2019-03-11_REPORT - C2009087 (2)

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Spoils. Two wells are used to monitor the water quality of the Spoils. Well 61 is located a half -mile south of the Pecoco Pond. It displays a stable IDS trend. Well 62 is located above NPDES 004 Pond. It displays an increasing TDS trend. Comparison of Ground Water Quality to Water Use Standards. The PSCM has compiled a list of ground water standards for agricultural uses (Table 5). This list is composed of Colorado Department of Public Health and Environment (CDPHE) ground water standards (CDPHE, Reg. 41, May 2008). Table 6 in Appendix A provides a comparison of ground water quality data collected this year to agricultural standards. The Paradox database generated table does not include the units of concentration (mg/l or ug/1) for each parameter. The units used for each parameter are the same as those listed on the standards table (Table 5) and are the same as those used in the water quality reports. The frequency column on Table 6 indicates, in this order: uncensored, that is, the number of exceedances above the Method Detection Limit (MDL) / the number of exceedances between the MDL and the Practical Quantitation Level (PQL) / censored, that is, the number of sample values below the MDL but the MDL was higher than the standard / the total number of samples. Below is a summary of standards that were exceeded. Given in parenthesis is the source and use of each standard. Parameter # of Wells / # of Excursions pH (CDPHE, irrigation) 2/2 Fluoride (CDPHE, irrigation) 1/1 Manganese (CDPHE, irrigation) 3/5 Elevated levels of fluoride may be attributed to natural (i.e., not mining related) conditions, since elevated levels for that parameter are not found in PSCM spoil wells. However, elevated values of fluoride were found in many wells before, as well as upgradient of mining. Well CW2701 had elevated levels of fluoride this year and has historically displayed X