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Lyons Quarry �� 112d Reclamation Permit Operations Technical Revision the site, drill and blast excavation will be required in the overburden sedimentary rocks to achieve a balance of the cut and fill quantities to re-grade the mined areas. In 2013, flooding destroyed the bridge access to the site. HDR understands that Boulder County is to replace the site's main access point via a bridge over South St. Wain Creek with an adequate tonnage capacity and vehicle clearance with respect to turn radius and overhead obstructions. Additionally, Boulder County Parks and Open Space, the current property owner, has contracted Matrix Design Group to develop restoration plans for the 3.2 mile stretch of South St Wain Creek, from the forest service boundary in the canyon to the Old Saint Wain Bridge off Highway 7. These restoration plans include the flat"meadow" area located between South St. Wain Creek and the mined high walls at Lyons Quarry. 2 Project Location and Description 2.1 Location Lyons Quarry is located southwest of Lyons, Colorado in Boulder County. Figure 1.1, Attachment A, shows the Lyons Quarry site just south of South St. Wain Creek, along Colorado State Highway 7 in Sections 25 and 26 of Township 3 North, Range 71 West of the 6th Principle Meridian. 2.2 Recent Flooding The floods in September 2013 changed the low-lying areas of the Lyons Quarry as up to 17 inches of rain fell over a three-day span raising the levels of the South St. Wain Creek to 100 and 500-year floodplains (Boulder County's annual precipitation is 20.7 inches). The flooding washed away the access bridge that crossed the South St. Wain from Highway 7. As of March 2017, the site remains inaccessible to motor vehicles. Figure 1.2 and Figure 1.3, Attachment A, display the pre- and post- flood conditions of the site as satellite images from October 7, 2012 and October 6, 2013, respectively. The extent of the flood destruction and change in creek flow especially at the east end of the site is shown on these images. 2.3 Lyons Quarry Lyons Quarry is currently inactive and is being prepared for closure and reclamation. The quarry consists of mined and leveled ground along the north end of the site, adjacent to South St. Wain Creek, with mined highwalls and overburden waste piles extending less than 1500 feet to the south of the creek. Figure 1.4, Attachment A, shows the mining operations at the site in September 2002. As of September 2013, several one story buildings and processing equipment were present near the entrance of the site but most were destroyed or lost during the 2013 flood. Many of these structures were cleaned up, stockpiled away from the drainageway or removed from the site during the initial flood recovery operations in 2013-2014. The surface elevation across the site ranges from elevation (EI.) 5,508 feet near the entrance of the site to above El. 6,000 feet at the south end of the site. Existing natural slopes in sedimentary rock strata are as steep as 1.75 horizontal to 1.0 vertical (1.75H:1.0V), where the sedimentary strata are February 2017 1 2