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HomeMy WebLinkAbout9001_UnionCoMSWLF_LFGAssmt2_DIN27835_20170527 -i- Landfill Gas Assessment Report May 25, 2017 TABLE OF CONTENTS 1.0 INTRODUCTION..............................................................................................................1 1.1 Project Information ................................................................................................. 1 1.2 Facility Operations .................................................................................................. 1 1.3 VOCs in Upgradient Detection Monitoring Well ................................................... 2 1.4 Previous Limited Landfill Gas Assessment ............................................................ 2 2.0 ADDITIONAL LANDFILL GAS ASSESSMENT .........................................................4 2.1 Landfill Gas Data Collection .................................................................................. 4 3.0 CONCLUSIONS AND RECOMMENDATIONS ...........................................................6 3.1 Conclusions ............................................................................................................. 6 3.2 Recommendations ................................................................................................... 6 FIGURES Attached Figure 1 – Site Location Map Figure 2 – Soil Gas Probe and Well Location Map TABLES Attached Table 1 Soil Gas and Groundwater Monitoring Well MW-1A Headspace Vapor Data In Text Table 2-1 Methane Data from Gas Wellpoints - May 5, 2017 APPENDICES Appendix A Laboratory Analytical Data Report Appendix B Well Construction Records Appendix C Field Data Sheets -1- Additional Landfill Gas Assessment May 25, 2017 1.0 INTRODUCTION 1.1 PROJECT INFORMATION Report Title: Additional Landfill Gas Assessment Project Site: Union County NC Landfill 2125 Austin Chaney Road Wingate, NC 28174 Facility Permit No. 90-01 Facility Owner/Operator: Union County Department of Public Works 500 N. Main Street, Suite 500 Monroe, NC 28112 County Representatives: Michael James, Assistant to the County Manager Union County Central Administration Chris Medlin, Landfill Manager Union County Department of Public Works Consultant: Civil & Environmental Consultants, Inc. (CEC) 1900 Center Park Drive, Suite A Charlotte. NC 28217 Consultant Contact: Edward H. Stephens, P.G. #1031 1.2 FACILITY OPERATIONS Union County owns and operates a Solid Waste Management Facility in Wingate, North Carolina. A site vicinity map is provided in Figure 1. The Solid Waste Facility contains a closed unlined Municipal Solid Waste (MSW) Landfill and an active Construction and Demolition (C&D) Landfill. The North Carolina Solid Waste Management Rules 15A NCAC 13B require that Union County monitor the quality of groundwater and surface water at the Union County Solid Waste Management Facility in accordance with an approved Groundwater Monitoring Plan, and to monitor for potential migrating landfill gas in accordance with an approved Methane Monitoring Plan. -2- Additional Landfill Gas Assessment May 25, 2017 1.3 VOCS IN UPGRADIENT DETECTION MONITORING WELL Low-level volatile organic compounds (VOCs) have been detected in groundwater samples from monitoring well MW-1A, which is situated hydraulically upgradient of the landfill waste disposal area, during recent landfill monitoring events. These detections were reported to the North Carolina Department of Environmental Quality (NCDEQ) Solid Waste Compliance Unit in past semi-annual monitoring reports. During a regulatory inspection of the landfill facility on July 6, 2016, the NCDEQ Hydrogeologist requested that a “quick” soil gas assessment be conducted in the area of the site monitored by MW-1A to determine whether landfill gas migration may be occurring between the landfill waste boundary and MW-1A. 1.4 PREVIOUS LIMITED LANDFILL GAS ASSESSMENT Limited Soil Gas and MW-1A Headspace Vapor Sampling As a part of a previous limited landfill gas assessment, CEC directed the installation of three temporary soil gas sampling points and subsequent collection of soil gas samples for laboratory analyses of targeted