Enhanced 3D Visualizations to Support CSM Development and Remedial System Optimization

Three-dimensional modeling of hydrostratigraphy and contaminant distribution was used to refine the conceptual site model (CSM) and optimize an in-situ bioremediation remedy at a chlorinated solvent impacted site in San Leandro, California. The original CSM relied on conventional investigation methods such as visual borehole logging and groundwater sampling from site monitoring wells. Two-dimensional analysis of available data did not capture the lateral continuity of higher transmissivity hydrostratigraphic units responsible for the bulk of solute transport. After four years of full-scale remediation and incomplete remediation at some locations, additional site investigations using high resolution methods such as cone penetrometer (CPT), hydraulic profiling tool (HPT) and membrane interface probe (MIP) were employed to gain an improved understanding of site hydrostratigraphy and preferred groundwater migration pathways. Historical and more recent high resolution data were integrated into a three-dimensional model using Environmental Visualization Software (EVS). Three-dimensional geologic modeling indicated lateral continuity of hydrostratigraphic units previously thought to be disconnected, providing a refined CSM to revisit nature and extent based on historical contaminant concentrations. The optimization of the remedial systems included the installation of additional infrastructure and abandonment of infrastructure deemed no longer necessary for operation and monitoring of in-situ treatment zones and remaining impacts. Another high resolution MIP investigation is currently planned for early 2011 to be used for remedy optimization in the source area. Additional added value of using a three-dimensional model has included a streamlined well screen selection process for infrastructure planning, visualization of the radius of influence of injected solutions, as well as reduced risk associated with potentially cross-screened wells. Three-dimensional geologic modeling at the site has been well suited for an adaptive approach to CSM development and the optimization of an in-situ bioremediation remedy.