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06/18/97 WED 08:32 FA% 5093548099 Rick Mills May 23, 1997 Twentymile Coal Company 29515 Routt County Road 27 Oak Creek, CO 80487 Rick, Yesterday I spoke with you concerning a proposed seismic monitoring test during the mine- through of the mid-panel entries. Tn some of our recent work in a hazdrock mine, we have developed a PC computer network-based seismic monitoring system that is fully automated. It is an outgrowth of some of the eazlier monitoring we did at Twentymile. To use these systems as effective engineering tools in coal mines requires fully-automated operation because of the much higher seismic event generation rate. Thus, we are interested in testing our automated processing software a; Twenrymile to see how well it handles the different chazacter of seismic signals and the higher event generation rates. Since some of my Spokane NIOSH colleagues aze also involved in the installation and monitoring of rock mechanics instrumentation surrounding the backfilled cross-panel entries, this opportunity is timely and very attractive for augmenting those studies. Access to the surface above the panels is also very easy. Enclosed please find a drawing showing the proposed layout of seismometers. Each seismometer would be buried in a hole approximately 12 to 18 inches deep and 12 inches itt diameter. t3y placing the dirt that is removed onto a plastic tarp, we have found that these holes are readily reclaimed afterwards. A small sheet of plywood is placed over the hole with the tarp and soil placed on top of it for the duration of the test. There will also be a plastic container on the ground at each site which contains the seismic amplifier. An individual cable will run i'rom each seismic sensor back to the wheeled travel trailer where the data acquisition, processing, and display computers will be housed. Where necessary, the cables will be fed under the rail in an existing c~a! vert. Depending upon the type and volume of traffic on the dirt road, the 1/4-inch diameter cables can either be ]aid down directly on the road surface, placed in a milled slot in planks, or buried. I understand that there is a power line running along the road between the 7-Right grout hole and the 10-Right dewatering shaft with possibly a transformer on a pole near an old home sate on the north side of the rail crossing. To be able to conduct this test, we would need to have 11.OV AC brought dov+n the pole so that we could use it in the trailer. We would :ike to monitor for a full week prior to the start of the mine-through of the entries, and for a few J:~ys following the thine-through. It will take us 2-3 days to set up. My understazlding is that the :nine-through will start at the very end of June or early July. At this stage of development, our system is not cattle-proof. We may test one of our digital radic transmission links at the time of the cabled-system test as a way of eliminating the cables to each sensor in the near future. Please let me know if this proposed test meets with your approval, if there would be any cattle r~ooz O