Overview
U.S. Air Force Plant 44 (AFP-44) is part of the Tucson International Airport Area Superfund site, where VOCs and chromium were found in soils and groundwater in the early 1980s. A large-scale pump-and-treat remediation system began operating in 1987, along with soil vapor and dual-phase extraction programs at source zones and in situ methods for nonaqueous-phase VOCs. In the early 2000s, however, 1,4-dioxane was detected not only in groundwater but also in the treated water that was being re-injected for plume control. The pumping/injection strategy was temporarily modified until treatment for 1,4-dioxane was brought on line in 2009. The site is currently undergoing PBR, which includes actions to expedite achievement of remedial goals.
Services
M&A was originally hired to support monitoring and remediation activities. Our work included developing a model to evaluate remedial alternatives for containing both TCE and 1,4-dioxane and to project future concentrations at exposure points as part of a risk assessment. As part of the PBR, M&A prepares annual reports that include updated model results to help demonstrate that remedial actions are projected to achieve performance goals.
Groundwater Modeling
- Updated and recalibrated the original AFP-44 model to simulate the effects of wellfield operation strategies on VOC capture and containment
- Recalibrated the model and ran flow and particle-tracking simulations to re-evaluate wellfield operations after 1,4-dioxane was detected
- Used the model to evaluate alternatives for containing VOCs while minimizing the off-site migration of 1,4-dioxane
- Adapted the model to simulate the transport of 1,4-dioxane to assess the risk of future exposure and to evaluate the benefits of implementing a treatment program
- As part of the PBR program, updated the conceptual site model and developed a geologic model using LeapFrog to incorporate new information about hydrogeologic conditions and transport processes
- Adapted a site-wide, flow-and-transport model for annual use in projecting plume capture and containment as part of OES design and performance evaluation
Groundwater Remediation
- Evaluated the ability of wellfield operation alternatives to achieve capture and containment objectives
- Evaluated potential remedial enhancements — including in situ chemical oxidation and bioremediation — and recommended approaches to address mass removal near the source areas
- Worked with the University of Arizona and a contractor to run pilot-scale tests for in situ chemical oxidation using potassium permanganate at two source areas
- Pilot-tested various in situ oxidation, bioremediation, and chemical-reductive processes to address chromium and VOCs at other source areas
- Provided field and analytical support for a pilot test of a groundwater remediation technology that entailed injecting and then recovering a solubility-enhancing reagent
- Provided support for the design of full-scale in situ remedial actions to address recalcitrant VOC, 1,4-dioxane, and chromium in fine-grained sediments beneath historical source areas
- Interpreted lithologic logs for injection wells to design in situ remediation programs using environmental hydrofracturing and biologic treatment
- Recommended modifications to extraction wells to mitigate conduit flow and enhance mass removal and plume containment
- Participated in regular agency and public meetings with the stakeholder group
- Gave project-status and innovative technology presentations at annual Superfund Site technical exchange meetings
Contaminant Investigation
- Designed programs to evaluate vertical yield and contaminant concentrations via spinner logging and depth sampling
- Collected depth-specific soil and groundwater samples during drilling to characterize the distribution of contaminants
- Developed a monitoring network to evaluate mass transport and containment at a property boundary in two critical aquifer zones