M&A uses traditional and cutting-edge technologies to remediate solvents and chromium in groundwater at a major Superfund site.
Client: Raytheon Company- Time frame: 1999–2007
- Location: Tucson / Pima County, Arizona
U.S. Air Force Plant 44 (AFP-44) is part of the Tucson International Airport Area Superfund site. In the early 1980s, soil and groundwater contamination — chromium and VOCs — was found underlying the plant. M&A was hired to conduct modeling and support for monitoring and remediation activities beginning in the late 1990s; we continued work at the site for almost a decade.
A large-scale, pump-and-treat, remediation system was installed and began operating in 1987 to capture, treat, and re-inject treated water for plume containment. Soil vapor and dual-phase extraction programs were implemented at the various source zones. In areas of the site where solvents had been disposed of and concentrations remained elevated, a different approach was taken to address nonaqueous-phase VOCs that were anticipated. In these areas, remedial enhancements were evaluated and implemented to accelerate groundwater remediation. In the early 2000s, 1,4-dioxane was detected in groundwater and in the treated water that was being re-injected for plume control. M&A was tasked with updating the AFP-44 model and evaluating the wellfield operation strategy and remedial alternatives to address this new concern.
M&A updated and recalibrated a two-dimensional model that simulated groundwater flow and TCE transport. Originally developed by Raytheon, the model was used to evaluate the feasibility of achieving remedial objectives. We later added a particle-tracking component to the model to simulate alternatives for controlling the VOC plume while minimizing the off-site migration of groundwater containing 1,4-dioxane.
Based on our modeling analyses and recommendations, an alternate pumping-and-injection strategy was adopted by EPA and ADEQ. Other tasks included adapting the model to simulate the transport of 1,4-dioxane and projecting future concentrations as exposure points as part of a risk assessment. The model also helped us evaluate the benefits of implementing a program to treat the 1,4-dioxane.
M&A has conducted ongoing investigations to evaluate wellfield operation strategies to optimize capture and containment. In one case, we worked with the University of Arizona and the IT Corporation to design, implement, and interpret results of a pilot-scale test for in-situ chemical oxidation using potassium permanganate at two AFP-44 source areas. As part of the program, we designed and supervised the installation of 10 wells that are used to extract VOCs, inject treatment solution, and monitor impacts of the in-situ oxidation program. During drilling, we collected depth-specific soil and groundwater samples to characterize the distribution of contaminants, a critical element in designing the remediation program.
In addition, M&A pilot-tested various in-situ oxidation, bioremediation, and chemical-reductive processes to address chromium and VOCs at other source areas. We also provided field and analytical support for a pilot-scale test to evaluate an advanced groundwater remediation technology that entailed injecting and then recovering a solubility-enhancing reagent.
M&A periodically developed maps showing concentrations of TCE; 1,4-dioxane; and chromium to meet the regulatory reporting requirements of ADEQ and EPA. We also participated in regular technical meetings with ADEQ and EPA staff to review and plan ongoing monitoring and remediation activities. Other activities included preparing work plans for various remedial programs and participating in public meetings with the stakeholder group to communicate ongoing project developments.
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