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outlier. The field conductivity indicates that the outlier TDS is <br />• caused 6y a lab error. The last three TDS values are greater <br /> than the HI aquifer would have likely contained in this area <br /> prior to mining, as expected. The TDS of the backfill aquifer in <br /> this area is probably only approximately 1.5 times the pre-mine <br /> value in the HI aquifer. TDS in backfill aquifers should be <br /> elevated for several years after mining until the readily <br /> dissolved constituents are removed. <br /> The QR aquifer is monitored downgradient of a portion of the <br /> mined E pit at well GF6. TDS measurements from this well have <br /> fluctuated (see Figure 8-19) but are thought to be well within <br /> the range expected for natural fluctuations. <br /> Well GF7 was completed during 1987 in backfill material. <br />• The TDS data collected to date are presented on Figure 8-20. The <br /> data presents gradually rising values for TDS with the exception <br /> of the September value. The September value is from water <br /> collected from a pumped sample. This was the first pumping of <br /> the backfill well since installation. Pumping should result in a <br /> better average concentration sample from the well and is probably <br /> a more representative value of the dissolvable constituents in <br /> water moving through the aquifer. The TDS values from the three <br /> bailed samples are probably indicative of only the upper portion <br /> of the aquifer. Future pumped samples will help determine if the <br /> pumped samples show higher dissolved solids versus bailed samples <br /> in this particular backfill well. The data indicates that the <br /> backfill water quality at well GF7 has a higher TDS value than <br />• that observed at backfill wells GFS, GF11 and 6D3. <br />3-5 <br />