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positively charged ions such as calcium (Ca2 +), magnesium (Mg2 +), potassium (K +), and sodium <br />(Na +)• <br />The tendency of chemical ions in solution to sorb to a given mineral varies. Ions in solution with <br />a greater electrical charge and smaller hydrated radius tend to sorb more than ions with a smaller <br />charge and large hydrated radius. For example, divalent ions such as calcium (Ca2 +) and <br />magnesium (Mg2 +) more readily sorb than monovalent ions such as potassium (K +) and sodium <br />(Na +). When a group of chemical elements have the same electrical charge, smaller hydrated ions <br />sorb more strongly than larger hydrated ions. For example, calcium (Ca2 +) sorbs more strongly <br />than magnesium (Mg2 +), and potassium (K +) sorbs more strongly than sodium (Na +) (Lloyd and <br />Heathcote, 1985). Domenico and Schwartz (1990) 'characterized the affinity of inorganic <br />constituents for sorption in the following sorption series: <br />Al'+ > Ca2+ > Mg2+ > NH4+ > K+ > Nat <br />One ion may replace another ion associated with a given mineral surface. This process is called <br />ion exchange, and it is common when groundwater flows through a clay - bearing aquifer. Calcium <br />and sodium ions are often involved in ion exchange. As groundwater flows through the aquifer, <br />calcium ions typically displace sodium ions from the surfaces of clay minerals. This exchange <br />causes the calcium concentration in groundwater to decrease while the sodium concentration <br />increases. Based upon the above ion exchange and sorption series, well M -14 would have <br />exhibited an increase in sodium concentration prior to a calcium increase, if the well was being <br />mixed with water from a source containing a high concentration of sodium, such as the LTF. This <br />was not the case in well M -14 and no increase in sodium concentration has been observed, as <br />shown in Figure 10. <br />6.3 Analytical Summary <br />As required under the LTF monitoring program, a grab sample is routinely collected on a monthly <br />basis from the LTF pond and on a quarterly basis from the collection ditch and collection pond <br />leak detention system for the LTF target constituents arsenic, calcium, copper, WAD cyanide, iron, <br />sodium, and zinc. A review of the historic LTF monitoring system analytical data was performed <br />to evaluate potential impacts of the LTF, as it relates to the increased elevations of TDS at M -14. <br />TR -32 M -14 TDS Response Plan Report AES, Inc. <br />Battle Mountain Resources — San Luis, CO 11 January 2015 (Update) <br />