Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

J.R. Reid


The Coyote I electrical operating station of the Montana Dakota Utilities Company (MDU) is located near Beulah, North Dakota. Flue gas cleanup {FGC) dry waste is generated by the facility in the conversion of coal to electricity. MDU submitted a permit application to the North Dakota State Department of Health {NDSDH) to dispose of FGC dry waste in a strip-mined area 1.6 kilometres northeast of the plant.

Two disposal pits were proposed by MDU, a Phase I and Phase II pit. The objectives of the investigation were to determine the hydrogeological and hydrogeochemical suitability of the site for FGC waste disposal and to develop a groundwater level and quality monitoring program for the landfill. These objectives were attained through installation of 18 monitoring wells and 3 test holes at the site.

Based on groundwater level information, groundwater was found to flow to the west-northwest. Two hydrogeologic units exist, a bedrock flow system and a glacial fill local flow system superimposed on the bedrock system. Water levels range from about 590 to 565 metres msl in the bedrock sediments and from 600 to 575 metres msl in the glacial fill sediments.

Background water quality was determined through a sampling procedure that focused upon groundwater at several stratigraphic horizons beneath the site. Chemical analysis indicates a brackish background water quality with total dissolved solids (TDS) concentrations ranging from 1200 to 5000 milligrams per litre (mg/L) and averaging 2515 mg/L. A significantly higher TDS concentration was detected in Coyote-ash leachate generated during Extraction Procedure (EP) toxicity testing (greater than 32,000 mg/L). The proposed Phase I pit lies from 12 to 18 metres above the local bedrock water table and is the site recommended for ash disposal. The proposed Phase II pit is not recommended for ash disposal as it lies, in part, within saturated low-permeability materials of the glacially-filled valley.

Strategically located monitoring wells which penetrate high-permeability lignite units at different stratigraphic levels were chosen to document the effects of waste disposal on the hydrogeology of the site. The groundwater quality monitoring plan should focus upon the uppermost bedrock aquifer. Two background water-quality and three down gradient detection wells are recommended.

The base of the proposed FGC dry waste disposal pit should be maintained above the water table and constructed with a scarified and recompacted layer of in situ sediment. A gently-sloped compacted cap over the disposal setting will minimize infiltration and prevent leachate formation. This setting should provide long-term ash disposal success.

Hunke (172888 kB)

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