Project Highlight: Comprehensive Remedial Services and Long-Term Monitoring and Operations and Maintenance, 
at former Williams Air Force Base, Arizona

Williams Air Force Base is a former military installation, first built in 1941, which operated as an active training base for both the U.S. Army Air Force and the U.S. Air Force until its closure in 1993. As part of the base realignment and closure (BRAC) program, BEM was responsible for carrying out comprehensive remediation services at the base.

Problem

The most challenging component of this project was the complex ST-12 site, where several million gallons of Jet Propellant 8 fuel (JP-8) had been released over a 50-year period. This resulted in the build-up of a substantial layer of Light Non-Aqueous Phase Liquids (LNAPL), and thick product layers, in a number of wells. In addition, high concentrations of benzene, toluene, and naphthalene impacted soil and groundwater to depths that extended to 245 feet below ground surface. The strata underlying the site consisted of a complex alluvial sequence of interbed fine-grained and coarse-grained geologic deposits, which trapped fuel beneath the water table. These physical characteristics would have limited the effectiveness of soil vapor extraction (SVE)—a standard application in similar conditions—and would have made free product pump and treat cost prohibitive. Contaminant fate & transport modeling estimated that the implementation of monitored natural attenuation, supplemented by SVE, would not have been sufficient to control the plume and degrade the contaminants of concern (COCs) to groundwater standards within an acceptable timeframe.

Solution

Combining a detailed analysis of site conditions with a thorough evaluation of existing remedial technologies, BEM was able to develop a feasible and efficient treatment option to satisfy the regulatory agencies. BEM successfully designed and implemented a pilot study using thermal enhanced extraction (TEE), in conjunction with SVE, for the vadose zone, or the region of aeration above the water table. The TEE system design was an innovative remediation approach and consisted of six steam injection wells and six extraction wells that connected to a flame oxidizer. Treatment was operated by a complex programmable logical controller (PLC) real-time data management system. Post treatment soil and groundwater results demonstrated a significant reduction of product and COC levels in groundwater to gain regulators’ (USEPA Region IX and ADEQ) approval for full scale implementation. Our utilization of fate & transport modeling, combined with our understanding of the underlying geology, allowed for our design engineers to develop the remedial approach based upon the site conceptual model that was subsequently approved by the USAF, USEPA, and the AEQ.

Challenge

Following construction and system implementation, adjustments were made to optimize overall efficiency to ensure proper treatment of impacted soil and groundwater. BEM utilized our programmable logic controller (PLC) system and optimization models to identify the necessary adjustments in pressures, temperatures, and injection rate for each treatment zone to maximize remedial treatment. This evaluation was an ongoing process, which ensured that the maximum benefit of remedial treatment was achieved.
Monitoring indicated that the system operated flawlessly for the first 12 months. But, the water table was rising throughout the design and execution phases of the project; and, as a result, the groundwater pumping requirements changed. The originally scoped pneumatic piston pumps were not designed to meet these increasing extraction needs, and thus became ineffective over time. The pneumatic piston pumps were replaced with electric submersible pumps, capable of compensating for the significantly increased hydraulic head by creating sufficient drawdown to maintain containment of the steam zone and exposing the vapor extraction well screens.