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Via Email
November 14, 2023
NCDEQ – Division of Waste Management
Brownfields Redevelopment Section
1646 Mail Service Center
Raleigh, NC 27699-1646
Attn: Ms. Carolyn Minnich
Re: 3rd Quarter 2023 MVIMS O&M Report
Phase 8 Brightwalk Development
Double Oaks Brownfields Site
Charlotte, Mecklenburg County
Brownfields Project No. 11037-07-060
H&H Project No. CHP-041
Dear Carolyn:
1.0 Introduction
On behalf of DreamKey Partners, LLC, Hart & Hickman, PC (H&H) is providing the 3rd Quarter
2023 Methane Vapor Intrusion Mitigation System (MVIMS) Operations and Maintenance (O&M)
report for the Phase 8 Brightwalk Development located in Charlotte, North Carolina (Site). The
Phase 8 Brightwalk Development is part of the Double Oaks Brownfields Site (Brownfields
Project No. 11037-07-060). A Site location map is provided as Figure 1.
The Double Oaks Brownfields property is developed with residential apartments, townhomes, and
single-family homes. The Phase 8 Development includes eight (8) single-family homes located
along Double Oaks Road which is near the former Double Oaks Landfill. As discussed in previous
reports, MVIMSs designed by Geoscience Group, LLC (Geoscience) were installed for each home
as part of the Phase 8 construction. The addresses for the single-family homes with MVIMSs
include: 2531, 2535, 2539, 2601, 2605, 2609, 2613, and 2617 Double Oaks Road (Double Oaks
Homes). The Phase 8 construction was completed in approximately December 2017/January 2018.
Each property consists of a two-story dwelling and detached garage. The detached garages are
Ms. Carolyn Minnich
November 14, 2023
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located in the rear of each property and closest to the former Double Oaks Landfill. A site map
depicting the locations of the Double Oaks Homes and primary components of the MVIMS system
is provided in Figure 2.
As discussed in the Methane VIMS Inspection and O&M Report – Revision 1 dated January 9,
2023, results of the MVIMS inspections and O&M visits conducted in October 2021 through
November 2022 indicated that a low point in the MVIMS piping between the home and the
detached garage resulted in water accumulation in the MVIMS and prevented the radial blower
from creating a vacuum below the slab of the home. As also discussed in the report, although a
vacuum was not present below the slabs of the homes (due to water accumulation in the MVIMS
piping), concentrations of methane were not detected below the slabs of the homes during the
October 2021 through November 2022 O&M visits.
To further evaluate potential subsurface methane migration to the Site and MVIMS influence,
H&H installed vapor pins in the garages of the Double Oaks Homes in July 2022. Following
installation of the vapor pins in the garages, sub-slab methane and differential pressure readings
were collected during the O&M visits conducted in July 2022 and November 2022. Results of the
differential pressure readings collected from below each garage slab indicated the presence of a
vacuum greater than 0.016 inches of water column (WIC). In addition, methane was not detected.
Because methane was not detected below the slabs of the homes and garages, H&H concluded that
the risk for methane vapor intrusion was low, and modifications to the MVIMS to improve sub-
slab differential pressure below the slabs of the homes were not warranted. To further demonstrate
that the risk for methane vapor intrusion is low, H&H proposed quarterly MVIMS O&M visits
and inspections in 2023. The first 2023 MVIMS O&M and inspection was conducted in March
2023 and results were provided to the Brownfields Redevelopment Section in the 1st Quarter 2023
MVIMS O&M Report with Sub Slab Vapor Sampling Results (March 2023 Report) dated May 26,
2023. Methane was not detected below the slabs of the homes or garages during the March 2023
visits.
Ms. Carolyn Minnich
November 14, 2023
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In addition to the MVIMS O&M and inspection activities conducted in March 2023, and in
accordance with DEQ’s request, sub-slab vapor samples were collected from each home for
laboratory analysis of volatile organic compounds (VOCs) by EPA Method 8260. Results of the
VOC sub-slab vapor sampling did not indicate a VOC vapor intrusion risk above DEQ acceptable
risk thresholds.
