ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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2.4 Alternative 3 — Pump & Treat, In-Situ Chemical or Biological Treatment, Intrinsic Remediation, and Institutional Controls Alternative 3 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 for five years, oo In-situ chemical/biological treatment of Industrial Avenue and Stockton Avenue treatment systems source areas; oo Intrinsic Remediation, and oo Institutional controls, as per Alternative 2 (above). In this alternative, MODFLOW/RT3D simulated groundwater extraction at the existing Industrial Avenue treatment system with wells EU-3 and EU-4 pumping at rates of 30 gpm each and extraction at the existing Stockton Avenue treatment system at a rate of 60 gpm at well E-2 and at 300 gpm at well E-6 for the first five years. In the Upper and Intermediate aquifers within the Industrial Avenue and Stockton Avenue treatment system areas, in-situ chemical/biological treatment is simulated via a 75% reduction in mass flux from these sources. This reduction is assumed to occur over the course of the first year of the model simulation. Figure 10 in the Revised Feasibility Study indicates the general location of the Industrial Avenue source area where the effects of theoretical in-situ chemical/biological are simulated in this modeling scenario. Following this simulation period of active in-situ mass removal (and mass flux reduction), TCE source concentrations cells were assumed to degrade at the base model-established intrinsic biodegradation rate of k = 0.000316 day'. The scenario simulation predicts groundwater elevations and TCE concentrations via a transient model run which runs 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 3: Table A3: Alternative 3 MODFLOW/RT3D Modeling Inputs Model Boundary Condition/Property Conditions in Alternative 3 Modeling Scenario Domestic/Agricultural Pumping Wells Pumping terminated for entire model run at wells MW-3, MW-11, MW-7, MW-9, and irrigation wells at Ripon Christian and Ripon Public schools (RC- 1, RC-2, RPS-1, and RPS-2). Average quarterly extraction rates from calendar year 2008 used for all other domestic and agricultural wells throughout transient model run. Remediation Wells Extraction wells EU-3 and EU-4 (Upper Aquifer IRAP wells) assumed to continue pumping at 30 gpm for the first 5 years. Extraction wells E-2 and E-6 are assumed to continue at 60 gpm and 300 gpm, respectively, for the first five years. All extraction wells (EU-3, EU-4, E-2 and E-6) assumed OFF beginning in year 6 through the remainder of the transient model run. 4