2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT faulting on the northeast side of the ridge, associated with collapse of the Gypsum Valley anticline, has truncated continuity of the Salt Wash Member. Therefore, groundwater flow to or from the Big Gypsum Valley towards the SMC area is suspected to be relatively minor. This is supported by observations during mining where little to no groundwater was observed in the shallow mine workings of the Salt Wash Member. The ridge between Big Gypsum Valley and Disappointment Valley acts as a hydraulic divide, any recharge that occurs at this location would eventually flow northeast or southwest. However, it is conceivable that any areal recharge that occurs to the Salt Wash on the northeast side of this divide could flow downdip to the southwest. The Dolores River, located several miles to the west and north of the SMC forms another hydraulic boundary. The Mesozoic rocks in the Dolores River canyon and further west dip gently to the east toward the axis of the Disappointment Valley syncline. A large area of exposed Salt Wash is present for several miles west and north along the flanks of the Dolores River canyon. The Salt Wash exposed in this area, likely receives areal recharge from infiltration of precipitation. The formation on the west side of the river may discharge groundwater to the river or provide lateral flow to the formation downdip to the east where the formation has not been truncated by the canyon. Elevations at the river due west of the SMC are between 5,540 to 5,500 ft amsl, similar to elevation heads measured in the area of the mines. The river may recharge water to the formation areas where it overlies or comes in direct contact with the Salt Wash. One such area is at and downstream of Slick Rock, Colorado. Further downstream, approximately one-half mile northwest of Slick Rock, Colorado, Cater(1955b) mapped the Summerville and Entrada Formations, which underlie the Salt Wash Member. Recharge from the river is not possible north and downstream of this area because the river has cut below the bottom of the Salt Wash; however, the Salt Wash may discharge to the canyon in the form of springs, seeps, or evapotranspiration. Hence, the presence of the Disappointment Valley syncline in combination with the hydraulic boundaries created by the ridge between Big Gypsum Valley and Disappointment Valley and the Dolores River provide for a limited flow domain for groundwater in the area. Weir(1983, Plate 2) presented a potentiometric map for the "upper groundwater system"which includes the Salt Wash Member. The map generally agrees with water level elevations Western Water& Land, Inc. 39