constituents. As depicted on Figure 2, soil gas sampling points were located within the vadose zone between the landfill waste disposal area and upgradient groundwater monitoring well MW-1A. A Geoprobe® 7822DT using direct push technology (DPT) was employed to advance the soil borings to install the soil gas probes. DPT refusal in the weathered Slate Belt mudstone was encountered in the borings at depths from approximately 8.75 to 12 feet below ground surface. Thus, soil gas sampling points were set at these depths. The subsurface materials encountered were gray to brown to yellow mottled clayey silts to silty clays. Soil gas samples were collected from each sampling point employing a soil vapor implant connected via Teflon tubing to a 1.4 L Summa canister. CEC subsequently submitted the gas samples to Enthalpy Analytical, Inc. for analyses of methane, carbon dioxide, carbon monoxide, hydrogen, nitrogen, and oxygen by ASTM D1946-90 Canister Analysis and low-level VOC analysis by EPA Method TO-15. The laboratory data report is included in Appendix A. -3- Additional Landfill Gas Assessment May 25, 2017 In addition to the soil gas sampling, CEC also collected a headspace gas sample from groundwater monitoring well MW-1A in which VOCs have been previously detected. Plastic tubing was lowered into the groundwater monitoring to a few feet above the gauged water level to collect the well headspace sample. The sampling flow rate was limited to approximately 200 milliliters per minute into a 1.4 L Summa canister. This canister was submitted along with the soil gas samples accompanied by a chain-of-custody record to Enthalpy Analytical, Inc. for similar laboratory analyses. Evaluation of Soil Gas and Well Headspace Data The laboratory analytical data detections for the limited soil gas and well headspace samples are summarized in the attached Table 1. Elevated methane and carbon dioxide were observed in the soil gas samples. Non-methane VOC concentrations were most elevated in soil gas probe (SGP- 1) located in proximity to monitoring well MW-1A. Also, soil gas VOC concentrations were significantly elevated in SGP-3, which was located approximately 30 feet from the landfill waste disposal area and 175 feet hydraulically downgradient of MW-1A. These data do not necessarily indicate that landfill gas is the source of the groundwater impacts in MW-1A; however, the distribution of the soil gas data does indicate a potential that landfill gas is a likely source of the groundwater VOCs. Only traces of methane and carbon dioxide were detected in the well headspace sample from groundwater monitoring well MW-1A. As shown in Table 1, similar VOCs where detected in the MW-1A headspace sample as were identified in the soil gas samples. Chloromethane, ethyl acetate, methyl methacrylate, 2-hexanone, styrene, 1,3-dichlorobenzene, and naphthalene were detected in the well headspace sample but not in the soil gas samples. Conversely, 1,3-butadiene and methylene chloride were not detected in the well headspace sample yet were detected in at least two soil gas samples. In general, the VOCs detected in the soil gas samples at the most elevated concentrations correspond with the VOCs historically detected in the aqueous phase in MW-1A. These VOCs include benzene, dichlorodifluoromethane, 1,1-dichloroethane, cis-1,2- dichloroethene, tetrachloroethene, trichloroethene, and vinyl chloride. -4- Additional Landfill Gas Assessment May 25, 2017 2.0 ADDITIONAL LANDFILL GAS ASSESSMENT Based on the findings of the previous limited landfill gas assessment, CEC recommended that landfill gas probes be installed within the waste mass along the southeastern landfill boundary to further evaluate the presence of landfill gas and its potential impact. This addition data would be used to aid in the design of a landfill gas control system, if deemed necessary. In a letter dated January 5, 2017, the NCDEQ Solid Waste Section approved these recommendations made by CEC. 2.1 LANDFILL GAS DATA COLLECTION On April 26, 2017, CEC directed Elite Techniques, Inc., an NC-certified driller, to install seven gas probes (GP-1 through GP-7) outside the permitted C&D waste