26015_Sawmill Hollow Methane WP_20240102

STATE
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
MICHAEL SCOTT
Dlrector
OAM V
NORTH CAROLINA
EnvlronmentalQualty
ATTACHMENT 1
DEQ Brownfields Redevelopment Section
Assessment Work Plan Approval Signature Page
To be completed by Development Team and returned to DEQ Brownfields for review & signature.
Brownfields Project Name:Sawmill Hollow Property
Brownfields Project Number:26015-22-100
Work Plan Title:MethaneAssessmentWork Plan
Date: 01/02/2024
RevisionNumber:
Be advised that this approval from DEQ Brownfields does not waive any applicable requirement to
obtain any necessarypermits,licenses,or certifications for the above listed activities nor does it waive
any requirement to comply with applicable law for such activities.
Prospeetive Developer (PD):NorthwesternHousingEnterprises,Incorporated
Contact Person:E.G."Ned"Fowler,President
Phone Numbers:Office: [phone] Mobile: [phone]
Email: [e-mail]
Property Owner (if different from above): Click or taphere to entertext.
Contact Person: Click or tap here to enter text.
Phone Numbers:Office: Click or tap here to enter text.
Email: Click or tap here to enter text.
Mobile: Click or tap here to enter text.
Environmental Consultant: GeosyntecConsultants
Contact Person: MikeBurcham
Phone Numbers:Office: [phone]
Email: [e-mail]
Signature:
of NC,P.C.
Mobile: [phone]
ARA
SEAL
050312
EEiRCHA
Date 1/5/2024
PG/PE SEAL HERE
Mobile: [phone]
Consultant: Geosyntec Consultants of NC,P.C.
PrintedName/Title/Company: MikeBurcham,P.E. / Senior
Brownfields Project Manager:William Schmithorst
Phone Numberx office: :[phone]
Email:[e-mail]
Signature:
Brownfields ProjectManager:Wiliam Schmithorst
DEO
Date Click or tap to enter a date.
North Carolina Department of Environmental Quality | Divislon of Waste Management
217 West Jones Street |1646 Mal Service Center |Raleigh,North Carolina 27699-1646
919.707.8200
01/05/2024
Geosyntec Consultants of NC, P.C. 2501 Blue Ridge Road, Suite 430 Raleigh, North Carolina, 27607 PH 919.424.1851 www.geosyntec.com
2 January 2024

Attention: Bill Schmithorst
Division of Waste Management – Brownfields Redevelopment Section
North Carolina Department of Environmental Quality
217 W Jones Street
Raleigh, North Carolina 27699-1646
[e-mail]

Subject: Methane Assessment Work Plan
Subject Site: Sawmill Hollow Property
Sawmill Hollow Road, Burnsville, North Carolina 28714
BRS Project # 26015-22-100

Dear Mr. Schmithorst:
On behalf of Northwestern Housing Enterprises, Incorporated (NHE; the Prospective Developer),
Geosyntec Consultants of NC, P.C. (Geosyntec) is pleased to submit the Methane Assessment
Work Plan (Work Plan) for the above-referenced property (Site) for your review and approval.
The Site is the 3.86-acre parcel at the intersection of Sawmill Hollow Road and US Highway 19E
in Burnsville, North Carolina identified under Yancey County Parcel Number 083003244675000
and is shown in Figure 1. A Letter of Eligibility (LOE) was received for the property on November
10, 2022, indicating that the Site was eligible for entry into the North Carolina Department of
Environmental Quality (NCDEQ) Brownfields Redevelopment Section (BRS) and for the eventual
finalization of a Brownfields Agreement (BFA). As of this letter a BFA has not been finalized.
INTRODUCTION
During supplemental Site assessment work in September 2022, Geosyntec installed 10 soil gas
probes and detected methane between 0.3 percent (%) by volume (%v) and 5.1%v at 5 of the
probes (Figure 2). The methane appears to be related to woody debris that was observed above
and below grade during the Site assessment and test pitting. The BRS is requiring that the woody
debris be removed from Site prior to redevelopment and that a subsequent methane assessment be
conducted to demonstrate that removing woody debris will effectively reduce methane
concentrations in soil gas such that further methane monitoring and mitigation will not be
necessary.
This Work Plan was prepared in general accordance with the NCDEQ Program Methane
Assessment Protocol (July 2020 – Rev. December 2020).

