IN SITU BIOREMEDIATION OF PENTACHLOROPHENOL
BY DISSOLVED OXYGEN INJECTION

William A. Newman (Remediation and Natural Attenuation Services, Inc.)
Martin Wangensteen (Bay West, Inc.)
Dale Olson (Andersen Corporation)

ABSTRACT: In September of 1982 a faulty valve on a railroad tank car resulted in the accidental release of a wood treating solution containing pentachlorophenol. Subsequent investigations indicated that the wood treatment dip tank had also been a source of soil and ground water contamination. A ground water and product extraction system was installed soon after the rail car release, but after 13 years of operation pentachlorophenol concentrations up to 14,000 ppb remained in the source area. In January of 1996 a dissolved oxygen injection system was installed using a bubble-less membrane fiber system (Membran Inc.) with liquid oxygen used as an oxygen source. Iron fouling required frequent acid cleaning, and limited the system to a flow rate of approximately 80 liters per minute (lpm) with dissolved oxygen concentrations of approximately 20 mg/L. The membrane fiber system was removed and replaced with an O2Zone spray chamber system, with oxygen generated onsite by pressure swing adsorption (PSA) oxygen generators. With the new system operation and maintenance costs were minimal and flow rates up to 150 lpm with 40 mg/L of dissolved oxygen were achieved. The system design allowed for flow rates over 200 lpm, but the water supply limited injection flow rates to approximately 120 lpm for long-term operation. By June 2003 the two dissolved oxygen systems had delivered over 9,000 kilograms of oxygen to the source area. During the June 2003 sampling all wells were below remediation goals with only one sample above detection limits at 5.4 parts per billion of pentachlorophenol