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i <br /> S EC ® R <br /> ARCO 595 t� <br /> May 5, 2004 <br /> Page 4 <br /> feet bgs The lateral extent of hydrocarbons adsorbed to soil has been defined by the existing <br /> monitoring well network The vertical extent of hydrocarbons adsorbed to soil has been delineated by <br /> deep soil borings PSB-1 and PSB-2 and deep monitoring wells DWM-1, DMW-2, and DMW-3 <br /> Historical soil analytical data is Included as Table 1 and historical soil sampling locations are Included <br /> In Attachment 2 <br /> Hydrocarbons In Groundwater <br /> Concentrations of TPHg, benzene, MtBE, and 1,2-DCA dissolved In shallow groundwater on January <br /> 8, 2004, are Illustrated on Figures 5 through 8, respectively Concentrations of MtBE and 1,2-DCA <br /> dissolved In deeper groundwater on January 8, 2004 are Illustrated on Figures 9 and 10, respectively <br /> Maximum dissolved concentrations In shallow groundwater have been observed In well MW-4 (now <br /> dry) The follow matrix outlines the delineation of the dissolved plume in both shallow and deep <br /> groundwater <br /> Delineation of the Dissolved Plume In Shallow Groundwater <br /> North South West East <br /> TPHg Delineated by Well Delineated by Well Delineated by Well Not Delineated <br /> MW-5(<50 ppb) MW-10(<50 ppb) MW-9(<50 ppb) <br /> (MCL = NA) <br /> Benzene Delineated by Well Delineated by Well Delineated by Well Not Delineated <br /> MW-8(<0 50 ppb) MW-3(0 68 ppb, MW-7(<0 50 ppb <br /> (MCL = 1 ppb) below MCL) <br /> MtBE Delineated by Well Delineated by Well Delineated by Well Delineated by Well <br /> MW-8(2 4 ppb, below MW-3(0 91 ppb, MW-9(all samples MW-1 (all samples } <br /> (MCL= 5 ppb) MCL) below MCL) below 1 ppb, below below 5 ppb below <br /> MCL) MCL) <br /> 1,2 - DCA Delineated by Well Delineated by Well Delineated by Well Not Delineated <br /> MW-8(<0 50 ppb) MW-10(<0 50) MW-9(no sample Laboratory detection <br /> (MCL = 0 50) detections above limits not low enough <br /> MCL) due to TPHg <br /> interference <br /> M <br /> Y <br /> d <br /> Delineation of the Dissolved Plume in Deep Groundwater <br /> North South West East a <br /> TPHg Adequately Delineated Delineated by Well Adequately Delineated Generally upgradient <br /> by Well DMW-1 (58 DMW-2(<50 ppb) by Well DMW-3(120 No deep wells t <br /> (MCL = NA) ppb) ppb) installed <br /> Benzene Delineated by Well Delineated by Well Delineated by Well Generally upgradient <br /> DMW-1 (<0 50 ppb) DMW-2(<0 50) DMW-3(<0 50 ppb) No deep wells <br /> (MCL= 1 ppb) installed <br /> MtBE Not Delineated Not Delineated Not Delineated Not Delineated <br /> (MCL= 5 ppb) <br /> 1,2 - DCA Not Delineated Not Delineated Not Delineated Not Delineated <br /> • (MCL = 0 50) <br /> I IARC0105951ReportslSde Conceptual Model doc <br />