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ASSOCIATES(YVATC I NC 2Cr04+ 3CaS5 + 8H2O -> 2Cr(OH)3 +3Ca(OH)2+4(OH)-+ 15S Eqn 2 CrT17 Cascade Crill S52-+31202 -+ S2032-+3S Eqn 3a 2Cr04_+ 3 S2032-+5H2O -> 2Cr(OH)3 +3SO42 +3S +4(OH)- Eqn 3b CrP7 Crill For CrVI reduction and stabilization, the manufacturer recommends using a sulfur to CrVI molar ratio of 10 According to the product literature Cascade (concentrated, as obtained from the manufacturer) contains 14 moles sulfur/gallon Thus, 0 071 gallons of Cascade is needed to treat 1 kg of CrVL which is equivalent to 0 27 ml Cascade/g CrVI However, Cascade is a non-selective reducing agent and may also react with soil, air and other metals It should be noted that the chronuum hydroxide formed by this treatment method is more soluble than an iron/chromium hydroxide However, better subsurface transport may be possible with Cascade® because it is slower to decompose than Is FeII The goals of the proposed treatability testing are to estimate the dose requirements for each reductant and to evaluate the effect of treatment on downgradient water quality . Methodology Sort and Water Buffermg Curves Because the reducing agents proposed can affect the pH of the soil and groundwater, buffering curves will be generated to determine how much reagent can be added without causing long-term effects Soil will be combined with dilute sulfuric acid (pH 1, pH 2, and pH 3) dilute sodium hydroxide (pH 9, 10, 11) in a 1 1 soil to liquid ratio and the pH of the aqueous phase monitored over time Groundwater will be titrated with dilute sulfuric acid and with dilute sodium hydroxide Clean site tap water will be titrated with dilute sulfuric acid (Groundwater will be titrated to estimate how much residual soil acidity or alkalinity it may neutralize, while clean site tap water will be titrated in order to determine how much acid will be needed if FeII is used as the reducing agent) Estinxa ion of Dose Requiremen&Effect on Downgra&ent Water Quality Batch tests will be conducted to estimate the amount of each reducing agent needed to reduce CrVI to below the clean-up criterion Tests will be performed on groundwater and on soil-groundwater slumes in order to determine whether soil affects the amount of reagent required The use of soil columns is not proposed based on the laboratory's experience (soil columns often do not exhibit sufficient permeability - even using pumping, it can take several hours or days to get enough water through a column to allow for all of the analyses required The correct number of pore volumes to pass through the column prior to collecting samples Is another issue) and the composition of the subsurface soils at the site which generally consist of silt and clayey silt . Two doses of each reducing agent will be used Controls in which clean water rather than reducing agent is added will also be performed After approximately 24 hours, the aqueous phases will be s lenvironmental1625$3\reportslRevisedWU-Bench testdoc 5