ARCHIVED REPORTS_XR0008006 - Laserfiche WebLink

Home Browse Search

Groundwater Concentrations Under a Worst Case Scenario As a worst-case estimate, the groundwater concentration of chromium was calculated assuming 100% of the metal in the sediments was transported into the groundwater (Table 3) The result of this calculation depends on the volume of water into which the metal is placed If it is assumed that all the metal moves into aquifer pores and dilution effects from groundwater flow are neglected, high groundwater metal concentrations result because of the aquifer's high solid to water ratio For comparison, Table 3 also shows the chromium groundwater concentration that would result if chromium in sediments at the ESL level were transferred into aquifer pores As shown by the high metal concentrations trations listed in Table 3, it is extremely unrealistic to assume that all of the chromium in the aquifer sediments will dissolve into the groundwater during ozone treatment Metals may be physically bound inside sediment particles or occur as mineral forms resistant to ozone oxidation At present, there is no basis for selecting what fraction, if any, of the sediment chromium would be mobilized by ozone treatment As noted earlier, a bench scale study of ozone reaction with aquifer sediments from the gasoline impacted zone would help predict the extent of metal mobilization during ozone treatment Geochemical Factors that Affect Water Quality and the Success of Ozone Treatment Water quality may be affected by ozone treatment This effect would be greatest if the aquifer were highly anaerobic, that is, methanogenic or sulfate reducing In this case, oxidation of reduced iron and manganese in the groundwater could lead to formation of insoluble iron oxide and manganese oxide particles that could conceivably affect aquifer hydraulic properties If sulfide minerals or dissolved hydrogen sulfide were oxidized, groundwater sulfate levels would rise increasing the overall dissolved solids in the groundwater Oxidation processes themselves generally release protons decreasing aquifer pH, although, Crimi et al (2003) reported both pH decreases and increases in different sediments treated with permanganate. Dissolution of carbonate and other minerals if present-in aquifer sediment may react with acidity produced by ozone treatment, helping to prevent a drop in pH Water extracts of aquifer solids contained 23 mg/L alkalinity reported as calcium carbonate (CaCO3) Assuming that all the pH buffering capacity in the aquifer is derived from groundwater alkalinity and from the water extractable alkalinity in the solid phase and assuming all the alkalinity measured in soil extracts from MW-9R is present in the solids as CaGO3, the aquifer could neutralize approximately 2,000 mEq/m3 aquifer from groundwater alkalinity and approximately 9,000 mEq/m3 aquifer from water extractable solid-phase alkalinity These calculations assume an aquifer porosity of 0 3 and a particle density of 2 65 g/cm3 A bench scale study, using materials from the gasoline impacted area, may help elucidate the actual changes in water quajity that could occur under ozone treatment Ozone will be consumed by the "reduction capacity" of the aquifer, lowering the ability of the oxidation treatment to remove target compounds -For-our-purposes,-the relevant-aquifer reduction-capacity is the -- -- G�Oocuments and 4 SetOngslcrtohnsonNr)osktop\Unocal\GeochemEvat—D November 2004 oc doc