To avoid potentially unnecessary modifications to the MVIMS, H&H recommended the
installation and sampling of methane monitoring points between the homes and the former Double
Oaks Landfill to further evaluate the presence of methane. In an email dated June 21, 2023, the
NC DEQ Brownfields Program concurred with the recommendation to install the methane
monitoring points. The methane monitoring points installation and sampling was subsequently
conducted during the June 2023 inspection and O&M visit. Results of the June 2023 inspection
and O&M visit and methane monitoring point installation and sampling were provided to DEQ in
the 2nd Quarter 2023 MVIMS O&M Report (June 2023 Report) dated August 14, 2023, and the
results are summarized below:
Methane was not detected below the slabs of the homes or garages.
The MVIMS fan at each home was observed to be operational.
Differential pressure readings collected below seven of the eight homes did not indicate
the presence of a differential pressure greater than -0.016 inches of water column (WIC).
Differential pressure readings collected below each of the detached garages indicated the
presence of a differential pressure greater than -0.016 inches of water column (WIC).
Two methane alarm sensors were confirmed to be present in each home and one methane
sensor was confirmed to be present in each garage. The methane sensors were observed to
be functioning properly.
Methane was not detected above 0.1% methane by volume in the newly installed methane
monitoring points (MGP-1, MGP-2, and MGP-3) located between the homes and the
former Double Oaks Landfill (Figure 3).
Ms. Carolyn Minnich
November 14, 2023
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Methane was not detected in landfill gas probes LG-23, LG-24, and LG-25 above 0.1 %
methane by volume located to the south of the former Double Oaks Landfill.
Static pressure measurements collected from LG-23, LG-24, LG-5, MGP-1, MGP-2, and
MGP-3 did not indicate the presence of sufficient subsurface pressure to drive methane
migration.
Based on the results of the June 2023 O&M and inspection, H&H recommended limiting the
remaining 2024 quarterly MVIMS O&M visits (September 2023 and December 2023) to the
collection of methane readings and static pressure readings from methane monitoring points MGP-
1, MGP-2, MGP-3, LG-23, LG-24, and LG-25 and confirming MVIMS fan operation.
In an email dated September 11, 2023, the Brownfields program approved limiting the September
2023 visit to the collection of methane readings from the methane monitoring points and
confirming MVIMS fan operation. The results of the September 2023 monitoring event are
provided below.
2.0 MVIMS Inspection & O&M
On September 20, 2023, H&H conducted the 3rd Quarterly MVIMS O&M visit and inspection. As
indicated above, the MVIMS O&M visit and inspection in September 2023 included confirming
MVIMS fan operation and the collection of methane readings and static pressure readings from
methane monitoring points. Methane readings were collected utilizing a calibrated Landtec GEM
5000™ (GEM). Because previous methane readings on two consecutive days did not indicate
significant differences based on the time of day, methane readings were collected on one day. The
calibration log for the GEM 5000™ is provided in Appendix A. Each of the MVIMS fans were
observed to be operational at the time of the MVIMS O&M visit.
Methane was not detected in the methane monitoring points (LG-23, LG-24, LG-25, MGP-1,
MGP-2, and MGP-3) above 0.0% methane by volume in September 2023. Static pressure
measurements collected from the methane monitoring points generally ranged from -0.03 WIC to
Ms. Carolyn Minnich
November 14, 2023
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0.03 WIC except for MGP-1 which was measured to be 0.65 WIC. As discussed in the June 2023
Report, a minimum of 2 WIC in the subsurface is generally required for subsurface methane
migration. A summary of the methane and static pressure readings collected from the methane
monitoring points is provided in Table 1.
3.0 Summary and Recommendations
Numerous methane readings have been collected from the Site beginning in November 2021. The
methane readings have included the collection of methane readings from sub-slab sampling ports
installed in the homes and garages, indoor air, and subsurface methane monitoring points located
around the perimeter of the former landfill and between the homes and former landfill. To date,
methane readings at the Site have not exceeded 0.1 % methane by volume. Further, recent data
collected from methane monitoring points indicate that subsurface pressure is not sufficient to
drive methane migration if methane were to be present. As such, the risk for methane vapor
intrusion into the homes is low. Consistent with H&H’s prior recommendation, H&H recommends
limiting future MVIMS inspections and O&M visits to confirming MVIMS fan operation and
collecting methane and static pressure readings from MGP-1, MGP-2, MGP-3, LG-23, LG-24, and
LG-5.
