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bicarbonates, sulfates and sodium. The high bicarbonate content <br />of most of the groundwater is mainly caused by contact with <br />the carbonate bedrock with additional contribution from the <br />leaching of the mineral nahcolite. Evapotranspiration further <br />increases the dissolved solids content. Table G-10 summarizes <br />the results of some of the goundwater analyses. <br />The quality of groundwater varies in the stratigraphic units. <br />Analyses of water from the Garden Gulch member show a much <br />poorer quality than was encountered in the Evacuation Creek <br />or Parachute Creek members. A decrease in water quality with <br />time was observed during air pumping of a well into the Garden <br />Gulch member as shown below: <br />Garden Gulch Member - Well (TH-9) <br />• Concentration, mg/1 <br />Constituent Initial value Value at t = 61 hr <br />Total dissolved solids 1,420 2,545 <br />Bicarbonate 890 1,450 <br />Alkalinity (M.O.) 728 1,190 <br />Chloride 207 580 <br />Source: Metcalf & Eddy, 1975 <br />G-25 <br />