TCE In Situ Technical Demonstration

Problem

A consortium of Japanese Corporations (i.e. Ebara, Organo, Sumitomo, Hitachi, Takanaka, Kumagai-gumi) and the Japan Environment Agency (JEA) through its contractor Japan Research Institute (JRI), was interested in performing a technology demonstration project at the Chiba City site in Chiba Prefecture, Japan. The purpose of this project is to demonstrate the efficacy of in situ bioremediation technologies and their effectiveness in treating chlorinated solvent contaminated groundwater.

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Solution

Pelorus was contracted to perform a site biological characterization and treatability study to determine the extent of intrinsic biodegradation and natural attenuation; develop a groundwater and contaminant transport model for the site; and design, fabricate, and install an in situ bioremediation system to bioremediate TCE from levels averaging 5.0 ppm. An extensive amount of interfacing with the Japan Environment Agency and the Ministry of International Development and Industry as well as local prefecture officials was required to gain acceptance of the process and ensure that ARAR’s (i.e., all relevant applicable regulations) were met. Pelorus developed an operating plan, operations manual and training program for Japanese personnel to operate and monitor the system. Pelorus provided services in analyzing process performance data, recommending operational adjustments to meet the prevailing site conditions. Using laboratory scale column tests during this ongoing program, Pelorus was able to define the critical operating parameters for an in situ methanotrophic process that biodegrades TCE and other chlorinated ethenes in the groundwater. An innovative injection scenario was developed for introducing methane and oxygen to the subsurface using an automated ISM (In Situ Module) in a manner that optimized the TCE degradation rates.

The in situ bioremediation system involved enhancing the natural biodegradative process by using three injection wells to introduce oxygen and methane. The ISM injected an oxygenated water into two wells and methanated water into a third well and allowed for dispersive mixing in the down gradient treatment zone. During this phase TCE flowing into the area from the upgradient was diluted to levels which allowed for stimulated growth of the methane oxidizing bacteria. Methane acted as an inducer of the microbial biodegradation pathway that enabled the bacteria to biodegrade the TCE. After 30 days, optimal growth of the methanotrophic bacteria had occurred and the injection wells were turned off, allowing the natural gradient to reestablish. Based on field tests and groundwater modeling simulations it was observed that the TCE levels would rebound in down gradient monitoring wells to initial levels (5.0 ppm) after 21 days. During the bioremediation implementation program, TCE levels in monitoring wells remained below regulatory levels and did not rebound for 90 days. Based on observations of increased chloride levels (i.e., 3 x background), it was determined that TCE and the other chlorinated ethenes were being bioremediated. In addition to the disappearance of chloroethenes, biodegradation was further documented by observing, oxygen consumption and pH changes in the treatment zone.

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