4903_IredellCoMSWLF_LFGRemediationReport_FID1838307_20240516

CEC
Carlson Environmental Consultants, pc
Landfill Gas and Solid Waste Specialists

1127 Curtis Street Ste 100 Monroe NC 28112 Phone [phone] ·Fax [phone]
Orlando, FL · Tampa, FL · Atlanta, GA · Columbia, SC · Richmond, VA · Statesville, NC
Olympia, WA · Cookeville, TN · Tullytown, PA
www.cecenv.com
May 14, 2024

Ervin Lane
Solid Waste Section
NCDEQ - Division of Waste Management
Raleigh Regional Office
1646 Mail Service Center Raleigh, NC 27699-1646

Subject: Methane Migration Monitoring Exceedances - Q1 2024 Remediation Plan
Iredell County Subtitle D Lined Landfills/Closed Unlined C&D Landfill
Statesville, North Carolina
Solid Waste Permit No. 49-03
Dear Ervin:
On behalf of Iredell County (County), Carlson Environmental Consultants, PC (CEC) is submitting
to the North Carolina Department of Environmental Quality (NCDEQ) Division of Waste
Management Solid Waste Section (SWS) the subject remediation plan for a recent methane
migration monitoring exceedance detected at the Subtitle D Lined Landfills/Closed Unlined C&D
Landfill facility that is owned and operated by the County.
As previously reported to NCDEQ in a notification letter dated March 18, 2024, there was one (1)
perimeter gas probe location with methane detections above the 5% lower explosive limit (LEL) during the first quarter 2024 monitoring event: MP-6A (53.1%).
Pursuant to NCAC 13B .1626(4)(c)(iii), the County has commenced implementation of the
attached remediation plan for explosive gas release at this location. In accordance with NCAC
13B .1626(4)(c)(iii), the plan describes the nature and extent of the exceedance and proposed
remedies. The attached remediation plan will also be placed in the operating record.
If you have any questions regarding this remediation plan, or require additional information,
please contact the undersigned at [phone].
Sincerely,

Kathryn Fauerby
Carlson Environmental Consultants, PC
CC: Teddy Boller, Iredell County
Jeff Webster, Iredell County
Amanda Higgs, CEC
Brock McNabb, P.E. CEC

Ervin Lane
May 14, 2024
Page 2
Introduction and Objectives:
The Subtitle D Lined Landfills/Closed Unlined C&D Landfill facility is located near Statesville, North
Carolina and is owned and operated by Iredell County in accordance with Solid Waste Permit No.
49-03. The facility operates a mandatory gas collection and control system and consists of a
network of landfill gas (LFG) collection wells and horizontal collectors, passive vents, and header
and lateral piping that route LFG to either a third-party LFG to energy developer or to a backup
utility flare for processing. The County also continuously monitors methane within all buildings
located on the landfill property using methane alarms that are maintained in accordance with the
Methane Monitoring Plan (dated November 20, 2014).
The County is required to conduct quarterly methane migration monitoring at multiple perimeter
gas probe and onsite structure locations in accordance with 15A NCAC 13B .1626(b)(ii), Solid
Waste Permit No. 49-03, and the Methane Monitoring Plan (dated November 20, 2014). The
purpose of monitoring is to determine if methane migration is occurring at or beyond the landfill
boundary. If methane is detected above the lower explosive limit (LEL) of 5% at perimeter gas
probes or above 25% of the LEL at onsite structures (i.e., 1.25%), the County is required to
initiate the following corrective actions in accordance with the Methane Monitoring Plan:
• Immediately take all necessary steps to ensure protection of human health (i.e., no
smoking), temporarily abandon the structure, and notify the NCDEQ - Division of Solid
Waste Management.
• Within seven (7) days of detection, place in the operating record the methane gas levels
detected and a description of the steps taken to protect human health; and,
• Within sixty (60) days of detection, implement a remediation plan for the methane gas
releases, place a copy of the plan in the operating record, and notify the Division of Solid
Waste Management that the plan has been implemented. The plan will describe the nature
and extent of the problem and the proposed remedy.
The County completed an initial investigation and notified the NCDEQ of the methane migration
monitoring exceedance in a letter dated March 18, 2024. Details of all corrective actions made to
date are annotated within the Initial Corrective Actions and Evaluations section of this remediation
plan. The specific objectives of this plan are as follows:
• Identify the nature and extent of the methane migration at the perimeter probe
exceedance location;
• Present the proposed approach for reducing and maintaining methane concentrations to
below the regulatory limit and to control subsurface methane migration;
• Describe a proposed monitoring program to verify no methane migration beyond the
landfill perimeter; and,
• Outline a proposed schedule for implementation and corrective actions.

