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HomeMy WebLinkAbout0403_ChambersMSWLF_LFGplan_December2017 LANDFILL GAS MONITORING PLAN ANSON COUNTY SOLID WASTE FACILITY SUBMITTED TO: NCDEQ DIVISION OF WASTE MANAGEMENT SOLID WASTE SECTION 217 W JONES STREET RALEIGH, NC 27603 PRESENTED TO: WASTE CONNECTIONS, INC. OF NORTH CAROLINA 375 DOZER DRIVE POLKTON, NORTH CAROLINA 28135 Prepared By: CIVIL & ENVIRONMENTAL CONSULTANTS, INC. CHARLOTTE, NORTH CAROLINA CEC Project 165-276 DECEMBER 2017 -i- Landfill Gas Monitoring Plan – 165-276 November 2017 TABLE OF CONTENTS 1.0 INTRODUCTION ..........................................................................................................1 1.1 Background Information ...................................................................................... 1 1.2 Regulatory Requirements........................................................................................ 2 1.3 Current Site Conditions ......................................................................................... 3 1.4 Monitoring Location Criteria .................................................................................. 4 2.0 LFG MONITORING .........................................................................................................5 2.1 Monitoring Devices and Procedures ....................................................................... 5 2.2 Monitoring Schedule ............................................................................................... 6 3.0 CONTINGENCY PLAN ...................................................................................................7 4.0 CERTIFICATION .............................................................................................................8 TABLES Table 1 – Summary of Gas Monitoring Probe Locations ATTACHMENTS Attachment A – Landfill Gas Monitoring Guidance from NCDENR Division of Waste Management Attachment B – Site Figures Attachment C – LFG Well Construction Schematic Attachment D – Landfill Gas Monitoring Field Log -1- Landfill Gas Monitoring Plan – 165-276 December 2017 1.0 INTRODUCTION The following plan has been prepared as a standalone document in accordance with current NCDEQ Solid Waste Section (SWS) guidance. The monitoring locations, methods, and thresholds for action are based on the SWS document "Landfill Gas Monitoring Guidance," November 2010, available online at http://portal.ncdenr.org/c/document library/get file?uuid=da699f7e-8cl3-4249-9012- 16af8aefdc7b&groupld=38361. The guidance contains specific requirements for well construction, equipment calibration, sampling procedures, and data keeping in a plan that is organized in a standardized format. This document is found in Attachment A. 1.1 BACKGROUND INFORMATION Landfill gas (LFG) is a by-product from the decomposition of organic waste in a landfill, which includes methane, carbon dioxide, water, and other constituents. Methane can be explosive under certain conditions, and LFG migration has been known to transfer certain contaminants into ground water. Subsurface gas normally migrates above the ground water table and is restricted laterally by streams. In the Slate Belt, the partially weathered rock (PWR) zone existing just above competent bedrock is often the most porous subsurface horizon and can preferentially serve as a gas migration pathway. Man-made subsurface conduits such as pipelines or trenches (if present) can serve as preferential LFG pathways. No occupied structures off-site appear to be at risk for gas migration. The Solid Waste Rules typically focus on the explosive properties of LFG from a public safety standpoint. Methane in landfill gas has the potential to create an explosion hazard. Methane is explosive between its lower explosive limit (LEL) of 5% by volume and its upper explosive limit (UEL) of 15% by volume. Because methane concentrations within the landfill are typically 50% (much higher than its UEL), methane is unlikely to explode within the landfill -2- Landfill Gas Monitoring Plan – 165-276 December 2017 boundaries. Oxygen is a key component for creating an explosion, but the biological processes that produce methane require an anaerobic, or oxygen-depleted, environment. Thus, subsurface drilling in the landfill mass is not likely to cause an explosion. As methane migrates and is diluted; however, the methane gas mixture may be at explosive levels. At the surface of the landfill, enough oxygen is present to support an