2014-10-10_REVISION - C1996083 (4)

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The applicant predicts that the maximum subsidence in the Spruce Stomp lease area will be about 5.7', occurring approximately 300' south of the West Fork of Terror Creek. Subsidence in the creek is expected to be about 5.1', resulting in no more than a 1.5% channel slope change. The average gradient of the West Fork of Terror Creek is 10.3 %, with steeper segments at 20% and flatter areas at 2.5 %; the segment of the creek running through the Spruce Stomp lease area is 5.5 %. The predicted gradient change for the segments overlying the mine workings would not be inconsistent with the overall stream gradient. Six ponds, three springs with ponds or tanks, and four springs lie within the Spruce Stomp lease area. The overburden depth beneath all of these features ( >800') is such that subsidence is not expected to impact these structures. The ponds and associated springs will be monitored quarterly to verify this prediction, and a mitigation plan has been proposed to repair, rehabilitate, or replace any damaged features with decreed water rights. B. The applicant has proposed a subsidence monitoring program, in accordance with Rule 2.05.6(6)(c), designed to determine the commencement and magnitude of subsidence movements. Map No. 27 depicts the location of monuments to be installed and structures to be monitored within the permit and adjacent area. The results of the monitoring program will be submitted to the Division semi - annually. The monitoring program is designed to extend for a time, beyond cessation of mining in any area, consistent with the need for verification of the subsidence prediction. The approved subsidence monitoring plan for the operation is located in Section 2.05.6(6) of the permit application package. Specific to Permit Revision No. 14 and the Spruce Stomp lease area, the applicant has committed to: o Quarterly monitoring of the Turkey Track Structures. o Quarterly monitoring along Stevens Gulch Road. o Semi -annual monitoring of two cross sections of Terror Creek. o Quarterly monitoring on the longwall panels within the Spruce Stomp lease area. o Lidar aerial survey of the flow line of West Terror Creek immediately after longwall mining is complete under the creek and again two years following completion of mining. Additionally, flows in the West Fork of Terror Creek, collected at flume monitoring stations SW -1 and SW -12, will be available in real time, updated hourly. In the absence of real time data, flow will be measured monthly, increasing to weekly when the West Fork of Terror Creek lies within the predicted angle of draw. Weekly flow measurements will be initiated three months prior and continue for six months following extraction under the West Fork of Terror Creek. While not likely, based on predictions in the permit application package, there may be Page 42 of 46