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6.0 SURFACE -WATER QUALITY -- Continued <br />6.2 pH <br />The pH of Streamflow Generally Is Almost Neutral <br />to Slightly Alkaline <br />The pH of streamflow fluctuates from 6.7 to 9.3. <br />The pH of water is a measure of its acidity. If <br />the pH is 7.0, the water is neutral. Water with a pH <br />less than 7.0 is acidic, and water with pH greater than <br />7.0 is alkaline. According to Hem (1970, p. 93), the <br />pH of streamflow generally is between 6.5 and 8.5 <br />unless it has been affected by pollution. The pH of <br />streamflow at sites in Area 61 is usually within this <br />range of values (fig. 6.2 -1), although values greater <br />than 8.5 have been measured at some locations. <br />Because pollution sources that might cause exces- <br />sively alkaline water are not known to exist in Area <br />54 <br />61, it is presumed that pH values greater than 8.5 are <br />caused by natural processes. For example, excessive- <br />ly alkaline water can result from use of dissolved <br />carbon dioxide by aquatic plants during periods of <br />active photosynthesis. These periods occur during <br />daylight hours when most measurements of pH in <br />Area 61 were made. Although data are somewhat <br />limited, the pH of water from sources related to coal <br />mining in Area 61 (table 6.2 -1) is neutral to alkaline, <br />but is within the range of pH values measured at <br />streamflow stations (fig. 6.2 -1). <br />