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.~ <br />well GP6 is approximately one-half of the value from well GPS. This <br />increase in TDS is thought to show the natural increase in TDS as <br />water moves downgradient in this aquifer. <br />The TDS concentration from Pyeatt alluvial well P1 has gradually <br />increased in the last four years. Recent concentrations are closer to <br />those values measured prior to 1964. The base flow in the Pyeatt <br />Gulch has gradually decreased in the last few years and the percentage <br />of the alluvial water near P1 which is contributed from the Lewis <br />Shale probably has increased. This increase would cause a natural <br />increase in the TDS in the alluvium in this area. The TDS for water <br />from the Lewis Shale well P3 has varied considerably. Water quality <br />• in a shale aquifer as the Lewis Shale would be expected to contain <br />high concentrations at times. TDS in well P3 has steadily increased <br />in 1987. TDS concentration in the Second White Sandstone well (P5) <br />has varied concentrations with time (see Figure B-25). TDS <br />concentrations have been rising since 1984. This variation is <br />probably caused by variable amounts of recharge. The TDS <br />concentrations from the Third White Sandstone (P8) in this area have <br />been much more stable. Figure B-26 shows a gradual increase in <br />concentrations with time, except for the August, 1983 value. <br />Only a few TDS data values are available for alluvial wells J1 <br />and Coy. Figure B-27 indicates an increasing trend in TLS for the <br />Johnson Gulch well. The 1986 value is significantly higher than other <br />. values, although it is believed to be a good measurement. A declining <br />3-6 <br />