It is increasingly apparent that contaminant mass flux/discharge provides the most representative measure of plume dynamics and risk to receptors. Consequently, remedial technologies focusing on long-term mass flux/discharge reduction will be increasingly favored. New strategies that focus on monitoring of the mobile contaminant mass and can accurately measure changes in mass flux/discharge over time will be more frequently implemented in the future. Flux-focused monitoring approaches are relevant for any type of contaminant source zone but will be particularly important in the future for assessing the risk and benefits of mitigation activities for per- and polyfluoroalkyl substances (PFAS) discharging from fire training areas and other sources.
The purpose of this project is to field-validate the Vertebrae™ segmented nested horizontal well system (Vertebrae system) for long-term monitoring of contaminant mass flux/discharge from source zones and high-concentration areas and for evaluating changes in mass flux/discharge over time. Flux measurement methods specific to the Vertebrae system will be developed and demonstrated through field testing and method comparisons. A user guide will be created to provide technology applicability and limitations, anticipated performance, design considerations, and costing information.
The Vertebrae system is a single, small diameter horizontal well that contains multiple isolated screen segments; essentially it is an engineered multi-port well that is installed horizontally instead of vertically. The Vertebrae system can provide another transect method option, as a complement or alternative to the conventional vertical transect option. The Vertebrae system is unique with many discrete screen zones running horizontally along its length with separate, small diameter tubing plumbed from each screen to the surface. Grout, which is tremied in, is used to isolate the individual tailor-designed screen intervals. The Vertebrae technology can be applied as a variation of the conventional transect approach. The difference is the monitoring points are installed horizontally instead of vertically, with improved coverage along the width of the plume at targeted depths with highest concentrations or flux. The approach is novel and advantageous because multiple closely spaced measuring points across a transect can be easily installed from a single boring (reducing costs) and contaminant zones that may have been previously inaccessible via vertical boreholes can be characterized. An accurate understanding of contaminant distribution within the site hydrostratigraphy from vertical borings is still required to optimize placement of the horizontal wells, and to select target intervals for the monitoring zones.
Further development of the application of the Vertebrae system technology will benefit the Department of Defense (DoD) and the environmental community at large because it will contribute to advancement with both cost and effectiveness in understanding contaminant mass flux/discharge in site assessment, remediation, and monitoring. In particular, the Vertebrae system will enable precise and repeatable monitoring of mass discharge with intervals oriented with high concentrations/flux emanating from complex source zones over time, supporting more reliable risk assessment, remedy performance assessment and optimization, and transition from active to passive remedies. The technology is applicable to any type of groundwater contamination; however, it offers particular potential in PFAS and chlorinated solvent applications. Scaled up across the portfolio of DoD sites, this could result in significant total remedy savings through more reliable characterization, risk assessment, flux-based decision making, and better remedy design and operation with improved performance monitoring.