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Pilot Study Workplan November 7,2014 Project#54.62583.0001 Page 10 With a screen interval of 25 feet, a target treatment radius of 10-15 feet, and an estimated porosity 0.40, the theoretical volume, or the volume of water to be displaced by the Cascade®, is 785 cubic feet or 5,872 gallons. While the treatability study determined that a 0.8 ml/L dose of Cascade® reduced hexavalent chromium in soil by 98%, that study also determined that not only is the rate of Cascade® oxidation is a function of the amount of oxygen present in the matrix, but it is also a function of the degree of mixing of Cascade® in groundwater. Furthermore, as previously noted it has been shown that the reduction of hexavalent chromium by calcium polysulfide was non-stoichiometric. Consequently, Cardno ATC proposes to use a dose of 25 ml/L to ensure a concentration of Cascade® in groundwater sufficient for the in situ reduction of hexavalent chromium. To achieve the dose of 25 ml/L, approximately 1,500 gallons of Cascade® need to be injected into the approximately 6,000 gallons of groundwater surrounding the screen of MW-3 within a radius of 10-15 feet. Therefore, Cardno ATC proposes to inject approximately 1,500 gallons of Cascade® into monitoring well MW- 3, which should also extend the radius of influence beyond 10-15 feet. A packer will be used to seal off the well at the top of the well screen and the Cascade® will be injected under a maximum pressure of 40 pounds per square inch (psi). The 40 psi maximum injection pressure is intended to avoid fracturing the formation and is based on the assumption that fracturing can occur at pressures exceeded 1 psi for every foot of formation overburden. To ensure that the calcium polysulfide solution is fully injected into the formation, Cardno ATC proposes to inject approximately 100 gallons of chase water into MW-3 following the Cascade® injection. This volume is slightly more than the volume of the 4-inch well casing plus the approximate volume of a 10-inch annulus with a porosity of 30 percent. Cardno ATC will begin performance monitoring at the time the injection begins. Performance monitoring will initially involve monitoring field parameters through the flow cell from the observation wells. ORP and pH will be the primary parameters used to evaluate for the influence of Cascade®, and field parameters will be periodically measured in the deeper observation well until a drop in the ORP or an increase in pH indicates that well is within the influence of the Cascade® (as the Cascade® reduces hexavalent chromium a concurrent drop in ORP should occur, and Cascade® has a pH between 11.3 and 11.5). At that time the downhole pump will be successively inserted into the shallow observation well and field parameters measured. This will enable Cardno ATC to evaluate the distribution of Cascade® throughout the water column. Once the observation wells are under the influence of the Cascade® as evidenced by the ORP, groundwater samples will be collected from the observation wells for laboratory analysis of total and hexavalent chromium according to the same methods described above. The injection will continue until all 1,500 gallons of Cascade® have been injected into MW-3, after which the 100 gallons of chase water will be injected. If samples from the observation wells are collected before the injection is completed, Cardno ATC will continue to measure field parameters in the observation well exhibiting the highest ORP until the injection is complete. 6.5 POST-INJECTION MONITORING Cardno ATC proposes to conduct three post-injection monitoring events at intervals of one, three and six months following injection. These monitoring events are intended to determine if a rebound in hexavalent chromium concentrations occurs. In each monitoring event groundwater samples will be collected from the observation wells and from MW-3 using the low-flow sampling methods discussed above. Groundwater samples will be analyzed for total and hexavalent chromium according the same analytical methods discussed above. Post-injection monitoring will continue in MW-3 as part of regular semiannual monitoring at the site.