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Contaminants disposed of at the land surface must migrate through the vadose zone before entering groundwater. Processes that occur in the vadose zone can attenuate contaminant concentrations during transport through the vadose zone. Thus, quantifying contaminant attenuation and contaminant transport processes in the vadose zone, in support of the conceptual site model (CSM) and fate and transport assessments, is important for assessing the need for, and type of, remediation in the vadose zone and groundwater. The framework to characterize attenuation and transport processes provided in U.S. Environmental Protection Agency (EPA) guidance documents was used to guide the laboratory effort reported herein.PNNL-26208 RPT-DVZ-AFRI-037 v all samples. In terms of desorption versus adsorption K d values, there was no clear trend across all of the samples.

Revision 1 of this document includes updates to the text and added descriptions of studies that were applied to address some of the data gaps identified in Revision 0. Descriptions of the changes are provided below. Changes to Existing Sections • The summary indicates that Revision 1 contains new information and updated text. • Section 1.0 (introductory paragraph) was updated to indicate that Revision 1 contains new information and updated text. PNNL-24709, Rev. 2 RPT-DVZ-AFRI-030, Rev. 2 vi • Section 2.3.5 was added to describe the results of experiments to evaluate formation of precipitates incorporating iodate during calcite precipitation. Previous literature information about coprecipitation of iodate and calcite from Revision 0 was included in this new section. • Section 3.1.2 was added to describe the results of a vadose zone modeling analysis of the 129 I source areas for the 200-UP-1 operable unit.