Ervin Lane
May 14, 2024
Page 3
Methane Migration Monitoring Exceedance Location:
During the first quarter 2024 methane migration monitoring event on March 15, 2024, methane
was detected above the 5% regulatory limit at one (1) perimeter gas probe: MP-6A (53.1%). As
shown in the attached site plan, MP-6A is located on the northwestern perimeter of the Existing
MSW Phases 3 & 4 areas and nearby the ICATS office.

Nature and Extent of Methane Migration:
LFG is a product of the natural biological decomposition of organic material contained in waste
deposited within the landfill. LFG results from anaerobic decomposition and is predominantly
comprised of methane and carbon dioxide. The production of LFG also creates a positive pressure
within the landfill. This pressure can act as a driver for methane migration through cover soils
into the atmosphere and surrounding soils. Additionally, LFG can diffuse through soils from a
higher concentration to areas of a lower concentration.

Since methane is combustible and present in LFG, the migration of LFG can create a hazard.
Methane can cause an explosion if allowed to accumulate in an enclosed area at concentrations
between 5 and 15% by volume in air when in the presence of an ignition source, better known
as the LEL and upper explosive limit (UEL) of methane. Please note that although MP-6A was
monitored with methane above the UEL, there may be health risks associated with elevated
methane concentrations within enclosed spaces. Because the detection of methane gas in
perimeter gas probe MP-6A was above the LEL on March 15, 2024, an initial evaluation of the
nature and extent of the methane migration was performed and is detailed in the following
section.

Initial Corrective Actions and Evaluations:
In accordance with the Methane Monitoring Plan, the County and CEC immediately reviewed the
gas quality data and surrounding perimeter gas probe and structure data to determine if the
current location of methane detection poses a threat to human health. Within the first seven (7)
days following the methane detections, the County completed the following initial corrective
actions:
1. Reviewed gas quality data for all nearby perimeter gas probes and structures and
confirmed that there were no methane detections above the 5% regulatory limit. No
methane detections present at the ICATS office structure nearest MP-6A.
2. Completed a visual inspection of the probe and vicinity of the probe location to confirm
that there were no apparent structural integrity issues or signs of subsurface oxidation
occurring (i.e., distressed vegetation, surface cracking, smoking, etc.). No such issues
were noted.
3. Ensured that all authorized monitoring personnel understood the risks associated with the
presence of elevated methane at the probe locations and ensured that all site safety
procedures (i.e., no smoking, 4-gas meter is worn) were followed.
4. Increased applied vacuum to existing landfill gas extraction wells in the active Phase 4
area to extract additional landfill gas from the waste perimeter nearest MP-6A.
5. Confirmed that methane detection alarms installed within the ICATS office structure were
working properly. County confirmed alarms were not detecting methane in building.
Ervin Lane
May 14, 2024
Page 4
Quarterly structure monitoring also confirmed that methane detections were below the
1.25% regulatory threshold.
6. Monitored nearby gas perimeter probe locations MP-5A and MP-7A on a weekly basis
and confirmed that there continue to be no methane detections above the LEL at any of
these locations.
As of May 8, 2024, methane concentrations continue to be above 5% at MP-6A (8.0%). The
County continues to increase vacuum to surrounding landfill gas extraction wells in Phase 4.
Vacuum is gradually being redirected to this portion of the landfill so it can be increased
incrementally. There continues to be little to no methane detected at MP-5A and MP-7A (0.0% -
0.1%) and at the ICATS office structure (0.0% - 0.1%). The County intends to continue
monitoring MP-6A and surrounding probes (MP-5A and MP-7A) weekly and will continue to
increase vacuum to nearby gas wells in the Phase 4 area.

To determine whether methane is migrating beyond the northwestern perimeter of the landfill
where MP-6A is located, the County and CEC has selected four (4) locations to perform barhole
punches in order to monitor for methane gas migration closer to the landfill’s property boundary.
(See siteplan attached in Exhibit B). The barhole punches will be installed to an approximate
depth of 3 feet and then monitored for methane, should no methane detections be found, it will
be assumed unlikely that methane is migrating beyond the landfill property.

All methane gas readings obtained at MP-6A to date are summarized in the attached site plan
Exhibit A.

