2005-05-23_REVISION - M1977424 - Laserfiche WebLink

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Logan Wash Mine 7R No. 6 A butterfly valve was installed in the 6-inch pipe on the upstream side of the dam and closed to prevent mine-water discharge. In September 2003, the dam was improved by applying 3-inches of shotcrete (gunite or aerated portland cement) to the mine ribs, floor and the top, front, and back side of the dam. The 6-inch pipe interface on both sides of the dam was also shotcreted. The shotcrete application increased the weight of the dam to a total of 18,840 lbs. The butterfly valve in the dischazge pipe on the upstream side of the dam was removed and placed on the downstream side of the pipe, approximately 50 feet outside of the portal. In addition, the pipe was instrumented with a manometer to allow measurement of head within the mine. A shallow concrete vault was installed to protect and access the valve and manometer for monitoring purposes. To prevent access to the mine, the portal was backfilled with a 40-ft long plug consisting of on- site mine bench materials. The plug extends from the portal to the steel door threshold that was used to access the mine. Therefore, a small gap of approximately 5 feet exists between the concrete dam and the soil plug. The mine- water discharge pipe was left in place to provide for an option of permanent drainage of mine water. During the normal season outfall flow period in 2003, water rose to a Level several inches above the bottom of the pipe. No discharge from the pipe or mine occurred during 2003. During 2004, no head was observed or measured at the manometer and no discharge from the mine occurred. 2.4 Existing Monitoring Program After the earth plug was installed, OOSI initiated monitoring of head within the mine. The monitoring program includes 1) monitoring of head behind the seal using the manometer installed behind the valve in the discharge pipe, and 2) monitoring of leakage of the earth plugs at the west and east portals. To confirm that the manometer was operating correctly, the butterfly valve is periodically opened slightly to confirm that no head exists in the mine. The monitoring of head behind the sea] allows an assessment of seasonal head variations and percolation from the workings into the country rock. Should the head reach levels that aze considered unsafe or near overtopping conditions of the concrete sack dam, and/or if leakage from the plugs becomes evident, the head can be relived by opening the valve and discharging mine water. Should it be necessary that water be released, OOSI will conduct sampling of the water in accordance with their NPDES permit. In addition, discharged mine water may be used for irrigation purposes at the mine site (to support revegetation efforts). To further stabilize the earth plug at the portal, the surface of the earth plug was revegetated as part of the Reseazch Bench revegetation effort in accordance methods described in Section 3.1 of TR No. 4. Western Water 8 Land, Inc.