted conditions at this site, PHS/EHD <br /> recommends the following modified sampling frequency: <br /> A DwOion of San Joaquin[uunry Hcallh r:a c ycmccs �, <br />