2013-01-31_REPORT - M1973021 (2)

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1.0 INTRODUCTION This report summarizes geotechnical observations made January 10 and 11, 2013 on the active and inactive mine areas at the Morrison Quarry operated by Aggregate Industries (AI). This report supplements the "2012 Notice of Intent to Continue Mining Operations / Annual Report" for the Morrison Quarry. Joint and foliation attitudes were mapped for areas mined in 2012 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 perimeter slope configuration at the quarry is conservatively defined at 1 H:1 V 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 (DRMS) 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 the North Quarry, in which active mining no longer occurs, but where a repository for undesirable material exists (North Repository); the Central Quarry, in which active mining no longer occurs, and where reclamation is ongoing, and the South Quarry, where active mining continued in 2012. The North Quarry was mined to an approximate elevation of 6220 feet above Mean Sea Level (MSL) utilizing highwalls and benches. No activity occurred in the North Quarry or the North Repository areas in 2012. The Central Quarry was mined to an approximate elevation of 6330 feet above MSL utilizing highwalls and benches and also contains a stabilized highwall located in the northeast section of the quarry. In 2012, material stripped from the South Quarry was placed in the Central Quarry. The South Quarry was mined between approximate elevations of 7450 to 6640 feet above MSL utilizing highwalls and benches. Other activity in the South Quarry included construction, relocation, and maintenance of haul roads as well as overburden stripping. 1 Morrison Quarry Annual Report 2012 P \23514\ 133 - 23514- 13002\Deliverables\Deliv -01 -2012 Annual Report \Annual_Report_20I2_Geotech doc January 2013