Loading...
HomeMy WebLinkAboutAppendix E_Backfill_PlanPiedmont Lithium Carolinas, Inc. I Response to Additional Information Request (dated January 14, 2022) Appendix E: Waste Rock Pit Backfill Plan — Technical Specifications PIEDAA'ONT LITHIUM E Appendix E: Waste Rock Pit Backfill Plan — Technical Specifications This page intentionally left blank. Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina Prepared for: Piedmont Lithium Carolinas, Inc. 32 N. Main Street Suite 100 Belmont, NC 28012 June 2022 Prepared by: Marshall Miller & Associates, Inc. 582 Industrial Park Road Bluefield, Virginia 24605 Waste Rock Pit Backfill Plan South and East Pits ►►' ►► �� Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina Table of Contents Page No. 1 Introduction.......................................................................................................................... 1 2 Waste Rock Pit Backfill Placement (Compliance with NCAC § 74-53).................................... 2 2.1 Waste Rock Material Placement............................................................................... 3 2.2 Compaction..............................................................................................................3 2.3 Demonstration Testing for Placement Lift Thickness ................................................ 4 2.4 Final Vegetative Cover.............................................................................................. 5 3 Reporting Requirements....................................................................................................... 6 4 Revegetation of Completed Areas......................................................................................... 6 4.1 Soil Slopes................................................................................................................ 6 4.2 Waste Rock Slopes................................................................................................... 6 5 Monitoring and Maintenance............................................................................................... 7 5.1 Waste Rock Quantities............................................................................................. 7 5.2 General Observations...............................................................................................7 5.3 Maintenance............................................................................................................7 5.4 Data Review............................................................................................................. 8 AppendixA..................................................................................................................................... 9 Marshall Miller & Associates, Inc. Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina 1 Introduction This Technical Specification has been prepared by Marshall Miller & Associates, Inc. (MM&A) for the proposed South and East waste rock pit backfill sites of the Piedmont Lithium Carolinas, Inc. (PLCI) site located approximately seven (7) miles north of Bessemer City, Gaston County, North Carolina. The excavated mine pits are proposed to be backfilled with waste rock from the PLCI, Carolina Lithium Project mine site and associated concentrate and conversion plants. The information contained herein provides details and technical specifications to PLCI for construction of the waste rock pit backfills in a manner consistent with the construction drawings, design assumptions and prudent engineering practices. PLCI or a third party selected by PLCI will conduct the transfer and placement of the material in conjunction with the construction of the waste rock conveyance system and associated drainage and outlet structures. The purpose of this document is to provide specifications to address requirements of NCAC § 74- 53(4). The specifications are intended to be incorporated as part of the overall project plan and the Monitoring, Operation and Maintenance Plan (that will be developed prior to and during operations) for the PLCI site. A PLCI qualified person will be actively involved to provide interpretation of items that may not be directly referenced. The proposed waste rock pit backfills will consist predominantly of coarse waste rock produced from the Carolina Lithium Project mine site. The backfill material will also contain a smaller component of fine waste rock, generated from the concentrate and conversion plants planned as part of the project. The coarse waste rock, which is approximately 93% of the backfill material, is crushed through a primary jaw crusher to minus 14-inch size. The fine waste rock, the remaining approximately 7% of backfill material, is crushed and processed to minus 1 mm material from the concentrate and conversion plants. All waste rock, combined coarse and fine, will be transported to the pit backfill locations continuously by conveyors. Once in the excavated mine