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total mass of species in the aquifer that will react with ozone The solid phase is the most important reservoir of reduction capacity in the aquifer due to the high solid to liquid ratio (Barcelona, 1991) Organic matter is often found to comprise the majority of the aquifer reduction capacity, although, reduced iron and sulfide minerals may also contribute (Barcelona, 1991, Hartog, 2002) Since the organic matter content and concentration of reduced mineral species in sediments at the site is not known, the aquifer's reduction capacity with respect to ozone is best estimated by a bench scale study using aquifer materials from the gasoline impacted area Summary Metals concentrations in the groundwater collected from MW-1 and MW-3 and in aquifer sediments collected from MW-9R fall below relevant MCL or ESL levels In particular, no chromium was found in the groundwater Chromium levels found in sediments from MW-9R are consistent with the lower levels usually observed in sandy sediments, as found in this aquifer Chromium, if oxidized to chromate by ozone treatment, may be mobilized into the groundwater Adsorption to iron oxyhydroxide minerals will control chromate groundwater levels How ozone treatment enhances or decreases this adsorption process cannot be predicted from available information After ozone treatment is finished, it is expected that chromium groundwater levels will return to their pre-treatment state, that is no detectable chromium, as the aquifer redox returns to its pre-treatment state References Barcelona, MJ and TR Holm 1991 Oxidation-Reduction Capacities of Aquifer Solids Environmental Science and Technology 25 1565-1572 California Code of Regulations, Title 22 September 12, 2003 Division 4 Environmental Health, CHAPTER 15 Domestic water quality and monitoring Article 4 Primary standard-inorganic chemicals Section 64431 Maximum contaminant levels-in organic chemicals Cnmi, ML, and RL Siegrist 2003 Geochemical effects on metals following permanganate oxidation DNAPLs Ground Water 41(4) 458-469 CRWQCB 2004 Screeningfor Environmental Concerns at Sites with Contaminated Soil and Groundwater Volume 1 Summary Tier 1 Lookup Tables California Regional Water Quality Control Board, San Francisco Bay Region Interim final-July 2003 space (updated 2/4104) Hartog, N and i Gnffioen, and CH Van Der Weijden 2002 The distribution and reactivity of 02- reducing components in sediments from a layered aquifer Environmental Science and Technology 36 2338-2344 C`Documents and 55 November 2044 S ettmgslcgohnsonlDesktop\UnocaAGeochemEval_D oc doc �i