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' Project Quarterly Update Report February 21, 1992 <br /> Southland, 9110 Thornton Road, Stockton, California Page 8 <br /> any of the sod samples above method detection limits Only one soil sample collected at 36 feet <br /> Below grade contained a detectable TPH-as-gasoline concentration, which was reported at 9 ppm <br />' One sample collected at 36 feet below grade contained a detectable lead concentration, which was <br /> reported at 6 8 ppm <br /> Monitonng data has documented an increase in the groundwater elevation of approximately 145 feet <br /> during this reporting period The average depth to water In December 1991 was 47 32 feet below <br /> surface grade, compared to a depth of approximately 20 feet Below surface grade in June 1986 <br /> The groundwater flow direction remained In an easterly direction at the average gradient of <br /> approximately 0 002 to 0 003 during the three month period <br /> On November 26, 1991, a total of 11 monitoring wells (5 wells and 2 three-well clusters) and one <br /> pumping well were sampled and analyzed for BTEX and TPH-as-gasoline Analytical results reported <br /> tno detectable concentrations for any constituents In any of the samples, including samples from the <br /> new monitoring wells <br /> A select group of nearby domestic wells were sampled three times during the quarter and analyzed <br /> for BTEX and TPH-as-gasoline The analytical results for the samples from the domestic wells <br /> reported no detectable BTEX or TPH-as-gasoline concentrations in any of the samples <br />' A review of the laboratory analytical results collected to date shows that decreases in BTEX and <br /> TPH-as-gasoline concentrations have occurred over the duration of the project to the current <br />' nondetectable levels in all monitoring and domestic wells It is apparent that the combined efforts of <br /> separate-phase product removal, groundwater extraction, the declining water table and In situ soil <br />' venting have proven effective In removing the gasoline hydrocarbon constituents from the <br /> groundwater over the life of the project <br />' The groundwater extraction and treatment system was not operated during this quarter at <br /> Southland's direction because of the low to nondetectable concentrations of petroleum <br /> hydrocarbons In the groundwater over the last nine months <br /> GROUNDWATER <br /> _ <br />' �TECHNOLOGY, INC <br />