pit, the waste rock will be spread and compacted by a mining -class bulldozer. The South and East excavated mine pits will be backfilled to the level of the original ground surface (to the pit rim) and then the placement of material will continue above the original ground surface level (above the pit rim). Placement of waste rock material above the pit rim will create a waste rock pile with two (2) horizontal to one (1) vertical bench slopes and a finished inter -ramp slope of three (3) horizontal to one (1) vertical. The waste rock piles will be domed on top to effectively shed stormwater and they will be covered with clay type, native soils for revegetation purposes. Marshall Miller & Associates, Inc. 1 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina Major work items include the following: > Surface Drainage Facilities -To minimize erosion of the ground surface surrounding the pit rim, intermediate benches, bench gutters, diversion ditches, and perimeter ditches will be constructed. > Vegetating Completed Areas -A program for seeding all completed outslopes to provide erosion protection of the final waste rock piles (which will be on top of the backfilled pits) is proposed. > Monitoring and Maintenance - A program for obtaining and reporting observations and monitoring data at regular intervals relating to the waste rock pit backfill performance is described herein. 2 Waste Rock Pit Backfill Placement (Compliance with NCAC § 74-53) Figure 1 illustrates the concept for waste rock disposal at the proposed South Pit and East Pit waste rock backfills. Detailed drawings for final design of pit backfill structures are included as Sheet Number OOG-004 — Reclamation Map; Sheet Number OOCO-008 — Concentrate Operations — Detail Sheet — Insets L, M, N, 0, and P; and OOCO-009 — Concentrate Operations — Detail Sheet — Insets Q, R, and S in Appendix B, Attachment 3 — Piedmont Lithium Detailed Drawings. Figure 1— Pit Waste Rock Backfill Typical Marshall Miller & Associates, Inc. 2 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina 2.1 Waste Rock Material Placement The majority of waste rock backfill into the proposed excavated mine pits will involve placement of waste rock material into the open pit of the mine with compaction using a mining -class bulldozer. Once the waste rock material reaches the original ground elevation, the waste rock material will be constructed with bench slopes no steeper than two (2) horizontal to one (1) vertical and an inter -ramp slope of three (3) horizontal to one (1) vertical or 18.4 degrees. Studies show the Angle of Repose for material similar to what is to be placed within the mine pits is 34.2 degrees.' The final slopes in all excavations in soil, sand, gravel, and other unconsolidated materials shall be at such an angle as to minimize the possibility of slides and be consistent with the future use of the land. 2.2 Compaction Placement of the waste rock material back into the proposed open excavated mine pit will be completed in a manner that ensures adequate compaction for stability of the rockfill and minimizes the potential for settlement, in the context of the subsequent land use. In the context of the current project, settlement is generally defined as the downward movement of the waste rock pile surface as a result of increased vertical stress (from piling up of the material) and the resultant compaction and reorientation of particles within the waste rock material. Settlement over large areas of the backfill, which is sometimes referred to as subsidence, is not expected to occur due to the consistent size of the crushed waste rock (-14-inch), the durability of the waste rock, the stability of the underlying bedrock, the 5-foot placement lift thickness, and the degree of compaction provided by multiple passes of the mining class dozer. Each final backfilled pit area will consist of an excavated mine pit filled with waste rock material with a waste rock material pile constructed on top of the waste rock -filled pit. The waste rock will be placed into the pit by a conveyor system that will deposit the rock in a pile. A mining -class bulldozer in the pit will be used to push the material from the conveyor discharge point and spread the material into placement lifts. Thickness of placement lifts for waste rock material placed into the excavated mine pit will be limited to five (5) feet until more detailed assessment of placement lift thickness is completed via an in -pit demonstration test area in the first pit to be backfilled. Details of the demonstration testing can be found in the next section (2.3). Four placement lifts, each a thickness of 5 feet, will be used to create the designed bench height of 20 feet. During and after placement of waste rock (both pit backfill and above original ground surface), the construction will be monitored monthly for compliance with placement lift restrictions utilizing modern survey equipment. The