explosion, but the methane gas usually diffuses into the ambient air to concentrations below the 5% LEL. In order to pose an explosion hazard, methane must migrate from the landfill and be present between its LEL and UEL. Such conditions may be present in open excavations, ditches, subsurface utility conduits, or other subsurface confined spaces. Active gas recovery is the primary means of controlling gas at this facility. A Landfill Gas Control Plan was implemented soon after landfill operations commenced. A network of extraction wells installed in the waste are connected to a blower station and the collected LFG flared. Methane monitoring wells (landfill gas probes) are installed above the water table using construction techniques that are otherwise similar to ground water monitoring wells. Components of the active gas recovery system are not to be monitored. LFG monitoring will be performed during the active life of the landfill and throughout the post-closure care period. Quarterly monitoring will be conducted at all probes and in all on-site structures located on the landfill property. 1.2 REGULATORY REQUIREMENTS NCAC 15A 13B .1626 (4) (a) requires monitoring for the following explosive gas limits: • 25% of the Lower Explosive Limit (LEL) or 5% methane in standard atmosphere within ALL on-site structures, excluding the gas recovery systems. • 100% LEL at the facility boundary -3- Landfill Gas Monitoring Plan – 165-276 December 2017 • No detectable concentration at off-site occupied structures. 1.3 CURRENT SITE CONDITIONS The subject landfill is situated high on a ridge bounded on three sides by blue line streams, which act as natural barriers to gas migration. Potentiometric contours reflect the surface topography, which slopes moderately to the north but diverges sharply to the east and west toward the streams located along the facility boundary. Topographic relief near the west stream is steep, with elevation changes from the footprint to the streams on the order of 70 feet with up to 20% slopes, but the land surface slopes gently to the east stream with slopes generally less than 5%. The landfill is lined and is mostly excavated to the approved base grades on the west side, while the footprint is built up with a constructed 15-foot high perimeter embankment along the east side. On-site soils are silt and clay weathered from meta-volcanic tuffs and fine-grained Triassic sedimentary formations typically exhibiting low permeability, which originally extended 20 to 40 feet beneath the surface. The soils gradually transition with depth to a variably thick layer of porous "partially weathered rock" overlying hard, low-porosity non-weathered rock. On the west and north sides of the disposal footprint, deep wide-spread excavation has removed much of the overburden soil. The water table is approximately 10 to 30 feet deep over most of the site, including the up-gradient side of the landfill, except near the streams where water levels are 5 to 8 feet deep. The approved base grades are 30 feet or more above the level of the streams and a minimum of 4 feet above groundwater and/or bedrock. Lateral separation to the streams is 50 feet minimum; these dimensions provide little opportunity for gas to migrate beyond the facility boundary on the three sides bound by streams. The nearest known residence exists approximately 1,700 feet to the south and east of the MSWLF. Other occupied structures include a maintenance building (metal shell on concrete slab) located approximately 500 feet southeast of the footprint and approximately 800 feet east of the gas flare. The scale house (mobile building) is located approximately 1,000 feet south of the waste boundary. A small cemetery exists approximately 400 feet -4- Landfill Gas Monitoring Plan – 165-276 December 2017 east of the Phase 1 footprint. The facility offices are approximately one-half mile south of the waste boundary. 