Management and remediation of fractured bedrock aquifers impacted with chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE), remain a significant environmental challenge for the Department of Defense (DoD). These challenges are due to a combination of the complex fracture flow field, uncertainties associated with contaminant distribution among fractures, microfractures, and the rock matrix, and ultimately the difficulties with understanding these complexities as they relate to remedial impacts on both short and long-term groundwater quality. The costs associated with drilling, testing, and monitoring in these fractured bedrock systems are also a great challenge for site management.
Dr. Charles Schaefer from CDM Smith has led a number of projects under both SERDP and ESTCP addressing contamination in fractured rock. He and his project teams have studied bioaugmentation as a cost-effective treatment for dense non-aqueous phase liquid (DNAPL) sources present in the fracture zones. They have also developed and evaluated a novel “push-push” remedial assessment technique, coupled with compound specific isotope analysis (CSIA), for use as a rapid and cost-effective means to assess the limits of in situ remediation in fractured bedrock systems.
The results of his projects have significantly improved the understanding of the relationships between DNAPL architecture and remedial performance. They have also provided detail on the source of observed rebound in rock matrices, improved estimates of natural attenuation timeframes, and provided a useful tool to confirm that abiotic dechlorination of TCE occurs in rock matrices.
These projects have demonstrated cost-effective technologies for the remediation of DNAPL at fractured rock sites. The resulting guidance and protocols from Dr. Schaefer’s projects will allow for improved evaluation and treatment of future applications of in situ treatment at DoD installations.
For his significant fractured rock work, Dr. Schaefer and his teams received the 2018 ESTCP Project-of-the-Year Award for Environmental Restoration for their projects titled Rapid Assessment of Remedial Effectiveness and Rebound in Fractured Rock and Designing, Assessing, and Demonstrating Sustainable Bioaugmentation for Treatment of DNAPL Sources in Fractured Bedrock.