Formatted Title
The Gift that Keeps on Giving: Post-Bioremediation Sustained Treatment
Background/Objectives
Sustained treatment describes the enhanced attenuation capacity within an in situ bioremediation (ISB) treatment zone that can prolong the benefits of active remediation after the depletion of the primary organic substrate. The advantage of sustained treatment is that it can prolong the treatment effectiveness period beyond what would be anticipated based on traditional design criteria (e.g., a one-to-two-year period of effectiveness) without the need for further injections or enhancements, thereby adding an element of sustainability to the remedial system. A lines-of-evidence approach for evaluating and documenting post-bioremediation sustained treatment following ISB at chlorinated solvent sites was developed as part of an Environmental Security Technology Certification Program (ESTCP) research project. The methodology was developed using data from 34 ISB sites with 3 to 16 years of post-ISB monitoring data. The dataset was supplemented with detailed data from focused field studies conducted at five field sites. A framework for assessing existing site data for the occurrence of sustained treatment will be presented.
Approach/Activities
Data from lab studies, desktop data mining studies, and field studies have been compiled to evaluate the occurrence of sustained treatment following ISB for the remediation of chlorinated solvents in groundwater. The dataset includes relevant literature findings from two-dimensional tank experiments, data from 235 groundwater remediation sites (a subset of which have long-term monitoring data following ISB treatment, and six field demonstration sites, including one mulch biowall site and five substrate injection sites. At each site, samples were collected from within the treatment zone, as well as at a nearby upgradient monitoring well location, to analyze for chemical, geochemical, and microbiological changes that potentially influence post-treatment chlorinated compound concentrations. Sampling was conducted 5 to 10 years following ISB implementation. Various data analyses were conducted to derive parameter assessment guidelines and critical values indicative of sustained treatment.
Results/Lessons Learned
Data mining from 34 sites indicates sustained treatment occurrence at about two-thirds to three-quarters of enhanced bioremediation sites up to 16 years after treatment. Field data from the six sites evaluated suggests the influence of enhanced bioremediation can last for at least 5 to 10 years after treatment. In sum, the results of the study suggest that a generally well-designed and implemented ISB project will most likely benefit from sustained treatment for at least three years to more than 15 years after treatment. Readily available site data collected following the application of ISB can be used to monitor the occurrence of sustained treatment using the lines-of-evidence approach developed from the project.