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Attachment Memo/Marion Dodson Pane -2- March 3, 1980 Section 2.1.9. Subsidence The treatment of subsidence presented in this section of the application 1s inadequate to scc(isfy the requirements of the federal Pcrenanent Regu- lations. Sections 184.20 and 817.121, 2, 4 P: f each apply to subsidence occurrence over underground coal mines. The regs (sec. 78n.20) require that the applicant submit a subsidence surve The survey is to deter- mine; (i) whether any structures or renewable resource lands exist within the permit and adjacent area; and if so, (2) whether subsidence could cause "material damage" or a reduction of the "reasonably fore- seeable usa" of thos? structures or renewable resource lands. The first task is straightforward. The applicant must inventory the permit and adl.acent area to delineate structures and renewable resource lands. Th^ fedr~ral regs define renewable resource lands as "aquifers . and assns of silvic;.;tural production of food and fiber, and arazinq lands." The Land ~~se portion of this anplication(Sec. 4.1) /ccoorts that, past, r_xistina and future use of the ma,iori*-v of the permit and adja,~ent area consists of wildlife habitat, ran 0el.end and limited agriculture. By d?finition, therefore, portions of thr_ area will comprise renewable resource lands. The results o` the inventory can probably hest he presented in man form. Thy second task is more complicated. Thy applicant must first project t•ihat subsidence is expected to occur within the permit and adjacent area. This technical analvsis must be pr?~~r?d by an aopropr~ately qualif~d prnfessional. This portion of the an°vey must rr.flect the state-nf-th?aart n` current subsidence prediction technolor,y. This analysis should consid?r both small sr_ale rock mechu~ts« of the affected rock materials (shear strength and comnressiv? str?ngth pararpeters) and large scale rock properties such as faulting and frac ring. Laboratory and core drilling data is important, but should be supplemented whenever possible with past observation of previous or current local mine workings. Subsidence prediction is not a definitive science. It is important for the applicant to confirm subsidence protections thheugh operational monitoring. Simplistic systems consist- ing of rows of drilled caisson-type concrete and rebar monuments cep tie installed and monitored above mine workings witho~it orbhibitive cost. Monthly monitoring of these monuments in initial mine workings can be utilized to fine-tune and ame~ld the design of later mine workings. Following the projection of subsidence, the appiicant must determine whether "material damage" or "diminution of reasonably foreseeable use" could result. The applicant should apply the following definitions in completing task tYO: 4aterial subsidence damage means, with respect to structures, any e~a.n9e~ which would make it technologically or e~cyonomically infeasible to promptly restore an affected structure to ZhL condition it would be in if subsidence had not occurred. Material, subsidence damage means, with respect to renewable resource lands, any changes which disrupt an aquifer, or the recharge area of an aquifer'