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Pilot Study Workplan November 7,2014 Project#54.62583.0001 Page 8 detection limit of 0.001 mg/L. In the presence of soil, Cascade® applied at a concentration of 0.4 ml/L decreased the hexavalent chromium concentration in groundwater from an initial concentration of 6.7 to 1.4 mg/L, and at an application concentration of 0.8 ml/L Cascade® decreased the hexavalent chromium concentration from 6.70 to 0.12 mg/L (Prima, 2005). These results represent efficiencies of 78 and 98 percent, respectively, for Cascade® in the presence of soil. While Cascade is less efficient in the presence of soil, the treatability study indicated this could be overcome by increasing the Cascade® concentration. The concentration of sulfate increased very little during the Cascade® tests, suggesting the end-product of Cascade® under these conditions is elemental sulfur, rather than sulfate. However, the presence of elemental sulfur prevented quantification of the amount of Cascade®remaining at the end of the testing period. Since the rate of oxidation of Cascade® is strongly dependent upon the amount of oxygen present and the degree of mixing, it is difficult to determine the amount of Cascade®that will be consumed by soil. The treatability study indicated that Cascade® did not have a significant effect on dissolved oxygen, methane, arsenic, copper, zinc or total organic carbon, nor did it generate methane, although in the presence of soil Cascade® did increase the dissolved manganese concentration. These results indicate that while Cascade® may reduce manganese, it appears to preferentially reduced hexavalent chromium over other potential oxidized species present in the subsurface. The soil reductant demand (SRD) for Cascade® could not be quantitatively determined in the treatability, study because of the rapid oxidation of Cascade® to elemental sulfur discussed above. However, the rate of Cascade® oxidation is a function of the amount of oxygen present in the matrix and the degree of mixing of Cascade® in groundwater (Prima, 2005), and a higher dose may be necessary for efficient in situ treatment. Concerning iron, the treatability study showed that Fe (II) also effectively reduced hexavalent chromium, and like Cascade® it was less effective in the presence of soil. However, as previously discussed, iron is not being considered for use at the site due to the potential for precipitation and subsequent aquifer "clogging," and because calcium polysulfide has proven effective at in situ applications. Finally, the treatability study showed that groundwater has little buffering capacity but the soil in the subsurface does have moderate buffering capacity. Specifically, the treatability study showed that application of the equivalent of approximately 10 mmol of Cascade® increased the pH to slightly over 10, but after 14 days the pH rebounded to 8.7 (Prima, 2005). Based on these results it is not anticipated that a significant or long term pH increase will result from application of Cascade® at the Diamond Foods site. However, if such an increase does occur groundwater can be neutralized by the addition of acid (Prima, 2005). 6.0 PROPOSED SCOPE OF WORK To evaluate the effectiveness of calcium polysulfide at reducing hexavalent chromium at the Diamond Foods site, Cardno ATC proposes to conduct a pilot test in which Cascade® solution would be injected into monitoring well MW-3 and the effects of the Cascade®would be monitored in MW-3 and an observation well nest to be installed near MW-3. Details of this proposed pilot test are provided below. 6.1 PILOT TEST SYSTEM Because the highest chromium impacts in groundwater at the site are in MW-3, Cardno ATC proposes to inject Cascade® directly into this well. The subsurface at the Diamond Foods site consists of lower conductivity materials and the Cascade® solution will likely have to be injected under pressure as opposed to being gravity fed. Specifically, well logs for monitoring wells indicate the lithology at the Diamond Foods site generally consists of alternating layers of sand, silty sand, silty clay and clayey silt. The well log for MW-3, which is