Over the last 10 yr, a mix of innovative and conventional characterization techniques has been used to assess the contamination of vadose zone sediments beneath the pilot-scale test facility known as TNX at the Savannah River Site in South Carolina. Shallow soils and groundwater beneath the TNX facility are contaminated with chlorinated volatile organic compounds (CVOCs), trichloroethylene (TCE), carbon tetrachloride (CCl4), perchloroethylene (PCE), and chloroform (CHCl3). An interim pump-and-treat remediation system was placed in operation in 1996 to provide hydraulic containment of groundwater containing greater than 500 μg/L dissolved TCE.
In 1994, a vadose zone study was initiated to determine the degree and extent of CVOC contamination above the contaminated groundwater. Headspace sampling and analysis, acoustic infrared spectroscopy, cone penetration testing, and vadose zone pumping tests were used to determine contaminant concentrations and physical properties related to soil vapor extraction (SVE). In 2001, SVE, a presumptive remedy for CVOCs in soils similar to those present beneath TNX, was selected to treat the CVOC contamination. Cone penetration testing with soil vapor sampling provided a detailed understanding of the subsurface geology and CVOC distribution, which was essential for proper well design and placement. Twelve SVE wells were installed using direct push technology and were tested to determine specific capacity and CVOC concentrations. This information was then used to develop a strategy for operating the SVE system. Based on the results of the baseline testing and previous studies, sets of two to three extraction wells will be treated using SVE at 1-month intervals. This will allow continuous operation of the SVE system and give individual wells up to 3 months for rebound between treatments. This method of operation is intended to maximize contaminant recovery from individual wells and reduce the overall capital investment and operating cost of the SVE system.
Jay V. Noonkester completed his B.A. degree in geology and computer science in 1990 from the University of Maine at Farmington. He has 14 years of environmental experience at the Savannah River National Laboratory. His interests include developing, deploying, and testing various characterization and remediation technologies.Ralph Nichols is a fellow engineer at the Savannah River National Laboratory, where he has conducted research related to soil and groundwater characterization and remediation for 17 years. He received a B.S. degree in geological engineering from the University of Missouri–Rolla and an M.S. degree in civil engineering from the University of Oklahoma. His primary research interests are in the collection and synthesis of data from multiple scales into conceptual models that are used to develop sustainable environmental management strategies.
Kenneth Dixon is a principal engineer at the Savannah River National Laboratory, where he has conducted research related to soil and groundwater characterization and remediation for 14 years. He received his B.S. and M.S. degrees in agricultural engineering from the University of Georgia and an M.E. degree in civil engineering from the University of South Carolina. His primary research interests are in pilot-scale testing of innovative remedial technologies and numerical modeling of contaminant fate and transport in the vadose zone.