ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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biodegradation rates, etc.) were established for TCE as part of the original model development and calibration process'. The scenario simulates predicted groundwater elevations and TCE concentrations via a transient model run which is run for 30 years into the future. The following table summarized the key boundary conditions and/or TCE source area conditions employed in the simulation of the Revised Feasibility Study Alternative 1: Table Al: Alternative 1 MODFLOW/RTM Modeling Inputs Model Boundary Condition/Property Conditions in Alternative 1 Modeling Scenario Domestic/Agricultural Pumping Wells Average quarterly extraction rates from calendar year 2008 used throughout transient model run. Remediation Wells All Nestle treatment system wells (EU-3, EU-4, E-2, E-6) assumed OFF throughout transient model run. Source Area Remediation No reductions in source mass flux implemented via RT3D boundary conditions. All TCE source area (fixed concentration) cells assumed to degrade at base model-established intrinsic biodegradation rate k = 0.000316 day-'). Other adjustments to base period None. conditions: The MODFLOW/RT3D model simulated the No Action alternative as described above. The primary areas of TCE impacts and changes over time in the Upper Aquifer (i.e. layer 3 in the model) under this future modeling are illustrated in figures A-1 through A-4; in the Intermediate Aquifer (i.e. layer 5 in the model) in figures A-5 through A-8; and in the Lower Aquifer (i.e. layer 7 in the model) in figures A-9 through A-12. Figure A-13 shows the 3D distribution of TCE concentrations greater than 5 pg/L beneath the Study Area after 30 years. 2.3 Alternative 2 — Pump & Treat, Intrinsic Remediation, and Institutional Controls Alternative 2 consists of the following key elements: oo Continued groundwater pump-and-treat at the Site from existing wells E-2, E-6, EU- 3 and EU-4, oo Implementation of additional groundwater extraction and treatment wells, oo Intrinsic Remediation, and oo Institutional controls, including decommissioning of vertical-conduit wells, water supply replacement, and municipal pumping coordination Alternative 2 assumes that current technologies in use at the Site continue as implemented as part of Interim Remedial Action Plan for 230 Industrial Avenue and five additional extraction and treatment wells will be installed in the Intermediate and Lower aquifers. Institutional controls would be implemented, including elimination of vertical conduits within or near the Site, coordination of pumping locations and rates with the City, and replacement of water supply wells as necessary. 2