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r P Tiu l f ~ (r`. ~~~ , ~~ III IIIIIIIIIIIII III ~ 999 CTL/THOMPSON, INC. CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS February 19, 1991 Colowyo Coal Company 5731 State Highway 13 Meeker, Colorado 81641 Attention: Mr. Bob Trumbly, P.E. Mine Planning Engineer Subject: Seismic Monitoring and Building Condition Evaluation Durham Ranch 396 Highway 13 Meeker, Colorado ob No. 17,5 { 8 Dear Mr. Trumbly: On January 10, 1991 a representative of CTL/Thompson, Inc. installed a Thomas S00 Seismograph at the above site, leaving it for your use in monitoring ground motion and air blast effects from the blasting at the Colowyo Coal Company mine upon the Durham Ranch. In addition, on January 10 and I I, 1991 we inspected structural and architectural elements of four buildings on the site. This letter describes The work performed on the site and includes a report of the initial building inspection. The Thomas 500 seismograph is a device for recording the output of a 3- directional geophone and a sensitive microphone. The device constantly monitors these outputs, recording significant seismic events on a magnetic disk only when the events exceed the ground motion or air overpressure limits that are programmed into the device's trigger mechanism. When triggering occurs, events are recorded on the magnetic disk and are graphically portrayed on the seismograph's printer. The seismograph was installed in the smokehouse located on the Durham Ranch property roughly 180 feet north of the ranch house (Building No. I in our structural-architectural evaluation). The geophone was embedded in the earth floor, the microphone was placed inside the structure adjacent to an open window, and the recording and analytical components were placed on a shelf protected from the weather and ground-dwelling rodents. These latter two components were connected to a 115 volt power source To maintain the battery charge, and were warmed constantly by a 150 watt flood-lamp hung IB inches overhead. The seismograph was adjusted to record seismic events that exceeded the trigger settings of 100 decibels of air overpressure, or 0.05 inches per secorid peak particle velocity. Shocks and sounds intentionally created caused proper triggering and recording, and at approximately 3:55 PM on January 10, 1991, the 197] WE5712TH AV ENUE DENVER. COLORAD080204 (303)825-0777