Laserfiche WebLink
u <br />TECHNICAL <br />(DRAFT) <br />TO: <br />FROM <br />DATE: <br />RE: <br />Mountain Coal Company <br />Kathy Welt and Christine Johnston <br />Wright Water Engineers, Inc. <br />Jon Jones, Jonathan Kelly, Gary Witt, Rich Dunrud and John Rold <br />March 7, 1997 <br />Probable Hydrologic Consequences Technical Revision Summary <br />I. PURPOSE <br /> <br />This technical memorandum evaluates the probable hydrologic consequences (PHCs) of the 1 <br />two topics which are [he focus of the PHC Technical Revision: 1) B East Mains fault inflow', U <br />and 2) Northwest (NW) and Northeast (NE) Panel sealed sumps. This memorandum focuses ? <br />on how these issues interrelate and how Mountain Coal Company (MCC) has managed the uj <br />unprecedented mine inflows that occurred in 1996 and early 1997. The following text and/or W <br />subject matter can be found in various locations throughout Section 2.05.6 of the February Z <br />1997 Technical Revision. t7 <br />II. PERSPECTIVE Z <br />W <br />TI>e West Elk Mine began operations in 1981. For 15 years, until March 1996, the PHCs from ii <br />both F- and B-Seam mining activities were predictable and not especially noteworthy. For Q <br />example: 3 <br />1. Lon term roundwater inflows were a roximatel l2 allons er minute m - <br />g- g PP Y g P (gP ) ~ <br />_ <br />modest by any standard. V <br /> <br />2. The maximum groundwater inflow rate was roughly 50 to 100 gpm, which tapered off in a 3 <br />matter of days to less than 5 gpm. <br />3. The quality of these groundwater inflows, like water from [he monitoring wells, was <br />suitable for direct discharge into the North Fork Gunnison River (North Fork). Because <br />of operational handling and intermingling with mine process water, MCC treated all mine <br />outflow water prior to dischazge. <br />4. Land subsidence in response to both room-and-pillar and longwall mining did not <br />measurably alter the pre-mining surface water hydrologic regime. <br />This PHC evaluation was completed by WWE in late January 1997. At approximately the time that WWE was <br />completing its study, a large new fault in0ow was encountered at the 1 SE Headgate at the N2 Entry•, between Cross-cuts <br />!!10 and NI I. MCC's instruction to WWE was to not evaluate the new fault inFlow in detail at this time, because the <br />overriding need was to present the revised PHC evaluation to CDMG. Also. MCC felt it important to collect enough <br />quantity/quality data fbr \V N'E to conduct a thorough evaluation of the nature and implications' of innows t}om the I SE <br />Headgate (cult. Therefore. W WE's evaluation addresses the new fault inflow to only a limited extent Ho++•ever, based <br />on the available data fur the I SE Headgate fauh inFlows as of late Januan• 1997, many of W WE's findings on the PHCs <br />of the B East Mains fault will probably also apply to the I SE Headgate fault. <br />' ~~~ II~I~~II~II~~ I~~ ~ <br />