2018-03-09_REPORT - C1981044 (2)

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Table 1 A presents a summary of hydrologic monitoring requirements for these sites under TC (modified from TRO 1-32, Appendix D of the TC monitoring plan). Table 1B outlines monitoring and sites required when off of TC. Water quality monitoring includes field parameters (Table 2), surface water quality parameters under TC (Table 3A), and off of TC (Table 313). CDPS parameters (Table 4) are the monitoring requirements page from CDPHE CDPS permit CO -0042142. 3.1 Groundwater Monitoring 3.1.1 Bedrock Wells Three sandstone aquifers are found beneath the subject site. In ascending order, they are: Trout Creek Sandstone, Middle Sandstone, and Twentymile Sandstone. The Eagle No. 5 and Eagle No. 6 Mines are located between the Trout Creek Sandstone and the Middle Sandstone. Water Levels Trout Creek Sandstone: Water level measurements in the Trout Creek Sandstone No. 5 Mine well are shown on Figure 3. Historical annual water level fluctuations of 20 to 200 feet have been observed at this well but no seasonal pattern is evident. Note that recent water levels (2006 to date) were lower than levels measured prior to TC. This drop is apparently from consistent subsurface dewatering with the No. 5 mine pump. Levels remained relatively consistent from 2006 through 2008. There was a general rise in water level of about 40 feet in 2009, through 2012. This is due to periodic down time from malfunctions of the No. 5 mine pump. During the last quarter of 2012, the pump failed, resulting in no discharge. The pump was replaced in the spring of 2012, but stopped operating in July 2013 when power was removed from the site. Note the higher water level for No 5 at the end of 2017 indicates how the water level had risen without pump dewatering over three years. The former Okie Plaza Trout Creek well was abandoned in June 1994 as mining advanced through its location. Middle Sandstone: The water levels in the Middle Sandstone formation as measured in wells TR -4, TR -7a, 81-01, 83-01, 83-02, and 83-03. Historically these show fluctuations which are apparently related to dewatering and past subsidence associated with Mines 5 and 6. Wells TR -4 water levels appear to be slightly rising since about 2008 (Fig. 4). Levels in TR -7A (Fig. 5) have risen about 11 feet since 2013. 8 1 -01 in 2017 is relatively consistent with that seen prior to TC (Fig. 6). The water levels in 83-01 (Fig. 7) have been on the rise since monitoring was reactivated in 2006. The water levels in well 83-02 (Fig. 8) are consistent with those found since monitoring was reactivated in 2006. The water level decline of about 150 feet from 1987 to mid 1990 in well 83-02 was determined to be related to mine dewatering as Mine 5 workings approached the location of the well. The more abrupt 200 foot decline in water levels observed in 1990 is thought to be a drawdown response due to subsidence as it is located only a few hundred feet horizontally from an F seam longwall panel which was mined in a similar time frame. The water level stabilized until 1994 when it recovered to the 1983 levels. 0