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HomeMy WebLinkAbout4117_A-1SandrockCDLF_GeologicSubgrade_Phase2B_DIN28525_20170905 Correspondence: Amec Foster Wheeler Environment & Infrastructure, Inc. 4021 Stirrup Creek Drive, Suite 100 Durham, North Carolina 27703 Tel (919) 381-9900 Fax (919) 381-9901 amecfw.com August 4, 2017 Mr. Ed Mussler, PE, Branch Head NCDENR Division of Waste Management Solid Waste Section Permitting Branch 1646 Mail Service Center Raleigh, NC 27699-1646 Subject: Construction Quality Assurance Documentation A-1 Sandrock CDLF Phase 2B Greensboro, North Carolina (Guilford County) Solid Waste Permit 4117-CDLF-2008 Dear Mr. Mussler: Amec Foster Wheeler Environment & Infrastructure, Inc. (Amec Foster Wheeler) is pleased to present this report on behalf of A-1 Sandrock, Inc., documenting the completion of Phase 2B of the approved CDLF expansion. This work was completed in pursuit of the Permit to Construct (PTC) issued by the Solid Waste Section (SWS) on September 11, 2015 (DIN 24959). Within this report, please find documentation for construction of Phase 2B, including the certification of a subgrade conditions and adherence to the approved construction plan. At this time A-1 Sandrock CDLF seeks the Section’s approval of the construction and the issuance of a Permit to Operate (PTO) for a five-year period. This report is organized into the following sections. 1. Letter Report 2. Appendices A. As-built construction drawings B. Test pits to confirm ground water separation and bedrock C. Design Hydrogeologic Report Amendment D. CQA meeting minutes and notes E. Photographic documentation F. Facility Plan Drawing Showing Modification to Mulch Storage G. Reserved A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 4, 2017 Phase 2B CQA Documentation and PTO Application Page 2 OVERVIEW This report is intended to satisfy the requirements of 15A NCAC 13B.0540 for documentation of a Construction Quality Assurance (CQA) program for Phase 2B at A-1 Sandrock CDLF. Phase 2B is a contiguous footprint covering approximately 3.42 acres, with the older CDLF (Phase 2A). Construction was divided into two equal sub-phases: Phase 2B-1 (Cell 1) in the higher elevations to the east and Phase 2B-2 (Cell 2) in the lower elevations to the west. Phase 2B is located in a balanced earthwork section with grades approved under an earlier report. The upper 24 inches of the soil was consisted of USCS classifications of mostly ML and SM, with some CL based on visual inspection of the Phase 2B construction. Soil classification was performed via 9 tests pits dug across Phase 2B-1 and 2B-2 by A-1 Sandrock. Amec Foster Wheeler is of the opinion, based on prior testing and experience, that visual classifications are sufficient to characterize these soils. The compaction and soil characteristics are consistent with those observed in Phase 1 and Phase 2A. The performance of the soils under load were confirmed via proof rolling to evaluate the soil density; a large piece of excavating equipment (track excavator) moved across the site with no indications of soft or pumping soil conditions. These methods are used extensively in the construction industry and are appropriate for this site. Major aspects of the new construction included: 1. Establish layout and grade control for construction using a third-party licensed surveyor; install permanent marker posts at the perimeter of the waste footprint. (See drawings, Appendix A) 2. Verification that fill within the upper 24 inches of finished base grades meets current NC DENR Solid Waste Section requirements for soil type. (See test pit logs, Appendix B) 3. Final grade elevations meet four foot separation requirements with regards to ground water and bedrock. 4. Address puddling of surface runoff from weather events to ensure proper drainage from phase. RESPONSIBILITIES AND DOCUMENTATION The Facility served as its own contractor (facility manager Ronnie Petty supervising) using in house staff and equipment, local surveying support (Allied Professional Services, PLLC, Clint Osborn, PLS surveyor), and field engineering support and CQA oversight (Amec Foster Wheeler, Michael Raup, PE supervising). Documentation of the work consists of field notes and "as-built" construction plans, plus a series of photographs, presented in separate sections of this report. (See Appendices) A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 7, 2017 Phase 2B CQA Documentation and PTO Application Page 3 Based on our familiarity with the facility and soils within the upper 24 inches, the project engineer was able to base the subgrade characterization on visual soil classifications and performance- based compaction criteria. Soils are well understood from the permitting and earlier construction. As a provision of Section 4.2.1 of the PTC Application, visual examination was used in lieu of laboratory testing. All soil work passed