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ECOSA Evaluation AdrianBrown <br />2.5 Underground Mines <br />Within the Diatreme underlying the ECOSA footprint are the small historic underground workings of <br />the School Section Mine and the Cameron Mine, hosted by northeast- trending structures (Plate 2). These <br />historic mines extend from near ground surface to a depth of approximately 1,000 feet below ground <br />surface (elevation 9,130 ft msl). <br />The historic mines are reported to contain water at a depth of at least 500 feet below ground surface, <br />which is below the elevation of Grassy Creek. <br />2.6 Climate <br />The hydrologic system in the District is controlled by precipitation. The precipitation in the District has <br />been measured since the current surface mining has been undertaken, and is presented by month in <br />Table 1. In the period 1992 -2011 the area received an average of 19.28 inches per year of total <br />precipitation; one quarter fell in the winter and spring (mostly as snow), and three quarters fell in spring <br />and summer. In addition a station was added in Grassy Valley in March, 2002. The amount of <br />precipitation recorded at this station is approximately 71% of the precipitation measured at Rigi Station, <br />the main station used for the data in Table 1 for 2003 -2010, when there is comparable data. <br />2.7 Surface Water <br />The only potential surface water flow in the vicinity of ECOSA occurs in Grassy Valley'. The surface <br />water flow in Grassy Valley has been monitored continuously at three monitor locations since mid - <br />2009 The results of the average daily flow measurements for 2010 are presented in Plate 5, together <br />with the daily precipitation. <br />The following conclusions are drawn from analysis of the data: <br />1. There is no surface water flow during mid - October through mid - April, representing the period of <br />the year when the average daily temperature is below freezing. <br />1 The results of the flow and quality monitoring in the district are presented in the Cresson Project MLE2, Hydrologic Evaluation, <br />Appendix 2. <br />2 The flow was monitored by hand on a periodic basis (approximately monthly) in Grassy Valley at five locations from 1997 through the <br />present. The results were reported in the Amendment No. 9 hydrogeochemical report (ABC, 2008). However, the monitoring did not <br />provide an accurate measure of the actual streamflow, because the flow was highly intermittent, with the stream not flowing for much of <br />the year except when the average daily temperature is above zero, and there is precipitation of more than approximately 0.24 inches <br />within the prior two days, or the small spring snowmelt is occurring, typically over a few days in mid - April. Further, flow readings <br />typically concentrated on periods of precipitation or snowmelt, resulting in an over - estimate of the overall flow from the basin. <br />Continuous monitoring was initiated in September 2009, and has been maintained since. The continuous monitoring of the flow in <br />streams at this elevation presents substantial challenges, due to freezing of the stilling well attached to the flume from mid - October <br />through mid - April, and erosion around and siltation within the Parshall flumes during the remainder of the year due to the storm - driven <br />flash -flood nature of much of the flow. As a result, a substantially complete record has only been obtained at one location (GV -03) for <br />one calendar year (2010). These data are used for the evaluation reported herein. <br />1385E.20120224 3 <br />