Midnite Mine Superfund Site 100 Percent Design Appendix R – Staging / Temporary Stockpiling Plan June 2015 Prepared for: Dawn Mining Company PO Box 250 Ford, Washington 990413 and Newmont USA Limited 6363 South Fiddler’s Green Circle Greenwood Village, Colorado 80111 Prepared By: MWH Americas, Inc. 2890 E. Cottonwood Parkway, Suite 300 Salt Lake City, UT 84121 TABLE OF CONTENTS R1.0 INTRODUCTION ............................................................................................................... 1 R2.0 MATERIAL HANDLING .................................................................................................... 1 R2.1 COMMON ELEMENTS CONSIDERATIONS FOR TEMPORARY STOCKPILES ........................................................................................................ 2 R2.2 EXISTING TOPSOIL STOCKPILES...................................................................... 2 R2.3 DEMOLITION DEBRIS FROM STRUCTURES IN CSZ ........................................ 3 R2.4 PHASE 1 SOIL REMEDIATION MATERIALS ....................................................... 4 R2.5 CSZ GRADING MATERIALS ................................................................................ 5 R2.6 HILLSIDE WASTE ROCK PILE MATERIAL PROCESS MATERIALS .................. 5 R2.7 PIT 4 – PIT BOTTOM CLEANUP AND GRADING ................................................ 6 R2.8 GROUNDWATER CONTROL SYSTEMS EXCAVATIONS .................................. 7 R2.9 PIT 3 – PIT BOTTOM CLEANUP AND GRADING ................................................ 8 R3.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN ......................... 9 R4.0 REFERENCES ................................................................................................................ 10 Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design i LIST OF ACRONYMS BODR Basis of Design Report CSWPPP Construction Stormwater Pollution Prevention Plan CSZ Construction Support Zone cy cubic yard EPA U.S. Environmental Protection Agency HSWRP Hillside Waste Rock Pile RA Remedial Action RD Remedial Design Site Midnite Mine Superfund Site SDTS Structure Demolition Temporary Stockpile STSP Staging and Temporary Stockpiling Plan SWMP Stormwater Management Plan SWRP South Waste Rock Pile TCSS Temporary Clean Topsoil Stockpile TISS Temporary Impacted Soil Stockpile WTP Water Treatment Plant Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design ii R1.0 INTRODUCTION This Staging and Temporary Stockpiling Plan (STSP) has been prepared to describe how waste rock and other excavated material will be managed to prevent contamination of previously uncontaminated areas, as well as preventing the release of contaminants to downstream areas during remedial actions (RAs) at the Midnite Mine Superfund Site (Site). This STSP is an appendix to the Midnite Mine Superfund Site Basis of Design Report (BODR), which presents the background and supporting information relevant to the Site and the planned RAs. The BODR also contains the engineering drawings, plans, and specifications for the Site remedial designs (RDs) that are necessary to implement the RAs. Specific locations and configurations of proposed temporary stockpiles discussed in this appendix are shown in the appropriate engineering drawings as referenced. R2.0 MATERIAL HANDLING This section of the STSP summarizes the material handling strategy to be used during the RA. This strategy includes minimizing the need for stockpiling of excavated material to the maximum extent practical by directly loading excavated materials into haul trucks for transport and placement in the waste containment area. Due to scheduling considerations, direct-hauling may not always be possible. Eight activities have been identified that will require temporary stockpiling of excavated materials. These eight activities/areas are: 1) Relocation of Existing Topsoil Stockpiles 2) Demolition Debris from Structures in the Construction Support Zone (CSZ) 3) Phase 1 CSZ Soil Remediation Materials 4) CSZ Grading Materials 5) Hillside Waste Rock Pile (HSWRP) Process Materials 6) Pit 4 – Bottom Cleanup and Grading 7) Groundwater Controls Systems Excavation 8) Pit 3 – Bottom Cleanup and Grading The stockpiling activities for materials from these eight activities are primarily associated with early phases of the RA, prior to preparation of the waste containment areas for placement of Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 1 waste. If additional materials requiring