BGI conducted a phased treatability study of in situ bioremediation as a potential technology to treat groundwater contamination at Sandia National Laboratories (SNL). BGI orchestrated the injection of more than 530,000 gallons of bioremediation solution and monitored the performance of in situ treatment for trichloroethene (TCE) and nitrate groundwater contamination.
Research at SNL in the 1960s focused on testing radiation effects on various weapon and reactor components. Wastewater and sanitary waste from this research were discharged into a drain field and several buried seepage pits during that time. This resulted in groundwater contamination with constituents of concern (COCs) including TCE and nitrate. The nitrate plume covers approximately 1.4 acres of SNL, while the TCE plumes covers approximately 13 acres.
Starting in 2017, BGI conducted a study of in situ bioremediation as a potential technology to treat groundwater contamination. The project included construction, mobilization, and operation of an above-ground injection system (AIS) and gravity-injection of a bioremediation solution in up to three injection wells. Phase I of this project consisted of pilot testing the AIS and then full-scale operation at one newly installed injection well. Phase II involves full-scale operation of the AIS into two further wells.
During the course of the project, BGI developed a method for the remediating bacteria to be directly side-stream-injected into the well during the substrate solution injection step. This allowed the bacteria to be pushed further into the groundwater formation with the necessary nutrient content to foster an optimal growth in situ and to avoid in-tank biofouling from growing bacteria at surface mixing tanks. The substrate solution, along with the biodegradation bacteria (dechlorinating and bioremediating microbial culture including Dehalococcoides), was gravity-injected into groundwater by way of the BGI constructed injection well.
After the pilot study, the full-scale treatability study began at the first injection well. During 111 separate injection events from October 2018 through April 2019, approximately 531,000 gallons of bioremediation solution containing TCE-degrading bacteria was injected into the well. After these injections, wells were monitored for the performance of in situ bioremediation. Further, one deep well and eight surrounding wells were monitored to determine potential broader impact on groundwater quality caused by the bioremediation solution. The injection period of Phase I was followed by two years of groundwater monitoring to determine the performance of the microbial cultures’ dechlorinating and bioremediation potential.
BGI reported on the bioremediation process, injections, groundwater sampling, and also documented groundwater TCE plume and nitrate concentrations to demonstrate the viability of bioremediation for degradation of COCs. BGI completed AIS operation reports at the end of the pilot-test and upon completion of the full-scale injections for Phase I of the study. These reports included scope of activities, work performed, field conditions, observations, results, and recommendations for proceeding with Phase II.
