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• ~• Bedrock GROUND WATER MONITORING Wells in the Wadge Overburden (which includes the Wadge Coal), overlying Twentymile Sandstone, and underlying Trout Creek Sandstone aze monitored in the mine site area. Three Trout Creek wells aze monitored for water level and water quality and one well is monitored for water level only. Four Wadge Overburden wells and two Twentymile Sandstone wells are monitored for water level and water quality. Fish Creek AVF mining area wells are reported in Appendix B. Water Levels Water levels in the Trout Creek Sandstone are plotted on Figures 3 through 6. The plot of the data for Well-83-106 (Figure 3) shows large water level fluctuations that result from frequent intermittent pumping, until 1991 when the well was pumped fairly continuously. The 1993 data for this well indicate slightly lower water levels than measured in previous yeazs due to the more continuous pumping. Plots of water level data from wells 001-83-107 (Figure 4) and 008-75-EFC-3-2 (Figure 5) do not indicate any long term trend in water level, althoughlhere annParc rhat there was a decline in 1993. The plot of water level data from well 006-83-48C (Figure 6), located within the mined area, indicates a declining trend since the spring of 1987, with the lowest water level recorded in the fall of 1991. Well 006-83-48C was mined through during the 1993 water year, and is replaced by FCMk2._ Completion problems with FCM#2 yielded a questionable pressure reading, which appears to have resulted in an anomalously 1 `~, ~ ~ water level value. The well is in the process of being reworked, and Halliburton wil ~ called to complete high ressure routin of the we If this grouting technique snot . ~` ~ work a new we will have to be installed. Present mine inflow data do n~ndicate any "' ~J~ significant contributions from the Trout Creek Sandsto very the water level declines in some monitorin wells indicates that som pressurization of the aquifer rn the vicinity of the mine may have occurred. of mining on the Trout Creek Sandstone Aquifer are much less than predicted in the "Probable Hydrologic Consequences" section of the mine permit application, as discussed in more detail in the "Impacts" section of this report. abandoned. Plots of water levels in the Twentymile Sandstone wells are presented on Figures 7 and 8. They do not indicate any pattern that might be related to impacts from underground mining. Well 006-82-48A was also mined through during the 1993 water year, and is replaced by previously installed well 91M005. Water levels in this well declined following undermining, but this is thought to be the result of the loss of the well seal below the sandstone as mining passed, given that this well was originally drilled to the Wadge and was then converted to a monitor well. This well has subsequently been -2- 6/10/94 1:23 pm