PNNL

Abstract

To date, the United States Department of Energy (DOE) has strived to understand the scope of long-term stewardship at DOE facilities. This paper identifies several challenges and needed innovations to provide cost-effective long-term subsurface monitoring. These challenges are significant, as DOE has identified greater than 100 candidate sites that may require subsurface monitoring for long-term stewardship. This enormous stewardship mortgage may be reducible through 1) cost-effective application of high-quality emplacement techniques for state-of-the-art monitoring systems and 2) the development of improved or completely new approaches for monitoring the subsurface environment that demonstrate the data produced are equally representative of the subsurface conditions and comparable over the long term. Currently, and for the near future, the only reliable subsurface/groundwater plume monitoring and assessment technique is sample collection and analysis via wells. At present, no geophysical technique can replace this approach and in situ sensors are just beginning to augment, not substitute conventional sampling. Long-term performance of wells and/or monitoring systems relies on: 1) access consistent with a zone of interest and 2) delivering samples representative of that zone for measurement. Well designs must anticipate the future behavior of the aquifer, as well as maintain chemical and physical stability. Long-term well-based network vulnerabilities can be subdivided into various categories, such as changes in the groundwater level and/or flow; subsurface heterogeneities; biological, chemical or physical reactions between the well screen or filter pack and the aquifer; changes in up-gradient and down-gradient relationships; and catastrophic events. Given the expense of accommodating such changes, site-wide (large-scale) hydraulic management of the aquifer may become cost-effective.