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Home My WebLink About3405_Forsyth_RJReynolds_RuralHall_Indus_ExcavationSummary_FID1453241_20200929ERM FRN Inc. FFa hone: +1 704 541 8345 Summit Avenue +1 704 624 7928 NC 28203 erm.com 29 September 2020 North Carolina Department of Environmental Quality Division of Waste Management 1646 Mail Service Center Raleigh, North Carolina 27699-1646 Attention: Ms. Jaclynne Drummond jaclynne.drummond@ncdenr.gov Via Email Reference: 0564782 Subject: Sediment Boil — Excavation Summary Permit #34-05 - Edwards Road Landfill Edwards Road Rural Hall, Forsyth County, North Carolina Dear Ms. Drummond: On behalf of R.J. Reynolds Tobacco Company (RJRT), ERM NC, Inc. (ERM) is providing this summary of excavation activities conducted 25 August 2020 in the area of a surface boil encountered at the Edwards Road landfill in Rural Hall, NC. The boil, located on the eastern slope of the landfill immediately west of sediment trap ST-1, was discovered 10 February 2020 during a routine post -closure quarterly inspection. Initial field investigation results were provided to the Division of Waste Management (DWM) in correspondence dated 16 April 2020 (ERM). An Excavation Work Plan (ERM) for additional assessment/ investigation activities was submitted to the DWM on 16 June 2020. Due to above average wet conditions in the area, field investigation activities have been delayed until dryer conditions are available to conduct field work. Background and Existing Site Conditions • Field investigation activities were conducted pursuant to ERM's Sediment Boil — Excavation Plan dated June 16, 2020 and submitted to NCDEQ - Division of Waste Management. • Field investigation activities were conducted by ERM on August 25, 2020 with labor and equipment supplied by Piedmont Industrial Services, Inc. (subcontractor to ERM). • Conditions on August 25, 2020 were clear and dry with temperatures ranging from mid-80s to low 90s. • Existing site conditions noted: o Silt fence previously placed down gradient of surface boil location was in place and in good condition. o Surface boil was not observed to be active at time of field investigation. Discharge from the surface boil was last observed on 24 May 2020. o Empty 5-gallon buckets remain placed at the boil area in the event sediments require removal. o Surface sediments were not observed at the time of field investigations. Page 1 of 8 I'MV111 29 September 2020 Reference: 0564782 Page 2 of 8 Existing site conditions of the morning of August 25, 2020 upon ERM's arrival on site Excavation Activities — Surface Boil • Using a "mini-trackhoe" with hand tools, excavation began at the location of the previously located surface boil (also adjacent to temporary piezometer PZ-6 previously installed by ERM). • Incremental excavation was performed removing approximately 1 foot of soil at a time followed by inspection of soils, probing and attempts to identify dark gray sediments. • Dark gray sediments were encountered approximately 3 feet below surface grade and observed to be contained in a small discrete pocket (approximately 12-inch diameter). A piece of rip rap stone was located in the center of the sediment pocket. • Dark gray sediments were not observed during excavation activities above 3 feet below ground surface. Initial excavation activities in area of surface boil T1M 29 September 2020 Reference: 0564782 Page 3 of 8 Discrete pocket of dark gray sediments observed approximately 3 feet below existing ground surface and extending to approx. 3.5 feet below ground surface. • Excavation continued in the area of the identified sediment pocket. Dark gray sediments were not observed below approximately 3.5 feet below ground surface. • Inspection and observation of the area did not identify a "pathway" of sediments entering the discovered pocket (from beneath the pocket or from horizontally upgradient or side -gradient). Final depth of excavation in area of surface boil �i Excavation Activities — Upgradient of Surface Boil 29 September 2020 Reference: 0564782 Page 4 of 8 • Without evidence of a preferred sediment migration "pathway", excavation continued from the surface boil location upgradient towards the closed landfill liner anchor trench. • Excavation continued in a manner as previously described using the mini-trackhoe and hand tools removing approximately 1-foot increments of soil to allow for inspection and observations. • The liner anchor trench was located and uncovered approximately 12 feet west (upgradient) of the surface boil location. • The anchor trench was completely uncovered and exposed to allow for visual inspection; no indications of dark gray sediments or wet soils observed. • Additional soils were excavated on the downgradient side of the anchor trench and along the anchor trench to allow for inspection of a broader area; no indication of dark gray sediments or wet soils observed. • Cover soils immediately upgradient (west) of the anchor trench were removed to allow for inspection of soil conditions above the composite liner; no indication of dark gray sediments or wet soils observed. Excavation continuing upgradient (west) of surface boil towards anchor trench 29 September 2020 Reference: 0564782 Page 5 of 8 Exposed liner anchor trench area • Lacking evidence of dark