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iii iiiiiiiiniiiiii 999 Doc Date:1211112001 • FISH CREEK ALLUVIAL VALLEY FLOOR STUDY AREA 2ND HALF 1993 1.0 INTRODUCTION As part of the approval to undermine and subside a segment of Fish Creek and its associated alluvial valley floor Twentymile Coal Company established and extensive hydrologic monitoring network. Additionally, Twentymile prepared channel profiles of Fish Creek which began upstream of the mined area and extended through and downstream of the mined area. Also, Twentymile conducted vegetation surveys pre and post mining in areas both within and outside of the mining areas. Finally, the information presented in the first section of this report presented the subsided data collected from the various subsidence monuments located within the Fish Creek study area. 2.0 STATION ELEVATION SURVEYS Tables 1 through 41 provide the hydrologic monitoring station elevation data collected during the period of July 22, 1993 through December 31, 1993. The July 22, 1993 data is used as the baseline elevation for the various sites, except as noted on table 2. This date was chosen due to the fact that mining activities have not • previously impacted any of the stations established along Fish Creek and in its valley floor, and that mining of panel 6 would begin in September, 1993. The approved mining plan indicates that panel 6 would have the greatest potential of subsiding Fish Creek and its valley floor. The survey data gathered during this time period showed that the following sites were subsided: GWA6, GWAP7 and GWB2. All of these wells showed that they have begun subsiding when they were surveyed on October 18, 1993. The extent of subsidence varied from 1 to 2.4 feet. The remainder of the stations did not experience any significant subsidence. Station GWAPS appears to warrant further review as the data indicates the well's measuring point is rising as opposed to subsiding. This may well be a survey error. 3.0 HYDROLOGIC DATA The field parameters for the various hydrologic monitoring stations are presented on tables 42 through 55. In general the majority of the stations have not been impacted by the mining operation. Of the various sites only three have been subsided by Twentymile's mining operation, those being: GWA6, GWAP7, and GWB2. Well GWB2 was replaced subsequently by well GWB2R. Well GWA6 started showing subsiding during October, with 1.0 feet • of subsidence being reported for this well on October 18, 1993. By the end of the year the well had subsided a total of 1.3 feet. The