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Lyons Quarry ��� <br /> 112d Reclamation Permit Operations <br /> Technical Revision <br /> 3.2 Quarry 2 <br /> To meet objectives of staying within the current footprint of site disturbance, Aggregate Industries <br /> proposes to reconfigure the reclaimed slope grading so that the Quarry 2 is backfilled to form a <br /> natural swale as this area originally had prior to mining activity. Fill slopes in the Quarry 2 area will <br /> be placed and compacted to achieve 50-foot-high benches, sloped at 21-1:1 V, with 15-foot wide <br /> benches. As referenced in the Background section, this area has already been partially backfilled by <br /> 29,000 CY of excess material obtained from a downstream reclamation project. Permit M-1977-141, <br /> Technical Revision#4 for the Area 2 floodplain references continuing backfill of this area with <br /> crusher fines from four areas of the floodplain. Any additional backfill material needed to bring the <br /> slopes up to a 21-1:1 V grade will be bladed down from the overburden soils at the top of the highwall. <br /> This operation will make use of nuisance crusher fines from the floodplain area, will stay within the <br /> quarry footprint, and require minimal, if any, blasting. The re-creation of a swale formation, shown in <br /> Attachment B—Grading Plan Sheet 01 C-02 and 01 C-03, Details A and B, will allow runoff collected <br /> within the re-contoured swale to be conveyed down to the large catchment basin of Quarry 1. This <br /> basin will allow for the settlement of potential suspended sediments and channel runoff water to <br /> South St. Vrain Creek through a new culvert installed within the catchment berm. <br /> 3.3 Rockfall Prevention <br /> After the Fountain Formation sandstone at the crest of the highwall has been excavated, the dacite <br /> highwall in Quarry 1 (northeast facing) as well as the dacite highwall between Quarry 1 and Quarry 2 <br /> (northwest facing), will be scaled to remove any loose rock that accumulated on the highwall <br /> naturally or is deposited during excavation of the Fountain Formation. Attachment B—Grading Plan, <br /> Sheet 01 C-03, Details C, D and E show the proposed configuration of the dacite highwalls along the <br /> northwest and northeast faces of Quarry 1. <br /> Scaling of the dacite highwalls removes potential high risk (removable) rocks as well as cleans and <br /> exposes the highwall to be evaluated for rock bolting. Where rock bolts will be needed to stabilize <br /> the highwall areas, efforts will be made to minimize the visual impacts of the rock bolts in order to <br /> preserve the exposed rock face to the extent possible. The Project team reviewed the options <br /> proposed in the Kleinfelder report to meet the objectives of maximizing slope variability while <br /> minimizing risk to the reclamation contractor and reducing the amount of material required for <br /> excavation. <br /> Section 7.1.1 of the Kleinfelder report recommends, "reinforcing potential wedge failures on the <br /> northeast facing slopes using rock anchors and shotcrete; or alternately constructing soil fills against <br /> the dacite on the northeast facing slopes". Permit M-1977-141, Technical Revision#2 recommended <br /> buttressing the dacite in this area with fill instead of using rock bolts as stabilization. <br /> The Kleinfelder report also notes, "The consequence of failure of a small rock wedge from the dacite <br /> on the northeast facing slopes is a rapid block slide that may cause undercutting of the Fountain <br /> Formation. These types of failures should be effectively mitigated by analyses during construction <br /> and rock bolt support utilizing adequate safety factors" (Kleinfelder, 2008). As mentioned in Section <br /> 3.2, the northeast-facing slopes in Quarry 2 will be backfilled for stabilization. Aggregate Industries <br /> March 2021 1 9 <br />