2013-03-06_REPORT - C1982057 - Laserfiche WebLink

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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 qualifier. In soils with a higher pH (as are found in the Seneca II -W region), a more appropriate standard would be 10 mg /l (EPA, 1976). This year, none of the Seneca II -W wells displayed a value higher than 2.02 mg /l. At the Seneca II--W shop well, Well 201TC, CDPHE drinking water standards were used to determine its suitability. No human health standards were exceeded. The secondary standard for iron (0.3 mg /1) was exceeded with a value of 0.52 mg /l. The secondary standard for manganese (0.05 mg /1) was exceeded with a value of 0.071 mg /l. However, bottled water is consumed at Seneca II--W. Also, since the aquifer for the shop well (Trout Creek Sandstone) starts at 280 feet below the Wadge Coal and is separated by confining shale layers, water from this well should not be affected by mining and, therefore, reflects the natural characteristics of the aquifer. Ground Water Points of Compliance A GWPOC have been established in the Dry Creek alluvium for the Seneca II -W Mine. Appendix 15 -33 of the Seneca II -W PAP provides the details. The .ground water standards for Dry Creek Alluvial Well DCAL -02 are provided in this AHR on Table 7. One exceedance of these standards occurred this year. The ambient -based standard for iron (8.06 mg /1) was exceeded with a value of 10.6 mg /1. However, see the discussion of iron in the previous section. This well displays an increasing TDS trend, with the peak occurring in May 2009. All values are less than 1700 mg /l. Ground Water Quality Summary. Increasing TDS trends were observed at eight wells downgradient of mining. Six downgradient wells exhibit stable or decreasing TDS trends. The GWPOC well for the Dry Creek Alluvium, DCAL -02, did not exceed the TDS GWPOC standard, 3195 mg /l, but did exceed the ambient -based iron standard. 7