 When something goes down the drain, it’s usually a cause for concern. But going down the drain is the goal of an innovative technology that quickly and efficiently injects surfactants into the subsurface to solubilize and flush out contaminants. In field tests undertaken by West Virginia University, a prefabricated vertical drain (PVD) system will be used to expeditiously deliver surfactants through low-permeability soils to contaminated soil and ground water. Once there, the surfactants can do their job of flushing out contaminants. The drain system will then extract the contaminant/surfactant solution for treatment on the surface. In comparison with conventional well fields and drains, PVDs can accelerate the soil flushing process, expedite contaminant recovery, and reduce both capital and operating costs. Installation of the PVD system is relatively simple and inexpensive with no drilling required. West Virginia University, through a cooperative agreement with the U.S. Department of Energy’s Office of Science and Technology, has guided the development of this technology from a laboratory concept to field testing. The cooperative agreement is administered by DOE’s Federal Energy Technology Center in Morgantown, West Virginia. The PVD project receives funding through the technology-based development program at FETC. (For information on other projects under WVU’s cooperative agreement with OST, see article on page 13.) A unique WVU worked with an industrial partner, NILEX Corporation of Denver, to configure an arrangement of drains for the injection of surfactants and the extraction of contaminant/surfactant solutions. The PVD system was built from off-the-shelf equipment and is based on an existing technology.
Field testing PVDs WVU has field tested PVDs for extracting contaminants at a site in West Virginia. Pilot-scale tests at an Ashland Petroleum Gas Station in Weston, West Virginia verified the effective and efficient removal of benzene, toluene, ethyl benzene, and xylene (BTEX) as a function of time, with the PVDs providing sustained flow rates. During full-scale tests at the Ashland site, 424 PVDs were installed over a period of 6 hours in three different test pads. BTEX flushing rates, fluid flow rates, and vacuum efficiencies were monitored over time. The fluid injection system was also verified.
Upcoming pilot-scale testing at an industrial site in Ohio will demonstrate PVDs’ ability to deliver surfactants to enhance in situ remediation of subsurface contamination. WVU has installed eight test PVDs and started extracting ground water. NILEX will install 800 PVDs at the 0.10-acre site, which is owned by RMI Titanium Company Extrusion Plant in Ashtabula, Ohio. From 1962 to 1990, RMI extruded and forged metallic uranium into fuel elements for defense production reactors and nuclear energy reactors. As a result, the facility’s soil and ground water are contaminated with trichloroethylene (TCE), technetium-99, and uranium. TCE is a highly recalcitrant environmental contaminant with low aqueous solubility and a density greater than water. It can contaminate ground water for decades because it is a dense nonaqueous-phase liquid with low solubility and tends to sink to the bottom of aquifers and dissolve slowly. Although the effective removal of contaminants has been verified during field tests in West Virginia, WVU hopes to go a step further at the RMI site: improve contaminant removal efficiencies by injecting surfactants to flush contaminants out and then extracting the resulting surfactant/contaminant solutions. Plans call for SpinTek Systems to use its patented centrifugal membrane technology (see Initiatives, October 1996) to separate surfactants containing contaminants, allowing release of the water and recycle of the surfactants. The Institute of Gas Technology will select and obtain appropriate surfactant solutions. IGT will also supply nutrient solutions for enhancing natural in situ biodegradation of residual contamination. RMI will provide all the necessary site support to conduct the test campaign. For more information about this project, call Dr. Madhav Ghate, DOE project manager, at FETC at (304) 285-4135. |
     |
PVDs are a system of wick drains. Each drain,
consisting of an inner core and an outer filter jacket,
measures 4 inches in width and about 1/4 inch in thickness. The
flexible inner core of extruded polypropylene forms
flow-path grooves along both sides of each drain’s
length. The outer jacket is a durable, nonwoven
polypropylene geotextile fabric that filters out soil
particles while allowing ground water to enter the drain
core. The system alternates a row of drains for injecting
surfactants or clean water into the subsurface with a row
of drains for extracting contaminants. 