The fourth quarterly O&M visit for 2023 will be conducted in December 2023. Unless fourth-
quarter 2023 data are cause for concern, MVIMS O&M visits in 2024 will be conducted on a semi-
annual basis. Results of each MVIMS inspection and O&M visit will be provided to DEQ within
approximately 30 days. If methane is detected in MGP-1, MGP-2, or MGP-3 above the DEQ
Brownfields threshold of 1.25% by volume during future O&M visits, DEQ will be notified within
48-hours and methane readings will be collected from the sub-slab sample ports in the homes and
garages in the Phase 8 development.
Table
Table 1
Summary of Methane Gas and Landfill Gas Probe Data
Brightwalk Phase 8 Development
Charlotte, North Carolina
H&H Project No. CHP-041
Sample ID Sample Date and Time
(where applicable)CH4 (%)3 CO2 (%) O2 (%)CO (ppm)H2S (ppm)Static Pressure
(in. H2O)
6/29/2023 9:49 0.0 8.0 8.6 0.0 0.0 -0.05
6/30/2023 12:49 0.1 6.6 8.1 0.0 0.0 0.00
9/20/2023 0.0 12.5 9.9 0.0 0.0 0.65
6/29/2023 9:58 0.0 1.4 16.8 0.0 1.0 -0.01
6/30/2023 13:07 0.1 1.8 17.0 0.0 0.0 -0.01
9/20/2023 0.0 6.9 14.5 0.0 1.0 -0.01
6/29/2023 10:05 0.0 3.3 15.7 0.0 1.0 0.04
6/30/2023 13:22 0.1 4.7 15.8 1.0 0.0 0.00
9/20/2023 0.0 14.9 6.8 0.0 0.0 0.02
5/21/2021 0.0 5.7 11.6 NM NM NM
10/1/2021 0.0 4.4 9.2 NM NM NM
3/1/2022 0.0 3.8 8.8 NM NM NM
7/25/2022 0.0 9.4 10.7 NM NM NM
11/18/2022* 0.0 1.8 20.0 0.0 0.0 -0.03
3/29/2023 0.0 4.2 13.8 0.0 0.0 0.03
6/29/2023 0.1 5.9 13.3 0.0 0.0 0.05
9/20/2023 0.0 8.2 5.6 0.0 0.0 -0.03
5/21/2021 0.0 9.4 10.5 NM NM NM
10/1/2021 0.0 10.1 10.8 NM NM NM
3/1/2022 0.0 11.3 11.1 NM NM NM
7/25/2022 0.0 15.3 6.2 NM NM NM
11/16/2022 0.0 11.1 10.5 0.0 0.0 -0.01
3/29/2023 0.0 9.0 13.8 0.0 0.0 -0.01
6/29/2023 0.1 15.1 3.6 0.0 0.0 -0.01
9/20/2023 0.0 16.6 5.5 0.0 0.0 0.01
5/21/2021 0.0 10.8 2.9 NM NM NM
10/1/2021 0.0 11.8 3.1 NM NM NM
3/1/2022 0.0 12.2 3.2 NM NM NM
7/25/2022 0.0 14.9 3.4 NM NM NM
11/16/2022 0.0 14.8 7.4 0.0 0.0 0.00
3/29/2023 0.0 5.7 11.0 0.0 0.0 0.02
6/29/2023 0.1 12.0 4.2 1.0 0.0 0.04
9/20/2023 0.0 15.9 3.6 0.0 0.0 0.03
Notes:
1) Methane gas probes installed by H&H on June 29, 2023
2) Landfilll gas probes installed by URS in August 2015.
3) The North Carolina Landfill Gas Monitoring Regulation is 5% methane (100% LEL) at the landfill property line.
*Water was removed from LG-23 on November 16, 2022 and sampled on November 18, 2022.
