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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
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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
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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
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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
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• 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
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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.
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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.
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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.
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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.
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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