the visual evaluation criteria. While inspecting the test pits and capturing photographs of the phase it was apparent that between phases 2A and 2B was a remnant of the original soil above the design grade was left in place. These surfaces show a relict rock-like texture, but the test pits confirmed that the materials did not contain bedrock within a depth of 4 feet beneath finished base grades. This material was excavatable using conventional excavating equipment, and visually classified as weathered rock. CERTIFICATION This is to certify that construction of Phase 2B of the A-1 Sandrock CDLF was completed in substantial compliance with (1) the CQA Plan, (2) the conditions of the Permit to Construct (3) the Solid Waste Management Rules, and (4) approved grades, as depicted on the “as-built” plans. Said plans were prepared based on a topographic survey by a licensed surveyor. Subgrade soil types meet the current regulatory requirements based on visual inspection. No ground water, detrimental soils, or bedrock were encountered at or above the approved subgrade elevations; site conditions are as anticipated and consistent based on the earlier permitting studies. Please contact us if you have any questions or comments. Cordially yours, Amec Foster Wheeler Environment & Infrastructure Michael C. Raup, P.E. G. David Garrett, P.G., P.E. Geotechnical Engineer Senior Engineer NC – PE 45271 NC – PG 0983 NC – PE 25462 Appendix A – As-Built Construction Drawings AMEC Foster Wheeler Environment & Infrastructure, Inc. 4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM, NORTH CAROLINA TEST PIT LOCATION PLAN A1 SANDROCK PHASE 2B GREENSBORO, NORTH CAROLINA DRAWN: CO DATE: JULY 2017 FIGURE ENG CHECK: MCR SCALE: NTS 1APPROVAL: GDG JOB NO.: 6468-17-7032 Reference: CLINT OSBORN ALLIED ASSOCIATES, P.A. AMEC Foster Wheeler Environment & Infrastructure, Inc. 4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM, NORTH CAROLINA BASE GRADE VARIATIONA1 SANDROCK PHASE 2B GREENSBORO, NORTH CAROLINA DRAWN: CO DATE: JULY 2017 FIGURE ENG CHECK: MCR SCALE: NTS 2APPROVAL: GDG JOB NO.: 6468-17-7032 Reference: CLINT OSBORN ALLIED ASSOCIATES, P.A. AMEC Foster Wheeler Environment & Infrastructure, Inc. 4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM, NORTH CAROLINA GROUNDWATER SEPARATIONA1 SANDROCK PHASE 2B GREENSBORO, NORTH CAROLINA DRAWN: CO DATE: JULY 2017 FIGURE ENG CHECK: MCR SCALE: NTS 3APPROVAL: GDG JOB NO.: 6468-17-7032 Reference: CLINT OSBORN ALLIED ASSOCIATES, P.A. AMEC Foster Wheeler Environment & Infrastructure, Inc. 4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM, NORTH CAROLINA BEDROCK SEPARATIONA1 SANDROCK PHASE 2B GREENSBORO, NORTH CAROLINA DRAWN: CO DATE: JULY 2017 FIGURE ENG CHECK: MCR SCALE: NTS 4APPROVAL: GDG JOB NO.: 6468-17-7032 Reference: CLINT OSBORN ALLIED ASSOCIATES, P.A. AMEC Foster Wheeler Environment & Infrastructure, Inc. 4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM, NORTH CAROLINA PIEZOMETER ABANDONMENTA1 SANDROCK PHASE 2B GREENSBORO, NORTH CAROLINA DRAWN: CO DATE: JULY 2017 FIGURE ENG CHECK: MCR SCALE: NTS 5APPROVAL: GDG JOB NO.: 6468-17-7032 Reference: CLINT OSBORN ALLIED ASSOCIATES, P.A. Appendix B – Test Pit Logs and Photographs Photo 1 Test Pit 1 Depth – 5.2’ Water Depth – Dry Visual Soil Classification – Reddish Orange, SILT (ML) Photo 2 Test Pit 2 Depth – 4.4’ Water Depth – Dry Visual Soil Classification – Tan Brown, Sandy SILT (ML) Photo 3 Test Pit 3 Depth – 4.7’ Water Depth – Dry Visual Soil Classification –Brown, Sandy SILT (ML) Photo 4 Test Pit 4 Depth – 5.7’ Water Depth – Dry Visual Soil Classification – Tan, Sandy SILT (ML) Photo 5 Test Pit 5 Depth – 4.6’ Water Depth – Dry Visual Soil Classification – Brown, Sandy SILT (ML) Photo 6 Test Pit 6 Depth – 4.2’ Water Depth – Dry Visual Soil Classification – Tan, Sandy SILT (ML) Photo 7 Test Pit 7 Depth – 5.0’ Water Depth – 0.4’ Visual Soil Classification – Tan, Sandy SILT (ML) Photo 8 Test Pit 8 Depth – 4.9’ Water Depth – 0.3’ Visual Soil Classification – Tan Brown, Sandy SILT (ML) Test Pit 9 Depth – 5.0’ Water Depth – Dry Visual Soil Classification – Tan Brown, Sandy SILT (ML) and Gray, Lean CLAY (CL) Appendix C – Design Hydrogeologic Report Amendment A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 4, 2017 Phase 2 Design Hydrogeologic Study Amendment Page 1 1. Historical Perspective A-1 Sandrock submitted a Design Hydrogeologic report for Phase 2 in May 2015 (DIN 24835), approved September 4, 2015 (DIN 24941). That report correlated new test pits performed after the mining activities to original data from the Site Suitability study; this study focused on Phase 2A, with the understanding that similar future study would be necessary for Phase 2B. The 2015 study revealed 1) water conditions shallower than originally anticipated in the lower elevations of Phase 2A, and 2) rock-like materials that were softer and easier to excavate with conventional