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CvvATC • A S S O C I A T E S I N C 37 feet The soil samples collected from beneath Vault 8 will be analyzed for total and hexavalent chronuum, alkalinity, ammonium/ammonia, arsenic, total organic carbon, copper, dissolved and total iron, dissolved and total manganese, methane, nitrate, dissolved oxygen, oxidation-reduction potential, sulfate, and zinc Soil collected from beneath Vault 8 will also be used for bench scale testing as described below All of the groundwater monitoring wells (MW-1 through MW-9) will be sampled for the constituents listed in the preceding paragraph to provide for baseline constituent concentrations Sampling of the monitoring wells for baseline characterization can be conducted commensurate with quarterly groundwater monitoring activities An unpreserved groundwater sample (3 liters) will be collected from MW-3 after the well has been purged of three well volumes using a submersible pump, and one liter of unpreserved tap water will be collected from the facility and delivered to the laboratory to be utilized for bench scale testing as described below The volume of soil and groundwater samples collected will be based on laboratory requirements BENCH SCALE TESTING Recent groundwater samples collected from the site contained up to 3 8 mg/1 of CrVL Two compounds that can reduce and stabilize CrVI and are suitable for infection into the subsurface are ferrous iron(Feil)solution and calcium polysulfide(Cascade solution) The following discussion is based on information was obtained from PRIMA Environmental • Ferrous Iron Solution Fell is prepared by dissolving ferrous sulfate heptahydrate in pH2 water (acidified with sulfuric acid) Generally, concentrated stock solution is prepared and a small amount is added to soil and groundwater to obtain the desired initial concentration FeII reacts with CM to form CrIH, which co-precipitates as an iron/chromium hydroxide when the pH is greater than about 5 (Eqn 1) CrVI+3Fell—> CrIlI+3FeM —i' iron/chromium hydroxides Eqn 1 Based on this stoichiometry, 3 2 grams (g) Fell are needed to reduce 1 g of CrV1 Fell must be added as an acidic solution (pH 2-4) in order to prevent it from oxidizing to FeIII, which is ineffective for treating CrVI In general, the buffering capacity of site soil and groundwater will allow pH to return to normal once application is complete As the pH increases to greater than about pH 5, the CrIII will co- precipitate with iron to form tron/chromium hydroxides, which are typically more stable (less soluble) than chromium hydroxide Excess iron will also precipitate as iron hydroxide [Fe(OH)3] Calcium Polysulfide(Cascade I Cascade is a purchased product that is used as received Cascade reduces CM to CrIII by a variety of chemical reactions that ultimately produce solid chromium hydroxide, sulfate, and sulfur Intermediate products may include sulfide and thiosulfates Concentrated Cascade is basic (pH 10), but the injection pH will be lower because Cascade is normally diluted prior to use In addition, the natural buffering capacity of site soil and groundwater will often minimize long-term changes in pH S lenvirornnentai1625831repoetSaCVLsedWKP-Bench testdoc 4