Aggressive Source Control to Support a Large-Scale Ground Water Remediation Program

Wednesday, April 22, 2009: 3:55 p.m.
Agave Ballroom (Hilton Tucson El Conquistador Golf & Tennis Resort )
William H. DiGuiseppi, PG , AECOM Environment, Englewood, CO
James W. Hatton , AECOM Environment, Englewood, CO
George Warner , U.S. Air Force Aeronautical Systems Center, Wright-Patterson AFB, OH
The groundwater remediation strategy at U.S. Air Force Plant 44 (AFP 44) in Tucson, Arizona, has been to aggressively eliminate contaminant migration and then conduct source zone remediation.  Implementation began with installation of a groundwater treatment plant with air stripping, and extraction and recharge wellfields in 1987 to reduce contaminant mass and contain the plume. 

Source removal began by excavating over 40,000 tons of contaminated soil and debris, and was followed by soil vapor extraction (SVE) and dual phase extraction (DPE), which removed over 100,000 lbs of VOCs from 6 sites.  Five of the six systems have been shut down after meeting the required remediation goals, and the USAF is in the process of shutting down the last of these systems.  Robust waste minimization programs were implemented to eliminate the possibility of future releases.  Because these remedial actions were successfully implemented, concentrations have declined from 600 to 20 µg/L trichloroethene in treatment plant infuent.  Chromium levels in the aquifer were sufficiently reduced to the point where treatment is no longer necessary. 

Currently, the USAF is exploring remedial technologies for TCE residuals in saturated soils.  Pilot testing has been conducted for bioremediation, vertical circulation wells, cyclodextrine flushing, chemical reduction of metals, and in situ chemical oxidation (ISCO).    

Recent discovery of 1,4-dioxane in groundwater at AFP 44 has become a confounding issue.  This compound is an emerging contaminant that was used as a solvent stabilizer.  AECOM Environment and the USAF are working to define the extent of this compound, re-engineer the treatment plant for more effective treatment, develop an aquifer remediation strategy, and test potential in situ technologies.  While groundwater issues at AFP 44 are not yet fully resolved, the USAF has made great strides in reducing source contributions to the regional groundwater and managing the plume to limit further migration.