GN9110/CAR230260 2 January 2024
METHANE ASSESSMENT ACTIVITIES
At least two weeks after NHE removes woody debris from the Site, Geosyntec will oversee the
installation of three soil gas probes in areas where mulch and buried woody debris have been
removed. Geosyntec will then screen each soil gas probe for methane during three separate events,
as required by BRS. The screening analysis plan is summarized in Table 1 and details of this scope
of work are provided in the sections below.
Health and Safety Planning and Utility Clearing
Prior to the start of work, Geosyntec will prepare a Site-specific Health and Safety Task Hazard
Analysis in general accordance with the Occupation Safety and Health Administration (OSHA)
rules (29 CFR 1910.120). Geosyntec will coordinate with NHE, and subcontractors/vendors to
open a North Carolina 811 ticket prior to drilling. Drilling locations will be hand cleared prior to
installation.
Soil Gas Probe Installation
Soil gas probes SG-11, SG-12 and SG-13 will be installed at locations shown on Figure 2. A North
Carolina certified well contractor will install each soil gas probe using direct push technology
(DPT) techniques. During installation, a soil boring will be advanced to at least 6 feet below land
surface (ft BLS) and Geosyntec will log and classify the soils observed. Soils will not be screened
for total volatile organic compounds (VOCs). Investigation derived waste will be managed by
spreading drill cuttings around each soil gas probe.
Soil gas probes will be installed to a target depth of 6 ft BLS. Based on the observations from the
soil boring, the soil gas probe depth may be adjusted shallower or deeper avoid low-permeability
soils or saturated conditions; however, the top of the sand filter pack will be installed at least 3 ft
BLS.
The probe will consist of ¼-inch diameter Nylaflow® tubing connected with a barbed fitting to a
prefabricated 6-inch stainless steel sampling probe (¼-inch-diameter). Probes will be installed
inside the borehole and a sand filter pack will be placed in the annulus to approximately 3 inches
above and 3 inches below sampling probe. A minimum 1-ft granular bentonite seal will be placed
above the sand pack and hydrated in lifts. Granular bentonite will be placed in lifts of a maximum
of 3 inches and hydrated with a small amount of distilled water after each lift. A slurry of powdered
bentonite or cement will then be placed from the top of the granular bentonite seal to land surface.
The top of the probe will be fitted with a compression-fit brass ball valve to maintain an air-tight
seal. Each probe will be enclosed with a flush mounted well vault within a concrete pad.

GN9110/CAR230260 3 January 2024
Methane Screening Frequency
Geosyntec will complete three methane screening events (baseline, Month 1, and Month 2) as part
of the methane assessment, which are summarized below:
• Baseline: Geosyntec will complete the baseline methane screening event within 1 week of
installing the soil gas probes and at least 2 hours after the soil gas probe installations (per
BRS guidance 1). The baseline methane screening event requires two screenings be
completed at least 24 hours apart and at different times of day; therefore, two sets of data
will be collected as part of the baseline methane screening event.
• Month 1: Geosyntec will complete the Month 1 methane screening event approximately
one month after soil gas probe installation.
• Month 2: Geosyntec will complete the Month 2 methane screening event approximately
two months after soil gas probe installation.
In total, Geosyntec will collect four sets of methane screening data. The data collected, and
methods used to collect the data, are described in the following section.
Methane Screening Procedure
Prior to methane screening, Nylaflow tubing will be connected to the soil gas probe using an
air-tight fitting without opening the pre-installed valve. Geosyntec will then open the valve and
measure static pressure (i.e., subsurface gas pressure relative to atmospheric pressure) using a
Landtec GEM 5000 (or equivalent multi-gas meter) and a hand-held micromanometer (DG-500 or
equivalent) for redundancy. Static pressure will be reported in Pascals (Pa) and inches of water
(in. H2O).
Once the static pressure is measured, Geosyntec will perform a shut-in leak check in the sample
assembly. Geosyntec will close the valve on the soil gas probe and generate a vacuum in the sample
train using a lung box or equivalent. A second valve near the lungbox will then be closed, and if
the vacuum does not dissipate in the sampling train after at least 30 seconds, the shut-in test will
be considered successful.
A helium shroud will also be used initially during purging as a tracer leak test to evaluate potential
outdoor air entrainment into the samples. However, commonly used helium meters (e.g., MGD-
2002) indicate in the operator manual that the presence of methane will interfere with the helium
meter screening results. This could indicate a false positive screening of helium in the sample train,
when the meter is actually detecting methane. In this event, multiple lines of evidence will be used
to evaluate the integrity of the soil gas probe and sample train seal: 1) a shut-in leak test will be

1 NCDEQ Brownfields Program Methane Assessment Protocol July 2020 (Rev. December 2020)

GN9110/CAR230260 4 January 2024
performed initially as discussed previously and 2) during the soil gas purging, the presence of
methane and carbon dioxide above atmospheric levels, in combination with decreased oxygen
concentration relative to atmospheric conditions, will be used as supporting evidence for the
integrity of the surface seal. If methane is not present in field screening samples, helium will be
used as a seal test.
Following a successful shut-in leak test, soil gas will be purged and screened for the parameters
listed in Table 1. Soil gas will be purged such that at least three times the volume of the soil gas
probe and sample train are purged prior to collecting and recording final soil gas measurements.
The soil gas probes will be purged using a lung box or peristaltic pump and purged soil gas will
be collected in a 1-liter Tedlar® bag. Each Tedlar bag of purged soil gas will be screened using a
multi-gas meter (Landtec GEM 5000, or equivalent).
REPORTING
Geosyntec will evaluate the methane screening results using the most recent BRS methane
screening criterion2. Geosyntec will document the methane assessment activities, results, and
evaluation in a letter (“Letter”) that will be submitted to the BRS for review and approval.
If the assessment reveals sustained methane concentrations in soil gas above 1.25%v, the Letter
will identify the buildings that require subslab soil gas to be screened for methane after the building
slab is poured. Details of the post-pour methane screening (including frequency of monitoring),
notification requirements, and criteria for installing methane mitigation system components will
be provided in the Letter.
CLOSING
Should you have questions regarding this submittal or need additional information, please do not
hesitate to contact Mike Burcham at [phone] or [e-mail].
Sincerely,

