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r Former Beacon Station No 419 April30 1911 <br /> Stockton, California Groundwater Monitoring Report <br /> 41 (TBA), methanol, and ethanol by EPA Method 8260 Laboratory results are summarized in <br /> Tables 1 and la Copies of the laboratory data sheets and chain-of-custody reports are <br /> 0 included as Attachment C <br /> Conclusions <br /> Water-level data collected by Doulos on March 26, 1999 were used to construct the <br /> Groundwater Contour Map (Figure 2) The average depth-to-water for the wells was <br /> approximately 41 3 feet below surface grade (bsg) Water levels have risen an average of <br /> approximately 4 2 feet since December 1998 The flow direction is generally toward the <br /> south (ranges from southwest to southeast) The groundwater gradient magnitude ranges <br /> from 0 001 to 0 003 foot / foot beneath the site <br /> Data collected from this sampling event was used to construct a Benzene Isoconcentration <br /> Map (Figure 3) Detectable concentrations of benzene were reported in four of the eleven <br /> water samples collected No detectable concentrations of benzene were detected in wells <br /> MW-1, MW-2, and MW-6 Dissolved benzene concentrations have decreased in wells MW- <br /> 3, MW-4, MW-5, MW-8, and MW-9 since the December 1998 sampling event, while <br /> dissolved benzene concentrations have increased in wells MW-7 and MW-10 since the <br /> December 1998 sampling event Wells MW-1, MW-2, and MW-6 remained at less than <br /> laboratory detection levels since the December 1998 sampling event <br /> Analyses for the oxygenated fuel additive compounds detected MTBE in wells MW-8 and <br /> VW-1 TBA was detected in wells MW-3, MW-7, MW-9, MW-10, and VW-1 Methanol <br /> and ethanol were detected only in well VW-1 <br /> Recommendations <br /> Horizon recommends continued quarterly monitoring <br /> Report Distribution <br /> We recommend a copy of this report be forwarded to <br /> Mr Michael J Infurna Mr Gordon Boggs <br /> Environmental Health Division CRWQCB - Central Valley Region <br /> San Joaquin County Public Health Services 3443 Routier Road, Suite A <br /> P 0 Box 2009 Sacramento, California 95827-3098 <br /> Stockton, California 95201 <br /> 99gmr q 1 <br /> Job No 1419 42 2 HORIZON ENVIRONMENTAL INC <br />