2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

Home Browse Search

SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT at the mines. This is related to the underlying geologic structure (i.e., the presence of the Disappointment Valley syncline). The mines of the SMC fall on the northeast limb of the syncline and the Dolores River is located on the opposing limb to the southwest. Any groundwater recharged to the Salt Wash will likely flow toward the synclines axis, which trends down the center of Disappointment Valley. This hydrogeologic condition, in addition to the low permeability of the Top Rim unit, suggests an almost stagnant flow regime where groundwater flow may oscillate between recharge and discharge at the Dolores River. In a case where flow may be to the Dolores River from the SMC area, indicated travel times would be measured in thousands of years. The occurrence of groundwater in the mine workings indicates that the Top Rim unit was basically unsaturated in the upper workings and only began to show saturated conditions in the deepest workings of the mines. Inflow in these areas is gradual and driven by the confined conditions of the aquitard at depth and the low pressure differential provided by the open workings. Mine inflow will continue until a "static" potential head is reached; this will likely be between 5,500 and 5,600 feet amsl. Groundwater chemistry data indicate an evolution of water chemical signatures in the downgradient direction; overall water quality decreases in this direction and water becomes more saline, a result of greater residence time. The exceedance of BSGWs in the downgradient areas is expected due to natural concentration of dissolved mineral constituents with time. There is no indication that up or downgradient groundwater has become contaminated as a result of mining activities. In a saturated condition, the naturally occurring dissolved constituents associated with the uranium and vanadium ore zones would be expected to be present in downgradient locations as a result of natural groundwater leaching and flow from the SMC area over geologic time. However, existing data appear to indicate that most of the mine workings have not been in a saturated condition since mining began. With the deeper workings penetrating the confined area of the Top Rim, areas not previously saturated will become saturated up to the static potentiometric level. If the mines were to remain inactive, groundwater chemistry in the flooded workings would, at least to some degree, reflect constituents present in the mineralized zones. This is not of great consequence since the Top Rim unit is of low permeability (an aquitard), Salt Wash groundwater is not and will likely not be used in the future in Disappointment Valley, and potential travel times to the Dolores River are exceedingly long. Western Water& Land, Inc. xiii