disposal area along the southeastern perimeter to evaluate landfill gas in this area. As shown on Figure 2, the gas probes were spaced approximately 50 feet apart across the edge of waste. Employing a Geoprobe® 7822DT equipped with 4.5-inch solid-flight augers, the probe borings were advanced either to the base of the waste mass or to auger refusal if waste mass was not encountered at the respective boring locations. The gas probes were constructed of two-inch Schedule 40 PVC 0.01-slot screen and riser pipe with a sand filter surrounding the well screen and bentonite seal above the filter pack. Well construction records are included in Appendix B. Once the gas probes were completed and sealed with a well expansion cap, the well headspace in each probe was allowed to equilibrate over several days. On May 5, 2017, CEC personnel took methane measurements with a Landtec GEM™ 2000 PLUS Landfill Gas Analyzer and Extraction Monitor. Methane readings and other gas measurements are presented in Table 2-1 below. CEC personnel performed a field calibration of the meter in accordance with the GEM™ 2000 PLUS Operation Manual. Prior to taking an actual reading, the meter was allowed to warm up until the indicator indicated a reading could be obtained. To obtain a reading, plastic tubing was connected to the tip of the meter and then extended into the wellpoint. The methane concentration was continuously read on the face of the meter until the percent methane reading stabilized. The percent methane was recorded by the technician on the Methane Monitoring Field Data Sheet included in Appendix C. -5- Additional Landfill Gas Assessment May 25, 2017 Table 2-1 –Methane Data from Gas Wellpoints May 5, 2017 Sampling Point % CH4 % LEL* % CO2 % O2 Barometric Pressure Comments GP-1 66.2 1,324 40.9 0.0 28.95 screened in waste mass; wellpoint pressurized GP-2 66.1 1,322 41.8 0.0 28.95 screened in waste mass; wellpoint pressurized GP-3 65.3 1,306 42.0 0.0 28.95 screened in waste mass; wellpoint pressurized GP-4 66.0 1,320 39.8 0.0 28.95 screened in waste mass; wellpoint pressurized GP-5 29.8 596 17.6 10.8 28.95 screened outside waste mass GP-6 46.0 920 24.5 8.7 28.95 screened outside waste mass GP-7 11.1 222 7.7 15.3 28.95 screened outside waste mass Atm. 0.02 3.0 0.0 20.9 28.95 * Calculated % LEL Elevated methane concentrations and pressures observed in gas probes GP-1, GP-2, GP-3, and GP-4 along the southeast edge of the closed MSW landfill indicate the potential for landfill gas migration to the southeast of the landfill waste boundary. The data obtained from soil gas probes GP-5, GP-6, and GP-7 confirm the presence of landfill gas beyond the waste boundary. Should low-level, non-methane VOCs be present in the landfill gas, vapor-phase transport with subsequent dissolution in groundwater is a possible mechanism for MW-1A area groundwater impacts. -6- Additional Landfill Gas Assessment May 25, 2017 3.0 CONCLUSIONS AND RECOMMENDATIONS 3.1 CONCLUSIONS The data collected and evaluated during the landfill gas study indicate significant methane concentrations and pressures exist at the southeast boundary of the closed MSW landfill. These data also confirm landfill gas migration in the area between the buried waste mass and upgradient groundwater monitoring well MW-1A located to the southeast of the disposal area. TO-15 analyses of the soil gas samples indicated the presence of low-level, non-methane VOCs that may be impacting groundwater in the southeast portion of the landfill facility, particularly in the vicinity of upgradient groundwater monitoring well MW-1A. It is important to note that quarterly methane monitoring data routinely measured at the landfill confirms that landfill gas is not migrating beyond the Methane Compliance Monitoring Boundary as referenced in the facility’s Quarterly Methane Gas Monitoring Data Reports 3.2 RECOMMENDATIONS CEC recommends that the seven gas wellpoints, as depicted at their approximate locations on Figure 2, be converted to passive vents equipped with wind turbines to exert a “pulling” pressure on the vents to extract landfill gas. The effectiveness of the passive vents in extracting landfill gas should be