earthwork techniques that indicated in the Site Suitability study in the higher elevations. Unfavorable drainage conditions during the excavation lead to base grade geometry that allowed the accumulation of surface water in the “sump” area of Phase 2A, resulting in saturation of the subgrade soils at the original base grade elevations. Wet conditions prevailed during the months leading up to the Phase 2A evaluation, but it could not be ascertained whether the soil saturation reflected true ground water or “perched” water conditions exacerbated by the permeability soils. A-1 raised the base grades in Phase 2A up to 4 feet to mitigate these conditions. A topographic survey was prepared for as-built base grades, and test pits confirmed that adequate vertical separation was present between the revised base grades and either groundwater or bedrock. 2. Recent Study of Phase 2B Nearly identical conditions existed in Phase 2B, as anticipated. Mining to near proposed base grades during 2016 and early 2017 encountered similar conditions with respect to shallow water on the west side, softer materials on the east side than indicated earlier by “auger refusal” in the Site Suitability report. Appendix A of this work presents four drawings, numbered Figures 1-4, which detail the findings test pit investigation of Phase 2B. Appendix B presents photos of each test pit showing a tape measure for depth reference. The June 23, 2017 Technical Memorandum (CQA minutes) includes three photos, labelled Figures 1-3. The following section (Findings) will reference these photos, as well as the Phase 2A photos presented in the June 2015 report. 3. Findings of Phase 2B Study Figure 1 in this work documents the as-built base grade and shows test pit locations that confirm the required vertical separation. Appendix E presents photos that depict Phase 2B grading near the completion. The diabase dike described in the Site Suitability report and the Phase 2 Design Hydrogeologic report was encountered in the mid-elevations (north side) of Phase 2B. The dike exhibited rounded nodules varying from cobble-size to small boulders at the surface and extending 10 to 15 feet below the original ground surface. Below these depths, the dike became less weathered and transitioned to a chunky, friable rock-like material that was excavated using conventional track-mounted excavators. These conditions are similar to those described in the Phase 2 Design Hydrogeologic report. In the earlier site studies, the dike was estimated to be 50 feet wide at the surface. The Phase 2B construction revealed the dike widens with depth. A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 4, 2017 Phase 2 Design Hydrogeologic Study Amendment Page 2 In the June 23, 2017 memorandum (see Appendix D), Figure 1 (photo) shows the northern end of Phase 2B looking west. The dark-color, chunky diabase is visible in the cut slope to the right side of the photo. The location of the diabase coincides with the dark red soil and chunky diabase shown in photos in the Phase 2 Design Hydrogeologic report. These locations are exactly where the diabase was expected, based on the Site Suitability report. However, boulders and/or local variations in density appear to have caused “auger refusal” conditions at depths shallower than A-1 was able to excavate. As such, the chunky material is not true bedrock; rather it is a less weathered form of the saprolite overlying the diabase bedrock. In the June 23, 2017 memorandum (see Appendix D), Figures 2 and 3 (photos) show water accumulated in the Phase 2B sump. A-1 removed the water pumping during the course of the Phase 2B investigation, over a several week period. The winter and spring leading up to the preparation of Phase 2B were very wet, and a lot of water accumulated in the sump. However, once pumped down the water did not recharge (without additional rainfall), thus Amec Foster Wheeler believes that the saturated subgrade conditions observed prior to digging the test pits is “perched.” In the interest of time, A-1 decided to raise the base grade in the sump to provide the required 4 feet of vertical separation. Figure 2 in this work presents an isopach map depicting the difference in grades between the as- built topography and the original design base grades (dating back to the Site Suitability report). The isopachs show thickness contours of the grade differences, denoted as “High” and “Low” as appropriate. Within the northwest portion of Phase 2B, the “sump,” as-built base grades typically vary from 2 to 4 feet higher than the original design grades. Areas within the northeast portion of Phase 2B vary from 2 to 6 feet lower than design grades. Amec Foster Wheeler evaluated these areas during the excavation work and recommended a minimum of 4 feet of soil “padding” to be placed above the excavated surfaces. Test pits presented in Appendix B showed the water levels were