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Home My WebLink About23061_Methane Soil Gas Report v1 Final_20210820 Environmental Consultants & Contractors August 20, 2021 File No. 02221300.00 Mr. William Schmithorst, PG North Carolina Department of Environmental Quality Division of Waste Management – Brownfield Program 1646 Mail Service Center Raleigh, North Carolina 27699-1646 Subject: Methane Soil Gas Assessment Report Caraustar and Savona Mills South Turner Avenue and Chamberlain Avenue NCBP #23061-19-060 Dear Mr. Schmithorst: On behalf the Prospective Developer (PD), Savona II, LLC, SCS Engineers, PC (SCS) is pleased to submit this Methane Soil Gas Assessment Report (Report) for the above referenced site (Site). SCS Engineers, PC is licensed to practice geology and engineering in North Carolina. Our certification numbers are C-444 for geology and C-1837 for engineering. Background SCS was retained by the PD to review the initial methane soil gas screening results (by Terracon Consultants, Inc.) and to conduct two rounds of methane soil gas sampling at the site. During our two rounds, methane gas was detected at a concentration less than 0.5 percent in two probes (2021-SV-04 and 2021-SV-07) on April 7, 2021 and at one probe (2021-SV-07) at a concentration of 0.3 percent on April 8, 2021. Based on the Terracon data, previous sampling events at the site detected methane gas concentrations in four probes (2021-SV-01, 04, 08, and 09) ranging from 0.1 percent to 5.4 percent. During soil gas sampling in April 2021, we observed that several of the probes were impacted with water in the probe’s sample tubing. We cannot be certain of the cause(s) of the water in the probes, but we believe the probe’s surface seal may have been compromised and/or cracks in the surrounding pavement has allowed surface water intrusion. Water in a probe can lead to erroneous results. Because previous sampling indicated elevated methane gas concentrations and the presence of water in the probes, SCS proposed to install new soil gas probes and to conduct two rounds of Mr. William Schmithorst, PG August 20, 2021 Page 2 methane gas sampling. Our proposed approach was submitted to NCDEQ in a document titled “Work Plan for Methane Gas Assessment”, dated June 21, 2021. Site Conditions The site consists of nine contiguous tax parcels totaling approximately 30.4 acres located on both sides of South Turner Avenue and Chamberlain Avenue in Charlotte, North Carolina. The southwestern portion of the site is developed with two warehouses and an office building associated with the former Savona Mill, Caraustar Industries and Old Dominion Box Company operations. The southeastern portion of the site includes the former Savona Mill facility, a small community garden and shed, paved parking lots, and a residence. The historical use of this Site does not suggest any waste or debris disposal activities. Ten existing soil gas probes were used by Terracon for the initial methane gas screening. The location of these probes was selected to correspond to future building footprints. Six of these probes may be compromised with water intrusion and/or damaged sample hose and valve. We recommended re-drilling these in our Work Plan. Four of the probes (2021-SV-03, 2021-SV-04, 2021-SV-05, and 2021-SV-06) appear in good condition and will remain. Soil Gas Probe Installation On July 16, 2021, SCS’s subcontracted driller (Versatile Environmental Resources Company “VERCO”), a North Carolina licensed driller, began installing the following six soil gas probes we identified as “compromised”: • 2021-SV-01A • 2021-SV-02A • 2021-SV-07A • 2021-SV-08A • 2021-SV-09A • 2021-SV-10A Five of the six probes were successfully installed. Soil gas probe 2021-SV-07A could not be installed due to borehole collapse underneath the existing concrete pad. Two attempts were made to install the probe, but saturated soil conditions continued to hinder the probe installation. Five 2-inch diameter soil gas probes were installed with a GeoProbe 6620DT. A Site Plan showing the probe locations is provided in Figure 1. The new probes were drilled to a depth of five (5) feet. The probes were completed with a 2-inch diameter PVC pipe (3 feet slotted, 2 feet solid, and a 2 feet stick up), sand pack around the slotted pipe, and a bentonite seal. Each probe was fitted with a 1- inch locking well vapor extraction plug with a brass quick connect fitting. See Figure 2 