1.4 MONITORING LOCATION CRITERIA Gas migration is a process of diffusion through porous media, affected by porosity and permeability, similar to ground water within an unconfined or partly confined porous aquifer. For gas, pressures and concentrations are higher near the source and gradually decrease with distance - unless a distinct conduit is present - thus a "halo effect" is often discernable. The gas can be confined in the soil by lower permeability clay layers and saturated layers impermeable to gas that can occur either above or below the porous layer. At this site, horizontal permeability for ground water flow appears to exceed vertical permeability, due in part to the shape of the saprolite aquifer as it conforms to the topography and upper bedrock surface; true for water and gas. The unsaturated saprolite or PWR is the likely gas conveyance and is the target of the gas monitoring plan. Placement of perforated pipe for gas monitoring above the water table is standard practice. The required horizontal placement for gas monitoring appurtenances (either wells or bar-hole punch locations) is not defined. Considering the similarities of gas migration to ground water, with a compliance boundary established at property lines, a sensible criteria for test locations is outside the perimeter of any gas conveyances (such as recovery system pipelines) and approximately half the distance from the source to the compliance boundary or no more than 150 feet if the property line is more than 300 feet from the source - thus establishing a review boundary. Gas probe locations are shown on Figure 1 (Attachment B). Distances between the probes are approximately 250 feet. -5- Landfill Gas Monitoring Plan – 165-276 December 2017 2.0 LFG MONITORING 2.1 MONITORING DEVICES AND PROCEDURES Equipment: A portable gas monitoring device, e.g. LandGEM 5000 or equivalent gas monitor, shall be used to measure methane gas in the probes. Concentrations shall be reported in the units of percent methane or percent of the lower explosive limit (LEL). The LEL for methane is approximately 5%. General sampling procedures are discussed below, relative to different types of monitoring appurtenances and locations but the instructions for the specific monitoring device should be followed. Occupied Buildings: Monitoring of all on-site structures will be conducted during regular monitoring events at the earliest possible time after the structure has been unused (e.g. early morning). Methane is heavier than air and tends to accumulate in the lower zones with restricted circulations, i.e. crawlspace vents, drainage pipes, and utility vaults. Alternatively, the buildings may be equipped with continuous explosive gas detection devices. Gas monitoring will also be conducted in any confined space requiring the entry of personnel for maintenance or inspection. The monitoring will take place prior to entry by personnel in accordance with OSHA regulations. Within the buildings, atmospheric sampling for methane shall be conducted. Ambient Monitoring: This includes a “walk-around” at the toe of landfill slopes to survey for gas that may be seeping through the intermediate or permanent cover. A key to potential side slope seepage includes stained soil, wetness with visible bubbling, or distressed (or absent) vegetation. Any detection of methane in the ambient monitoring should be noted on a site map and a special notation recorded in the monitoring report. Bar-Hole Punch Locations: Gas monitoring in bar-hole punches will consist of punching a hole with a 3-foot probe. Tubing that is open-ended and perforated on the bottom should be placed in the bottom of the hole, taking care not to plug the bottom of the tubing with soil. The peak methane reading should then be recorded for each bar-hole probe location. -6- Landfill Gas Monitoring Plan – 165-276 December 2017 Methane Monitoring Wells: Permanent gas monitoring wells installed to appropriate monitoring depths, which for this site have been established as 15 feet or the water table, whichever is encountered first. Each gas monitoring well will be constructed with a 10-foot perforated section sealed below a bentonite plug, similar to ground water monitoring well construction with appropriate stickups for visibility and locking covers. Each well shall be “sniffed” with a gas meter (calibrated for methane) equipped with a probe or open-endedtube that can be inserted into the sampling port set within the well cap. Readings should be taken over a five- minute period (or as recommended by the manufacturer) and the peak methane reading should then be recorded, either as percent methane or percent LEL depending on the meter output. SWS guidelines include a well construction schematic found in Attachment C. Record-keeping: The sampling technician shall record the date, time, location, sampling personnel, atmospheric temperature, reported barometric pressure, and general weather conditions at the time of sampling, in addition to the concentration of combustible gases. The sampling results are to be recorded on a form, such as the example Landfill Gas Monitoring Field Log shown in Attachment D. The records will be maintained in the landfill operating record for the life of the facility. 