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Fred Banta and Brian Munson -3- June 19, 1981 <br />applicant should state what angle of draw was assumed in projecting the <br />limits of possible subsidence indicated on the subsidence protection plan <br />maps. <br />(2) The applicant states that no renewable resource lands have been delineated <br />within the permit area. This implies that no alluvial valley floors, aquifers <br />or areas of recharge to aquifers exist within the permit area. If this is <br />not the case, considerable amendment may be necessary in order to demonstrate <br />compliance with the protection of these critical elements. For the purposes <br />of this review I have assumed that the applicant's opinion will be <br />acceptable to Jerry 2impfer and Roy Cox. <br />(3) The applicant projects maximum subsidence magnitude of approximately 11 <br />feet. The applicant's response to an OSM query regarding this unsupported <br />projection appears on page 90 of volume 9. The response is still inadequate. <br />The applicant should describe how this projection was made. If-specific <br />empirical techniques ~r literature references were utilized, the applicant ,.~ <br />should describe in detail their use in completing the projection. <br />(9) The applicant states the opinion the company owned structures are not <br />subject to the subsidence monitoring requirements of the regulations. The <br />Division disagrees with that opinion. Appropriate subsidence monitoring <br />monuments should be installed in the area of Corthern No. 1, No. 2 and No. 3 <br />surface structures, if they will be undermined. Particular concern should be <br />focused upon structures such as change houses and offices, in which employees <br />and public could be exposed to. hazards, such as explosion due to ruptured gas <br />services. If the applicant prefers, monitoring can be avoided if an acceptable <br />"subsidence control plan", in conformance with Rule 2.05.6(6)(f), is developed <br />for these particular structures. <br />(5) Appropriate subsidence monuments must be installed at the waste disposal <br />pile. Dissruption of the pile caused by differential settlement could result <br />in slope instability. <br />(6) The applicant submitted a map of a "proposed subsidence monitoring program" <br />and a typical subsidence monument detail in letter form on May 28, 1981. The <br />proposed subsidence monument should be amended to extend the concrete plug <br />beneath frost line in order to avoid freeze/thaw rravement of the monument. <br />(7) The applicant vaguely states that subsidence monitoring will cease when <br />appropriate. Monitoring and reporting must continue until the Division <br />approves its cessation. The monuments should be initially surveyed upon <br />installation. Active monitoring should cormnence prior to the approach of <br />mining within the envelope circumscribed by the projection of the angle of <br />draw from the monument to the seam being mined. <br />(8) The applicant states mining will be limited to room and pillar advance <br />mining without secondary recovery within the P-seam. This may unnecessarily <br />restrict resource recovery. The applicant should describe the proposed <br />operations within the P-seam in order Co justify limited recovery of the <br />contained resource. <br />(9) The applicant presents a plan for protecting Nighway 13 from potential <br />subsidence damage by appropriate buffer~of barrier pillars. The applicant <br />should thoroughly develope the pillar buffer concepts based on specific angle <br />of draw projections pillar strength calculations. The York Canyon empirical <br />data on angles of draw is acceptable as a comparable example. Northern Coal <br />Company's subsidence monitoring program will allow determination of site-specific <br />design parameters which can be utilized to revise buffer delineation if <br />appropriate. State Nighway 13 should be actively monitored by operational <br />