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r• _ , <br />., i' <br />Trapper Mining Inc. <br />Box 187 <br />Craig, Colorado 81626 <br />(303)824-4401 <br />July 1, 1983 <br />Mr. Mike Savage <br />Colorado Mined Land Reclamation Division <br />423 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />Dear Mike: <br />Please accept the following explanation including the enclosed plan map and <br />illustrative cross section as our plan for verification of the 25X overburden <br />swell factor which we have projected for the Trapper Mine. We intend to use <br />photogrammetric methods in combination with our own historical survey data for <br />this verification. <br />I have outlined four study areas as shown on the plan map which cover <br />regraded areas of our three active pits. We will construct north-south cross <br />sections within each study area on 150-200 foot centers ._. ..This will enable the <br />cross sections to coincide with the individual cut 'toe' lines where we have <br />adequate elevations to construct a profile of the pit floor. With the four <br />study areas combined we will have 43,750 feet of cross sections through a total <br />area of 188 acres. <br />The enclosed cross section will serve to illustrate and explain our swell <br />calculation method and to show how the aerial survey data will be combined with <br />our past pit surveys to produce [he composite sections. <br />The aerial survey company that does our surface mapping project this summer <br />(Aug. or Sept.) will also develop cross sections in the areas indicated on the <br />plan map. These cross sections will include the regrade line and the original <br />'topo' line, with the regrade line based on the new aerial mapping and the <br />original 'topo' line digitized from our 1975 topographic maps. After receiving <br />the cross sections, we will produce the two lower lines from our survey records. <br />The 'pit floor line' is the pit bottom after all overburden, partings, and coal <br />seams have been removed and the 'top of coal' line represents the total coal <br />thickness (all mineable seams combined) above the pit bottom. A and A as <br />defined on the cross sectional drawing, will then be digitizeds by computer <br />methods and the swell factor calculated by the following formula: <br />X Swell Factor ° [(As/Ab)-1] 100. <br />The aerial mapping project should start in August or September when our <br />summer reclamation work is complete. With a 60-75 day turnaround time between <br />