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Elevated levels of iron and fluoride may be attributed to natural (i.e., <br />not mining related) conditions, since elevated levels for those <br />parameters are not found in Seneca II spoil wells. In the case of <br />fluoride, the two wells (8P1 and 19) that have elevated levels have <br />historically displayed high levels. Those wells are also unique in <br />displaying a sodium bicarbonate type water; with almost no calcium, <br />magnesium, or sulfates; and with relatively high pH values. It is <br />suspected that the high fluoride values are related to this type of <br />water chemistry (Hem, 1989, pg. 121). All wells exist within the Seneca <br />II permit boundary. <br />In the case of iron, the one Wadge Underburden well (7) exhibiting high <br />levels may have higher than usual concentrations of iron pyrite in the <br />rock. The high levels of iron displayed in Alluvial Well 71 may be the <br />result of organic matter and plant debris present in the alluvium (Hem, <br />1989, pg. 77). These wells have historically exhibited high iron values <br />and all exist within, or upstream of, the Seneca II permit boundary. <br />High manganese values may, in part, be due to recharge from the spoil <br />aquifer, although high values are often common, especially in alluvial <br />material (Hem, 1989, pgs. 86-89). Manganese exceedances have occurred <br />at all alluvial wells, including the one Grassy Creek alluvial well <br />upstream of Seneca II (Well 71). This standard is used to protect crops <br />grown in soils with a pH value lower than 6.0. In January 2008, CDPHE <br />revised their ground water agricultural standard to reflect this pH <br />qualifier. In soils with a higher pH (as are found in the Seneca II <br />region), a more appropriate standard would be 10 mg/l (EPA, 1976). This <br />year, none of the Seneca II alluvial wells displayed a value higher than <br />3.04 mg/l, and no spoil wells displayed a value higher than 4.40 mg/l. <br />One spoil well (27) exceeded the selenium standard, 20 ug/1. However, <br />the selenium value from Seneca's GWPOC well in the Grassy Creek basin <br />was less than the standard (see below). <br />7