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George Patterson <br />July 19, 2013 <br />Page 5 <br />connected to the mine workings. The water levels in the wells have not recovered at this time, <br />approximately 15 years after dewatering activities have ceased. This is expected due to the low <br />hydraulic conductivity and limited horizontal contiguity of the Vermejo Formation and the coal <br />seams at this location. This continued trend of repressed water levels in the monitoring wells <br />supports the slow rate of inflow into the mine which has been expected and observed. <br />Due to the fine grained nature of the Vermejo Formation, the low hydraulic conductivities and <br />limited horizontal contiguity of lenticular layers, the dewatering of the mine is not expected to have <br />any effect on any of the other geologic units in the area and monitoring of other units or coal seams <br />is not necessary. <br />We agree with Mike Boulay's assessment presented in the June 3, 2013 interoffice memorandum to <br />Dan Hernandez that the use of the MW -23 and MW -65 wells is adequate to determine the effects of <br />mining activities on the quantity and quality of ground water in the area due to the extent of the mine <br />workings and the hydrogeology of the local units especially considering that there will be no water <br />at the MW -NW location to sample for at least 106 years, if not as long as 120 years, into the future. <br />North Entry Well (MW -NW) Monitoring <br />Because it is projected that water in the mine will not reach the observation point elevation for the <br />MW -NW well for approximately 106 to 120 year years after the year 2000 or until between the years <br />2106 and 2120 and there are two existing wells that can currently be monitored as part of the <br />Southfield Mine monitoring program, the monitoring of the MW -NW well or any other well at that <br />location does not provide any additional information regarding the ground water conditions resulting <br />from the previous mining operations. Accordingly, the MW -NW well could be removed from the <br />monitoring program without affecting the findings of the monitoring program. <br />If you have any questions or need additional information, please give us a call. <br />Very truly yours, <br />BISHOP - BROGDEN ASSOCIATES, INC. <br />/' <br />Timothy A. Crawford, P.G. <br />Project Manager /Hydrogeologist <br />TAC /jeb <br />Enclosures <br />2018.04 <br />