surveying work will include field controls, either through field survey and/or calibrated onboard GPS systems installed on the working equipment. Completing ' Froehlich, Ph.D., P.E., D.WRE, M.ASCE, (2011) Mass Angle of Repose of Open -Graded Rock Riprap, Journal of Irrigation and Drainage Science Engineering, ASCE, July 2011. Marshall Miller & Associates, Inc. 3 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina monthly surveying of the backfilled areas and constructed piles using modern survey equipment and techniques will allow for a detailed understanding of the rate and magnitude of any settlement. Settlement data collected throughout the course of the pit backfilling and waste rock pile construction will enable PLCI to accurately predict the duration of any settlement that may occur following completion of each waste rock structure. 2.3 Demonstration Testing for Placement Lift Thickness The demonstration test will involve construction of various placement lift thicknesses and measurement of the achievable compaction at the completion of each placement lift. Compaction for the placement lift thickness testing will be achieved by using a mining class dozer to complete the leveling passes. Compaction results during demonstration testing will be measured with standard electronic survey equipment to determine the loose placement lift thickness (before compaction) and the compacted placement lift thickness (after compaction). The results of the testing will facilitate an understanding of the achievable compaction with varying dozer passes for variable placement lift thicknesses. The results of the demonstration testing will be recorded in PLCI's Monitoring, Operations and Maintenance Plan and records maintained at the site. Using the results from in -pit compaction testing with the actual waste rock and the actual project dozer will ensure that the final placement lift thickness is appropriate for the waste rock fill application. Review of available information for similar mining operations indicates that a lift thickness of 33 feet is used for pit backfilling at a large open pit metal mine in the southeastern United States. Following completion of pit backfilling operations, PLCI will conduct an additional placement lift thickness/compaction test to determine the most applicable placement lift thickness for material placed above the pit rim. The in -pit testing described above is important for determining the placement lift thickness that is applicable to the conditions. The material being backfilled into the pits is rock, and it is expected to exhibit minimal residual settlement (as compared to soil). In addition, the waste rock is being placed into a rock excavation (the pit), which is expected to exhibit little or no settlement after the initial placement and compaction with the mining size dozer (as compared to compaction that may occur due to placement of waste rock onto native soil). It is important to note that no subsidence is expected in the proposed mine excavation pit because of its high strength, competent mineral bedrock without voids and minimal preferential flow pathways for groundwater. In addition to placement methods required and/or applicable placement lift thickness, it is also important to consider the proposed subsequent land use in the backfilled pit area. In this case, which is a backfilled pit area topped with a constructed waste rock pile, the resulting landform is going to be a vegetated hill with 18.4-degree inter -ramp slopes including safety benches, and a domed top to reduce infiltration. As a result, future construction of man - Marshall Miller & Associates, Inc. 4 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina made structures on the backfilled pits and accompanying waste rock piles is not included in the reclamation plan. In summary, the demonstration testing will be used to verify and test the following: > Proper placement lift thickness to be used. > The required number of passes with a mining -class dozer necessary to seat, stabilize, and compact the waste rock fill so that settlement and void spaces are minimized in the waste rock fill. > Determination of the need for any additional testing required to verify that the placement lift thickness and methods for observing dozer compaction of the waste rock are sufficient to achieve the required results. 