Planned Corrective Actions and Remediation Approach for MP-6A
The County continues to monitor and implement corrective action measures to mitigate elevated
methane detections at the MP-6A location. The following planned corrective actions and
remediations are being proposed moving forward:
1. Continue to monitor MP-5A, MP-6A and MP-7A on a weekly basis. If methane
concentrations at MP-6A are below 5% for two (2) consecutive months, the County
intends to reduce the monitoring frequency on MP-5A, MP-6A and MP-7A to monthly. If
methane at MP-6A is monitored below 5% for two (2) consecutive quarterly monitoring
events, the County intends to resume a quarterly monitoring frequency on MP-5A, MP-6A
and MP-7A and would consider the remediation plan to be complete.
2. Perform barhole punch sampling between MP-6A and the landfill perimeter on a monthly
basis to confirm that methane migration is isolated to the probe area and there are no
other areas of concern that need to be investigated further. Monthly barhole punch
monitoring will continue until methane at MP-6A is monitored below 5% for two (2)
consecutive monthly monitoring events.
3. Perform weekly monitoring at the ICATS office structure to confirm there to be no
methane migration within the structure. If methane concentrations at MP-6A are
monitored below 5% for two (2) consecutive months, the County intends to reduce the
monitoring frequency to monthly at the ICATS office structure. If methane at MP-6A is
Ervin Lane
May 14, 2024
Page 5
monitored below 5% for two (2) consecutive quarterly monitoring events, the County
intends to resume a quarterly monitoring frequency at the ICATS office structure.
4. The landfill currently has a toe drain installed around the Northwest corner of Phase 4 of
the landfill. The County intends to connect the toe drain to the active LFG extraction
system in order to help capture any gas migration that may be pushing over top of the
landfill anchor trench and in the direction of probe MP-6A.

The methane migration remediation efforts will be accomplished in accordance with the following
schedule:

Corrective Action Measure: Anticipated Schedule:
office structure Ongoing
To begin May 2024
existing toe drain To begin July 2024
To begin July 2024*
*Dependent on when materials arrive onsite.

Contingency Plan for MP-6A:
Should the proposed corrective action measures not mitigate elevated methane concentrations
detected at MP-6A, the County proposes the following contingency plan and completion timelines:

Contingency Plan Measures: Anticipated Schedule:
As needed
December 2025
passively vent gas between MP-December 2025
June 2026
The contingency plan measures listed above are all individual options the County proposes to
help resolve the methane migration issue. However, it may not be necessary for the County to
perform all of the above listed Contingency Plan measures if the methane migration issue can be
resolved by only one or more of the measures listed above.

Ervin Lane
May 14, 2024
Page 6
Exhibits:
A – Site Plan Depicting Exceedance Location and Methane Data
B – Site Plan Depicting Approximated Barhole Punch Locations
C – Site Plan Depicting Existing Toe Drain Location
D – Photos of Exceedance Location

