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Effects of Surface Mining Upon Shallow Aquifers in the Eastern Powder River Basin, Wyoming


This is a report summarizing WRRI ground water research activities at the Belle Ayr Mine during FY 1976-77. The year's activities focused upon aquifer recharge, hydrology of the alluvial valley floor along Caballo Creek, and reclaimed spoil hydrogeology. Recharge to Wasatch formation overburden aquifers amounts to less than one percent of the area's precipitation. Direct recharge to coal underlying the Wasatch formation is too small to measure. Significant recharge to or discharge from the coal occurs where alluvium and coal are in direct contact. Recharge probably also occurs via scoria units.

Underflow through the Caballo Creek alluvium is less than 0.4 acre feet per month. This is because the alluvial sands are so fine and silty that transmissivities are very low.

Permeability of reclaimed spoil, determined by slug tests, is less than 100 gallons per day per foot. Quality of ground water in the spoil ranged from a total dissolved solids content of 1170 mg/l to 2490 mg/l in October 1976.

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