2.4 Final Vegetative Cover Vegetation of final backfilled mine pits topped with waste rock pile shall be accomplished by placing a low permeability natural soil cover or other materials capable of supporting vegetation on the surface of the waste rock material and subsequently planting to establish a continuous stand of vegetation. The low permeability cover soil shall consist of a minimum thickness of twelve (12) inches of soil with surface organic matter that is capable of supporting final vegetation. All earth moving equipment used to place cover soil shall be sized to limit impacts to over -compaction of soil that may hinder vegetation growth. Once the backfill has reached the ground surface and construction of the overlying waste rock pile begins, seeding will generally be initiated following completion of each twenty (20) foot elevation interval once final grading of the bench and topsoil coverage has been achieved. In no event shall any provision of this section be construed to allow small pools of water that are, or are likely to become, noxious, odious, or foul to collect or remain on the mined area. Suitable drainage ditches or stormwater management piping will be constructed or installed to minimize and avoid surface erosion and concentrated stormwater flow conditions. Upon construction of the final regrade benches of the waste rock pile sitting on top of the backfilled pit, stormwater runoff will be directed to a flume to convey the water from the benches and minimize erosion. Once vegetation is established, perimeter ditches will be graded to prevent pooling or standing water onsite. The dome -like nature of the final reclaimed surface will minimize infiltration and minimize the potential for flat or depressed areas to form and collect pools of water. The type of vegetative cover and the methods of its establishment shall be specified and shall conform to accepted and recommended agronomic and reforestation/restoration practices as established by the North Carolina Agricultural Experiment Station and Department of Environmental Quality. Advice and technical assistance may be obtained through the State soil and water conservation districts. Marshall Miller & Associates, Inc. 5 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina 3 Reporting Requirements During construction, observations (including photographs) shall be recorded by a competent person on a regular basis in PLCI's Monitoring, Operations and Maintenance Plan. During waste rock disposal operations, stability evaluations of the waste rock fill with field observation results shall be recorded as they occur in PLCI's Monitoring, Operations and Maintenance Plan by a competent person. 4 Revegetation of Completed Areas 4.1 Soil Slopes Final soil slopes and soil linings in ditches shall be seeded and mulched to provide a continuous stand of vegetation. The seeding schedules presented in Appendix A shall be utilized to re - vegetate the final graded slopes. 4.2 Waste Rock Slopes Re -vegetation of final waste rock pit backfill slopes can be accomplished by placing a cover of soil on the surface of all final waste rock slopes and subsequently planting to establish a continuous stand of vegetation. The final slopes of the waste rock pit backfills (extended above ground) shall be covered with a minimum of twelve (12) inches of soil and seeded at the completion of each 20-foot elevation interval. Soil cover and vegetation shall be in accordance with the North Carolina Department of Energy, Mineral and Land Resources regulations as presented in Appendix A. a. Temporary Seeding - Areas left disturbed for long periods of time shall be stabilized by seeding per state regulations. Temporary seeding, fertilization, mulch and soil amendment proposed are presented below. b. Permanent Seeding - Areas seeded during the acceptable permanent seeding period shall be stabilized by permanent seeding requirements. Permanent seeding, fertilization, mulch and soil amendment proposed are presented in Appendix A. Marshall Miller & Associates, Inc. 6 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina 5 Monitoring and Maintenance 5.1 Waste Rock Quantities Records of waste rock quantities disposed of at the facility shall be maintained by PLCI. These records permit comparison with the quantities used for design and facilitate modifications to the design, if necessary. The records shall be reviewed semi-annually. 5.2 General Observations Observations of the waste rock pit backfill embankment above the pit rim and related features shall be made at intervals not exceeding 30 days and immediately following any unusual events such as floods, heavy rainfalls, heavy frost periods, abnormal structural behavior, etc. Reports or records from field observations and testing results shall be maintained at the mine office. A report of the observations shall be reviewed at least semi-annually. Any unusual features shall be reported immediately to mine management or competent person. Items to be recorded by PLCI include the following: a. Slopes - Any irregularities such as tension cracks, scarps, slumps, wet areas or vegetation disturbance shall be recorded. b. Working Disposal Surface - Irregularities shall be recorded. c. Bench and Perimeter Sediment Ditches - General condition of channels, soil erosion adjacent to or beneath riprap and seeded slopes, blockage by debris, etc., shall be recorded. d. Areas in Vicinity of the Backfilled Pit - General conditions throughout the area of the pit backfill shall be observed to note any changes overtime. 