2011-08-09_REVISION - M1981185 (56)

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Conceptual Hydrogeologic Model — May Day Mine — La Plata County, Colorado Prepared by: Frank Hagar, C.Hg.,P.G., C.E.G Geospatial Analysis, Inc. 1.0 PURPOSE The purpose of this study is to propose a conceptual model of ground water flow in the general vicinity of the Idaho No. 1 and the May Day No. 1 and No. 2 Mines located in La Plata County, Colorado. The secondary purpose of the conceptual model is to provide postulated flow regime descriptions that accommodate discharge from the Idaho No. 1 mine portal and describe potential sources of that discharge. The majority of the data for this study is from literature review as noted in the document. However, specific additional information regarding onsite conditions was solicited from Mr. George Robinson as the review was performed which he provided as anecdotal personal communication. This conceptual model should be refined as additional field data becomes available. 2.0 GEOGRAPHY The area in question is located on the nose of a southerly sloping hillside bounded on the southeast by Little Deadwood Gulch and on the west by La Plata River. The elevation increases in a northerly direction to the drainage divide of the La Plata River which is located approximately 8 miles north of the mine locations. The Idaho No. 1 and No. 2 Mine Portals are located in a watershed that drains into the La Plata River. The May Day No.1 Mine Portal is located in a watershed that drains into Little Deadwood Gulch and then into the La Plata River downstream of the Idaho Mine portals watershed (Figure 1). Figure 1 depicts both slopes of the watershed. The portal of the Idaho No. 1 mine is situated at approximately 8792 feet above mean sea level (AMSL). The portal of the May Day Mine No. 1 is located approximately 9318 feet AMSL. 3.0 GEOLOGY The Mayday and Idaho mines are located within southward- dipping sedimentary rocks cut by a series of east -west faults. Ore - bearing veins are north- trending, mainly found within the Entrada Formation (Eckel, 1949). The general stratigraphic relationship from youngest to oldest is: • Morrison Formation. Consists of upper Brushy Creek member bentonitic mudstone and lower Salt Wash member interbedded fine- grained gray sandstone and green -gray mudstone. The unit does not host ore. • Junction Creek Sandstone. Light -gray to tan, highly cross - bedded to massive, fine- to coarse - grained eolian sandstone (ore bearing). • Wanakah Formation. Consists of two members. This upper marl member is mostly white to tannish to pale- reddish colored, fine- grained sandstone, mudstone, and marl.