Measurements were collected by H&H using a calibrated LANDTEC GEM 5000
Negative static pressure values indicate that subsurface pressure is lower than ambient air pressure
CH4 = methane; O2 = oxygen; CO2 = carbon dioxide; CO = carbon monoxide; H2S = hydrogen sulfide;
in H₂O = inches of water; % = percent by volume of air; ppm = parts per million; NM = not measured
Methane Gas Probes1
LG-23
Landfill Gas Probes2
LG-24
LG-25
MGP-1
MGP-2
MGP-3
https://harthick.sharepoint.com/sites/MasterFiles-1/Shared Documents/AAA-Master Projects/Charlotte Mecklenburg Housing Partnership - CHP/CHP-041 Double Oaks Methane/Report/2023 Reports/September 2023/Table 1 - Landfill Gas Probe
10/20/2023
Table 1 (Page 1 of 1)
Hart & Hickman, PC
Figures
0 2000 4000
APPROXIMATE
SCALE IN FEET
N
U.S.G.S. QUADRANGLE MAP
QUADRANGLE
7.5 MINUTE SERIES (TOPOGRAPHIC)
NORTH: DERITA, NC 1996
SOUTH: CHARLOTTE EAST, NC 1991
TITLE
PROJECT
SITE LOCATION MAP
DREAMKEY PARTNERS BRIGHTWALK PHASE 8
BROWNFIELDS PROJECT 11037-01-060
CHARLOTTE, NORTH CAROLINA
DATE:
JOB NO:
REVISION NO:
FIGURE:
06-04-2021 0
1CHP-041
SITE
REVISION NO. 0
JOB NO. CHP-041
DATE: 12-8-22
FIGURE NO. 2
DREAMKEY PARTNERS BRIGHTWALK PHASE 8
DOUBLE OAKS ROAD
CHARLOTTE, NORTH CAROLINA
METHANE VAPOR MITIGATION
SYSTEM COMPONENT MAP
LEGEND
PARCEL BOUNDARY
BRIGHTWALK PHASE 8 DEVELOPMENT
PROPERTY ID
SUB-SLAB SAMPLE PORT
UPPER LEVEL METHANE SENSOR
LOWER LEVEL METHANE SENSOR
METHANE VAPOR MITIGATION FAN
AND EXHAUST
2923 South Tryon Street-Suite 100
Charlotte, North Carolina 28203
704-586-0007(p) 704-586-0373(f)
License # C-1269 / #C-245 Geology
NOTES:
1. AERIAL IMAGERY OBTAINED FROM MECKLENBURG
COUNTY GIS (2022).
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2 2535 DOUBLE OAKS ROAD
3 2539 DOUBLE OAKS ROAD
4 2601 DOUBLE OAKS ROAD
5 2605 DOUBLE OAKS ROAD
6 2609 DOUBLE OAKS ROAD
7 2613 DOUBLE OAKS ROAD
8 2617 DOUBLE OAKS ROAD
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REVISION NO. 0
JOB NO. CHP-041
DATE: 7-10-23
FIGURE NO. 3
DREAMKEY PARTNERS BRIGHTWALK PHASE 8
DOUBLE OAKS ROAD
CHARLOTTE, NORTH CAROLINA
SITE AND METHANE SAMPLE LOCATION MAP
LEGEND
PARCEL BOUNDARY
LANDFILL GAS PROBE
BRIGHTWALK PHASE 8 DEVELOPMENT
PROPERTY ID
LOCATION OF METHANE MONITORING
POINT
2923 South Tryon Street-Suite 100
Charlotte, North Carolina 28203
704-586-0007(p) 704-586-0373(f)
License # C-1269 / #C-245 Geology
NOTES:
1. AERIAL IMAGERY OBTAINED FROM MECKLENBURG
COUNTY GIS (2022).
2. LG = LANDFILL GAS
MGP = METHANE GAS POINT
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4 2601 DOUBLE OAKS ROAD
5 2605 DOUBLE OAKS ROAD
6 2609 DOUBLE OAKS ROAD
7 2613 DOUBLE OAKS ROAD
8 2617 DOUBLE OAKS ROAD
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Appendix A
GEM5000 Calibration Log