stockpiling are identified as the RA construction progresses, it may become necessary to amend this STSP to include these materials and any new stockpiles areas required for their temporary storage. Any amendments to this STSP will be subject to EPA review and approval prior to implementation. R2.1 COMMON ELEMENTS CONSIDERATIONS FOR TEMPORARY STOCKPILES The following criteria are addressed for each of the eight stockpile areas to the extent they are applicable: • Staging/Schedule for material stockpiling and final placement • Estimate of material volume • Estimated material properties, moisture conditions, contamination levels • Stockpile area location, stockpile space (i.e. surface area) requirements • Temporary soil cover requirements, primarily for temporary stockpiles of demolition debris • Potential interim revegetation requirements, primarily for uncontaminated material stockpiles that may remain in place for a number of years R2.2 EXISTING TOPSOIL STOCKPILES Existing topsoil stockpiles located in the CSZ, which includes the construction support facilities and the proposed water treatment plant (WTP) and ponds, are shown on Drawings 2-1, 2-2, and 2-3. Key components of the Existing Topsoil Stockpiles STSP include: • Grading the CSZ prior to construction of the new construction support facilities needed for the RA. The material in the Existing Topsoil Stockpiles will need to be relocated as part of site preparation and grading work and will be relocated as part of initial site preparation. • Preliminary testing performed on soils in the southwest topsoil stockpile (Drawing 2-2) indicate these materials meet soil cleanup standards and may be used for clean soil cover during RA construction (MWH, 2013). If further testing verifies that these soils, and any soils in the other stockpiles shown on Drawings 2-1, 2-2, and 2-3, meet soil cleanup standards, then they will be relocated to a temporary topsoil stockpile. This Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 2 temporary clean topsoil stockpile (TCSS) will be located at the proposed WTP pond site as indicated on Drawings 2-1 and 4-1. The WTP equalization ponds are planned for construction at the end of Phase 1 and soils stored in the TCSS will be used in initial phases of cover construction. This material will be used on Pit 4 or other areas where clean cover is required for RA construction (e.g., for areas in the footprint of the Pit 4 Overburden Pile where soil cover is needed after mine waste removal). Prior to stockpiling clean cover soils in the TCSS at the WTP pond site, soil cleanup and verification will be performed as needed so the materials placed in the temporary topsoil stockpile will not become contaminated. If further testing indicates some of these materials do not meet soil cleanup standards, they will be temporarily stockpiled within the existing mine waste area at the Phase 1 Temporary Impacted Soil Stockpile (TISS) on the north end of the South Waste Rock Pile (SWRP). The TISS material ultimately will be consolidated in the Pit 4 waste containment area. The location of the Phase 1 TISS is also shown on Drawings 2-1 and 4-1. Materials placed in the Phase 1 TISS will be placed in Pit 4 during Phase 1 construction. • Current estimates indicate that approximately 60,000 cubic yards (cy) of material exists in the southwest topsoil stockpile of the CSZ, approximately 13,000 cy of material exists in the southeast topsoil stockpile, and a total of approximately 25,000 cy of material exists in the northwest and northeast stockpiles. • As discussed above, the locations of temporary stockpiles will be dependent upon whether or not the topsoil material meets soil cleanup standards (so either TCSS or TISS). • If it is determined that some, or all, of the existing topsoil materials meet soil cleanup standards, then it is likely that the TCSS will be in place for a number of years prior to using this material in RA construction. As a result, these stockpiles of excavated topsoil will receive interim revegetative treatment to reduce the potential for erosion. R2.3 DEMOLITION DEBRIS FROM STRUCTURES IN CSZ Existing structures in the CSZ areas shown on Drawing 2-1 will be demolished as described in Appendix H, and the demolition debris relocated to a stockpile area as part of site preparation and access development work. Key components of the CSZ Demolition Debris STSP include: Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 3 • Demolition of these structures and relocation