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S E C O R
<br /> • 2003 Feasibility Study Report and Site Assessment Work Plan
<br /> July 18, 2003
<br /> Page 9
<br /> 3.2 Groundwater Contamination
<br /> The highest reported concentrations of TPHd, TPHg and MtBE in groundwater at the site were
<br /> 1,900,000, 740,000, and 45,000, respectively. These concentrations were detected in the shallow
<br /> groundwater (Upper A-Zone and A-Zone) around the loading rack area and near Tank 137.
<br /> SPH has historically been detected in wells MW-1 UA, MW-3UA, MW-7A, MW-8A, MW-14A, MW-
<br /> 15A, MW-16, and MW-36UA through MW-42UA. These wells are located around the loading rack
<br /> area and near tank 137. During the first quarter of 2003, SPH was detected in monitoring wells MW-
<br /> 15A, MW-36UA, MW-37UA, MW-38UA, MW-40UA, and MW-42UA ranging from 0.01 feet to 0.28
<br /> feet. The maximum SPH thickness was measured in MW-40UA at 0.28 feet (SECOR, 2003c).
<br /> Groundwater at the site has been separated into three water bearing zones (Upper-A Zone, A-Zone,
<br /> and B-Zone). In the shallow aquifers (Upper A-Zone and A-Zone), concentrations of TPHd, TPHg
<br /> and MtBE are not defined down-gradient of the site. During 1Q03, concentrations of TPHd, TPHg,
<br /> and MtBE were reported in a down-gradient perimeter well (MW-47A) at concentrations of 700,ug/I,
<br /> 2,800 ,ug/I, and 8,700 ,ug/I, respectively. However, groundwater monitoring data for off-site
<br /> monitoring wells and grab samples collected in the adjacent field indicate that concentrations of
<br /> TPHd, TPHg, and MtBE are generally delineated in the down gradient direction. In the B-Zone,
<br /> concentrations of TPHd, TPHg, and MtBE appear to be defined downgradient of the site. During the
<br /> first quarter of 2003, highest concentrations of TPHd, TPHg, and MtBE in the B-Zone were 530 Ng/I,
<br /> <50,ug/I, and 58 Ng/I, respectively.
<br /> The vertical extent of hydrocarbons in groundwater is defined by B-Zone wells MW-12B, MW-13B,
<br /> MW-22B, MW-23B, MW-50B, and MW-64B. These wells are screened from approximately 55 feet
<br /> bgs to 65 feet bgs.
<br /> Groundwater analytical data, including tables and figures, presenting the hydrocarbon distribution in
<br /> groundwater are presented in Attachments C and F, respectively.
<br /> 4.0 CONTAMINANT FATE AND TRANSPORT
<br /> The objective of performing a fate and transport model is to estimate the migration of hydrocarbon
<br /> compounds in the saturated zone. Analytical results from soil and groundwater samples collected at
<br /> the site indicate the presence of petroleum hydrocarbons in groundwater beneath the site. Due to
<br /> the presence of these hydrocarbon constituents, chemical fate and transport modeling in soil was
<br /> conducted to evaluate the potential of future migration of the groundwater plume. Results from this
<br /> modeling exercise can then be used in the Risk-Based Corrective Action (RBCA) process. This
<br /> section presents the methodology and results of the fate and transport modeling conducted for the
<br /> Site.
<br /> 4.1 Contaminant Fate and Transport Properties
<br /> The following sections describe the components that control or affect the fate and transport of
<br /> contaminants that are dissolved in groundwater. The chemicals of concern (COC) consist of TPHg,
<br /> TPHd, and MTBE;each are considered to be light non-aqueous phase liquids (LNAPLs).
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