2008-05-14_REPORT - C1981014 - Laserfiche WebLink

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EFCI Southfield Mine -Year 2007Annual Hydrology Report April 21, 2008 3.0 GROUND WATER AND SURFACE WATER MONITORING RESULTS 3 1 Ground Water Monitoring Results Mine Area In the Mine Area, ground water occurs in surficial alluviaUcolluvial 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 alluviaUcolluvial deposits, these units do not store or transmit appreciable quantities of ground water 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 units known to be an aquifer in this area and bedrock ground water occurrences are limited to isolated units and zones that have sufficient local recharge and characteristics that allow it to store and transmit water. Therefore, in this area, isolated shallow perched ground water zones may develop. Additional "minor" ground water storage may occur in abandoned and flooded mine workings, which serve as collection and storage reservoirs as well as for origination of fracture flows (refer to Section 2.04.7 of the Southfield Mining and Reclamation Plan document for more details). In the Mine Area, the current ground water monitoring program includes the following monitoring wells, located as shown on Figure 1, Mine Monitoring Stations: Well Location Depth/Completion Completion Zone MW-16 E'/~NW'/<, Sec 30 136ft/106-136ft Jack O'Lantern Coal Seam MW-23 E'/zSW'/o, Sec 19 179ft/149-179ft Red Arrow Coal Seam MW-65 W'/zSW'/<, Sec 24 1,448ft1968-988ft Jack O'Lantern Coal Seam MW-NW W'/zSW'/<, Sec l9 380ftI360-380ft 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. Well MW-8 was mined-through in 1993 and immediately went dry. Subsequent monitoring showed that the borehole had collapsed to a point 336 feet below the surface. The water level recovered and gradually increased from the 280 foot level beginning in early 1996. Measured water levels in this well indicated that sub-surface conditions above the point of collapse had stabilized. In the final quarter of 1999, however, ongoing monitoring indicated that the well had again collapsed at approximately 250 feet below ground surface, making further water level measurements impractical. Caving occurred in MW-10 around May, ]996. The well was dry between May 1996 and eazly 2002, except for Mazch 2001. Monitoring was officially discontinued in October 2003 (TR-35). A former dewatering well, referred to as the North Well, was originally used to dewater mine workings in the Red Arrow Coal Seam north of the main mine. It was discontinued as a dewatering well in 1994. In 2003, it was converted to a monitoring well and subsequently referred to as monitoring well MW-NW. 2007 AHR.doc WP Page 6