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requires careful management practices. <br />A majority of the other major ions follow a pattern similar to one <br />observed for TDS. Plots of magnesium (Figure 3.3-18) for both <br />sites on Alkali Creek and the Colorado River show the same seasonal <br />trend as TDS, higher concentrations during base flow and low <br />concentrations during high flow. <br />Analysis of the data indicate that the difference between the <br />upstream and the downstream site is greatest during high flow and <br />almost equal during base flow. A possible explanation of this is <br />that. the upstream site is influenced primarily by overland flow, <br />which is greatest in the spring and early summer as a result of <br />snowmelt. This runoff is good quality water, low in TDS and other <br />ions, so it results in dilution. Because there are no major <br />impoundments upstream of the upstream monitoring site to regulate <br />flow, the concentrations observed at the upstream monitoring are <br />lowest during high flow. <br />Flows at the downstream site are regulated by irrigation impound- <br />ments on Alkali Creek, thereby reducing the dilution during periods <br />of high runoff. This is reflected in the different water quality <br />concentrations between the up and downstream stations during <br />periods of high flow. However, during periods of low or base flow, <br />concentrations at the two monitoring sites are similar. Observed <br />differences in water quality are small, but the higher concentra- <br />tions for some species at the downstream site may be due to local <br />geology. The upstream station is located on the Wasatch and Ohio <br />Creek Formations, which are sandstones and siltstones, whereas the <br />downstream station is located on the shales and coals of the Upper <br />Mesa Verde Formation. <br />• <br /> <br />No unusual field measurements were observed during the period of <br />monitoring on Alkali Creek. At times during the summer months, it <br />was often difficult to obtain representative flow rates and samples <br />from the downstream site, because a portion, and at times, all of . <br />NCEC - Coal Ridge #1 3-48 ASC/1145/900301 <br />