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r <br /> RESULTS OF QUARTERLY 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 December 7, 1998 The <br /> groundwater elevation has decreased by an average of 0 07 feet at the five monitor wells <br /> since the previous quarterly monitoring round on September 9, 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 0 002 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 December 7, 1998 are shown in Table 1 Copies of the laboratory <br /> reports are included as Appendix C of this report <br /> TPH-G concentrations ranged from a maximum of 27, 000 ug/1 at MW 1 to less than the <br /> laboratory detection limits of 50 ug/l at the remaining four monitor wells <br /> Benzene concentrations ranged from a maximum of 2900 ug/l at MW 1 to less than the <br /> laboratory detection limits of 0 5 ug/1 at the remaining four monitor wells <br /> MTBE concentrations ranged from a maximum of 240 ug/l at MW1 to less than <br /> laboratory detection limits of 0 5 ug/l in the remaining four monitor wells <br /> Figure 5 shows the distribution of TPH-G, BTEX, and MTBE in groundwater as <br /> determined from groundwater samples collected on September 9, 1998 The decrease in <br /> groundwater elevations since the previous quarterly monitoring round in September 1998 <br /> has been accompanied by an decrease in TPH-G, BTEX, and MTBE concentrations at <br /> MW 1 and the absence of these analytes at the remaining four monitor wells <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 10-12 1998 <br />