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TENTATIVE <br /> Constituent Units Concentration Water Reference <br /> Range Quality Limit <br /> Human Assessment <br /> Iron 1 33 to 132 300 California Secondary MCL <br /> Manganese µg/1 Non-detect to 50 California Secondary MCL <br /> 20 <br /> Total Dissolved mg/l 185-450 500 California Secondary MCL <br /> Solids <br /> Nitrate(as mg/1 12 to 41 10 California Primary MCL <br /> nitrogen) <br /> Sulfate -mi-g/1 13 to 26 250 California Secondary MCL <br /> 11. The purpose of the Phase 1 pilot study is to demonstrate that injecting calcium polysulfide into <br /> groundwater will effectively reduce hexavalent chromium to trivalent chromium, and to assess the <br /> radius of influence of a single injection of calcium polysulfide/ethanol. The purpose of the Phase <br /> 2 pilot study is to demonstrate the effectiveness of the direct multiple-injection remediation <br /> approach and the persistence of reducing conditions in the shallow groundwater plume zone. <br /> 12. During the Phase 1 pilot study,the Discharger proposes to inject up to 5,000 gallons of 3 percent <br /> calcium polysulfide solution and 50 gallons of ethanol into boring INJ-1 from 60 to 80 bgs over a <br /> period of two days. In addition to the calcium polysulfide and ethanol, sodium bromide, a non-toxic, <br /> inorganic tracer will be included in the solution at a concentration of 200 milligrams/liter(mg/1). The <br /> tracer will be used to demonstrate that the observed reduction in hexavalent chromium concentrations <br /> is due to chemical reduction rather than dilution by the injected solution. Temporary wells including <br /> an injection well and six monitoring wells will be installed to supplement the existing monitoring well <br /> network. Attachment B, a part of this Order,illustrates the location of the injection well and monitoring <br /> wells. <br /> 13. The Discharger submitted chemical analyses of the calcium polysulfide mixture and ethanol solution. <br /> Metals and minerals were not present at detectable levels in either the calcium polysulfide mixture or <br /> the ethanol solution. <br /> 14. During Phase 1, groundwater will be monitored for hexavalent chromium(Cr VI),total Cr,bromide <br /> (Br), copper(Cu), arsenic(As), iron(Fe),manganese(Mn), sulfate(SO4),Nitrate(NOA and Total <br /> Dissolved Solids (TDS)by laboratory analysis. The oxidation/reduction potential (ORP)will be <br /> measured in the field along with dissolved oxygen(DO),electrical conductance(EC),temperature, and <br /> pH. Monitoring will begin prior to the calcium polysulfide/ethanol injection, and will continue at <br /> periodic intervals after injection until it is no longer deemed necessary.Phase 1 will be deemed <br /> complete when monitoring shows that the chemical reaction of hexavalent chromium with the injected <br /> solution is complete as demonstrated by stabilized hexavalent chromium levels, and the radius of <br /> influence of the injected solution is determined. Monitoring will continue to assess long-term potential <br /> geochemistry changes. <br /> 15. During the Phase 2 pilot study, the Discharger proposes to install up to 75 direct injection points <br /> into one to four treatment zones based on the results obtained from the Phase 1 study. The <br /> injection points are intended to encompass the width of the shallow chromium groundwater plume <br /> upgradient of the highest hexavalent chromium concentration areas. The application area, <br /> treatment zones, and injection grid are illustrated in Attachment C, a part of this Order. At each <br /> injection point, approximately 5,000 gallons of 3 percent calcium polysulfide solution with 50 <br />