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1 <br /> Project Quarterly Update Report May 1, 1991 <br /> 9110 Thornton Road, Stockton, California Page 13 <br />' SUMMARY <br />' Analytical data from groundwater monitoring have documented an Increase In the water table elevation <br /> of approximately 17-feet during this reporting period The groundwater gradient remains In an easterly <br />' direction The average gradient has been approximately 0 002 ft/ft during this three month period <br />' On February 21, 1991, eight monitoring wells were sampled and analyzed for the presence of BTEC and <br /> TPH-as-gasoline concentrations Analytical results reported no detectable TPH-as-gasoline <br />' concentrations In any of the monitoring well samples. A sample collected and analyzed from monitoring <br /> well MW-15A contained a detectable toluene concentration of 0 5 ppb The sample collected and <br /> analyzed from monitoring well MW-17b contained a toluene concentration of 0 4 ppb None of the other <br /> samples analyzed contained detectable BTEC concentrations at the Method Detection Limits <br />' A select group of nearby domestic wells were sampled twice during the quarter All analytical results for <br /> the samples from the domestic wells were at non detectable levels for all parameters analyzed <br /> It appears that the current drought conditions, combined with the high water usage 4n this region of <br /> California, have caused a fairly steady drop in the water-table elevations from approximately 18-to <br /> 20-feet below mean sea level in June 1986 to approximately 35-feet below mean sea level in March 1991 <br /> This decline in the water table elevations has served to enhance the use of soil venting and reduce <br />' dissolved levels in the groundwater since hydrocarbons have adsorbed onto soils as the water <br /> table dropped <br /> I <br /> A review of the laboratory analytical results collected to date shows that substantial decreases In the <br /> concentrations of BTEX and TPH-as-gasoline have occurred over the duration of the project It is <br /> apparent that the combined efforts of separate-phase product removal, groundwater extraction, the <br /> I declining water table and insrtu soil venting have proven effective in removing the gasoline hydrocarbon <br /> constituents from the subsurface <br /> CLOSURE <br /> Groundwater Technology, Inc Is pleased to provide Southland Corporation with this Project Quarterly <br /> Update Report if you have any questions or need addMonal information regarding this site, contact <br /> IGroundwater Technology's office at (415) 671-2387 <br /> ❑��J <br /> E1❑Dn�GROUNMATER <br /> TECHNOLOGY rhC <br />