Mike Burcham, P.E. (NC, TX) Todd N. Creamer, P.G. (NC, CA, PA, WY)
Senior Engineer Senior Principal

cc. Ned Fowler, Northwestern Housing Enterprises, Incorporated

2 NCDEQ Brownfields Program Threshold Criteria For Methane Site Development (December 2020)

GN9110/CAR230260 5 January 2024
Attachments Table 1: Methane Screening Analysis Plan
Figure 1: Site Location Map
Figure 2: Methane Screening Location

TABLE

SG-11
SG-12
Former Mulch Pile SG-13
Notes:
Acronyms:
BRS: North Carolina Brownfield Redevelopment Section
BLS: below land surface
ft: feet
Screen for methane concentrations pursuant to BRS
guidance1 6
1. Screening criteria are defined in the NCDEQ Brownfields Program Methane Assessment Protocol July 2020 (Rev. December 2020)
Table 1
Methane Screening Analysis Plan
Sawmill Village - Burnsville, North Carolina
Static Pressure,
Methane,
Carbon Dioxide,
Oxygen,
Barometric Pressure,
and Hydrogen Sulfide
Former Buried Woody Debris
Sample Area Soil Gas Probe ID Sample Objective
Anticipated
Boring Depth
(ft BLS)
Screening Parameters
Anticipated Sand
Filter Pack (ft
BLS)
5 to 6
1 of 1

FIGURES

\\Raleigh-01\PRJ\N\Northwestern Housing Enterprises\Sawmill Village\7.0 GIS\MXDs\202312_Methane_Assessment_WP\F1_Site_Location_Map.mxd 12/20/2023 4:32:37 PM
0 1,000Feet
³Sawmill Hollow Brownfields PropertyBrownfields Project No: 26015-22-100Burnsville, North Carolina
Site Location Map
Figure
1Asheville, NC January 2024
Legend
Notes:1.Base map from USGS National Topographic Map.2.Parcel Boundary Data from Yancey County GIS.
Site Location
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Site Location
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!.Sawmill Hollow RoadUS Highway 19E
F air H a v en D rive
SG-13
SG-12
SG-11
TP-07
TP-12
TP-10
TP-03
TP-09
TP-11
TP-06
TP-08
TP-05
TP-01
SB-06
SB-07
SB-05
SB-04
SB-03
SB-02
SB-01
SB-08
SB-09
SB-10
SG-04
SG-05
SG-03
SG-02
SG-01
SG-08
SG-06
SG-07
SG-09
SG-10
VP-3
VP-4
VP-2
VP-5
\\Raleigh-01\PRJ\N\Northwestern Housing Enterprises\Sawmill Village\7.0 GIS\MXDs\202312_Methane_Assessment_WP\F2_Proposed_Screening.mxd 12/26/2023 9:57:31 AM
Sawmill Hollow Brownfields Property
Brownfields Project No: 26015-22-100
Burnsville, North Carolina
Proposed Methane Screening Locations
0 50
Feet
³Figure
2
Asheville, NC January 2024
Legend
Site Boundary
Former Building
Proposed Community Center
Proposed Housing Unit
Proposed Road
Perimeter of Obvious Mulch Pile
Approximate Extent of Buried
Woody Debris
"")Test Pit with Woody Debris
")Test Pit without Woody Debris
!(Soil Boring Location
!(Soil Gas Sample Location
&>Historical Soil Vapor Probe
!.Proposed Soil Gas Probes for
Methane ScreeningNotes:1.Parcel boundary from Yancey County GIS.2.Methane screening results and initial pressure measurements collected using GEM 5000 landfill gas meter.3. Initial pressure measurements collected using a Dwyer Series 475-3-FM manometer prior to purging.
Methane screening results collected using a GEM 5000 landfill gas meter in September 2023.4.Basemap from Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community.
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-01 0.0 0.0
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-02 0.0 0.0
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-03 0.0 0.0
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-04 0.0 1.3
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-05 0.0 5.1
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-06 0.0 1.2
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-07 0.0 0.3
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-08 0.0 0.0
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-09 0.0 0.4
Sample
Location
Static Pressure
("H2O)
Methane
(% volume)
SG-10 0.0 0.0