11037_Sub-Slab Sampling Work - Plan Rev 1

Via Email

February 27, 2023

NCDEQ – Division of Waste Management
Brownfields Program
1646 Mail Service Center
Raleigh, NC 27699-1646

Attn: Ms. Carolyn Minnich

Re: Sub-Slab Sampling Work Plan – Revision 1
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 this Sub-Slab
Sampling Work Plan (Work Plan) for the Phase 8 Brightwalk Development located in Charlotte,
North Carolina. The Phase 8 Brightwalk Development is part of the Double Oaks Brownfields
Site (Brownfields Project No. 11037-01-060). A Site location map is provided as Figure 1. This
Work Plan has been revised in accordance with comments received from the Brownfields
Program on February 27, 2023.

2.0 VIMS O&M

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 the January 9, 2023
Methane VIMS Inspection and O&M Report – Revision 1, H&H will conduct methane vapor
intrusion mitigation system (MVIMS) operation & maintenance (O&M) visits on a quarterly
Ms. Carolyn Minnich
February 27, 2023
Page 2

https://harthick.sharepoint.com/sites/MasterFiles-1/Shared Documents/AAA-Master Projects/Charlotte Mecklenburg Housing Partnership - CHP/CHP-041 Double Oaks Methane/Sub-Slab
Sampling Work Plan/Sub-Slab Work Plan.docx
basis in 2023 at the eight (8) single-family homes located at 2531, 2535, 2539, 2601, 2605, 2609,
2613, and 2617 Double Oaks Road (Double Oaks Homes). A Site map is provided as Figure 2.
The VIMS O&M visits will include the following:

 confirming MVIMS fan operation,
 confirming the presence and operation of methane sensors in each home and garage,
 collection of differential pressure and methane measurements from the sub-slab sample
ports in each home and garage, and
 collection of methane measurements from landfill gas probes LG-23, LG-24, and LG-25

It is anticipated that the quarterly O&M visits will be conducted in March 2023, June 2023,
September 2023, and December 2023. Results of the MVIMS O&M visits will be provided to
DEQ on a quarterly basis.

In addition, as requested by the North Carolina Department of Environmental Quality (DEQ),
H&H will collect sub-slab vapor samples for analysis of volatile organic compounds (VOCs).
These VOC samples will be collected from a minimum of four (4) of the eight (8) single-family
homes during the O&M visit in March 2023. The option to collect sub-slab samples from the
remaining four homes will be offered to the homeowners. A description of the proposed sub-slab
sampling activities is provided below.

3.0 Sub-Slab Sampling for VOCs

The sub-slab vapor samples for VOC analysis will be collected from the rear sub-slab sample
port in each home (Figure 2). The sub-slab samples will be collected utilizing a 1-liter or 3-liter
(depending on laboratory availability) individually certified stainless steel Summa® canister
connected to an air-flow regulator calibrated by the laboratory to collect the sub-slab sample at a
rate of approximately 200 ml/min.

Ms. Carolyn Minnich
February 27, 2023
Page 3

https://harthick.sharepoint.com/sites/MasterFiles-1/Shared Documents/AAA-Master Projects/Charlotte Mecklenburg Housing Partnership - CHP/CHP-041 Double Oaks Methane/Sub-Slab
Sampling Work Plan/Sub-Slab Work Plan.docx
Prior to collection of the soil gas samples, a “shut-in” test will be conducted on the sampling
train and helium leak checks will be conducted at each sub-slab monitoring point. The purpose of
the shut-in test and helium leak check is to ensure short-circuiting with ambient air does not
occur during sampling. A description of the shut-in test and helium leak testing procedures is
provided below.

The shut-in test will be conducted by connecting the flow regulator with the vacuum gauge to the
Summa® canister and sealing the flow regulator with the laboratory-provided brass cap. Once the
sampling train is “closed”, the sample valve on the Summa® canister will be opened and the
reading on the vacuum gauge will be recorded. The Summa® canister sample valve will then be
closed and the vacuum gauge will be observed to ensure no vacuum loss occurs. If the vacuum
reading remains the same, the shut-in test will be considered successful. If vacuum loss occurs,
the flow regulator and/or brass cap will be reseated and the shut-in test will be repeated until the
vacuum reading remains stable.

Following the shut-in test, the Summa® canister will be connected to the sample point via
Teflon® sample tubing using a brass nut and ferrule assembly to create an air-tight seal and the
leak check will be performed. The leak check will be performed by constructing a shroud over
the sampling train and flooding the shroud with helium gas. A calibrated helium gas detector will
be utilized to measure helium concentrations within the shroud. Once helium concentrations
stabilize within the shroud, the sample tubing will be purged outside of the shroud using a
syringe and a three-way valve to collect purged soil gas into a Tedlar® bag. The purged soil gas
will then be analyzed using the helium gas detector to ensure that helium concentrations in the
sub-slab point are less than 10% of the helium concentrations measured within the shroud.

Following successful leak checks, the valve on the flow regulator will be fully opened to allow
collection of the sub-slab vapor samples. Vacuum readings on the Summa® canister will be
recorded prior to and following the sampling period to ensure adequate sample volume was
collected. A vacuum of approximately 5 inches of mercury will be maintained within the
canisters at the conclusion of the sampling event in accordance with DEQ DWM guidance.
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
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
SITE 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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1 2531 DOUBLE OAKS ROAD
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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