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RESULTS OFQUARTERLY GROUNDWATER MONITORING <br /> GROUNDWATER GRADIENT AND FLOW DIRECTION <br /> Figure 4 shows the groundwater elevation gradient and flow direction determined from <br /> depth to water measurements at the five on-site monitor wells on September 9, 1998 <br /> The groundwater elevation has decreased by an average of 3 0, feet at the five monitor <br /> wells since the previous quarterly monitoring round on June 6, 1998 The general flow <br /> direction is to the west, from the former UST's towards MW3 and Mission Road The <br /> overall gradient is 0 004 feet/linear foot <br /> RESULTS OF CERTIFIED ANALYSIS OF GROUNDWATER SAMPLES <br /> The results of the certified analyses of groundwater samples collected from the five <br /> monitor wells on September 9, 1998 are shown in Table i Copies of the laboratory <br /> reports are included as Appendix C of this report <br /> TPH-G concentrations ranged from a maximum of 30,000 ug/1 at MWI to less than the <br /> laboratory detection limits of 50 ug/1 at monitor wells MW2, MW4, and MW5 <br /> Benzene concentrations ranged from a maximum of 4900 ug/l at MWI to less than the <br /> laboratory detection limits of 0 5 ug/I at monitor wells MW2, MW3, and MW5 <br /> MTBE concentrations ranged from a maximum of 260 ug/l in MWI to less than <br /> laboratory detection limits of 5 ug/l in monitor wells MW2, MW4, and MW5 <br /> Figure 5 shows the distribution of TPH-G, BTEX, and MTBE in groundwater and the <br /> lateral limits of the TPH-G in groundwater as determined from groundwater samples <br /> collected on September 9, 1998 The decrease in groundwater elevations since the <br /> previous quarterly monitoring round in June 1998 has been accompanied by an increase <br /> in TPH-G and BTEX concentrations at MWI <br /> RECOMMENDATIONS <br /> 1) Continue quarterly groundwater monitoring <br /> 2) Construct new workplan for the site that includes overexcavation of the tank pit area <br /> as originally proposed by William Hunter and Associates and the installation of two <br /> additional monitor wells to measure TPH-G, BTEX, and MTBE concentrations at depths <br /> below the current monitor well slotted intervals <br /> 3 Sanchez QM 7-9 1998 <br />