monitored along with routine quarterly groundwater monitoring at MW-1A as required by the landfill permit. CEC understands that Union County Landfill staff will convert the existing gas wellpoints to passive vents with design assistance from CEC where requested. The gas vent conversions will be completed by June 15, 2017. FIGURES REFERENCE DATE:DWG SCALE: DRAWN BY:CHECKED BY:APPROVED BY: PROJECT NO: FIGURE NO.: SITE LOCATION MAP 151-7971"=5000'DECEMBER 2015 PNP EHS EHS 1 UNION COUNTY LANDFILL 2125 AUSTIN CHANEY ROAD WINGATE, NORTH CAROLINA www.cecinc.com 1900 Center Park Drive - Suite A - Charlotte, NC 28217 3KÃ)D[ NORTH DATE:DWG SCALE: DRAWN BY:CHECKED BY:APPROVED BY: PROJECT NO: ATTACHMENT: SOIL GAS ASSESSMENT WELL PROBE LOCATION MAP 151-7971"=50'MAY 2017 PNP EHS EHS 2 UNION COUNTY LANDFILL 2125 AUSTIN CHANEY ROAD WINGATE, NORTH CAROLINA REFERENCE www.cecinc.com 1900 Center Park Drive - Suite A - Charlotte, NC 28217 Ph: 980.237.0373 · Fax: 980.237.0372 NORTH LEGEND TABLES Table 1 Soil Gas and Groundwater Monitoring Well MW-1A Headspace Vapor Data Union County Landfill CEC Project No. 151-797.0005 Carbon Dioxide Carbon Monoxide Hydrogen Methane Nitrogen Oxygen ppbv µg/m3 ppbv µg/m3 ppbv µg/m3 ppbv µg/m3 Propylene 1,627 2,800 3,639 6,262 2,107 3,625 30.8 53.0 Dichlorodifluoromethane (Freon 12) 152 754 15.2 75.1 171 846 50.0 247 Freon 114 189 1,323 315 2,203 95.4 667 4.89 34.2 Chloromethane ND ND ND ND ND ND 3.34 6.9 1,3-Butadiene 19.6 43.4 8.44 18.7 11.8 26.2 ND ND Vinyl Chloride 1,950 4,984 201 515 613 1,568 3.37 8.6 Bromomethane ND ND ND ND ND ND ND ND Chloroethane 29.7 78.4 3.07 8.09 16.9 44.5 1.33 3.51 Trichlorofluoromethane (Freon 11) ND ND ND ND 7.4 41.6 0.254 1.43 Ethanol 285 537 813 1,532 80.8 152 26.5 49.8 Acrolein ND ND ND ND ND ND ND ND Trichlorotrifluoroethane (Freon 113) ND ND ND ND ND ND ND ND 1,1-Dichloroethene 40.2 160 ND ND 10.3 40.7 5.09 20.2 Acetone 52.5 125 99.6 237 40.5 96.1 305 724 Carbon Disulfide 8.14 25.4 17.4 54.2 14.3 44.7 0.532 1.66 Isopropyl Alcohol 20.6 50.6 10.8 26.6 16.0 39.3 2.13 5.23 Acetonitrile 46.2 77.5 27.4 46.0 130 218 2.17 3.64 Methylene Chloride 4.7 16.3 ND ND 285 989 ND ND trans-1,2-Dichoroethene 172 682 23.9 94.9 126 500 2.6 10.3 Hexane 350 1,232 622 2,194 189 667 11.6 40.9 1,1-Dichloroethane 106 428 4.44 18 113 456 29.1 118 Ethyl Acetate ND ND ND ND ND ND 4.23 15.2 Vinyl Acetate ND ND ND ND ND ND ND ND cis-1,2,-Dichloroethene 3,864 15,319 373 1,478 10,701 42,428 259 1,027 2-Butanone (MEK) ND ND ND ND ND ND ND ND Chloroform 2.32 11.3 ND ND 6.63 32.4 0.708 3.46 Tetrahydrofuran ND ND ND ND ND ND ND ND Cyclohexane 289 993 480 1,653 120 412 30.7 106 Carbon Tetrachloride ND ND ND ND ND ND ND ND Benzene 207 661 280 894 808 2,581 28.4 90.7 2,2,4-Trimethylpentane 244 1,142 486 2,270 140 654 8.75 40.9 Heptane 627 2,569 788 3,231 197 809 0.762 3.12 Trichloroethene 1,745 9,375 100 538 804 4,321 442 2,375 Methyl Methacrylate ND ND ND ND ND ND 1.76 7.19 1,2-Dichloropropane ND ND ND ND ND ND ND ND Methyl Isobutyl Ketone 90.4 370 ND ND ND ND 0.193 0.79 Toluene 60.4 228 330 1,245 95.4 360 814 3,066 Tetrachloroethene 117 793 51.8 352 402 2,727 228 1,547 2-Hexanone ND ND ND ND ND ND 0.216 0.884 Chlorobenzene 21.1 97.1 3.65 16.8 8.28 38.1 8.07 37.1 Ethylbenzene 14.8 64.2 10.6 46.1 127 552 1.79 7.77 Styrene ND ND ND ND ND ND 0.367 1.56 m-/p-Xylenes 60.9 264 31.1 135 828 3,597 1.77 7.68 o-Xylene 25.6 111 11.3 48.9 400 1,737 0.715 3.1 1,1,2,2-Tetrachloroethane ND ND ND ND 14.5 100 ND ND 4-Ethyltoluene ND ND ND ND 11.1 54.5 ND ND 2-Chlorotoluene ND ND 5.43 28.1 ND ND ND ND 1,2,4-Trimethylbenzene 2.21 10.9 ND ND 101 498 0.324 1.59 1,3,5-Trimethylbenzene ND ND ND ND 95.5 470 ND ND 1,3-Dichlorobenzene ND ND ND ND ND ND 0.228 1.37 1,4-Dichlorobenzene 2.55 15.3 ND ND 10.1 60.9 0.413 2.48 Naphthalene ND ND ND ND ND ND 0.37 1.94 ppbv = parts per billion per volume µg/m3 = micrograms per cubic meter 28.0 1.06 J SGP-1 SGP-2 40.0 0.110 ND 0.247 ND 6.88 40.5 0.828 J 13.1 MW-1ASGP-3 46.8 0.109 ND 0.246 ND Percent (%) 17.8 35.5 0.213 ND 0.478 ND 5.67 43.5 1.55 J 0.640 J 0.101 ND 0.227 ND 0.0825 ND 70.8 APPENDIX A LABORATORY ANALYTICAL DATA REPORT APPENDIX B WELL CONSTRUCTION RECORDS APPENDIX C FIELD DATA SHEETS