REP48253 - Laserfiche WebLink

Home Browse Search

Page 4 Carol Russell April 8, 1981 The applicant should resolve this significant discrepancy. Appropriate boring logs should be provided to demonstrate the actual :>tratigraphic Location of the Middle sandstone in relation to the F seam. 4.6.2.14 Previous Subsidence Experience Map iV-1 and SV-7 indicates two areas of known previous subsidence. The applicant delineates an area above a fully extracted por;`ion of the Wise Hill #4 mine as an example of "trough-type subsidence". :lir photo examination of the permit .area .discerns that the area outlined on the maps also appears to be a meander scar of the Williams Fork River. The app:ication should discuss the:~specific reasons and observations upon which the applicant's designation was founded. If the operator has specific evidence of surface depression it should be included within the narrative. The second area delineated by the applicant on the maps oirerlies the workings of the Eagle #5 mine, approximately 1500 feet north northesast from the #5 mine portals. The text of the application references observed surface cracking and surface depression as evidence of subsidence within this area. Examination of the air photos of the mine permit area, flown in September of 1980 under contract with the Division, asceri:ained the existence of a sink-hole type collapse approximately 800 feet south of the designated area and 900 feet northeast of the #5 mine portals. The reaps should be amended to indicate this significant additional subsidence artifact. The applicant's subsidence analysis narrative should also be eimended to specifically discuss this example of surface disruption. The occurrence of such sink-hole type subsidence could have drastic consequences. This pax•ticular occurrence appears to overlie: the third south submain set within the d`5 mine. This three submain set continues down dip beneath the alluvium and channel of the Yampa River. The application should specifically address why this event occurred above what should be an area of controlled grounc!. This is particularly important in Light of the applicant's reliance upon limited extraction as a controlled technique to prevent such subsidence from occurring. In preparing this discussion a cross-section prepared from the #5 mine portals along the third south submain route and then north beneath the Yampa River would be helpful. The overburden and seam thickness map included within the application for the F seam does not appear to accurately reflect the topography in this specific area. Therefore, the Divisior, has experienced difficulty resolving proper relations of coal seams, ground surface elevations and the Yampa River within this area. An air photo examination of the permit and adjacent areas has also discerned instances of peculiar soil moisture concentration which cc•uld be indicative of collapsed depressions caused by subsidence of neighboring historic mine workings. R brief examination of the Colorado Geological Survey's records indicate that several dozen abandoned coal mines exist within the immediate (cont'd)