WIDE Application for Subsurface Hydraulic Head Control

This paper addresses field testing and numerical modeling that investigated use of the Well Injection Depth Extraction (WIDE) technology for saturating a subsurface profile. Although not detailed in this paper, the purpose of delivering liquid to the unsaturated subsurface zone was to extract radioactive contaminants (primarily cesium) at the U.S. Department of Energy Columbus Closure Site's West Jefferson North (WJN) facility (JN-1 Abandoned Filter Bed). The objective of the field testing was to investigate injection flow rate distribution through the piping header and manifold assembly to the soil, investigate the rise in subsurface water table corresponding to pulse and gradual injection modes, and establish water table mounding with time. Results show that a pulse injection caused a localized rise in the subsurface water elevation with subsequent decline over 2–3 hours. A gradual injection leads to a more uniform rise in piezometric head albeit at a smaller magnitude. In one specific test, 4,164 liters of injected water resulted in a mound that extended approximately 10 m down gradient of the test pad area and 5 m up gradient. The maximum mounding front occurred approximately 2 to 3 hrs after completion of the injection cycle. Approximately 0.3 to 0.6 m of rise in subsurface water elevation was recorded with the gradual injection model. In this case, the impacted zone was contained within the area of injection (4.5 m x 4.5 m). Pulse injection from pumped delivery was determined to be more effective than gradual injection in rising and maintaining subsurface water elevations to levels necessary for saturation of soil containing the maximum cesium contamination. Modeling results using Seep/W Version 5 from Geo-Slope International compared well with field measurements.