Innovative technologies and vadose zone treatment of chlorinated volatile organic compounds: Case study

Abstract

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 g/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.