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Item Evaluation ClriterW - Coh1r #s*W�ussi�ort <br /> Based on the pre- and post-remediation soil data, the <br /> extents of total petroleum hydrocarbons as gasoline <br /> (TPHg), benzene, and methyl tertiary butyl ether <br /> (MTBE) are defined both laterally and vertically <br /> Historical soil data tables and maps are presented in <br /> Attachment 1 <br /> 2 3 Separate-Phase Hydrocarbon Separate-phase hydrocarbons (SPH) were historically <br /> Definition Status observed in wells MW-2, MW-3, MW-4, and MW-7 1►1Gd"gym <br /> in 1989 and the early 1990s A maximum of 4 48 <br /> feet of SPH were recorded in well MW-2 in <br /> December 1989 SPH has not been observed in any <br /> site well since February 1993 An SVF system <br /> operated at the site from 1992 to 1996 and removed <br /> residual SPH SPH data are included in the Well <br /> Concentrations table in Attachment 2 <br /> 2 4 Groundwater Definition Status The highest TPHg and benzene concentrations were <br /> (TP11g/BTEX) detected beneath the current and former USTs TPHg <br /> and benzene are detected in groundwater to a <br /> maximum depth of 91 fbg The lateral extents of <br /> these constituents are defined in the shallow water <br /> zone by the existing monitoring well network The <br /> lateral extent of TP11g and benzene detected in <br /> CPT-a CPT-10, and CPT-11 at depths ranging from <br /> f 47 to!"g is undefined Their vertical extents are <br /> ylgy defined in the presumed source areas by the CPT <br /> I borings Figure 5 presents TPHg and benzene <br /> concentrations Groundwater data tables are included <br /> in Attachment 2 and TPHg and benzene <br /> isoconcentration maps are included in Attachment 3 <br /> 2 5 TPHg/BTEX Plume Stability and Groundwater data indicate that TPHg and BTEX <br /> Concentration Trends concentrations are decreasing and the plume is <br /> shrinking in the shallow water zone <br /> TPHg and benzene concentration graphs for select <br /> source area wells are included in Attachment 4 <br /> Based on these concentration reductions, TPHg and <br /> benzene concentrations should be near or below <br /> water quality objectives within the next few years <br /> Estimated times to reach water quality objectives are <br /> included in Attachment 4 <br /> 2 6 Groundwater Definition Status MTBE and tertiary butyl alcohol (TBA) source and <br /> (Oxygenates) distribution is similar to TPHg and benzene <br /> (Attachment 3) The extent of MTBE north of MW-9 <br /> and east of CPT-11 is not defined MTBE has a <br /> similar vertical distribution ingroundwater- with the <br /> 0778 2 <br />