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SFNf BY~ 8- 4-93 ;12~44PM ; CANONIE ENGLEWOOD-~ ;#12/19 <br />• • <br />7 <br />7.0 GEOCHEMICAL EVALUATION <br />The analysts of seep water collected from subdrains below the falling dam (PS-1) <br />provides the expected chemistry of water that potentially could impact Williams Fork <br />River. The seep water has large concentrations of iron, fluoride, manganese and <br />sulfate, but it has a median pH that is near neutral. At this pH, most rnetais in the <br />seep water wilt be present as suspended particles rather than 1n a dissolved form. The <br />dominant transport of metals via ground water is as dissolved species. Therefore, <br />ground water metals movement from the falling dam probably would be limited. <br />Sulfate and pH can be used as indicators of potential movement of water from the <br />fallings dam. Sulfate Is a good Indicator of water movement because sulfate is <br />present In large concentrations in the seep water and sulfate tends tb move with the <br />ground water. Metals such as cadmium, copper, iron, lead, manganese and zinc react <br />with soil materials and move more slowly than sulfate. As long es geoc:hemical <br />conditions, such as pH and oxidation potential IEhI, are favorable, reactions remove <br />these metals from the ground water. <br />The movement of seep water wiU gradually resuh in a decrease In soli phi as the <br />buffering capacity of the loll Is depleted. When this occurs, some metals will be <br />mobilized and move with the ground water. The first metals to move as pH decreases <br />are cadmium, manganese and zinc. Iron and copper generally will become mobilized <br />next, with lead being the last metal to mobilize. <br />The relative movement of chemical parameters can be used to detect the first <br />appearance of seep water. The parameters that would be detected first would be <br />Increased sulfate and manganese and decreased pH. Iron Is not expected to be <br />detected prior to manganese because both are present In the seep water In similar <br />Concentrations, and manganese is generally more mobile than Iron. The occurrence <br />of Iron at HW-4 may Indicate enotfier source downstream of HW-7 nut upstream of <br />the site. <br />NI~W:YJ~17111r1~MLL.IR IA19•I.IK01 <br />