2013-06-14_HYDROLOGY - C1981014 - Laserfiche WebLink

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Dan Hernandez Page 13 June 3, 2013 Groundwater monitoring has been limited to the coal seams and underground workings given the very low probability of any impact to the underlying Trinidad Sandstone or the overlying colluvial /alluvial deposits. Additional monitoring in the isolated saturated zones that may exist in the Vermejo Formation above the Red Arrow and Jack O'Lantern coal was not implemented because these perched zones are laterally discontinuous and have very low hydraulic conductivity. Establishing a network of monitoring wells above the coal seams mined was deemed impractical particularly since exploration drilling within the mine area did not encountered any significant aquifers or other groundwater resources. Given the extensive past surface and underground coal mining in the study area, groundwater impacts (both magnitude and extent) are difficult to predict. Results from the current monitoring program show that there has been little change in water quality within the coal seams and flooded mine workings of the Southfield Mine. AHRs have indicated that in general the water quality in the monitoring wells at the mine site has not significantly degraded over time. Groundwater within the coal seams and workings was likely compromised by historical mining prior to the current mining operation. Groundwater in the flooded mine workings, as well as water in coal or low permeability rock interbedded with coal down gradient of the flooded mine workings, does not need to meet water quality standards as indicated in the citizens complaint presented by the Vento family. As previously described and stated in Regulation No. 41, "Mining activities are recognized to occur within ground water bodies and that water quality within the disturbed area will obviously change." Further, and of major importance here is the fact that the Colorado Division of Water Resources recognizes that groundwater obtained from coal zones is known to be of degraded quality and advises against completing wells for domestic or agricultural purposes in these zones. I don't find any indication that wells within or adjacent to the permit area have been impacted by the current mining operation. There are three privately owned wells completed above the Southfield workings within and adjacent to the permit area as described previously. The Corley Company Well and the Thompson Well are both permitted by the Division of Water Resources. If the present landowners wish to install wells on the property for domestic or agricultural purposes then these should be located outside of the coal zones. Since existing groundwater quality within the coal seams and underground workings is known to be of degraded quality and likely also reflects the effects of previous coal mining activities, the Trinidad Sandstone or the shallow colluvial /alluvial deposits would be a better source for groundwater to be put to beneficial use. These geologic units have been unaffected by the mining. The mining operation has ceased and the workings have been properly sealed. There should be no reason to expect further disturbance at the site or further degradation of water quality within the Red Arrow /Jack O'Lantern coal seams or workings. MW -65 is operational and serves as the current down gradient monitoring well completed in the Jack O'Lantern coal seam. MW -65 is completed to a depth of 988 feet below ground surface. Additional monitoring of the coal zone is not warranted. Given the surface topography and geologic structure, to install additional wells down gradient of the mining activity one would have to go higher in elevation and drill a deeper well targeting the coal seam(s). Since groundwater in the coal seams is already known to be of degraded quality and unlikely that it would be put to beneficial use, this would provide little additional information and be both technically and economically challenging. Given the above