more than 4 feet below finished base grades. Within the south portion of Phase 2B, the excavation encountered harder materials at the depths anticipated based on the Site Suitability data, thus these areas are left at, or slightly higher, than design grades. Along the west portion of the slope, including the area above the sump, the isopachs show the ground to be 4 to 6 feet lower than design grades. This is due to scraping the perimeter “berm” (actually a cut slope in native Sandrock) to remove vegetation. A continuous ditch occurs along the inside perimeter of the roadway, to convey surface water from higher elevations without flooding Phase 2B. This area is sufficiently strong to resist the weight of the future wastes without sliding or overturning, in the opinion of the engineer. Historically, the engineer has tracked variations from the design base grades in Phases 1 and 2 to confirm that the airspace is staying within the permitted volumes. Figure 3 in this work depicts ground water contours derived in part from those original contours found in the Site Suitability report, modified with information developed in the Phase 2 Design Hydrologic report and this investigation of Phase 2B. The contours reflect the maximum probable A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 4, 2017 Phase 2 Design Hydrogeologic Study Amendment Page 3 ground water elevations within Phase 2B based on the test pit data, summarized in the figure. Most of the test pits are dry, except TP-7 and TP-8, which encountered water deeper than 4 feet below the as-built grades in the sump area. All the test pits went deeper than 4 feet below as- built grades. The ground water contours are the assumed maximum water levels that could exist under these conditions, i.e., maximum surface exposure (high infiltration) and wet prevailing climate. Figure 3 shows that the minimum vertical separation requirement has been met. Figure 4 in this work depicts bedrock contours derived in part from those original contours found in the Site Suitability report, modified with information developed in the Phase 2 Design Hydrologic report and this investigation of Phase 2B. Historically, data at this site (and others) show a transitional nature in the change from soil to rock, whereas the soils become progressively denser with increasing depth and gradually transition to rock. Engineers and geologists use the term “saprolite” for this transition zone, which can include dense soil with a relict rock-like texture and materials exhibiting variable density, termed “partially weathered rock” or “PWR” by the local engineering community. The PWR forms along joints and other fractures in the rock, and can extend many feet deeper than “auger refusal” conditions. The top of “bedrock” can vary across the site and may result in excavations that extend deeper than originally anticipated. Whereas the test pits encountered no bedrock, the contours in Figure 4 depict the highest theoretically possible bedrock contours, assuming the bedrock exists just beneath the bottoms of the test pits. Figure 4 shows that the minimum vertical separation requirement has been met. 4. Piezometer Abandonment Figure 5 shows three borings within the Phase 2B footprint, B-15, B-18 and B-25, and one on the boundary with Phase 2A, B-29. The latter boring was abandoned with Phase 2A. Of the three in Phase 2B, two were dry, B-15 and B-25. A piezometer pipe was installed in B-15, but no water was ever recorded. No piezometer was installed at B-25. At B-18, records show a piezometer was installed in Unit 1, the saprolite overlying the granite, also known as “Sandrock.” The water level was recorded at approximately El. 760. Hydraulic conductivity at B-18 was 1 x 10-6 cm/sec measured using slug tests. Current base grades at the location of B-18 are 11 feet below the original ground surface. However, the boring terminated at a depth of 29 feet and, thus, it is likely that the Sandrock excavation removed the piezometer at B-18, and at B-15. However, there is no documentation of this occurrence. Site personnel were questioned, but none have recollection of even seeing the piezometers, but there has been some staff turnover. 5. Conclusions Drawings presented as Figures 1-4 (Appendix A of this work) depict the currently understood conditions for base grades, ground water and bedrock, modified from earlier work. Groundwater and bedrock surfaces vary somewhat from the earlier study, i.e., the Site Suitability report, but these conditions are nearly identical to those described in the Phase 2 Design Hydrogeologic report and encountered in Phase 2A. The test pit logs (Appendix B of this work) confirm the A-1 Sandrock, Inc., CDLF (Solid Waste Permit 41-17) August 4, 2017 Phase 2 Design Hydrogeologic Study Amendment Page 4 presence of 4 feet of vertical separation between as-built base grades and either groundwater or bedrock. Materials encountered in the excavation are as expected with respect to composition and density. Where possible, the as-built base grades are lower than original design grades (from the Site Suitability report), while maintaining the required vertical separation. This work, as an amendment to the Phase 2 Design Hydrogeologic study, confirms conditions as nearly identical in both Phases 2A and 2B. The lack of a piezometer abandonment record for B-15 and B-18 is not considered harmful to ground water resources, whereas neither boring penetrated the bedrock and low permeability soils were indicated by earlier field work. No changes to the ground water or landfill gas monitoring programs are warranted. 