Whose Fault is it? Structural Geologic Controls on Remediation of Hydrocarbon Contaminants in Southern California

Groundwater remediation in fractured bedrock can be extremely challenging, impracticable, or even impossible within reasonable timeframes due to unmapped structural controls on groundwater flow and contaminant transport. California’s geology in particular is rich with tectonic activity including faults, folds and other deformation structures that influence remedy effectiveness. Such features complicate the development of accurate conceptual site models and evaluation, selection, and implementation of effective remediation strategies. Hence, petroleum hydrocarbon-impacted sites in California slated for remediation must consider structural geologic features during design and implementation. Failure to account for these controls during remediation can result in remedies that are ineffective and can exacerbate problems. In this work, we re-designed groundwater remediation programs at hydrocarbon-impacted sites where previous remedial efforts were thwarted because they did not consider structural geologic controls and resulted in the implementation of costly and ineffective remedial strategies.

We evaluated the influence of geologic faults on remedial effectiveness at the field scale using technologies including bedrock coring, downhole acoustic and optical televiewers, and high-resolution groundwater monitoring devices, as well as standard site investigation methods such as fracture analysis, hydraulic testing, geochemical evaluations, and laboratory analysis of intact rock samples. The new information was used to re-conceptualize the site, evaluate failure modes, and re-design the final remedial programs.

Results showed that geologic faults at the two sites exerted significant structural controls on fate and transport and resulted in complex plume shapes and migration patterns that would not be predicted under an assumption of homogeneous and isotropic conditions. Not considering these geologic structures during site characterization and initial remedial design and implementation resulted in the need to re-design remedial strategies. New approaches to remediating these sites that include the influence of geologic structures have resulted in successful remediation programs. The presentation will include recent data, analysis, and descriptions of remedial programs.