2011-02-25_REPORT - C2009087 - Laserfiche WebLink

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number of exceedances out of the total number of samples (i.e., 1/2 indicates one exceedance out of two samples). Below is a summary of standards that were exceeded. Given in parenthesis is the source and use of each standard. Parameter pH (CDPHE, irrigation) Fluoride (CDPHE, irrigation) Iron (CDPHE, irrigation) Manganese (CDPHE, irrigation) Selenium (CDPHE, irrigation) Zinc (CDPHE, irrigation) # of Wells / # of Excursions 9/9 3/3 1/1 9/15 1/1 1/1 Elevated levels of iron and fluoride may be attributed to natural (i.e., not mining related) conditions, since elevated levels for those parameters are not found in PSCM spoil wells. In the case of fluoride, the two PSCM wells (8P1 and 19) that have elevated levels have historically displayed high levels. All three wells are also unique in displaying a sodium bicarbonate type water; with almost no calcium, magnesium, or sulfates; and with relatively high pH values. It is suspected that the high fluoride values are related to this type of water chemistry (Hem, 1989, pg. 121). All wells exist within the PSCM permit boundary. In the case of iron, the one Wadge Underburden well (7) exhibiting high levels may have higher than usual concentrations of iron pyrite in the rock. This well has historically exhibited high iron values and exists within the PSCM permit boundary. High manganese values may, in part, be due to recharge from the spoil aquifer, although high values are often common, especially in alluvial material (Hem, 1989, pgs. 86-89). Manganese exceedances have occurred at all alluvial wells, including the one Grassy Creek alluvial well upstream of Seneca II (Well 71). This standard is used to protect crops grown in soils with a pH value lower than 6.0. In January 2008, CDPHE revised their ground water agricultural standard to reflect this pH 7