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SERVICESPUBLIC HEALTH <br /> SAN JOAQUIN COUNTY 4 <br /> U): :[ <br /> JOGI KHANNA M.D.,M.P.H. <br /> Health Officer <br /> l,FOA�: i <br /> 1601 East Hazelton Avenue) • Stockton, California 95201 i <br /> P.O.Box 2009 • ( i <br /> (209) 468-3400 <br /> SRIKANTH DASAPPA <br /> PO BOX 1839 406 i APR 1 1993 <br /> _'Liu.... <br /> SANTA MONICA CA 90 <br /> 1356 <br /> 2500 <br /> SITE CODE.RE: USA Petroleum 465 i' <br /> i 2500 W. Lodi Avenue i <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/E1-1D agrees that a reduction in the frequency of the groundwater sampling for this site <br /> is warranted at this tune. However, semi-annual groundwater sampling of the eight on <br /> wells would not provide adequate data to effectively monitor the subsurface conditions at <br /> this'site' i <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 ofcontaminants 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 /> f <br /> A L)Msion of San Joaquin Counry Health'(-me serviccs <br />