Laserfiche WebLink
Logan Wash Mine TR No. 4 <br />investigation is underway and resulted in the construction of interim detention structures in the <br />east adit during the summer of 2003. <br />Proposed Reclamation <br />During the summer of 2003, an effort was made to stem the flow from the east portal in order to <br />minimize analytical costs associated with sampling during adit pipe dischazge periods. A <br />concrete sack (Quickcrete®) dam was constructed over the earth/bentonite dike and discharge <br />pipe, which had been installed in the mine approximately 45 ft from the portal. The Quickcrete® <br />dam was initially installed as a temporary detention dam. Prior to construction of the dam, the <br />drift floor at the base of the dam footprint was cleared of unconsolidated rock and fill, and a <br />concrete floor was poured in the resulting shallow trench. The Quickcrete® dam consisted of <br />224 60-1b bags of Quickcrete® cement product; a total of 13,444 lbs of concrete. The dam was <br />constructed in the form of a wedge with a 5 ft base and a height of 4.5 ft above the drift floor. <br />During installation, the Quickcrete® was constantly wetted to enhance curing of the concrete <br />mix. <br />A butterfly valve was installed in the 6-inch pipe on the upstream side of the dam and closed to <br />prevent mine-water discharge. During the normal season outfall flow period, water rose to a level <br />several inches above the bottom of the pipe. No dischazge from the pipe or mine occurred during <br />2003. <br />On the basis of the initial success of the Quickcrete® sack dam, it was decided to enhance the <br />dam and make it an initial component (initial detention dam) to a potential permanent portal seal. <br />The dam was improved by applying 3-inches of shotcrete (gunite or aerated portland cement) to <br />the mine ribs, floor and the top, front, and back side of the dam. The 6-inch pipe interface with <br />the face of the dam was also shotcreted on both sides. The shotcrete application increased the <br />weight of the dam to a total of 18,840 lbs. The butterfly valve in the pipe on the upstream side of <br />the dam was removed and placed on the downstream side of the pipe, approximately 50 feet <br />outside of the portal. <br />The portal was then backfilled with a 40-ft long earth plug consisting of on-site mine bench <br />materials. The plug extends from the portal to the steel door threshold that was used to access <br />the mine. Therefore, a small gap exists between the concrete dam and the soil plug. The mine <br />water conveyance pipe was left in place. However, a manometer was installed on the pipe on the <br />outside of the earth plug upstream of the butterfly valve. A shallow concrete vault was installed <br />to protect and access the valve and manometer for monitoring purposes. <br />Engineering calculations were performed to evaluate the safety factors associated with the <br />construction of the dam and plug. The engineering calculations aze shown in Attachment C and <br />are discussed below. OOSI will implement a monitoring program to (1 evaluate adit plug <br />performance and safety, and (2 the ability of the mine workings and host rock to store and <br />convey mine water behind the adit plugs. During the spring runoff season, the west portal plug <br />and the east portal closure will monitored on at least a weekly basis. This monitoring program is <br />discussed below. <br />Western Water 8 Land, Inc. 17 <br />