2012-05-03_REPORT - C1981014 (2)

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EFCI Southfield Mine — 2011 Annual Hydrology Report April 25, 2012 3.0 GROUNDWATER AND SURFACE WATER MONITORING RESULTS 3.1 Groundwater Monitoring Results Mine Area In the Mine Area, groundwater occurs in surficial alluvial /colluvial deposits and as water table conditions in the sequence of sedimentary rocks corresponding to the Vermejo, Raton, and Poison Creek formations. Due to semi -arid conditions and the limited extent and continuity of the alluvial / colluvial deposits, these units do not store or transmit appreciable quantities of groundwater in the general mine area. There is limited lateral or regional continuity of potential water - bearing units due to variable lithology and significant cross- bedding and inter - bedding within the bedrock units. As a result, there are no known aquifers in the mine area, and bedrock groundwater occurrences are limited to isolated units and zones that have sufficient local recharge and characteristics that allow it to store and transmit water. Therefore, only isolated shallow perched groundwater zones may develop. Additional "minor" groundwater storage may occur in abandoned and flooded mine workings, which serve as small collection and storage reservoirs as well as for origination of fracture flows (refer to Section 2.04.7 of the Southfield permit application for more details). In the mine area, the approved groundwater monitoring program includes the following monitoring wells: Well MW -I6 MW-23 MW-65 Location Depth /Completion Zone Geologic Completion Zone r ; E' /2N W' /4, Sec 30 136' / 106' -136' Jack O' Lantern Coal Seam E'/ S W' /4, Sec 19 179' / 149' -179' Red Arrow Coal Seam W % S W' / <, Sec 24 1448' / 968' -988' Jack O' Lantern Coal Seam MW -NW W%SW1/4, Sec 19 380' / 360' -380' Red Arrow Coal Seam (mine void) Monitoring wells MW -7A, MW -7B, MW -8, MW -10, and MW -22 were previously included in the monitoring program, but have since been mined- through and eliminated from ongoing monitoring. Wells MW -7A, MW -7B, MW -22 were mined - through by Dorchester Coal Co. prior to 1985. EFCI later mined - through wells MW -8 and MW -10 during mining operations. A former mine dewatering well known as the North Well was originally used to dewater abandoned mine workings in the Red Arrow Coal Seam north of the main mine entries. EFCI discontinued its use as a dewatering well in 1994, later removing the pump and associated equipment. In 2003, it was converted to and approved for use as a monitoring well designated MW -NW. In Technical Revision 35 (TR -35), the approved groundwater monitoring schedule was reduced from quarterly to semi- annually and is typically conducted in June and December at the four monitoring wells. Field measurements and laboratory data for active monitoring wells are summarized in the following discussions. Field and laboratory data for 2011 are provided in Appendix A. Measured water levels for all wells are summarized in Table 3, Monitor Well Water Levels, for years 2000 -2011. Previous well water level data for all monitoring wells are documented in AHR's on file at the Division. All historic water level data are presented graphically for the four monitoring wells on Figures 3, 4, 5, and 6. 2011 AHR text doe Page 5