EXHIBIT A
MP-6A EXCEEDANCE LOCATION & METHANE DATA
CO
CO
CO
CO
CO
C/O 207
MH CO
C/O 208
EXISTING MSW
PHASE 4
C/O P4-2
C/O P4-1
213
203
217
208
215
216
202205
218
206 201
209
A219
223
222
221
B220
224
207
228 229
227
230
232
233
231
234
C/O P4-3
C/O 209
W240
W226R
W225R
W214R
W204R
W212R
W210R
W211R
CS3-1
C/O P4
C/O P3
CS4-1
W
W
W
W
W
MP-5A
MP-4A
ICATS
MP-6A
MP-7A
LCR-4
LCR-3
EXISTING MSW
PHASE 3
WMP-6A
EXCEEDANCE DATA
IRDLMP6A
INITIAL 3/15/2024: 53.1% CH4
RECHECK 3/22/2024: 52.1% CH4
RECHECK 3/28/2024: 57.6% CH4
RECHECK 4/5/2024: 46.4% CH4
RECHECK 4/11/2024: 61.8% CH4
RECHECK 4/18/2024: 57.8% CH4
RECHECK 4/25/2024: 43.7% CH4
RECHECK 5/2/2024: 30.0% CH4
RECHECK 5/8/2024: 8.0% CH4
PROPERTY BOUNDARY
GRAPHIC SCALE (FEET)
0
TITLE:
PROJECT:
CLIENT:
EXCEEDANCE PROBE MP-6A
CARLSON ENVIRONMENTAL CONSULTANTS, PC
1
IREDELL COUNTY SOLID WASTE
1 2 3 4 5 6 7 8
E
D
C
B
A
E
D
C
B
A
1 2 3 4 5 6 7 8
REV DWN BY APP BYDESCRIPTION
SHEET NO.:
1OF
DATE:
DWG:IC.MMM.MP6A.REM.1
PROJECT NO.:
1127 CURTIS STREET STE 100
MONROE, NORTH CAROLINA 28112
[phone]
FAX [phone]
SCALE:1"=80'CEC COA#: C-2533
WWW.CECENV.COM
CEC
24016080
MAY 2024
104.01.69
MMM REMEDIATION PLAN
TWIN OAKS SOLID WASTE FACILITY
STATESVILLE, NC 28625
FOR
INFORMATION
PURPOSES
ONLY
CELL BOUNDARY
10 FT TOPOGRAPHIC CONTOUR LINE
PERMITTED LIMITS OF WASTE
LEGEND
2 FT TOPOGRAPHIC CONTOUR LINE
EXISTING FEATURES
NOTES:
1.AERIAL TOPOGRAPHY COMPILED BY COOPER AERIAL SURVEYS, INC. FROM AERIAL
PHOTOGRAPHY FLOWN ON FEBRUARY 16, 2022.
2.THE PROBES SHOWN ARE TAKEN FROM LFG MONITORING PLAN SW PERMIT #49-03.
3.NOTE THAT SOME LFG SYSTEM FEATURES MAY BE DIFFERENT THAN SHOWN HERE
DUE TO MODIFICATIONS MADE BY THE OWNER OR THEIR CONTRACTORS TO
ACCOMMODATE LANDFILL OPERATIONS AND/OR ODOR REDUCTIONS.
4.CEC HAS NOT INDEPENDENTLY VERIFIED ANY SITE EXISTING CONDITIONS.
LFG REMOTE EXTRACTION WELL
LFG CONDENSATE KNOCKOUT
LFG EXTRACTION WELL
REMOTE WELLHEAD
LEACHATE CLEANOUT
W514
W129
DATE
W METHANE MIGRATION PROBE
W METHANE MIGRATION PROBE (EXCEED)
PROPERTY BOUNDARY

EXHIBIT B
APPROXIMATE BARHOLE PUNCH LOCATIONS

CO
CO
CO
CO
CO
C/O 207
MH CO
C/O 208
EXISTING MSW
PHASE 4
C/O P4-2
C/O P4-1
213
203
217
208
215
216
202205
218
206 201
209
A219
223
222
221
B220
224
207
228 229
227
230
232
233
231
234
C/O P4-3
C/O 209
W240
W226R
W225R
W214R
W204R
W212R
W210R
W211R
CS3-1
C/O P4
C/O P3
CS4-1
W
W
W
W
W
MP-5A
MP-4A
ICATS
MP-6A
MP-7A
LCR-4
LCR-3
BHP4-1:
LAT: 35.77237
LONG: -80.83805
BHP4-2:
LAT: 35.77249
LONG: -80.83720
BHP4-3:
LAT: 35.77269
LONG: -80.83633
BHPO4-4:
LAT: 35.77247
LONG: -80.83550
EXISTING MSW
PHASE 3
WMP-6A
BHP4-1
BHP4-2
BHP4-3
BHP4-4
PROPERTY BOUNDARYAPPROXIMATE BARHOLE
PUNCH LOCATION (TYP)
GRAPHIC SCALE (FEET)
0
TITLE:
PROJECT:
CLIENT:
APPROXIMATE BARHOLE PUNCH LOCATIONS
CARLSON ENVIRONMENTAL CONSULTANTS, PC
1
IREDELL COUNTY SOLID WASTE
1 2 3 4 5 6 7 8
E
D
C
B
A
E
D
C
B
A
1 2 3 4 5 6 7 8
REV DWN BY APP BYDESCRIPTION
SHEET NO.:
1OF
DATE:
DWG: IC.MMM.MP6A.REM.2
PROJECT NO.:
1127 CURTIS STREET STE 100
MONROE, NORTH CAROLINA 28112
[phone]
FAX [phone]
SCALE: 1"=80'CEC COA#: C-2533
WWW.CECENV.COM
CEC
24016080
MAY 2024
1040169
MMM REMEDIATION PLAN
TWIN OAKS SOLID WASTE FACILITY
STATESVILLE, NC 28625
FOR
INFORMATION
PURPOSES
ONLY
CELL BOUNDARY
10 FT TOPOGRAPHIC CONTOUR LINE
PERMITTED LIMITS OF WASTE
LEGEND
2 FT TOPOGRAPHIC CONTOUR LINE
EXISTING FEATURES
NOTES:
1. AERIAL TOPOGRAPHY COMPILED BY COOPER AERIAL SURVEYS, INC. FROM AERIAL
PHOTOGRAPHY FLOWN ON FEBRUARY 16, 2022.
2. THE PROBES SHOWN ARE TAKEN FROM LFG MONITORING PLAN SW PERMIT #49-03.
3. NOTE THAT SOME LFG SYSTEM FEATURES MAY BE DIFFERENT THAN SHOWN HERE
DUE TO MODIFICATIONS MADE BY THE OWNER OR THEIR CONTRACTORS TO
ACCOMMODATE LANDFILL OPERATIONS AND/OR ODOR REDUCTIONS.
4. CEC HAS NOT INDEPENDENTLY VERIFIED ANY SITE EXISTING CONDITIONS.
LFG REMOTE EXTRACTION WELL
LFG CONDENSATE KNOCKOUT
LFG EXTRACTION WELL
REMOTE WELLHEAD
LEACHATE CLEANOUT
W514
W129
DATE
W METHANE MIGRATION PROBE
APPROXIMATE BARHOLE PUNCH LOCATION
W METHANE MIGRATION PROBE (EXCEED)
PROPERTY BOUNDARY