6. Certification This report represents a true representation of the hydrogeologic conditions for the Phase 2B area of A-1 Sandrock, Inc. CDLF, as presently understood by Amec Foster Wheeler. This document was prepared in support of a Permit to Operate application for the same. All work was performed by, or under the supervision of, a North Carolina licensed professional geologist. Appendix D – CQA Meeting Minutes Correspondence: Amec Foster Wheeler Environment and Infrastructure, Inc. 4021 Stirrup Creek Drive, Suite 100 Durham, North Carolina 27703 Tel (919) 381-9900 Fax (919) 381-9901 amecfw.com July 17, 2017 TECHNICAL MEMORANDUM TO: Project Number 6468-17-7032 FROM: Michael Raup – Amec Foster Wheeler Environment & Infrastructure RE: CQA Progress Meeting Summary A1Sandrock, CDLF Phase 2B Greensboro, North Carolina (Guilford County) Solid Waste Permit 4117-CDLF-2008 The following is a transcription of field notes pertaining to various Construction Quality Assurance (CQA) inspections and meetings for the referenced work site prepared by Michael Raup of Amec Foster Wheeler Environment and Infrastructure. The work consists of site inspections and soil evaluation to meet North Carolina Solid Waste Rules. The work was substantially completed by the A1 Sandrock CDLF, staff, with partial oversight provided by Michael Raup, P.E. and grade control by Allied Professional Services, PLLC. The following notes are arranged by date of my inspections, i.e., minutes of the CQA meetings, which are intended to serve as documentation of the construction and CQA oversight. Included with this document are relevant photographs and relevant drawings of "as-built" conditions. Please be advised that this document shall be presented to the NC DENR Division of Waste Management in support of forthcoming Permit to Operate application. A summary of key observations made on the indicated dates of inspection follows: 2/10/17 Amec Foster Wheeler inspected final grading activities and advised client to confirm grades before preforming test pits. Surveyors had placed grade control stakes and A1 Sandrock was in the process of preparing the phase to final grade elevations. Amec Foster Wheeler A1 Sandrock agreed to notify Amec Foster Wheeler once final grades had been achieved so that test pits could be performed. 6/15/16 Amec Foster Wheeler visited site to inspect P.L.S. grade elevation and perform test pits. Upon arrival there was a heavy rain event and test pits were rescheduled. Recommendations given to address puddled water in the lower depression area of the phase due to weather. Recommendations were made regarding final grading with respect to drainage before next site visit. July 17, 2017 Page 2 Page 2 6/22/16 Amec Foster Wheeler visited the site to inspect subgrade and grade elevations. Recommendations in regards to final grading from previous site visit were made. Puddled water was still present but improved from previous site. Test pits were performed 24 hours in advance to allow for ground water levels to stabilize. Visual classifications of soils was completed to ensure permit requirements were met, and confirm four foot separation of final grade and water table or bed rock. This was conducted using 9 test pits placed across Phase 2B phase such that a good representation of the phase was shown. The lower end of the phase had some puddled water from previous rain events. The two test pits next to this area showed four feet or greater separation in grade and water table, confirming separation requirements had been satisfied. Observations were documented and photographed. 6/23/17 Michael Raup prepared CQA documentation report. End of notes. July 17, 2017 Page 3 Page 3 Figure 1 – View of Phase 2B from haul road looking down towards the bottom of Phase 2B. Test Pit locations are also shown. Figure 2 – View of Phase 2B from southern side of phase. July 17, 2017 Page 4 Page 4 Figure 3 – View from bottom of Phase 2B towards upper southern side of Phase. Puddled water is shown along with test pits. Appendix E – Photographic Documentation Appendix F – Facility Plan Drawing Showing Modifications to Mulch Storage Appendix G – Reserved B-24B-25B-16 B-7 MW-4 B-14 MW-1 B-8 B-13 B-15 MW-3