ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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6 injection, followed by a subsequent decline to background concentrations in the 0.5 mg/L to 2.5 mg/L range after week 8. This is indicative of the initial contribution of DO from the KMn04 injection, followed by a decline in DO as the potassium permanganate is consumed through chemical reaction with soils and/or TCE. The Eh field measurements followed a similar trend, where a large increase was observed from baseline levels (-29 to +77 mV) to post-injection levels that ranged from +400 to >+600 mV. The elevated Eh results then fluctuated after the initial increase in several pilot test wells except for monitoring wells EU-1 and EE-1 which consistently remained above +540 mV for 27 weeks. These two wells are closest to the injection locations and are the only wells that maintained elevated potassium and manganese concentrations, while simultaneously showing a decrease in TCE concentrations to near non-detect levels or below detection levels. 4.2 Evaluation of In Situ Oxidation of VOCs Using Permanganate TCE concentrations decreased in seven monitoring wells located within the pilot study area within two weeks of initiating permanganate injection. Concentrations of TCE in groundwater samples from some of the wells remained low after the first two weeks, and others showed varying degrees of rebound. Two wells, EE-1 and EU-1, produced groundwater samples with TCE concentrations that were 99% lower than baseline conditions for six months at distances of 19.9 and 15.6 feet, respectively, from the closest injection locations. After hydraulic mixing, EU-1 demonstrated some rebound in TCE concentrations. The following table summarizes TCE concentrations over the pilot study: Well Maximum 28 Weeks Minimum Max— Min ID TCE Conc. TCE Conc. (Ng/L) TCE Conc. Difference (Pg/L N /L in TCE Conc. N /L M-1 A 370 100 100 270 ED-1 360 220 5.5 355 ED-2 500 190 180 320 EE-1 270 < 0.5 < 0.5 270 EI-1 360 170 8.2 352 EU-1 250 82 < 0.5 250 EW-1 350 270 4 346 averse 348 147 33 315 Concentrations of the TCE daughter product cis-1,2-d ichloroethylene (cis-1,2-DCE) occurred at lower concentrations within the pilot study area. Analytical results indicated a drop in cis-1,2-DCE wherever TCE was oxidized by permanganate. The estimated TCE mass removal after six months was approximately 12 pounds of TCE. This calculation was made based on initial groundwater and soil concentrations of TCE, and average post-pilot study (28 weeks after injection) concentrations. The average changes in concentration were applied across an estimated 12,500 sq. ft. by 30 ft. thick volume, with an assumed aquifer porosity of 0.3, in order to arrive at the estimated removal of approximately 12 pounds'.