Oxidation-reduction capacities of aquifer solids

Measurements of the oxidation (i.e., of aqueous Cr{sup 2+}) and reduction (i,e., of aqueous Cr{sub 2}O{sub 7}{sup 2{minus}} and H{sub 2}O{sub 2}) capacities of aquifer solids and groundwater have been made on samples from a sand-and-gravel aquifer. The groundwater contributed less than 1% of the system oxidation or reduction poising capacity. Reduction capacities averaged 0.095, 0.111, and 0.136 mequiv/g of dry solids for oxic, transitional, and reducing E{sub h} conditions, respectively. Measured oxidation capacities averaged 0.4 mequiv/g of dry solids over the range of redox intensity conditions. These capacities represent considerable resistance to the adjustment of redox conditions even at uncontaminated sites. Hydrogen peroxide reduction to microbially mediated decomposition. This study indicates the need for closer scrutiny of the predictability and cost effectiveness of attempts to manipulate redox conditions in poorly poised aquifer systems.