of the demolition debris will occur as part of initial site preparation work prior to the development of the Pit 4 waste containment area. • Demolition debris from CSZ will be stockpiled on the north end of the SWRP in the CSZ Structure Demolition Temporary Stockpile (SDTS). The CSZ SDTS will be located adjacent to the TISS as shown on Drawings 2-1 and 4-1. • Those portions of the demolition debris that could be transported by wind or surface water runoff will be protected by placement of a temporary 1.5-foot-thick cover of waste rock. • Once the Pit 4 waste containment area is sufficiently developed, this demolition debris will be consolidated in an “unclassified waste zone” in the Pit 4 waste containment area (see Drawing 8-5). The volume of this demolition debris is estimated to be approximately 2,000 to 3,000 cy. R2.4 PHASE 1 SOIL REMEDIATION MATERIALS The Phase 1 soil cleanup operations that will occur prior to backfilling in Pit 4, and thus require temporary stockpiling, primarily include soil removal activities associated with construction of the CSZ. Specifically, this will include remediation of soils within the CSZ, Whitetail Creek Drainage cleanup area, and existing West Access Road as shown on Drawings 2-1, 2-2, 2-3, and 2-4 that do not meet the soil cleanup standard. The actual extent of the cleanup areas will be determined during the Phase 1 construction. Key components of the Phase 1 Soil Remediation Materials STSP include: • Any contaminated materials excavated during remediation of the CSZ will be temporarily stockpiled within the Phase 1 TISS within the existing mine waste area. • Contaminated soils from the Whitetail Creek Drainage and existing West Access Road (Drawing 2-4) also will be temporarily stockpiled within the Phase 1 TISS and ultimately will be consolidated in the Pit 4 waste containment area. • Although the volume of material to be excavated during the Phase 1 soil cleanup is not currently known, it is expected to be relatively small (20,000 to 25,000 cy). Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 4 R2.5 CSZ GRADING MATERIALS Preliminary grading designs for the CSZ are shown in Section 9 (Water Treatment Plant) and Section 2 (Construction Support Facilities) of the Drawings. Key components of the CSZ Grading Materials STSP include: • Grading the CSZ as shown on Drawings 2-14 through 2-20 during initial site preparation work. It is anticipated that excess cut material will be generated during these site grading operations, and that this material, after verification sampling, likely will be relocated to the TCSS. • These clean materials in the TCSS will be used as soil cover or in other areas requiring clean fill as part of RA construction. • If these temporary stockpiles of cut materials remain in place for a number of years prior to using this material in RA construction, they will receive interim revegetative treatment to reduce the potential for erosion. R2.6 HILLSIDE WASTE ROCK PILE MATERIAL PROCESS MATERIALS HSWRP materials will be processed by screening and crushing without washing to produce drain rock for the underdrain systems in Pit 3 and Pit 4. Key components of the HWSRP processing STSP include: • Underdrain Layer. As the underdrain layer is the first backfill layer to be placed in Pit 3 and Pit 4, both the drain rock material, and reject materials from the screening/crushing operation will need to be temporarily stockpiled prior to placement in the pits. HSWRP material processing will occur in two stages; the first stage occurring immediately prior to Pit 4 backfilling at the start of Phase 1 and the second stage immediately prior to Pit 3 backfilling at the start of Phase 2. • Volume estimates for processed drain and reject material that will be necessary for Pit 3 and Pit 4 processing are presented in the Material Balance section of Appendix D. • HSWRP material will be processed without washing. As a result, all processed drain and reject material will be in a relatively dry state at the time of placement in temporary stockpiles. Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 5 • The primary stockpiling area for HSWRP material will be in Area 5 of Site. This stockpile area will be expanded by relocating Protore Stockpile 7 material to the top of Protore Stockpile 6 as shown on Drawing 2-22. Once Protore Stockpile 7 is removed, the drain material stockpile footprint will be overlain with reject material from the screening operation or other quartz-monzonite-derived (lower reactivity) waste to a depth of 1 foot. This will form a “clean base” for the drain material stockpile should the underlying material be contaminated. Care will be taken during loading of stockpiled drain material for transport and placement in the pits so that processed materials are not mixed with underlying base material or penetrated and mixed with the underlying potential contaminated wastes. • The existing safety berm along the southerly edge of Area 5 crest (at the northerly crest of the Pit 3 highwall) will be enhanced and maintained as shown on Drawing 2-23 and on Detail 19 on Drawing 2-29. Material will not be stockpiled within 15 feet of this safety berm. R2.7 PIT 4 – PIT BOTTOM CLEANUP AND GRADING Sediments and coarse rock that has accumulated in the bottom of Pit 4 will be removed after completion of dewatering and prior to pit-bottom grading. The volume of pit-bottom sediments is estimated to be approximately 2,400 cy (MGC, 2011). Additional coarse rock material will result from the cleanup of gravel-to-boulder-sized material that currently exists on portions of the pit floor, as well as material that will be produced during pit-wall scaling, pit-bottom grading and underdrain sump excavation. Key components of the Pit 4 Bottom Cleanup and Grading STSP include: • Pit-bottom sediments will be dried in place, either by natural evaporation or by adding drying agents once the pit has been dewatered. As a result, the majority of these sediments will be relatively dry and will be removed with common earth-moving equipment and transported to a temporary stockpile area on the relocated Ore Stockpile 7. Measures will be taken to avoid intermingling of this potentially higher-activity waste with the lower-activity mine waste once it is removed from the pit bottom. The temporary stockpile area used for storage of these low-moisture sediments from Pit 4 will be located in pits excavated into the upper surface of the relocated Ore Stockpile 7 (see Drawing 2-22). These pits will be lined with non-woven geofabric to prevent Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 6 migration of Pit 4 sediments into the underlying waste rock. These relatively dry sediments will be covered with approximately 1-foot of waste rock to avoid erosion by wind or water. • Final cleanup of the Pit 4 bottom could require wash down of the remaining fine-grained materials to a low-lying sump area in the pit bottom where, if necessary, they will be pumped into geotubes for dewatering. The geotubes will be placed on a temporary pit- bottom sediment drying pad configured as shown on Detail 7 on Drawing 4-80. This temporary pit-bottom drying pad will be located adjacent to the ramp leading into the Pit 4 as shown on Drawing 4-12. This drying pad is located approximately 35-feet above the limits of the southerly end of the drain layer, so that the geotubes can be allowed additional time to dewater during final preparation of the pit bottom, placement of the drainage layer and geomembrane, and initial placement of mine waste backfill layers. With the geotubes placed in this location, any remaining water that drains from these geotubes will flow back into the pit bottom. Impacted water that passes through the geotube fabric will be relatively free from sediment. Once mine waste placement reaches the elevation of the temporary drying pad used for pit-bottom sediment, the geotubes and other materials associated with the drying pad will be placed in the central portion of the Pit 4 backfill lift in an area designated for placement of unclassified waste (including high reactivity and/or high activity wastes). • Coarse rock material removed during pit bottom cleanup, as well as coarse waste rock spoils from pit-bottom sump excavation, will be placed directly on flat areas remaining on Protore Stockpile #6, the top surface of the relocated Ore Stockpile #7, or on top of the waste rock cover placed over dry sediments, as described above, to provide additional erosion protection. R2.8 GROUNDWATER CONTROL SYSTEMS EXCAVATIONS The groundwater control systems are discussed in Appendix G. As part of site preparation for construction of the groundwater control systems, level working platforms will be excavated in the three stream channels down gradient of the Mine Area as shown in Section 7 of the Drawings in Volume II. Key components of the Groundwater Control Systems Excavations STSP include: Appendix R – Staging/Temporary Stockpiling Plan June 2015 100 Percent Design 7