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r Page 2 Pfr. J. Herron December 11, 1980 Northern Coal Company amount of subsidence, Northern has located five subsidence monitoring points in the valley bottom overlying and adjacent to the area to be mined. These locations and elevations are also noted on the attached map PfE-7960-10-1/2. These points represent locations directly over mined entries (points 8;.10, 11 and 12) and locations within the area of influence of mining (HRJ-1 and HRG-1). Two horizontal survey control points (P and.JLW No. 1) and one vertical survey control point (USGS Benchmark H384) are also noted on the map. This approach will allow us to obtain a full range of information in the area. The elevation of these points has been surveyed in prior to mining and will be measured again six months after mining has occurred and information will be forwarded to the CMLR staff. We are sure that by leaving the barrier pillars in place, no subsidence will occur and we feel confident that the post mining subsidence information forwarded to CMLR will reflect this also. Subsequent monitoring of these points can be done if it is apparent' from noticeable changes iri the highway .that subsidence may be occurring or that water is entering the mine. At this time, we have not scheduled ' additional surveying for these points. II. Monitoring the Volume of Water Encountered Burin Paining Obviously, one indication that our mining is having an'~effect upon Curtis Creek would be that noticeably greater amounts of water would be encountered during mining under Curtis Creek. If greater volumes of water were encountered, it would be a signal that surface water and ground water monitoring fre- quency should be increased in order to determine 'whether .the surface or ground water flow of Curtis Creek had been significantly diminished. First, it must be pointed out that mining in the Meeker area has always resulted in some water being produced underground. The real problem is to determine how much water is being encountered over and above 'that amount which is "normal". In order to determine how much water' is normally encountered,'Northern has implemented a system for monitoring the flow of water as it is pumped away from the face. This system is designed around a totalizing flow meter attached to a 7~ inch Hays pump. The pump has a 130 gpm capacity. The system works as follows: At a minimum of once a week, starting at least three weeks prior to mining under:Curtis Creek, the faces will be pumped completely dry. A log book is being kept at the pump and the starting time will be logged in. When the face is dry, the pump will be turned off and the shut off time will be logged in the log book. Then.the flow meter will be used and the gallons will be entered into the log book.