25054_Mt Gilead VIMS Design Addendum 1

Hanley Environmental, PLLC
323 Manning Drive
Charlotte, North Carolina 28209
NC Engineering License P-2407
T: [phone]
www.hanleyenvironmental.com

August 10, 2022

Ms. Carolyn Minnich
Brownfields Project Manager
Brownfields Program
North Carolina Department of Environmental Quality

Subject: Vapor Intrusion Mitigation System Design Addendum #1
Mt. Gilead Cotton Oil Company Brownfields Property
Mt. Gilead, Montgomery County, North Carolina
Brownfields Project No. 25054-21-062
Hanley Environmental Project Number: PJ22017

Ms. Minnich,

This Vapor Intrusion Mitigation System (VIMS) Design Addendum #1 presents a modification
to the design of a VIMS for a proposed building to be constructed at the Mt. Gilead Cotton
Oil Company Brownfields Property (Site ID 25054-21-062) in Mt. Gilead, Montgomery County,
North Carolina (the site). The site is located at 299 Industry Avenue and 0 South Wadesboro
Boulevard. The site is being redeveloped by Prospective Developer (PD) Mt Gilead DG, LLC
for commercial use including a one-story retail facility (Dollar General).
A VIMS Design Report dated June 29, 2022, prepared by Hanley Environmental, PLLC was
approved for compliance with the VIMS Design Submittal Requirements Checklist by the
North Carolina Department of Environmental Quality (NCDEQ) Brownfields Program in a
letter dated July 5, 2022. Hanley Environmental has been contracted by the PD to prepare
this VIMS Design Addendum #1 which describes proposed changes to the system design.

Summary of Proposed Design Modifications

The proposed changes pertain to the routing of the four soil gas exhaust vent pipes (R-1
through R-4). As originally designed, these pipes were planned to extend straight up from
VIMS Design Addendum #1 Hanley Environmental, PLLC
Mt. Gilead Cotton Oil Company Brownfields Property
Page 2

the sub-slab through the building roof and exhaust above the roofline. The proposed design
modifications will allow for exhaust vent riser pipes to run horizontally within the building
and exit the building envelope through the side walls rather than the roof. Exhaust pipes will
exit sidewalls within approximately two feet of the height of the roof and then will turn to
run vertically and exhaust at least 18 inches above the roof line and 10 feet from any
openings in structures, air intakes, or breathing spaces where individuals congregate or
traverse. Horizontal pipe runs shall maintain slope to drain condensate toward soil and shall
be secured with bracing per local building codes. Other design parameters will still apply as
specified in the VIMS Design Report (e.g, pipe labeling, exhaust outlet vent pipe caps, etc.)
Changes will be reflected in as-built drawings in the VIMS Installation Report.

Certification
This VIMS Design Addendum #1 has been certified by a North Carolina licensed Professional
Engineer in accordance with 21 NCAC 56 .1103.
The VIMS detailed herein is designed to mitigate intrusion of subsurface vapors into the
subject building from known Brownfields Property contaminants in a manner that is in
accordance with the most recent and applicable guidelines including, but not limited to,
NCDEQ Department of Waste Management (DWM) Vapor Intrusion Guidance, Interstate
Technology & Regulatory Council (ITRC) guidance, and American National Standards Institute
(ANSI)/American Association of Radon Scientists and Technologists (AARST) standards. The
sealing professional engineer is satisfied that the design is fully protective of public health
from known Brownfields Property contaminants.
Use of specific guidance documents in development of this VIMS Design is described in
Section 2.0 of the VIMS Design Report.
This VIMS Design requires implementation of the specified QA/QC procedures, pre-
occupancy testing requirements, post-occupancy OM&M, and reporting procedures. Failure
to implement these procedures and requirements may limit the system’s effectiveness.
VIMS Design Addendum #1 Hanley Environmental, PLLC
Mt. Gilead Cotton Oil Company Brownfields Property
Page 3

As specified in the Brownfields Property Reuse Act §130A-310.32, implementation of a
brownfields agreement will result in use suitable of the property “fully protecting public
health and the environment instead of being remediated to unrestricted use standards”.
Accordingly, risk-based standards will be used in evaluating system effectiveness and the
proposed VIMS is designed to reduce risk to non-residential receptors to below the NCDEQ
Brownfields Program’s acceptable risk thresholds (incremental lifetime cancer risk of 10-4
and hazard index of 1) for contributions of known volatile compounds originating from
subsurface contamination. These risk thresholds are considered “fully protective of public
health” in the context of this Brownfields property.
Closing

Please do not hesitate to contact me with any questions regarding this submittal.

Sincerely,

David Hanley, PE
Hanley Environmental, PLLC