, the Pacific Northwest Laboratory has been conducting a geohydrologic in
This report was .prepared as an account of work sponsored by an agency of t h e United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for t h e accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by t h e United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.. . DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Preface This report was originally published in May 1993 as a thesis for the degree of Master of Science with a major in hydrology through the University of Idaho. Research for the report was conducted between June 1989 and May 1990. The report contains valuable Wrmation on the hydrogeology along the southern boundary of the Hanfbrd Site; therefbre, the GroundWater Surveillance Project agreed to publish it as a Pacific Northwest Laboratory technical report. Because the report was published in 1993, references are made to activities, organizations, and/or previous investigations that were pertinent at the time, but may no longer be applicable, or have since been updated. Hence, the report remains essentially as it was originally written.
Potential leak detection, monitoring, and mitigation (LDMM) techniques are being developed to support Hanford single-shell tank (SST) retrieval operations. In July and August 2001, Pacific Northwest National Laboratory (PNNL) demonstrated LDMM technologies for CH2M HILL Hanford Group, Inc. (CHG) at the Mock Tank Site in the 200 East Area as part of a tank leak detection demonstration (TLDD). These subsurface air flow and extraction technologies (collectively referred to as SAFE) use air injection and extraction wells, creating an advective air flowfield beneath a tank. SAFE includes the following nine technologies: Leak detection: in-tank tracers, flowfield disturbance, radon displacement, and tank waste vapor Leak monitoring: the partitioning tracer and reactive tracer methods Leak mitigation: soil desiccation before and after leakage and in situ gaseous reduction Subsurface characterization: interfacial tracers. Of this suite of technologies, four were demonstrated in fiscal year (FY) 2001: in-tank tracers, flowfield disturbance, the partitioning tracer method, and soil desiccation. This report provides an overview of these SAFE technologies and describes the FY 2001 Mock Tank Site demonstration activities and results. TLDD Activities at the Mock Tank Site were organized around four scheduled injections of a leak simulant solution that was allowed to drain into the subsurface via an access point in the center of the tank. A total of 3495 gal was leaked. At the time, the first and third injections were blind. In-tank tracers employ gases or volatile liquids having appropriate partitioning coefficients with water and brine to allow transport with a tank waste and the ability to be readily stripped from the leaked tank waste by a subsurface air flowfield. The concept is for tracers to be added to the tank during waste dissolution operations. Detection in the subsurface advective flow stream indicates a tank leak. The intank tracers used in FY 2001 include nitrous oxide, difluoromethane, and chlorodifluoromethane. Although the in-tank tracer method is under development and the testing used a different protocol, leak detection was achieved by this method all three times after only 135, 120, and 150 gal of solution entered the subsurface. Based on the field testing results and additional laboratory experiments and method development, realistic leak detection sensitivity using the in-tank tracer method could ultimately be in the range of 10 to 100 gal for a full-size SST. However, this depends on several factors, including hydraulic flow and transport properties not fully evaluated in the FY 2001 program. Flowfield disturbance is a leak detection technology based on changes in subsurface air flow behavior due to changes in pneumatic conductivity that result from liquid infiltrating into the subsurface. Conservative tracers such as methane and pentafluoroethane are used. The tracer elution curves are analyzed for perturbations resulting from leak-induced porosity changes in the swept pore volume under a tank. Varying a...
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