From Ground Water Currents, June 1996, Issue No. 15

Unique Field Laboratory To Research Planned Aquifer Releases

The Groundwater Remedi-ation Field Laboratory (GRFL), located at Dover Air Force Base, Delaware is the first facility in the United States where researchers can conduct carefully planned contained releases of chlorinated solvents and fuel into a natural aquifer. It is the second such faciility in the world. GRFL is part of the National Environmental Technology Tests Sites Program (NETTS) which was established under and funded by the Strategic Environmental Research and Development Program (SERDP) to enable efficient and relevant demonstrations of innovative and emerging clean-up technologies. SERDP is a multi-agency program to respond to the environmental requirements of the military and those problems that they share with the Department of Energy and EPA.

The GRFL provides a test bed and infrastructure for evaluating the transport of dense non-aqueous phase liquids (DNAPL) contamination in ground water and soil and for the demonstration and verification of remediation and monitoring technologies. The GRFL allows for detailed evaluation of emerging technologies by conducting contained release experiments. These experiments allow researchers to conduct mass balance type studies in a controlled field setting. The results of these studies will provide information necessary to design and engineer improved treatment systems for contaminated soils and ground water. The State of Delaware Department of Natural Resoures and Environmental Control has issued a permit to GRFL under Title 7 Chapter 60 of the State Code.

The first experiment will look at the co-oxidative bioventing of a mixture of jet fuel and chlorinated solvents. This technology, if successful, will have wide application to the remediation of mixtures of organic compound in the vadose zone and may represent a cost effective remediation tool.

Here is the history of the construction of the GRFL. The site characterization effort involved a complex, integrated program of field and laboratory studies to analyze a broad range of hydrogeological and biogeochemical properties. The characterization effort was broken into two phases with multiple tasks. Tasks included: surface geophy-sics, cone penetrometer survey and soil borings, laboratory analyses of soil properties, pumping test, tracer test, unsaturated hydraulic conductivity, air conductivity and a 3-D ground water model.

Surface geophysical stu-dies were performed on a 10 meter grid that was established at the site. Geophysical surveys included ground penetrating radar (GPR), high resolution seismic, surface resistivity and low frequency electromag-netics. These studies were completed by a team of researchers and consultants including Applied Research Associates, the University of Delaware and the Air Force Phillips Laboratory. All the surface geophysical data produced similar results on site geology. The site consists of a water table aquifer 11 to 14.5 meters thick underlain by an aquitard which ranges from 8 to 12 meters thick. The water table is approximately 8 meters below ground surface.

Soil samples were sent for analyses of physical, chemical, microbiological, mineralogical properties by the Air Force Wright Lab, the University of Delaware and Virginia Polytechnical Institute and State University. Results of these studies show the water table aquifer to consist of a fining upward sequence overlain by a coarsening upward sequence of fine to medium sands with varying amounts of silt, clay and gravel. The soils are slightly to moderately acidic and have relatively low cation exchange capacities due to low clay contents and the predominance of kaolinite in the clay fraction. The microbiological study indicated that both the total population and activity of microorganisms decreases with depth. Samples from the aquitard were determined to be silty clays and clayey silts with significant amounts of montmorillonite clay.

Infrastructure at the site consists of a doubled walled sheet pile test cell, an on-site trailor mounted cone penetrometer system, and a GIS based data acquisition and control system (DACS).

A modular building was set up to provide on site office and laboratory capabilities for the permanent GRFL staff and visiting principle investigators.

The sheet pile test cell was constructed using the patented Waterloo Barrier Sealable Joint Sheet Pile. The test cell is approximately 5 by 10 meters and surrounded by a second 7 by 12 meter cell of the same construction. Although unique groutable joints require the box to be built above ground, it is keyed into underlying aquitard 12 meters below ground surface. Once construction is completed, the joints are flushed and grouted to ensure a complete seal. An average hydraulic conductivity for the test cell has been determined to be in the 10E-9 cm/sec range.

After construction of the test cell is complete, the cell is covered with a temporary structure to prevent rain water from infiltrating the cell. This allows for better control of environmental factors affecting a remedi-ation process.

The Air Force's new trailer mounted cone penetrometer (CPT) unit is capable of installing wells and collecting soil samples within the confines of the test cells. The CPT system has the capability of conducting CPT tests for soil type; collecting soil, water and soil gas samples; and installing monitoring wells up to 2 inches in diameter.

The DACS will collect and maintain a data base of all experimental data and has the ability to perform some control functions for experiments in the field. The DACS may be remotely accessed to provide researchers not on site with real time data. The office laboratory contains an area for sample preparation and has an HP6890 GC with ECD and FID detectors for analyses of soil, water or soil gas.

The Dover NETTS site provides support to environmental technology demonstrations at various sites around Dover Air Force Base. Additionally, GRFL has participated in the Partnership for Peace program by hosting visiting scientists and engineers from North Atlantic Treaty Organization (NATO) members and Eastern European countries. For more information, call GRFL's Principal Investigators Mark Noll at 302-677-4147 and/or Alison Thomas at 904-283-6303.