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_lg_ <br />Ground water resources in the permit and adjacent areas are limited in extent <br />due to lenticular lithologies of the potential water-bearing units and because <br />of previous mine dewatering. Three adjudicated wells were identified within <br />the permit and hydrologically adjacent areas: the Corley Mine Well, the <br />Corley Co. Well and the Thompson Well. The Corley Mine Well produces water <br />from mine workings in the Vermejo Formation. The Corley Co. Well produces from <br />the Raton formation. The Thompson well is within the permit area and was <br />developed in a localized coarse gravel Tense on top of a sandstone above the <br />Rex Carbon Seam. <br />It is evident from monitoring well records that a piezometric surface exists <br />in the permit area which is higher in elevation than the seam proposed for <br />mining. Drawdown effects to the Corley Wells would not be expected at present <br />due to their distance from the mine operation. However, as mining progresses <br />to the north drawdown effects could be seen. The Division has required <br />monitoring wells be installed and monitored in the area immediately north of <br />the permit boundary. These wells will serve to monitor both water quality and <br />quantity effects before they extend to the wells to the north. If in the <br />future data suggests that drawdown to the Corley wells may occur, Dorchester <br />Coal Company may be required to install additional monitoring wells closer to <br />the wells of interest and meet the requirements of Rule 4.05.15 pertaining to <br />water rights and replacement. <br />A well permit was issued for the Thompson Well in 1941. Total depth of the <br />well was 338 feet into the Rex Carbon Seam although the source of water is a <br />thin unit above a sandstone at a depth of about 320 feet. Subsequently, the <br />Rex Carbon Underground Mine was developed beneath this area and eventually <br />encountered the well casing. A pipe was connected to the well within the mine <br />workings and water was routed to the surface as a water supply for the <br />Thompson Ranch. At present, the pipe within the mine has been damaged. Also <br />the casing at the surface has been obstructed; both mine and Division <br />personnel have been unable to detect any water level within the casing because <br />of the obstruction. The Thompson Ranch is not inhabited. Available information <br />on the well indicates it is at present abandoned. Extensive drilling adjacent <br />to this area by Dorchester Coal Co. did not reveal any laterally continuous <br />aquifer that could serve as a regional water source. This would indicate that <br />the Thompson well is an isolated discontinuous water bearing unit. <br />Dorchester is mining the Dirty Jack Coal Seam about 380 feet beneath the <br />abandoned Rex Carbon Mine below the Thompson Well. This area has already been <br />mined under prior permits. Dorchester is proposing to retreat mine this area <br />within this permit term. The Thompson Well may have already been affected to <br />some degree by historic mining in the Rex Carbon and Dirty Jack Coal Seams. <br />Dorchester Coal Co. is not predicting any additional impacts to this well from <br />their operation due to their location below the well and intervening competent <br />sandstones. However, Dorchester has agreed to comply with Colorado Water Law <br />if an injury from their operation should occur to a valid active water right <br />holder. For the purposes of this assessment the Division is assuming that the <br />Dorchester operation will affect this isolated water source; a worst case <br />assumption. However, depending on the nature and magnitude of subsidence, <br />impacts to this water source may be insignificant. In the event of an impact <br />the operator has committed to taking remedial action under Colorado Water Law. <br />In order to verify the actual impact it will be necessary to monitor the <br />Thompson well. Therefore, the following stipulation is required: <br />