2008-04-30_REPORT - M1973021 (3)

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• i • 1.0 INTRODUCTION This report summarizes geotechnical observations made February 7, 2008 on the active and inactive mine areas at the Morrison Quarry operated by Aggregate Industries (AI). This report supplements the "2007 Notice of Intent to Continue Mining Operations /Annual Report" for the Morrison Quarry. Joint and foliation attitudes were mapped for areas mined in 2007 in order to characterize the rock mass exposed. Other features affecting stability such as shear zones, faults, or failure surfaces, were described and mapped as well. The field data collected was used to make recommendations regarding the configuration of future mine slopes. This addendum, therefore, provides information required by Permit Amendment #5 (carried over from Permit Amendment #3 and #4) to Mining Permit M-1973-021. 1.1 Observational Method Previous Permit Amendments describe the "Observational Method", which is a process of observing highwall development to evaluate the rock mass stability and recommend slope angles. The default slope configuration at the quarry is conservatively defined at 1H:1V highwall height to bench width. Ongoing observation of the rock mass is used to alter the default slope configuration when necessary for safety or desirable for production. Annual Geotechnical Addendums as well as Technical Revisions to the Permit convey the information gathered using the Observational Method to the Colorado Division of Reclamation, Mining, and Safety (DBMS) for review. 1.2 Site Description The Morrison Quarry is located west of Colorado Highway 8 approximately 1/2 mile north of U.S. Highway 285 in Jefferson County, Colorado as shown on Figure 1. The site is situated in the Front Range foothills west of the Dakota hogback. Mount Falcon Open Space Park is located west of the site. The Quarry currently consists of a central mined area, the Central Quarry, in which active mining no longer occurs, a north mined area, the North Quarry, where active mining occurred in 2007, and a south mined area, the South Quarry, where active mining began in 2007. The Central Quarry has been mined to an approximate elevation of 6330 feet above Mean Sea Level (MSL) utilizing highwalls and benches and also contains a stabilized slope located in the northeast section of the quarry. The North Quarry has been mined to an approximate elevation of 6220 feet above MSL utilizing highwalls and benches. Other activity in the North Quarry included slope reclamation consisting of placing stripped overburden and weathered rock material on slopes above approximately elevation 6500 feet above MSL. The South Quarry has been partially stripped and mined to an approximate elevation of 7000 feet above MSL. Other activity in the South Quarry included construction of haul roads and stripping overburden. 2.0 2007 MINING SUMMARY 2.1 Central0uarry Mining in the Central Quarry was completed as of December, 2001. The Central Quarry is currently being used as a raw water reservoir for the use of the Town of Morrison and Aggregate Industries with an approximate water level elevation of 6430 feet above MSL at the time of this report. As such, the only rock disturbance in the Central Quarry for 2007 was the -1- F:\3919 038\Annual_Rcport_2007\Gcotcch_Addendum_2007Wnnual_Rcpon_2007_Gcotcch.doc Apri12008