Background/Objectives. While many regulatory documents now recommend a review of high-resolution site characterization (HRSC) alternatives and much of the environmental industry has seen the benefits of these practices, it can be difficult to appropriately design and optimize an investigation program to meet the needs of a particular site at a particular point in its lifecycle. Often the investigation and remediation goals are not understood to a fine enough point to allow for an HRSC program to run fully dynamically in the field, or for the resulting data to be put to its highest use in refining the conceptual site model and influencing remedy design. In this case study, an approach incorporating each of these methods yielded an efficient response to new site information that did not fit the existing conceptual site model (CSM).

Approach/Activities: On a site in North Carolina, a team from Duncklee & Dunham and Cascade Environmental teamed to use a dynamic Waterloo Advanced Profiling System (Waterloo^APS) program to understand a trend of increasing cobalt concentration in groundwater in a downgradient sentinel well. The resulting groundwater samples, Index of Hydraulic Conductivitiy (I_K), and vertical head data were incorporated into a the existing data set, which included concentration and head data from monitoring wells, geological information from soil borings, and hydrostratigraphy from HPT investigations. The combined data set was presented in three-dimensional visualization software and used to determine the extents and transport pathways of the cobalt impacts to groundwater. A set of monitoring wells were designed based on this model and confirmed the validity of the HRSC investigation. Finally, the updated CSM was used to design a new set of extraction wells to hydraulically contain the downgradient edge of the plume.

Results/Lessons Learned: When faced with new data that did not fit the existing CSM, an HRSC approach to improving the understanding of contaminant fate and transport at the site proved to be cost-effective and timely. Traditional methods of investigation were used in a limited manner solely to confirm the results of more advanced tools and to provide for long-term monitoring. Of particular impact was the combination of HRSC and three-dimensional modeling in aiding the design of alterations to the existing extraction well network.