5.3 Maintenance The following maintenance shall be performed regularly: a. Routine Maintenance - Continuous maintenance, including replacement or patching of grouted riprap, gutter reseeding, debris removal from ditches at the site, etc. b. Maintenance After Unusual Meteorological Events (Heavy Rainfall, Extreme Frost Periods, Severe Droughts, Floods, High Winds, Etc.) -The most important maintenance tasks at these times are the immediate backfilling of all scarps or slumps, repair of erosion rills or gullies, and the repair and improvement of drainage systems and riprap lined ditches. c. Maintenance After Abnormal Changes in the Behavior of the Structure- If abnormal behavior of any portion of the backfill is observed, qualified persons knowledgeable of the facility Marshall Miller & Associates, Inc. 7 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina design characteristics shall be advised immediately and any recommended maintenance measures undertaken. d. Measures to Address Development of Pools — During mine pit backfill construction, inspections will be conducted weekly to ensure the material is being placed in accordance with established placement lift thickness parameters and per the design slope (once fill material reaches original ground). As final lifts and regrade benches are achieved, these inspections will continue to be conducted on a weekly basis until final grading. Once the pile is seeded and vegetated, inspections of the surface will occur monthly for the first year to ensure no surface water is pooling on the pile. If surface water pooling is located during review of the area, the location will be regraded for positive drainage, seeded, and revegetated. Inspections of the backfill areas will be reduced to quarterly after the first year until final permit release. 5.4 Data Review All facility performance and maintenance data obtained during periodic inspections shall be reviewed by qualified persons knowledgeable of the facility construction and must meet the requirements described in this document. If the waste rock pit backfill procedures do not meet these specifications during construction, PLCI will determine a suitable course of mitigative action. Marshall Miller & Associates, Inc. 8 Waste Rock Pit Backfill Plan South and East Pits Technical Specifications Carolina Lithium Project Piedmont Lithium Carolinas, Inc. Gaston County, North Carolina Appendix A LDM - RATE OF APPLICATION O s,'xm): $re appliczdca roll m stall mat! m be cm&K-%dby fszaae 3cwww. is boa of tills a:: spgly 2.000-3.0w bs Kam ourw rioW-44;md4,00M.X0mz.=om5w--somvWsoils.F-aofrFFltarcancx�an3adbr�oP:CI}lQVCr.7olan and Sodmum Cmtra Plaza and Dw.-.tR SSz—I - Cb" 6. FERTILIZER - A-'tiAI-YSIS AND RATE OF APRUCATION (potmd: acre,, Sale rpplicat ca came ca sods cost» bo ceodwtod bs 5r= courmer. bamar, is pep cf :c:: 2*7 apply a 10.10-10 pa& nraiisar as Rim a ap0.-=oa recc==ndad by tba NCDEQ VC Ercr-vz and Sodimau t.,=m Plmaioc aai 7v.:Lm Jixatssl - : b:Fmc 5. SEED - Ti-PE(S) AND RATE(S) Of APPLICATION INCL=G ITAR-ROUND SEEDLYG SCHEDULE (paunds'aue): [.;OTE: hirhi& Legumes] Seed Tom: Seedise Dates: Setdiar Rghes_ Perammest 5erd 45 lb,. ace Naai o ljskiex fcr 5tri \Lae: [Eli. it-] 11] ixmgdzc t 2C lb-. =a ass S%KF S:Cpo NaX 7Cm ink Il':.,=L [-0111CLW(-31] Fobroxy 13-Aumi t ' EC lb: a= N". ti m S r aF Scpe NL-m aids Czain Aga iEgZSi- ISi-2j -i:iLw 15-Fot m• : ` ? 51b -- =a TeanponzT Cmw Sled Srv=zop=Law Fobrua -:5:;ssau:T:` LCIb:acro .4=31." pram tgml 15-Foh =- : ` 3C Ib: aco `X SaKa kp Uzt =M11 1Cis a szmp Jopo = for the R:dmox and ''aa: z l 1Y.= roams. cf N.C, Tlns poDinata- fnza&-=pans&.food mdcasw:arnz7dhm.Tlx:sad=c beptrcha: LomERNSTSa3: • \ass Eaabv:x 3x Sam tfaot � �'{it-111 � :: an ac-.aca :C�:1 mj .-.r v.at�ca 1mx l: ; x pear -•.,a.- ��x fa mldl:h cam and polbazkr •hab=t m d6---bod uw. Tbi. sad nu can bo pc --thud Emn DRUNST coed: ' a='Q Saar Shss Nfu srh Cry RA lIItti3fx-181.21 is a stoop :lope r=m t; a si: wad amx nri Zt= r v u a ca e ate.:clndo: nJaaf_;: %'Lti.a -A"m .pg}} and pastr4a pox (i Adral ..0 u :pp;, both Of Bch ale lsatzmms spocim. T71 soil ma tau bo 7=r asod fr= ES`I5T Sao& \fLICH - n Pr XC tAT° OF PP'L:CATICiv '�P�-. a ra).ADD bSEiFCD OF Xw.-r72%rJ: ice_:z_xrr.r.cEabaa --rr:sullbe4.}:0lbsacn Onis::-1an3:1%Iip tackisactreq®od Oeslopes31crcaatrr,roc: av;"-rtnr :: req:.ror Rua of a�:raca zecoCs:oodod b<• � tit�EQ P7C Erosim sail Sodazob C'errcl ?+mom= aa3 iv.:� Sirmi: - :hzptar E. - OTHER VEGETATIVE COVERS — ME (S) ANT, RATE (S)OF APPLICATION D CLUDIhG SEEDU G SCHEMLE (pmm& acre, aves.'aa-e, spacing of tm'shtn . etc): Dxmr toy �arscrz a ¢t o poseur sca cm be --), d fr= E]LNST Swd rt •;�_ ha uc�toied : a : =x : a p :4 : s :sod mil. - Rec•egemtian mdfor tefaesmam plan approved by: S=arze � Date 12-08-21 prrs \ame DAVID H. WEST Tirle SR. LANDSCAPE ARCHITECT; RLA NORTH CAROLINA #2076 Ageng HDR.INC. Marshall Miller & Associates, Inc.