Bioaugmentation for Groundwater Remediation of Mixed Chlorinated VOCs in a Fractured Shale Aquifer

Bioaugmentation technology was applied to a mixed plume of chlorinated ethenes and methanes, primarily dissolved trichloroethene (TCE) and carbon tetrachloride (CTC), in a residual source area at the head of a 132-acre plume. This study demonstrates the notable effectiveness on CTC and chloroform in fractured rock, the challenges with commingled TCE, the importance of high-resolution hydrogeologic characterization in remedial design, and the need for targeted and advanced performance monitoring.

The mile-long commingled VOC plume in bedrock extends through a densely populated area located in the Newark Basin of northern New Jersey where residential wells are still in use. The primary reason bioaugmentation was chosen was the lack of naturally-occurring bacteria in the bedrock aquifer, unlike the overburden aquifer. The goals of bioaugmentation were to reduce the time and cost associated with bioremediating the residual mass, to mitigate contaminant mass-flux and to demonstrate the effectiveness of bioaugmentation as a potential remedy scalable to larger areas.

The design basis was a high-resolution mapping of the fracture network, which includes bedding plane partings as well as tectonic fractures. Using hydraulic conductivity data from discrete fracture zones gathered in part from tracer studies, over 8,500 gallons of customized EVO products, with suitable droplet sizes tailored to specific fracture zones, were injected in November 2015. The EVO was augmented with SDC-9, a DHC-containing bacterial culture. We evaluated the results of six performance monitoring events in 2016 and 2017. Chlorinated methane remediation (CTC and chloroform) was particularly robust. The use of custom droplet sizes to address the variable groundwater velocities (<1 to >10 fpd) and vertical extent (>200 feet deep) will be reviewed. Challenges and solutions that will be discussed include transient decreases in pH to very low (toxic) levels, excessive iron production, complex geochemistry, biofilm and biocrust formation, and unpredicted distribution of amendments.