2022-09-06_REPORT - C1982056 (3)

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Foidel Creek Mine C-82-056 2021 Annual Hydrology Report Middle Creek Alluvial Groundwater: TC has no active Middle Creek alluvial wells. In 1996, two Middle Creek alluvial wells (AVM-1 and AVM-2) were incorporated into the monitoring network however, per TR03-42, these wells were abandoned in the Fall of 2003. Refer to previous AHRs for earlier data. 3.2.1 Points of Compliance Rule 4.05.13(1)(b) requires formal establishment of groundwater points of compliance for coal operation which has the potential for negatively impacting the quality of groundwater for which quality standards have been established by the Colorado Water Quality Control Commission. The Commission's Rule 41 sets forth Basic Standards for groundwater. These Standards are applicable to groundwater at the Foidel Creek Mine. In the judgment of DRMS, these Standards are applicable to groundwater at the Foidel Creek Mine, however it is also the judgment of DRMS, the Foidel Creek Mine does not have the potential to negatively impact bedrock aquifers due to the nature of the geology (i.e., synclinal basin) found at the mine's location. Wells 008-AV-2 (Foidel Creek alluvium), 008-AU-3 (Fish Creek alluvium), and well 008-AT-1 (Trout Creek alluvium) will satisfy the requirements for alluvial groundwater points of compliance. Water quality at these three wells were within the agricultural use groundwater standards for all parameters except for a single sample for iron at 008-AT-1. During the 2020 report period, the sample from 008-AT-1 collected on 8/30/20 had a dissolved iron concentration of 5.55 mg/L, and it was thought that the filter ruptured allowing solids typically removed during the required sample filtration to influence the analysis. The sample collected in May 2020 indicated the dissolved iron was 1.36 mg/L, which is more characteristic of the iron concentration at this well, and within the agricultural use groundwater standard. However, the two dissolved iron results from the 2021 report period showed concentrations of 17.2 and 35.8 mg/L for an unknown reason. The statistics reports show these are not the highest dissolved iron results for the well. Although dissolved manganese at all three wells exceeded the base agricultural use standard of 0.2 mg/L, its important to acknowledge that CWCC Regulation 41 specifies that this standard is only applicable to irrigation water applied to soils with pH values lower than 6.0. For alkaline soils, as are found in the area, a more appropriate standard would be 10 mg/L (EPA, 1976). Therefore, none of the manganese results above 0.2 mg/L are considered exceedances of the standard. 15