Vadose Zone Hydrogeology Data Package for the 2004 Composite Analysis

Abstract

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Combined Estimation of Hydrogeologic Conceptual Model, Parameter, and Scenario Uncertainty with Application to Uranium Transport at the Hanford Site 300 Area

“…None of these measurements were on 300 Area sediments. As part of the composite analysis being conducted for the Hanford Site, best estimate K d values were selected for various waste chemistry/source categories and impact categories (Last 2004). Estimates of minimum and maximum values were also provided.…”

Vadose Zone–Attenuated Artificial Recharge for Input to a Ground Water Model

“…In the case of a surface water body, artificial recharge is reduced by evaporation. In our calculations, this is accounted for by deducting the evaporation calculated from a combined aerodynamic and energy balance Penman equation in a separate set of calculations reported in Last et al (2006a). The calculated monthly evaporation is subtracted from the liquid discharge record and the resulting quantity introduced as a time‐dependent liquid source in the vadose zone simulation.…”

“…From 1944 to 2006, more than 1.5 billion m 3 of water was extracted from the Columbia River, transported to various facilities, and subsequently disposed of by infiltration in ponds, trenches, or reverse wells as a consequence of production, environmental restoration, and sanitary disposal operations. Most of these discharges occurred in the 200 East and 200 West Areas (Figure 2) in the area known as the Central Plateau that overlies a vadose zone that is typically 80 to 90 m thick (Last et al 2006a). These discharges were significantly greater than the volume of recharge from natural sources during this period.…”

Performance Assessment Monitoring Plan for the Hanford Site Low-Level Burial Grounds

“…These data packages are being prepared to provide conceptual models and numerical input parameters for the Systems Assessment Capability (SAC, e.g., Bryce et al 2002). The numerical simulations include modules for atmospheric data (Napier and Ramsdell 2004), waste site locations and environmental settings (Last et al 2004a), Columbia River dynamics (Rakowski et al 2004), vadose-zone hydrology (Last et al 2004b), and groundwater (e.g., Cole et al 2001). The performance assessment, composite analysis, disposal authorization statement, closure plan (Pratt and Skelly 2000), waste acceptance requirements, and monitoring plan are part of the radioactive waste management basis (DOE M 435.1).…”

“…Sources of natural recharge to the uppermost-unconfined aquifer system are infiltration and runoff of precipitation and runoff on the reaches of the Yakima and Columbia Rivers. The movement of precipitation through the vadose zone has been studied at several locations on the Hanford Site (e.g., Gee 1987; Routson and Johnson 1990;Rockhold et al 1990;Fayer et al 1991;Gee et al 1992;Fayer and Walters 1995;Last et al 2004b), with the general conclusions being that very little infiltration occurs where the soil is relatively fine grained and deep-rooted vegetation is present. Where soil is coarse and vegetation is shallow rooted or absent (e.g., backfilled areas with no cap), infiltration can be considerably higher.…”