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1 ' 7-Eleven/Stockton 15 March 1991 ' On October 23, 1990, nine monitoring wells were sampled and analyzed for the prescence of BTEX and TPH-as-gasoline concentrations Analytical results reported detectable BTEC or TPH-as- ' gasoline concentrations in only two of the nine monitoring well samples A sample collected and analyzed from monitoring well MW-1 contained detectable BTEC compounds and had a TPH-as-gasoline ' concentration of 51 ppb The sample collected and analyzed from monitoring well MW-17b contained only toluene at a concentration of 0 8 ppb and TPH-as-gasoline at 1 ppb A select group of nearby domestic wells were sampled three times during the quarter All analytical results of samples from the domestic wells were at non detectable levels for all parameters tanalyzed except for one sample collected from domestic well TMG on December 28, 1990 Analytical results for this sample were not detectable with respect to BTEX compounds, but reported a TPH-as- ' gasoline concentration of 3 ppb More recent laboratory analyses conducted since the December 1990 sampling round have shown non detectable levels of BTEC and TPH-as-gasoline These additional ' laboratory reports will be provided in the next quarterly update report ' A review of the laboratory analytical results collected to date shows that substantial decreases in the concentrations of BTEC and TPH-as-gasoline have occurred over the duration of the project ' Assessment worm from 1986 to 1988 showed that monitoring wells MW-1, MW-3, and MW-4 contained separate-phase hydrocarbon compounds, and that a number of other monitoring and pumping wells at the site contained dissolved-phase concentrations It is apparent that the combined efforts of separate- phase product removal and groundwater extraction along with soil venting have proven effective in removing the gasoline hydrocarbon constituents from the subsurface ' ItaPPe ars that the current drought conditions, combined with the high water usage in this region g of California, have caused a fairly steady drop in the water-table elevations from approximately 18- to 20- feet below mean sea level in June 1586 to approximately 36- to 38-feet below mean sea level in December 1990 This reduction in the water table elevations has served to enhance the use of soil venting on a number of monitoring wells and soil-vent points at the srte L- GROL ND"ATER TECHNOLOGY INC