EXHIBIT C
EXISTING TOE DRAIN LOCATION

CO
CO
CO
CO
CO
C/O 207
MH CO
C/O 208
EXISTING MSW
PHASE 4
C/O P4-2
C/O P4-1
213
203
217
208
215
216
202205
218
206 201
209
A219
223
222
221
B220
224
207
228 229
227
230
232
233
231
234
C/O P4-3
C/O 209
W240
W226R
W225R
W214R
W204R
W212R
W210R
W211R
CS3-1
C/O P4
C/O P3
CS4-1
W
W
W
W
W
MP-5A
MP-4A
ICATS
MP-6A
MP-7A
LCR-4
LCR-3
EXISTING MSW
PHASE 3
WMP-6A
EXISTING TOE DRAIN
PROPERTY BOUNDARY
GRAPHIC SCALE (FEET)
0
TITLE:
PROJECT:
CLIENT:
LFG GAS TRENCH LOCATION
CARLSON ENVIRONMENTAL CONSULTANTS, PC
1
IREDELL COUNTY SOLID WASTE
1 2 3 4 5 6 7 8
E
D
C
B
A
E
D
C
B
A
1 2 3 4 5 6 7 8
REV DWN BY APP BYDESCRIPTION
SHEET NO.:
1OF
DATE:
DWG: IC.MMM.MP6A.REM.3
PROJECT NO.:
1127 CURTIS STREET STE 100
MONROE, NORTH CAROLINA 28112
[phone]
FAX [phone]
SCALE: 1"=80'CEC COA#: C-2533
WWW.CECENV.COM
CEC
24016080
MAY 2024
1040169
MMM REMEDIATION PLAN
TWIN OAKS SOLID WASTE FACILITY
STATESVILLE, NC 28625
FOR
INFORMATION
PURPOSES
ONLY
LEGEND
EXISTING FEATURES
NOTES:
1. AERIAL TOPOGRAPHY COMPILED BY COOPER AERIAL SURVEYS, INC. FROM AERIAL
PHOTOGRAPHY FLOWN ON FEBRUARY 16, 2022.
2. THE PROBES SHOWN ARE TAKEN FROM LFG MONITORING PLAN SW PERMIT #49-03.
3. NOTE THAT SOME LFG SYSTEM FEATURES MAY BE DIFFERENT THAN SHOWN HERE
DUE TO MODIFICATIONS MADE BY THE OWNER OR THEIR CONTRACTORS TO
ACCOMMODATE LANDFILL OPERATIONS AND/OR ODOR REDUCTIONS.
4. CEC HAS NOT INDEPENDENTLY VERIFIED ANY SITE EXISTING CONDITIONS.
W514
W129
DATE
W
W METHANE MIGRATION PROBE (EXCEED)
PERMITTED LIMITS OF WASTE
10 FT TOPOGRAPHIC CONTOUR LINE
2 FT TOPOGRAPHIC CONTOUR LINE
CELL BOUNDARY
TOE DRAIN
PROPERTY BOUNDARY
LFG EXTRACTION WELL
LFG REMOTE EXTRACTION WELL
LFG CONDENSATE KNOCKOUT
REMOTE WELLHEAD
LEACHATE CLEANOUT
METHANE MIGRATION PROBE

EXHIBIT D
EXCEEDANCE LOCATION PHOTOS

IREDELL COUNTY LANDFILL
MP6-A
CEC
Location of MP-6A near Phases 3 & 4.