National Dam Safety Program. Unimin Tailings Dam (Inventory Number VA 06918), Potomac River Basin, Frederick County, Commonwealth of Virginia. Phase I Inspection Report.

Unimin Tailings Dam is an earthfill embankment approximately 84.9 feet high and 574 feet long. The principal spillway is a 30-inch bituminous coated corrugated metal pipe riser and the emergency spillway is natural, topographic saddle on the right side of the reservoir. The dam is on Mine Spring Run approximately 1.2 miles south of Gore, Virginia, and is used for waste tailing storage by the owner, Unimin Corporation. Unimin Tailings Dam is an 'intermediate' size- 'high' hazard structure as defined by the Recommended Guidelines for Safety Inspection of Dams. Adequate stability analyses were available for review during these investigations which evaluated the factors of safety against complete and partial failures of both the upstream and downstream embankments. All of the analyses performed indicated acceptable factors of safety against failure. Using the Corps of Engineers' screening criteria for initial review of spillway adequacy, the Probable Maximum Flood (PMF) was selected as the spillway design flood (SDF). The spillways are capable of passing 100 percent of the PMF without overtopping the crest of the dam, therefore, they are adjudged as adequate.