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~ Water Quality • Summaries of the water quality for Station 109 are presented on Tables 52 and 53 and for Station 115 is presented on Table 58. The plots of field conductivity of the Pond D and Site 109 dischazges are presented on Figures 46 and 47. Prior to the second half of 1986 the average conductivity level was approximately 2000 umhos/cm. In the second half of 1986 the level increased to approximately 3300 umhos/cm. No significant increases have been noted since those observed in 1986. This increase probably has occurred from the advancement of the front of high dissolved solids water in the Wadge Overburden aquifer as indicated by the 1986 and 1988 Inflow Studies. This is confirmed by the quality of the water discharged with the dewatering of the old workings. The dischazged water is a mixed cation -sulfate water type. Most metal concentrations are low. Iron at Station 109 was relatively high in 1987 to 1993, with the exception of 1991. Due to the loading problems encountered with routing the discharge from the old workings to Pond D, this discharge was re-routed to [he Fish Creek Borehole through the gob area underground. The plot of field conductivity for the Fish Creek Borehole discharge and Fish Creek is presented on Figure 45. Conductivities during 1993 ranged from 2500 to 7200 umhos/cm for Site 115, while Fish Creek monitoring stations showed consistent levels which were within the range of previously measured values. Total dissolved solids range from 1658 to 6652 mg/1. No significant long-term increase in conductivity or TDS is C apparent in Fish Creek resulting from discharge from the Fish Creek Borehole. • Monitoring indicated an increasing trend in the observed TDS values as dewatering activities flushed through the underground azeas, but data indicates that this was transitory in nature. In early June, the pumps at the borehole failed, and could not be replaced due to circumstances beyond TCC's control until late July. Following start-up, elevated TDS and iron levels were observed. Steps were taken to address possible treatment options and to minimize discharge to the greatest degree practicable without endangering the mine. Following completion of the dewatering activities and the implementation of a revised treatment system, fall 1993 and 1994 data has shown TDS and iron levels to have returned to near normal or below normal, respectively. It is thought that the detention of the water for an extended period behind the seals underground while the pumps were being replaced presented an opportunity for iron reducing bacteria to flourish in the low-oxygen atmosphere. This in turn resulted in elevated iron levels as noted in the data report segment of the AAR. It is also thought that the increased retention time of the water behind the seals contributed to higher than anticipated TDS levels for a short period of time. ~• ~ ~ o~ `~`' ~~ -12- ~ ~ 6/10/94 1:23 p 1 1~ ~~,vu"~1~` ~ ~,~, w~~