Using Groundwater Model to Evaluate Remediation of RDX Residual Plume at Umatilla Chemical Depot, Herminston, Oregon

At the U.S. Army Umatilla Chemical Depot, the alluvial aquifer overlays fractured basalt formations.  The depot is located outside the towns of Hermiston and Umatilla in northeastern Oregon and about 3 miles south of the Columbia River.  During the 1950s and 60s, two unlined lagoons received waste water containing explosive contaminates.  The groundwater remediation treatment plan consisting of three extraction wells and infiltration galleries began operation on January 5, 1997.  Between 1997 and today, the existing remediation system has resulted in a significant reduction of the contaminant source.  This system has reached a point where the system was not efficient in the reduction of the remaining plume.  A finite element groundwater model was developed to evaluate several scenarios for generating more efficient means of the clean-up the remaining plume.  This paper summarizes the groundwater model that was developed and summarizes the scenario evaluations.