Date of Award
Master of Science (MS)
The Grand Forks Municipal Landfill, located in the Red River Valley of eastern North Dakota, accepts household refuse from the city of Grand Forks and from surrounding rural communities including several towns in northwestern Minnesota. The landfill occupies 160 acres (64.8 hectars) and another 160 acres (64.8 hectars) is available for expansion. The trench method of disposal is used at the landfill.
A geologic and hydrogeologic investigation was undertaken at the landfill to determine the characteristics of the shallow, saturated, fine-grained lacustrine sediments for solid waste disposal. Test holes were drilled to collect core samples for textural analysis, clay mineralogy analysis and cation-exchange-capacity analysis. Fifty-nine shallow wells and piezometers were installed to determine the groundwater flow regime, the hydraulic conductivity, leachate and groundwater chemistry in the shallow subsurface. The wells were sampled for general chemistry, BOD, coo, trace metals and pesticides.
The Sherack and Brenna Formations are composed of silt loam, silty clay and clay. The clay content ranges from over 10 percent to 97 percent. The predominant clay mineral is montmorillonite and the sediments have high CEC values due to this clay mineral. Hydraulic conductivity values range from xiii 1. 4 x 10 ·5 m/s in the upper Sherack Formation to 8. 6 x 10·10 m/s in the Brenna Formation. The groundwater flow regime is dominated by vertical flow and hydraulic heads fluctuate greatly in the shallow subsurface. The vertical gradients are generally downward from spring to fall and upward in the winter. Hydraulic conditions in the landfill cells are stagnant throughout the year indicating that there is little hydraulic connection with the surrounding area.
The natural groundwater in the area is saline due to the influx of saline water from the Dakota Aquifer, which pinches out just west of the landfill. The average TDS is about 25,000mg/L. The water is classified as a calcium, sodium, magnesium, chloride water and is high in sulfate.
The leachate contains higher levels of iron, manganese, bicarbonate, ammonium, COD and BOD than the natural groundwater. These indicators were used to identify landfill effects in surrounding wells, as were trace metals and pesticides. No strong evidence was observed which indicates that the landfill has an effect on the local groundwater; however, one well nest located just north of the landfill did contain some leachate indicators.
Water samples were collected in drainage ditches both north and south of the landfill. Some of the leachate indicators were elevated while others were not. It is believed that some leachate-affected water may be entering surface water due to seepage from the landfill.
Betcher, John T. B., "The Hydrogeology of a Landfill Located in Fine-Grained Lacustrine Sediments in a Saline Discharge Area West of Grand Forks, North Dakota" (1989). Theses and Dissertations. 19.