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Logan Wash Mine TR No. 4 <br />Evaluation of Mine Water Storage and Portal Closure Integrity <br />Within the period of record monitored by OOSI, the maximum total seasonal volume of water <br />that discharged from the Research Mine was calculated to be 288,500 ft3 in 1997. The estimated <br />storage volume of the lower workings is 298,930 ft3. This includes the main north-trending drift, <br />side drifts, and rooms, and the workings at the same level associated with the west drift. The <br />estimated storage volume is the volume available for mine flood water storage if the mine was <br />flooded to the back of the workings behind secure portal plugs. The maximum observed <br />discharge volume is nearly equal to the available volume in the lower workings. Although it is <br />known that water in the lower workings advances and recedes seasonally, the critical information <br />that is not known is the percolation rate of stored water in the lower workings. That is, if water <br />is held in the mine and allowed to cumulate from season to season, at what rate will the stored <br />water recede by percolation into the surrounding shale (Parachute Creek Member). <br />Additional storage would be available in the upper workings of the west drift. Any flooding of <br />the upper portions of the west drift would result in additional head pressure on the mine edit <br />plugs. <br />To evaluate the integrity of the portal closure, OOSI prepared engineering calculations that <br />analyze the stability of the concrete dam and earth plug (see Attachment C). Of primary <br />importance is the integrity of the earth plug as it provides a more significant mass for retaining <br />water in the mine. The calculations were performed without knowledge of alab-determined soil <br />classification. Since the calculations were performed, alab-determined classification was <br />conducted resulting in a Unified Soil Classification System (USCS) classification of SM for the <br />east portal earth plug material. Sliding calculations show that high safety factors can be expected <br />for the soil plug in the case of maximum water depth of 9 ft, and that the safety factors are <br />conservative because they do not include effects of friction along the sides of the soil plug. <br />Internal erosion of the earth plug was estimated using the weighted creep ratio. Results of the <br />calculations applying the SM soil type indicate that a potential for internal erosion at certain <br />water depths may exist. Overtopping of the earth plug is a valid concern as construction <br />methods did not provide for a compacted plug against the back (roof) of the edit. OOSI will <br />monitor head within the mine such that water levels to not overtop the earth plug. Please see <br />Attachment C for calculations and narrative on the Quickcrete® dam. <br />Monitoring Program <br />A monitoring program will be initiated at the Research Mine portals to inspect portal closure <br />(earth plug) integrity and assess the transient behavior of head within the mine. The monitoring <br />program will include 1) monitoring of head behind the seal using the manometer installed behind <br />the valve in the discharge pipe, and 2) monitoring of leakage of the earth plugs at the west and <br />east portals. The monitoring of head behind the seal will allow an assessment as to seasonal <br />head variations and percolation from the workings into the country rock. Should the head reach <br />levels that are considered unsafe or near overtopping conditions, and/or if leakage from the plugs <br />becomes evident, the head can be relived by opening the valve and discharging mine water. At <br />any time mine water is released, OOSI will conduct sampling of the water in accordance with <br />Western Water 8 Land, Inc. 12 <br />