Geology topics
D.W. Clark
Publications and source records attributed to D.W. Clark.
Geochemical processes in ground water resulting from surface mining of coal at the Big Sky and West Decker Mine areas, southeastern Montana
A potential hydrologic effect of surface mining of coal in southeastern Montana is a change in the quality of ground water. Dissolved-solids concen- trations in water in spoils aquifers generally are larger than concentrations in water in the coal aquifers they replaced; however, laboratory experiments have indicated that concentrations can decrease if ground water flows from coal-mine spoils to coal. This study was conducted to determine if decreases in concentrations occur onsite and, if so, which geochemical processes caused the decreases. Solid-phase core samples of spoils, unmined over- burden, and coal, and ground-water samples were collected from 16 observation wells at two mine areas. In the Big Sky Mine area, changes in ground- water chemistry along a flow path from an upgradient coal aquifer to a spoils aquifer probably were a result of dedolomitization. Dissolved-solids concentrations were unchanged as water flowed from a spoils aquifer to a downgradient coal aquifer. In the West Decker Mine area, dissolved-solids concentrations apparently decreased from about 4,100 to 2,100 milligrams per liter as water moved along an inferred flow path from a spoils aquifer to a downgradient coal aquifer. Geochemical models were used to analyze changes in water chemistry on the basis of results of solid-phase and aqueous geochemical characteristics. Geochemical processes postulated to result in the apparent decrease in dissolved-solids concentrations along this inferred flow path include bacterial reduction of sulfate, reverse cation exchange within the coal, and precipitation of carbonate and iron-sulfide minerals.
National Water-Quality Assessment program; northern Rockies intermontane basins
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Plan of study for the Regional Aquifer-System Analysis of the northern Rocky Mountains Intermontane basins, Montana and Idaho
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Pesticides in soils and ground water in selected irrigated agricultural areas near Havre, Ronan, and Huntley, Montana
Three areas in Montana representing a range of agricultural practices and applied pesticides, were studied to document whether agricultural pesticides are being transported into the soil and shallow groundwater in irrigated areas. Analytical scans for triazine herbicides, organic-acid herbicides, and carbamate insecticides were performed on soil and shallow groundwater samples. The results indicate pesticide residue in both types of samples. The concentrations of pesticides in the groundwater were less than Federal health-advisory limits. At the Havre Agricultural Experiment Station, eight wells were installed at two sites. All four soil samples and two of four water samples collected after application of pesticides contained detectable concentrations of atrazine or dicamba. In an area where seed potatoes are grown near Ronan, eight wells were installed at two sites. Pesticides were not detected after initial application of pesticides and irrigation water. The site was resampled after irrigation water was reapplied, and aldicarb metabolities were detected in four of five soil samples and one of five water samples. At the Huntley Agricultural Experiment Station, five wells were installed in a no-tillage corn field where atrazine was applied in 1987. Soil and water samples were collected in June and July 1988; pesticides were not detected in any samples. Results indicate residue of two pesticides in soil samples and three soluble pesticides in groundwater samples. Therefore, irrigated agricultural areas in Montana might be susceptible to transport of soluble pesticides through permeable soil to the shallow groundwater system. (USGS)
Seepage studies of the Weber River and the Davis-Weber and Ogden Valley canals Davis and Weber Counties, Utah, 1985
Studies of selected reaches of the Weber River, Davis-Weber Canal, and the Ogden Valley Canal in Davis and Weber Counties, Utah, were made to determine gains or losses of flow in those reaches. Three to five sets of seepage measurements were made on the river and each canal during 1985. Adjustments for fluctuations in flow were made from information obtained from water-stage recorders operated at selected locations during the time of each set of seepage measurements. The studies indicated a loss of 20.0 cubic feet per second in the upstream reach of the Weber River and a gain of 17.0 cubic feet per second in the downstream reaches or a net loss of 3.0 cubic feet per second. Study results also indicated a net loss of 17.0 cubic feet per second in the Davis-Weber Canal and a net loss of 4.0 cubic feet per second in the Ogden Valley Canal.
Ground-water resources of northern Utah Valley, Utah
An evaluation was made of the ground-water resources of northern Utah Valley, Utah, to describe the ground-water system and to document changes in ground-water conditions since 1963. The principal ground-water reservoir is in basin-fill deposits. It consists of three major confined aquifers and an unconfined aquifer in pre-Lake Bonneville deposits along the mountains that adjoin the valley. The principal ground-water reservoir contains about 10 million acre-feet of recoverable water.