Date of Award

1979

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

L. Clayton

Abstract

A local groundwater study is a necessity before the opening of any lignite mine in North Dakota. The study becomes an important reference for the environmental impact during mining and after reclamation.

This report is a groundwater study of the Proposed Garrison Lignite Mine, McLean County, North Dakota. The mineable lignite is in the lower Sentinel Butte Formation (Paleocene). The remainder of the Paleocene material at the proposed mine site is mostly fluvial silty clay deposits with some sand beds. Pleistocene deposits, mostly pebble loam (till), cover the Sentinel Butte at the mine site.

Ninety piezometers in twenty-eight nests were installed at the Proposed Garrison Lignite Mine. Data from these piezometers show that the direction of groundwater flow in the pebble loam and silty clay is predominately downward into the lignite. Within the lignite, the water flows laterally toward the buried valleys at the west and south borders of the mine site. After flowing a short distance in the lignite, the water passes into the silty clay below the lignite or into Pleistocene sand and gravel above the lignite. The small amount of water that passes into the buried valleys probably remains in the valleys and flows generally toward the south.

Chemical analysis of the groundwater shows that the groundwater in the till is generally high in total dissolved solids with dominant concentrations of sodium, calcium, bicarbonate, and sulfate. By passing through silty clay into lignite, total dissolved solids decrease and there are dominant concentrations of sodium, bicarbonate, and sulfate. As the groundwater flows deeper into the Sentinel Butte Formation, total dissolved solids increase and the dominant ions become sodium and bicarbonate.

The information in this report shows that the physical and chemical groundwater systems at the proposed mine site resemble the groundwater systems at other mines in North Dakota,

Because the direction of groundwater flow is mostly downward, the removal of the lignite will probably have no major effect outside of the mine site, But mining plans must be made carefully so that the buried valleys at the proposed mine site are not dewatered.

Morin plate.zip (75652 kB)

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