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Reclamation Plan Technical Revision Front Range Aggregates Parkdale Quarry Freemont County, Colorado Colorado Division of Reclamation, Mining, and Safety Permit #M-1997-054 Front Range Aggregates, LLC (FRA) has prepared this Technical Revision (TR) to address potential changes in reclamation slope geometry and pit liner design for reclamation of the Parkdale Quarry alluvial material mining pit. The Parkdale Quarry is located in Freemont County, Colorado approximately 12 miles west of Canon City. Originally permitted in 1998, the Parkdale Quarry is permitted to mine reserves of Quaternary alluvium (alluvial deposit), Precambrian granite (granite deposit), and an approximate five -acre area of Cretaceous Dakota sandstone (sandstone deposit). The Parkdale Quarry was initially owned and mined by Agile Stone, who operated the quarry from 1998 until 2002. The quarry was purchased by CIG in 2003, and mining of the site resumed in 2004. The quarry is currently operated by FRA, a subsidiary of CIG. The alluvial deposit was the initial deposit mined at the Parkdale Quarry, and as of June, 2015, provides the majority of the material being mined on the site. Mining of the alluvial deposit was initially limited to the material above high groundwater. In 2008 the mine permit for the Parkdale Quarry was amended to allow the alluvial deposit to be excavated to bedrock, to allow for additional mining of the granite deposit, and to change the mine reclamation end use for the granite and alluvial deposits to water storage. The alluvial deposit was originally permitted to be excavated only to the level of ground water. In 2008, the mine permit was amended to allow the alluvial deposit to be excavated to bedrock and to change the mine reclamation end use for the pit resulting from mining of the alluvial deposit to water storage. The walls of the alluvial deposit pit must be lined in order to meet the State of Colorado Water Engineer's impermeability requirements. The current reclamation plan specifies 3:1 (horizontal to vertical) slopes with a 15 -foot thick compacted clay liner underlying the surface of the reclaimed slopes. Packer testing indicates that the bedrock underlying the alluvial deposit is generally impervious enough to not require the placement of a floor liner. The approved reclamation plan anticipates that the alluvial reservoir will have a storage capacity of approximately 3,100 acre-feet. Factor -of -safety (FOS) analyses performed for FRA by Applegate Associates, Inc. (Applegate) demonstrates that slopes steeper than the currently specified 3:1 (horizontal to vertical) can be constructed that meet or exceed Colorado State Engineer's requirements for factor -of -safety and with a leakage rate less than Colorado State Engineer Guidelines. Applegate performed FOS analyses of alternate designs with slopes of 2:1(horizontal to vertical), 1.75: 1 (horizontal to vertical), and 1.5: 1 (horizontal to vertical). The slopes analyzed has FOS' ranging from 2.226 for a 2:1 (horizontal to vertical) slope to 1.681 for a 1.5:1 (horizontal to vertical) slope. The minimum FOS for dam embankments specified in the Colorado Office of the State Engineer's Rules and Regulations for Dam Safety and Dam Construction is 1.5. Copies of the FOS analysis report, and supporting information are appended to this TR request. Our proposed revision to the reclamation plan is to change from the prescriptive 3:1 slope and compacted clay liner currently specified in the reclamation plan to a standards-based design with a slope with a minimum FOS of 1.5, but not steeper than 1.5:1 (horizontal to vertical), and a liner that is designed to meet the Colorado State Engineer standards specified in State Engineer Guidelines for Lining Criteria for Gravel Pits August 1999.