gray sediments beyond the initially located discrete pocket, excavation of this area did not continue. • Due to the location of the sediment pocket near the crest of an exterior containment berm, excavation did not extend deeper than approximately 4 feet below ground surface (no dark gray sediments observed below 3.5 feet). • The excavated area was backfilled and compacted using excavated soils. The area was seeded with erosion mat installed with staples over the disturbed area. • A PVC pipe was placed to mark the outer limits of the liner anchor trench for easy identification in the field for future activities. Excavation area backfilled and stabilized with PVC pipe locating outer anchor trench limits Observations • Only one discrete pocket of dark gray sediments was observed during field activities. • A preferred pathway of dark gray sediment migration was not encountered. • Excavated soils were dry upon inspection. �i 29 September 2020 Reference: 0564782 Page 6 of 8 Majority of soils excavated were observed to be clayey silts or silty clays; soils have plasticity. Rip rap was encountered and excavated in the immediate vicinity of the surface boil area. No flow was observed from anchor trench drains or underdrain outlet. Cross Section Development Utilizing field observations and measurements, ERM developed the enclosed cross section of the excavation area. Information from as -built drawings developed from liner cap installation were utilized to assign elevations. From development of the cross section, the following is noted: • Elevation of ground surface at the surface boil location is approx. 831.9. • Elevation of dark gray sediment pocket observed is approx. 828.4. • Elevation of bottom of anchor trench is approx. 831.9. • The outer limit of liner anchor trench is approx. 12 feet upgradient of surface boil location. • Based on as -built drawings and photos documenting the landfill closure project, a minimal depth of ash (5 to 10 feet) was placed immediately upgradient of the liner anchor trench in the area of the surface boil. • Investigation of the boil area included excavation of soils below elevations of upgradient liner anchor trench and ash placed immediately upgradient of the anchor trench. • Underdrain installed in 2012 to drain an area of saturated ash encountered during closure is located approx. 105 feet west (upgradient) of surface boil location at an elevation of approximately 828. Conclusions • Based on Site observations, there is no apparent risk to human health or the environment related to the sediment boil. • The surface boil was not actively flowing at the time of field investigation activities and all surrounding soils removed during excavation were observed as dry. • Based on inspections by RJR following significant rainfall events in the region, the surface boil has not been observed as active for over two months prior to these excavation activities. Since the installation of the liner in 2012, no sediment boils have been observed at the Site prior to the extreme wet conditions of 2020. • Previous surface water sampling results indicate that no exceedances of NC Surface Water Standards have occurred in the nearby Leak Creek. • A preferred "pathway" of sediment migration could not be visually identified during these field activities. • Based on observations of the section of liner anchor trench that was exposed immediately upgradient of the surface boil, there is no visual indication of wetness or gray sediment migration associated with the liner trench. • Based on the previously submitted Sediment Boil — Excavation Plan dated June 16, 2020 (ERM), with the lack of "pathway" identification, further assessment, monitoring and/or investigation is warranted. Next Steps Based on field investigation activities and observations, a video camera inspection of the previously installed underdrain system is planned to evaluate the structure for potential collapse or obstructions. Following initial installation, continuous flow from the underdrain has not been �i 29 September 2020 Reference: 0564782 Page 7 of 8 observed, including during periods of peak flow from the sediment boil. Elevations of the underdrain and dark gray sediment pocket observed during field excavation activities are similar. Additional investigation steps may be considered following the camera inspection. The boil area and nearby soil saturation conditions will continue to be monitored following significant rainfall events plus inspections and maintenance of the previously installed silt fence and coir wattles will be conducted as necessary for protection of human health and the environment. Ongoing monthly updates will be provided to NCDEQ as investigation and monitoring of the sediment boil continue. Please contact Mr. Max Hopkins of R.J. Reynolds Tobacco Company at 336-741-6932 or me if you have any questions or comments. Sincerely, Dave Wasiela, P.E. Project Engineer Attachments: Cross Section Figure A�rti'n, P.G. Project Manager cc: Mr. Scott Snow — R.J. Reynolds Tobacco Company Mr. Max Hopkins — R.J. Reynolds Tobacco Company Mr. Tom Wilson — ERM 870 860 850 840 830 820 810 800 790 780 770 760 760 Y 1 X CREEK 350 340 330 320 310 300 290 280 270 260 250 240 230 220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 N SCALE IN FEET 0 6.25 12.5 25