ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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Source Area Remediation Effects of in-situ treatment at Industrial Avenue and Stockton Avenue source areas in the Upper and Intermediate aquifers simulated through 75% reduction of fixed TCE concentration value in source area cells during the first year of the model run. Following first year of model run, 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 Vertical transmissivity at municipal wells MW-4 conditions: and MW-6, and Neenah Paper Company wells TH-8, TH-10, S-1, S-2, S-3, S-4, S-5 adjusted to mitigate vertical migration at these locations. This scenario reduces the time needed to lower concentrations of TCE in the Upper Aquifer below 5 pg/I, primarily due to the effects of in-situ remediation and mass flux reduction at the Industrial Avenue source area. As with Scenario 2, predicted transport of TCE away from source areas decreases significantly in all aquifers, again primarily due to the reduction or elimination of pumping at municipal wells. The primary areas of TCE impacts and changes over time in predicted TCE distribution in the Upper Aquifer under this future modeling are illustrated in figures A-27 through A-30, in the Intermediate Aquifer in figures A-31 through A-34; and in the Lower Aquifer in figures A-35 through A-38. Figure A-39 shows the 3D distribution of TCE concentrations greater than 5 pg/L beneath the Study Area after 30 years. 2.5 Alternative 4 — Pump & Treat, In-Situ Remediation, and Institutional Controls Alternative 4 consists of the following key elements: oo Continued groundwater pump-and-treat at the Site from existing wells EU-3 and EU-4 for three years, oo In-situ chemical/biological remediation the Target Treatment Area; and oo Institutional controls. MODFLOW/RT3D simulated groundwater extraction at the existing Industrial Avenue treatment system with wells EU-3 and EU-4 at a pumping rate of 30 gpm each for three years. In this alternative, within the 150 ft. by 200 ft. Target Treatment Area, in the Upper Aquifer' (from approximately 50 to 90 feet bgs) in-situ chemical/biological treatment is simulated via a 75% reduction in mass flux from this source over the course of one year of the model simulation during the first year (year 4 of the model run) following the shut down of the Industrial Avenue extraction and treatment system. Municipal and private wells (MW-11, MW-9, and irrigation wells at Ripon Christian and Ripon Public schools, and the Caltrans well) are assumed no longer extract groundwater as part of the institutional controls proposed for this Alternative. a For purposes of numerical simulation,the Upper Aquifer in the 2007 Final Groundwater Model Report is divided into Layer 1 (0 to 28 feet bgs),Layer 2(28 to 50 feet bgs)and Layer 3 (from 50 to 90 feet bgs) 5