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19 February 1997 <br /> AGE-NC Project No 95-0105 <br /> ' Page 3 of 4 <br /> ' in well MW-4 at concentrations of 52 ppb, 680 ppb, 540 and 1,400 ppb, respectively Benzene, <br /> toluene,and xylenes were detected in well MW-3 at concentrations of 0 93 ppb, 0 93 ppb and 0 57 <br /> ppb, respectively Toluene was detected in well MW-i and MW-2 at concentrations of 0 79 and <br /> 0 31 ppb, respectively MTBE was not detected in any of the monitoring wells TPH-d was detected <br /> in well MW-4 concentrations 1,000 ppb <br /> Petroleum hydrocarbons were not detected in the samples collected from the down gradient well <br /> MW-6, or in the cross-gradient well MW-5 The analytical results for the ground water samples are <br /> summarized in Table 2 -Analytical Results of Ground Water Samples The laboratory report (AAL <br /> Batch 1D 96-1218-005), chain-of-custody form and QA/QC are included in Appendix B <br /> ' 4 0. CONCLUSIONS <br /> Based on data collected from the site, AGE has formed the following conclusions <br /> ' • Theround water flow <br /> g direction is north to northwest and the depth to ground water is <br /> approximately four to five feet below surface grade (bsg) <br /> • Between August and December 1996, concentrations of TPH-g and/or TPH-d decreased in <br /> monitoring wells MW-1 through MW-5, while toluene was detected in wells MW-1, MW-2 <br /> ' and MW-3 for the first time The concentration of benzene continued to decrease in samples <br /> collected from well MW-4, and is currently quantified at the lowest concentration yet <br /> detected in that well <br /> ' The down gradient extent of the petroleum hydrocarbon-impacted ground water has been <br /> delineated over a wide band Monitoring well MW-5 represents the northeastern limit of the <br /> ' dissolved hydrocarbon plume, well MW-6 represents the northern'limit of hydrocarbon <br /> impacted ground water, and according to Mr Steve Sasson of the PHS-EHD, petroleum <br /> hydrocarbons have not been detected in a well located approximately 90 feet northwest of <br /> ' well MW-4 on the City of Tracy Fire Department property <br /> • A receptor survey concluded that no domestic ground water wells were located in an area of <br /> ' environmental concern <br /> s <br /> ' 5.0. RECOMMENDATIONS <br /> Based on present site conditions, AGE has the following recommendations <br /> 1 ` <br /> Soil and purged ground water from previous investigations should be disposed at a licenced <br />