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Mr Jeffrey Wong <br /> C A M B R I A February 23, 2006 <br /> Item Evaluation Criteria Comments/Discussion <br /> groundwater beneath the site Release volume is <br /> unknown <br /> 12 Discuss Steps Taken to Stop The USTs were removed and replaced in <br /> Release December 1994 and significant over-excavation was <br /> performed at that time <br /> 2 Site Characterization <br /> 21 Current Site Use/Status The site is currently an active Econo Gas fuel station <br /> 22 Soil Definition Status The lateral and vertical extents of TPHg and benzene <br /> in soil have been defined around the USTs by borings <br /> SB-2 through SB-5 The lateral and vertical extents <br /> of TPHg, benzene, and fuel oxygenates in soil have <br /> been adequately defined in the vicinity of the <br /> dispensers by borings GP-3 through GP-6 The <br /> vertical extent of fuel oxygenates in soil near the <br /> USTs (presumed source area) is defined by CPT-1 <br /> and CPT-2 The lateral extent of fuel oxygenates in <br /> soil is defined by MW-5 through MW-10 and <br /> MW-12 through MW-15 <br /> 2 3 Separate-Phase Hydrocarbon No separate-phase hydrocarbons have been detected <br /> (SPH) Definition Status on site <br /> 2 4 Groundwater Definition Status TPHg and BTEX are consistently below reporting <br /> (TPHg/BTEX) limits, although some reporting limits are elevated <br /> Maximum historical concentrations detected are <br /> 183 ppb TPHg and 10 ppb benzene Detection linuts <br /> for TPHg currently range from <50 to <20,000 ppb <br /> and benzene detection limits range from <0 50 to <br /> <200 ppb <br /> 2 5 TPHg/BTEX Plume Stability and Because the detection linuts are elevated, it is <br /> Concentration Trends difficult to assess TPHg and BTEX plume stability or <br /> concentration trends However, these concentrations <br /> do not appear to be increasing <br /> 2 6 Groundwater Definition Status The lateral extent of MTBE is defined by wells <br /> (Oxygenates) MW-6, MW-8 through MW-10, and MW-12, and the <br /> lateral extent of TBA is defined by wells MW-3, <br /> MW-5 through MW-10, MW-12, MW-13, and <br /> MW-14 In the deeper zoite, MTBE and TBA were <br /> not detected in well MW-1 i at were present at 31 and <br /> 63 ppb,respectively, in well MW-15 <br /> 27 Oxygenate Plume Stability and MTBE and TBA show decreasing trends in the on- <br /> Concentration Trends site wells <br /> 28 Groundwater Flow Direction, Groundwater flow direction is predominantly to the <br /> Depth Trends and Gradient southeast Depth to water ranges from 46 7 to <br /> 54 6 fbg Current groundwater flow is influenced by <br /> pumping from well MW-4 <br /> 29 Stratigraphy and Hydrogeology The site is underlain primarily by alternating layers <br /> of silts and sands or silty sands to the total explored <br /> 10 <br />