for the probe completion diagram. Field reports are provided in Appendix A. Mr. William Schmithorst, PG August 20, 2021 Page 3 Also, the following soil gas probes were decommissioned: • 2021-SV-01 • 2021-SV-02 • 2021-SV-07 • 2021-SV-08 • 2021-SV-09 • 2021-SV-10 Decommission procedures consisted of removing the existing sample tubing and permanently sealing the hole with grout. Soil Gas Survey SCS conducted a methane gas survey on the existing 4 probes and new 5 probes on July 21 and 22, 2021. The following procedures were followed for the survey: 1. The LandTec GEM 5000 was calibrated per manufacturer’s instructions using 15 percent methane calibration gas. 2. Prior to sampling the soil gas probe, the static pressure of soil gas inside the probe was measured with the LandTec GEM 5000. 3. Each probe was purged for 1 minute using the LandTec GEM 5000. 4. Soil gas was sampled at each probe using the LandTec GEM 5000. The following was recorded: percent methane, percent carbon dioxide, percent oxygen, barometric pressure, and percent balance gas. Field reports are provided in Appendix A. Results During the July survey events, methane gas was not detected in any of the nine soil gas probes. Static pressure ranged from -0.03 to 0.04 inches of water column. See Table 1 for soil gas probe survey results. Recommendations Based on the results of the methane soil gas assessment conducted by SCS Engineers between July 16 and July 22, 2021, SCS Engineers recommends no further assessment activities at the Site related to methane gas in the subsurface. We also recommend no methane mitigation measures (such as membranes, pipes or methane sensors) be required for any development on the subject property. Mr. William Schmithorst, PG August 20, 2021 Page 4 Closing If you require any additional information or have any questions, please contact Steve at 704-576- 4731 or slamb@scsengineers.com. Sincerely, Steven C. Lamb, P.E. Eric R. Peterson, P.E. Project Director/Vice President Project Director/Vice President SCS Engineers, PC SCS Engineers, PC SCL/erp Enclosures cc: Bill Morrison, Senior Vice President, Portman Holdings Greg Pappanastos, President, Argos Real Estate Advisors FIGURES FIGURE 1 - SITE PLAN SCS ENGINEERS, PC SCS ENGINEERS, PC FIGURE 2 - TYPICAL MONITORING WELL CONSTRUCTION TABLES M:\PROJECT FILES\02221300.00\Data and Calculations\July 2021 - New Sample Probes\Savona Mills Field Reading New Wells Caraustar and Savona Mill NCBP #23061-19-060 7/21/2021 1023 0.02 1025 -0.003 1026 0.0 0.0 14.7 85.3 29.28 7/22/2021 1041 0.01 1043 -0.004 1045 0.0 0.0 13.2 86.8 29.35 7/21/2021 1033 0.03 1034 -0.003 1035 0.0 5.3 8.5 86.2 29.28 7/22/2021 1100 0.03 1102 -0.001 1104 0.0 5.3 8.6 86.1 29.35 7/21/2021 1041 0.04 1043 0.032 1044 0.0 3.5 11.9 84.6 29.28 7/22/2021 1121 -0.01 1123 0.009 1125 0.0 3.5 11.8 84.7 29.35 7/21/2021 0938 -0.01 0940 -0.003 0942 0.0 0.4 5.3 94.3 29.28 7/22/2021 1001 -0.01 1003 -0.004 1005 0.0 1.1 6.7 92.2 29.35 7/21/2021 1050 -0.01 1052 -0.006 1055 0.0 9.8 9.5 80.7 29.28 7/22/2021 1145 0.02 1147 -0.012 1149 0.0 9.7 9.5 80.8 29.35 7/21/2021 1100 -0.03 1102 -0.004 1104 0.0 0.1 11.1 88.8 29.28 7/22/2021 1159 -0.01 1201 -0.007 1203 0.0 3.2 9.9 86.9 29.35 7/21/2021 1007 0.02 1009 -0.02 1011 0.0 0.0 14.9 85.1 29.28 7/22/2021 1021 0.01 1023 -0.03 1025 0.0 2.1 14.7 83.2 29.35 7/21/2021 0926 0.02 0928 -0.02 0931 0.0 8.2 12.0 79.8 29.28 7/22/2021 0955 0.03 0957 -0.02 0959 0.0 7.8 12.8 79.4 29.35 7/21/2021 0955 0.02 0958 -0.07 1000 0.0 3.9 15.1 81.0 29.28 7/22/2021 1009 0.02 1011 -0.004 1013 0.0 3.1 14.9 82.0 29.35 Notes: 2021-SV-07A could not be installed due to collasping soils. Site Name: Site Location: SCS Project No.: Charlotte, NC 02221300.00 2021-SV-02A 2021-SV-03 2021-SV-04 2021-SV-05 2021-SV-06 2021-SV-08A 2021-SV-09A 2021-SV-10A 2021-SV-01A Time Time Time DateSample ID Differential Pressure [in wc] Static Pressure [in wc] Table 1 Methane Soil Gas Survey Results (July 2021) CO2 Concentration [%] O2 Concentration [%] Bal. Gas Concentration [%] Barometric Pressure [in Hg] CH4 Concentration [%] Site Personnel: David Walker Weather:78ºF, Sunny Devices Utilized: GEM 5000 Date(s): July 21-22, 2021 APPENDIX A M:\PROJECT FILES\02221300.00\Data and Calculations\Daily Field Reports\07.16.2021 Daily Field Report.docx SCS ENGINEERS DAILY FIELD REPORT Project Name: Savona Mills Soil Gas Probe Installation and Monitoring Project Number: 02221300.00 Task: N/A Labor Code: 990000 Project Manager: