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Groundwater has low manganese concentrations (typically less than 0.050 mg/1), whereas,the <br /> sulfate high was 190 mg/l (but typically less than 50 mg/1). There are no analyzed trace metals of <br /> concern. <br /> 7.0 GROUNDWATER HYDROGEOLOGY <br /> 7.1 Geology <br /> The La Plata Mountains are a laccolithic type mountain group produced by the domal uplift of <br /> sedimentary rocks intruded by igneous stocks, dikes and sills (Eckel, 1949). Sedimentary rocks <br /> present within the La Plata district are shown within Table 1. <br /> The mine sites are located at the northern boundary of the San Juan Hydrogeologic Basin <br /> (Topper et. al., 2003). The Morrison Formation aquifer is the only designated hydrogeologic unit <br /> of the San Juan Basin present within the permit area. Insufficient data exists in the northern part <br /> of the San Juan Basin, including the May Day Idaho mine site, thus precluding the preparation of <br /> representative potentiometric surface maps (Dam et. al., 1990). <br /> Levings et. al. (1996)prepared a conceptual model describing groundwater flow within the San <br /> Juan Basin and the relevant controlling factors. The Morrison Formation is underlain by a <br /> confining layer(Wanakah Formation). <br /> The conceptual model of the San Juan basin developed by Levings et. al. (1996) includes the <br /> following components: <br /> • Precipitation on outcrops; <br /> • Stream channel loss as streams cross outcrops. (losing stream) ; <br /> • Discharge; <br /> • Springs and seeps in topographically low parts of the outcrop; and <br /> • Discharge from outcrop to stream channels. <br /> The Mayday and Idaho mines are located within southward-dipping sedimentary rocks cut by a <br /> series of east-west faults. Ore-bearing veins are north-trending, mainly found within the Entrada <br /> Formation (Eckel, 1949). <br /> The general stratigraphic relationship (from youngest to oldest) is: <br /> • Morrison Formation. Consists of upper Brushy Creek member bentonitic mudstone and <br /> lower Salt Wash member interbedded fine-grained gray sandstone and green-gray mudstone. <br /> The Morrison formation unit does not host economic mineralization. <br /> • Junction Creek Sandstone. Light-gray to tan, highly cross-bedded to massive, fine-to <br /> coarse-grained eolian sandstone (ore bearing). <br /> May Day Idaho Mine Complex <br /> M-1981-185 <br /> January 19, 2017 <br /> Page 1 -8- <br />