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Rimrock Mine Sediment Pond Certification Summary <br />The sediment pond at the Rimrock Mine was designed by Greg Lewicki during the <br />initial permitting process of the mine in 1989-1990. The pond was constructed in <br />December of 1992 and January of 1993 after the permit was granted. I supervised and <br />certified the actual pond construction. <br />In 1995, a revision was submitted to the DMG to allow the pond to permanently <br />remain as a stock pond for the post mining land use of grazing. This was approved. <br />Water samples were taken at that time which showed that the water quality of runoff <br />captured in the pond was acceptable for livestock use. <br />Since the initial installation, the pond has been inspected by a professional engineer <br />(primarily myself] and reports have been supplied to the Division based on these <br />inspections. Over the past 10 years when the mine has been in reclamation, the pond <br />has held water after storm events and has certainly held water long after the nearby <br />intermittent stream, Engleville Gulch, has dried up. Quarterly site inspections of the <br />site over the past 10 years have revealed no problems of any kind. Since the vegetation <br />took rapidly in the first year after seeding, no significant soil erosion has occurred, as <br />has been evidenced by the fact that no sediment buildup has been seen in the pond over <br />a 10 year period. <br />As part of the quarterly inspections over the reclamation period, the items below were <br />checked to see if they coincided with the design shown in the mine permit application. <br />Any evidence of problems or other issues were noted. <br />1) Constructed Elevations: The elevations listed below were checked with a precision <br />level and stadia rod: <br />-Dewatering pipe inlet <br />-Dewatering pipe outlet <br />-Top of Dam <br />-Bottom of Emergency Spillway <br />-Toe of Dam (outside and inside) <br />-Bottom of Pond <br />-A number of points within the pond <br />All elevations were found to be acceptable. The inlet to the principal spillway was <br />placed at a slightly higher elevation to allow more sediment storage. The 10 year - 24 <br />hour runoff storage was still present above the principal spillway. <br />