2.2 MONITORING SCHEDULE The Solid Waste Rules require quarterly monitoring. Landfill gas monitoring will be performed during the active life of the landfill, currently estimated at 20+ years, and throughout the post-closure care period. -7- Landfill Gas Monitoring Plan – 165-276 December 2017 3.0 CONTINGENCY PLAN Solid Waste Rule NCAC 15A l3B .1626 (4) (c) specifies that, upon detection of methane exceeding the threshold values (described above), the facility management must perform the following: • Immediately take steps required to protect human health and notify the Division. • Within seven days place in the operating record a report of the methane gas levels and the location of the detection, along with a description of the response to protect human health. • Within 60 days implement a remediation plan for the methane gas release; place a copy of the plan in the Operating Record; and notify the Division that the plan has been implemented. The plan shall describe the name and extent of the problem and the proposed remedy. -9- Landfill Gas Monitoring Plan – 165-276 December 2017 Table 1 - Summary of Gas Monitoring Probe Locations Probe Location GP-1 Southeast corner of Phase l, near maintenance building GP-2 South of Phase l, near gas works GP-3 East of Phase l, over diabase dike GP-4 South of Phase l, near southwest corner GP-5 South of Phase l, near Phase 2 line GP-6 East of Phase 2 GP-7 South of Phase l, near railroad cut GP-8 West of Phase 3, near future southwest corner GP -9 West of Phase 3 GP -10 West of Phase 3 GP -11 North of Phase 4 GP -12 North of Phase 4 ATTACHMENT A LANDFILL GAS MONITORING GUIDANCE FROM NCDENR DIVISION OF WASTE MANAGEMENT ATTACHMENT B SITE FIGURES 8 A B 34567 12 C D E F G H 8 34567 12 A B C D E F G H DESCRIPTIONDATENOREVISION RECORDwww.cecinc.com1900 Center Park Drive - Suite A - Charlotte, NC 28217Ph: 980.237.0373 · Fax: 980.237.0372DATE:DWG SCALE:DRAWN BY:CHECKED BY:APPROVED BY:PROJECT NO:SHEET OF DRAWING NO.:EXISTING BUILDING STRUCTURESMONITORING POINTS165-2761"=400'AUGUST 2017CTHNTBSLB1 1 1 NORTH REFERENCE CHAMBERS DEVELOPMENT OF NORTH CAROLINA, INCPERMIT APPLICATIONANSON COUNTY LANDFILL GAS MONITORINGANSON, NORTH CAROLINALEGEND ATTACHMENT C LFG WELL CONSTRUCTION SCHEMATIC ATTACHMENT D LANDFILL GAS MONITORING FIELD LOG Revised – March 6, 2017 NC Division of Waste Management - Solid Waste Section Landfill Gas Monitoring Data Form Notice: This form and any information attached to it are "Public Records" as defined in NC General Statute 132-1. As such, these documents are available for inspection and examination by any person upon request (NC General Statute 132-6). Facility Name: Permit Number: Sampling Date: NC Landfill Rule (.0500 or .1600): Sample Collector Name & Position: Gas Meter Type & Serial Number: Gas Meter Calibration Date: Field Calibration Date & Time: Field Calibration Gas Type (15/15 or 35/50): Field Calibration Gas Canister Expiration Date: Gas Meter Pump Rate: Ambient Air Temperature: Barometric Pressure (in. or mm Hg): Weather Conditions: Instructions: Under “Location or LFG Well”, list monitoring well # or describe monitoring location (e.g., inside field office). Attach a test location map or drawing. Report methane readings as both % LEL and % CH4 by volume. Convert % CH4 (by volume) to % LEL as follows: % methane (by volume)/20 = % LEL. *Hydrogen Sulfide (H2S) gas monitoring may be required for Construction & Demolition Landfills (CDLFs). See individual permit conditions and/or Facility LFG monitoring plan. Location or LFG Well ID Sample Tube Purge Time of Day Time Pumped (sec) Initial % LEL Stabilized % LEL % CH4 (volume) % O2 (volume) % CO2 (volume) % H2S* (volume) NOTES NOTE: If needed, attach additional data forms to include additional LFG monitoring data locations for the facility. ACTION LEVELS: Methane: >1.25% by volume (inside structures) AND >5% by volume (at facility boundary) Hydrogen Sulfide: >1% by volume (inside structures) AND >4% by volume (at facility boundary) Certification To the best of my knowledge, the information reported and statements made on this data submittal and attachments are true and correct. I am aware that there are significant penalties for making any false statement, representation, or certification including the possibility of a fine and imprisonment. SIGNATURE TITLE