Toxic Substances Hydrology Program -- Norman Landfill Project
Toxic Substances Hydrology Program Research Project
Biogeochemical and Geohydrologic Processes in a Landfill-Impacted Alluvial Aquifer, Norman, Oklahoma
The Norman Landfill is a closed municipal landfill located on alluvium associated with the Canadian River in central Oklahoma. The U.S. Geological Survey began a multi-disciplinary investigation in 1994 at the Norman Landfill, as part of the Toxic Substances Hydrology Program, in collaboration with scientists at the University of Oklahoma, Oklahoma State University, and the Environmental Protection Agency. The contamination of the shallow alluvial aquifer at the Norman Landfill provides an excellent opportunity to study the spatial variability of biogeochemical processes and the resulting effects on the fate of degradable contaminants in the leachate plume. The emphasis of this multi-disciplinary research project is on developing a unified understanding of the processes controlling contaminant distribution and migration. The vast number of landfill sites and ubiquitous nature of alluvial deposits will make the results of this study highly transferable.
The Research Site
The landfill accepted solid waste from 1922 to 1985, when it was closed, covered with a clay cap, and vegetated. The landfill was estimated to have received about 1,128 tons of municipal waste per week in 1982. The landfill is excavated in alluvium adjacent to the Canadian River. The alluvium ranges in thickness from 10 to 15 meters and consists of lenticular beds of unconsolidated clay, silt, sand, and gravel. Depth to water is shallow, ranging from land surface to about 4 meters. Beneath the alluvium is a confining unit, the Hennessey Group, consisting of reddish-brown shales and mudstones, with a few thin beds of very fine-grained sandstone.
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Depth to ground water was measured in the Canadian River alluvium in the winter of 1995-96 to construct a potentiometric-surface map (Scholl and Christenson, 1998). The winter was chosen to minimize the effects of transpiration of water by plants at the site, many of which have root systems that extend to the water table. A network of shallow, small diameter, temporary wells was constructed to measure depth to water. The wells consisted of 2.64-centimeter inside-diameter, schedule-40 stainless steel line pipe, with threaded couplings, attached to stainless steel screened sandpoints with a screen length of 0.76 meter. The wells were driven using an electric jack hammer until the well screen was just below the water table. The elevations of the wells were determined using dual-frequency, carrier-phase global positioning system (GPS) receivers and depth to water was determined by lowering a steel tape into the well and noting the water mark. The potentiometric surface in the Canadian River alluvium near the Norman Landfill was a relatively simple surface during the winter of 1995-96. The surface slopes toward the Canadian River, indicating that ground water is moving through the alluvium toward the River. The hydraulic gradient was approximately 2.8 meters/kilometer north of the Norman Landfill and 1.4 meters/kilometer south of the Landfill.
Extent of the Plume
Geophysical electromagnetic induction surveys were performed on the alluvial plain surrounding the Norman Landfill in January and February 1995 (Lucius and Bisdorf, 1995; Bisdorf, 1996). The purpose of these surveys was to determine the vertical and horizontal extent of the leachate plume. Electromagnetic Induction Surveys measure the electrical conductivity of the aquifer materials, both soils and fluids. The surveys show higher conductivity south of the landfill, which is consistent with hydraulic and geochemical evidence indicating a leachate plume has developed and is flowing toward the Canadian River. Conductivity measurements and dissolved organic carbon analyses confirm that the plume has migrated beneath the slough and extends through the entire thickness of the alluvium.
Quick Facts: Why is the Norman Landfill Research Site Valuable?