SX Tank Farm Interim Surface Barrier Vadose Zone Monitoring

Abstract

ii Abstract The Hanford Site, in southeastern Washington State, has 149 underground single-shell tanks to store hazardous radioactive waste. A number of these tanks and their associated infrastructure (e.g., pipelines, diversion boxes) have leaked. While some of the leaked waste has entered the groundwater, the majority still resides in the vadose zone. Corrective measures are being taken to mitigate the groundwater impacts from past leaks and spills from contaminants that still reside within the vadose zone. Washington River Protection Solutions, LLC, constructed three interim surface barriers (identified as south, north, and expansion barriers, respectively) in 2018 over the 241-SX Tank Farm to minimize the migration of the residual contaminants in the vadose zone. Two monitoring instrument nests were installed in the south and north barriers, respectively, in 2018 and the data acquisition system was put into operation in September 2019. This document summarizes the monitoring methods, the instrument calibration and installation, and the vadose zone monitoring plan for the interim barriers in the SX tank farm. PNNL-PNNL-29136 RPT-DVZ-SX-0002