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Christy Woodward <br />July 31, 2008 <br />Page 11 <br />For vadose zone leachate, adsorption is one of the most dominant processes controlling <br />natural attenuation. Adsorption is a process where dissolved metals or metalloids attach to <br />the surface of solid particles and are removed from the dissolved phase. Adsorption can be an <br />important attenuation mechanism to reduce the potential for constituents mobilized from <br />development rock to affect either surface water or groundwater resources. Evaluation of the <br />geochemical sorption potential of soils and shale underlying the development rock piles <br />facilitates incorporation of this important attenuation mechanism into evaluations of fate and <br />potential transport of constituents from the development rock piles. <br />The geochemical sorption potential is expressed in terms of a value called the distribution <br />coefficient (Kd), which can be expressed as follows: <br />Kd = <br />Concentration of constituent adsorbed to the solid <br />Concentration of constituent in solution <br />This value is used to evaluate potential natural attenuation of constituents as development <br />rock leachate moves through soil or shale underlying or adjacent to the piles. Determination <br />of the geochemical sorption potential, will be determined using a modified ASTM D4646-03 <br />method(ASTM 2004). This method involves a series of batch-type experiments in which a <br />solution containing known concentration of a constituent of interest is equilibrated with a <br />known mass of soil or rock. After a 24-hour mixing period, the mixture is assumed to have <br />equilibrated and the supernatant is extracted from the test vessel, filtered, and analyzed for <br />the constituent(s) of interest. The method measures adsorption of the constituent of interest to <br />the soil or rock during the 24-hour test. This evaluation will include a series of batch tests to <br />measure adsorption at various concentrations and/or solid to solution ratios. Selected <br />constituents and further specific details of this method (e.g. type of solution, concentrations, <br />etc.) will be included as an addendum to this data collection work plan. The CDM Denver <br />Laboratory will perform the geochemical sorption potential tests, and the supernatant <br />samples will be submitted to Energy Laboratories for analysis. <br />The evaluation of geochemical sorption potential data will be based on a geochemical mixing <br />cell model approach, which simulates the natural fate and transport processes. The mixing <br />cell model approach uses estimated water infiltration and site specific Kd values to estimate <br />natural attenuation that would occur as the water moves through soil or rock zones <br />underlying or adjacent to the development rock piles. USCS field data will be used in <br />unsaturated flow modeling to estimate the infiltration through the development rock area. <br />Evaluation of the fate and transport processes based on determination of soil geochemical <br />sorption potential and associated geochemical modeling presents a more robust evaluation of <br />the potential for development rock leachate to affect either surface water or groundwater <br />resources. <br />0:\64986 - Denison\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.1 - Soil Ore Rock Data Collection PlanTinal Denison Sunday Mines Group Soil Ore Rock Data <br />Collection Work Plan.doc