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. Table 3.6.1-14 <br />Copper Concentrations Observed <br />on North Thompson Creek <br />(all values in mgJl) <br />DATE UPSTREAM DOWNSTREAM <br />9/29/82 0.010* 0.022* <br />6/11/81 (0.001 (0.001 <br />8113/81 0.011* 0.001 <br />12116/81 0.009 (0,001 <br />3/26/82 0.006 0.047* <br />• *Exceeds CDOH standards of 0.01 mg/1. <br />These copper values are explainable when the regional geology is con- <br />sidered, Coal formations often have high concentrations of metals <br />associated with them. In addition, tertiary intrusion, which are com- <br />mon throughout the area, are also high in metals. As these formations <br />weather, the metals come into solution; but, because of the high pH of <br />the water in the region, the metals quickly precipitate out of solu- <br />tion or form complex compounds with clay and other metals and are not <br />readily in solution. <br />Figure 3.6.1.2-5, presents a graph showing values of zinc measured <br />during each sampling episode versus time. The pattern shown <br />corresponds with most of the parameters monitored on North Thompson <br />Creek. <br /> <br />3-79 <br />