Steve Lamb Field Personnel: Brian Eigenberger Date: 07/16/2021 Vehicle: Personal Miles Billed: 20 Travel Time: 40 min Weather: 85º sunny CQA Daily Overview Oversee the drilling and completion of six soil vapor monitoring wells. CQA Detailed Daily Record Onsite: 0830 Drillers arrived on site at 0915. Using a Geoprobe 6620DT, the drillers mobilized the drill rig to drill 2021-SV-07A. 2021-SV-07A was drilled to the design depth of 5 feet below grade. Following the drilling, the soil beneath the concrete pad was too saturated and caused the borehole to collapse at approximately 1 foot below grade. These conditions were not suitable to set the well. Another borehole was drilled approximately 5 feet to the west of the first borehole. Again, the sub-slab soil was saturated and caused the borehole to collapse approximately 1 foot below grade. It was determined that the sub-slab soil conditions were not conducive to installing the soil gas probe at the time of drilling. The two boreholes were abandoned at the end of the day by grouting to the surface. 2021-SV-08A, 2021-SV01A, and 2021-SV-02A were each drilled and installed in accordance to the approximate location on FIGURE 1- SITE PLAN. 2021-SV-09A and 2021-SV-10A were proposed to be installed in a moderately trafficked parking lot. To prevent any damage to the wells caused by vehicles 2021-SV-09A was offset ~40ft south and 2021-SV-10A was offset ~15ft east. The five wells were completed in accordance to FIGURE 2- TYPICAL MONITORING WELL CONSTRUCTION. At the end of the day the bentonite was hydrated and vapor extraction plugs were installed on each monitoring well. Offsite: 1200 M:\PROJECT FILES\02221300.00\Data and Calculations\Daily Field Reports\07.16.2021 Daily Field Report.docx Drilling of SV-08A Well setting process at SV-08A Drilling of SV-09A Drilling of SV10A Drilling of SV-01A Drilling of SV-02A M:\PROJECT FILES\02221300.00\Data and Calculations\Daily Field Reports\07.16.2021 Daily Field Report.docx Grout abandonment of SV-07A SV-08A completion SV-09A completion SV-10A completion SV-01A completion SV-02A completion Prepared by: Brian Eigenberger Reviewed by: Steve Lamb M:\PROJECT FILES\02221300.00\Data and Calculations\July 2021 - New Sample Probes\07.21.2021 Daily Field Report.docx SCS ENGINEERS DAILY FIELD REPORT Project Name: Savona Mills Soil Gas Probe Installation and Monitoring Project Number: 02221300.00 Task: N/A Labor Code: 990000 Project Manager: Steve Lamb Field Personnel: David Walker Date: 07/21-22/2021 Vehicle: Personal Miles Billed: 20 Travel Time: 40 min Weather: 78º sunny CQA Daily Overview Oversee the drilling and completion of six soil vapor monitoring wells. CQA Detailed Daily Record Onsite: 0900 Arrived at the site to sample the existing and newly redrilled soil gas probes at Savona Mills. First, the Landtec GEM5000 gas analyzer unit was calibrated to 15% Methane using calibration gas. The new probes, 2021-SV-01A, 2021-SV-02A, 2021-SV-08A, 2021-SV-09A, and 2021-SV-10A were given over 48 hours to equilibrate after each well was drilled. 2021-SV-07 was not redrilled and was unable to be read due to a damaged sample tubing at the existing sample point. The remaining existing sample ports did not show signs of damage and were sampled using the existing sample tubing. At each point, the proposed sampling methodology was followed per the approved work plan where a static pressure reading was collected, followed by a 1-minute purge using the GEM5000, followed by a gas reading to collect percent methane, percent carbon dioxide, percent oxygen, and perfect balance gas. For all newly installed sample points, the sample was collected by connecting the GEM5000 tubing to the vapor extraction plug at the top of the PVC well casing. For all existing sample points, the sample was collected by connecting the GEM5000 tubing to the existing sample tubing. Samples were collected on July 21, 2021 and again at least 24 hours later on July 22, 2021. In all samples collected between July 21, 2021 and July 22, 2021, no methane value greater than 0.0 percent was recorded. M:\PROJECT FILES\02221300.00\Data and Calculations\July 2021 - New Sample Probes\07.21.2021 Daily Field Report.docx Typical construction for all redrilled sample points Vapor extraction plug for all redrilled sample points Sampling 2021-SV-10A Sampling 2021-SV-01A Sampling 2021-SV-08A Sampling existing 2021-SV-04 Prepared by: David Walker Reviewed by: Steve Lamb