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I 'Y' <br /> 0 <br /> 1 <br /> A S S O C I A T E S I N C <br /> 10--_ <br /> 4.2 Groundwater Conditions <br /> 1 4 2 1 Site Hydrogeology <br /> ' From February 1999 to June 2004, static water levels have fluctuated from approximately 21 88 <br /> to 29 27 feet bgs in groundwater monitoring wells MW1 through MW3 Depth to water levels <br /> has been observed to fluctuate, however, the groundwater table elevation has decreased by <br /> approximately six feet from February 1999 to June 2004 The most recent quarterly monitonng <br /> was performed in June 2004, groundwater was measured at depths ranging from 28 47 to 28 78 <br /> feet bgs Since 1999, groundwater flow direction has been calculated to be predominantly <br /> towards the northeast Groundwater flow directions towards the north and northwest have also <br /> been calculated A northwesterly groundwater flow direction has been the predominant <br /> 1 groundwater flow direction observed during the last two years of quarterly groundwater <br /> monitoring activities conducted at the site Hydraulic gradients ranging from 0 002 to 0 0004 ft/ft <br /> have been calculated for the site <br /> 1 Figure 3 shows a groundwater contour map generated from the June 2004 data, groundwater <br /> elevation measurements are presented in Table 3 <br /> 4 2 2 Petroleum Hydrocarbons in Groundwater <br /> ' Groundwater monitoring wells MW 1 through MW3 have been sampled since February 1999 <br /> Groundwater analytical data are included in Table 2 Historically, petroleum hydrocarbons have <br /> been consistently detected in wells MW1 through MW3 Benzene has been detected sporadically <br /> ' at very low concentrations in wells MW2 and MW3 since September 2002 Concentrations of <br /> petroleum hydrocarbons in all of these wells have generally decreased since monitoring was <br /> initiated at the site <br /> ' The following is a summary Yof groundwater impact based on laboratoryanal tical data from <br /> 1 previous subsurface reports and quarterly groundwater monitonng reports <br /> • Well MW1 is located approximately 47 feet southeast of the former tank excavation pit in a <br /> ' hydraulically upgradient to crossgradient direction TPHg and BTEX concentrations in <br /> groundwater samples collected from well MW1 have shown a decreasing trend of 4,700 <br /> ug/1 (TPHg) and 13 ug/i (benzene) in February 1999 to concentrations of 370 ug/1 (TPHg) <br /> 1 and 10 ug/1 (benzene) in June 2004 Dunng the second-quarter 2004 quarterly <br /> groundwater monitonng event conducted on June 4, 2004, TPHg was detected at a <br /> concentration of 370 ug/1 This was the lowest concentration since sampling began and <br /> 1 represents a 92 1% reduction in TPHg concentration Additionally, benzene and <br /> ethylbenzene were detected at low concentrations of 10 ug/I and 3 2 ug/l, respectively <br /> MTBE has never been detected in the groundwater samples collected from MWI. A <br /> hydrograph depicting TPHg and benzene concentrations associated with MW1 is shown on <br /> w 1149811reporU\closure doe 5 <br /> 1 <br />