25054-Mt Gilead-Post-Occupancy Monitoring Report-Response-20240208

ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
MICHAEL SCOTT
Director
Sent Via E-mail
Mr. David Hanley, PE
NORTH CAROLINA
Environmental Quality
February 8, 2024
Hanley Environmental, PLLC
323 Manning Drive
Charlotte, NC 28209
[e-mail]
Subject: VIMS Post -Occupancy Monitoring Report
Mt. Gilead Cotton Oil Co.
Mt. Gilead, Montgomery Co.
Brownfields Project No. 25054-21-062
Dear Mr. Hanley:
The North Carolina Department of Environmental Quality (DEQ) Brownfields Redevelopment
Section (BRS) has received and reviewed the VMS Post -Occupancy Monitoring Report
dated May 22, 2023 (Report) for the above referenced Brownfields Property. The Report
summarized sub -slab soil gas assessment activities performed as required by the approved Vapor
Intrusion Mitigation System Design Report -Revision 2, dated June 29, 2022, and approved on July
5, 2022.
The Report concludes with the request to cease sampling, given the risk cumulative risk evaluation.
However, review of the data demonstrates a significant increase in several compounds, particularly
the primary site contaminant tetrachloroethylene (PCE),which, among others, increased to by an
order of magnitude above from the previous sampling event. In addition, the data indicates the
presence of trichloroethylene (TCE), at an estimated concentration of 1.09 ug/m3, which was not
detected in the preceding sampling event. This significant increase demonstrates that the
concentrations in the sub -slab have not stabilized, which is necessary to approve a reduction or
cessation of monitoring.
Given the significant increases observed in the latest sampling results, and the appearance of TCE
in the most recent sub -slab vapor sampling results, and the initial presence of PCE and TCE in
groundwater samples taken prior to development, the BRS cannot approve the cessation of
sampling at this time. As such, the BRS requires a minimum of one additional sampling event, in
accordance with the methodologies outlined in the Vapor Intrusion Mitigation System Design
D E Q�� North Carolina Department of Environmental Quality I Division of Waste Management
217 West Jones Street 1 1646 Mail Service Center I Raleigh, North Carolina 27699-1646
NORTH CAROLINA -
Dewrtmemm W—menmi auai\ 919.707.8200

Report -Revision 2 to evaluate if sub -slab concentrations have stabilized, or if there is an increasing
trend that warrants monitoring.
If you have any questions, please feel free to contact me at 910-796-7408, or via e-mail
at samuel.watsongdeq.nc.gov.
Sincerely,
i'7Qa�rris�il
Samuel P. Watson
Project Manager
Brownfields Property Management Branch
ec: Chad McClary [e-mail]
Joselyn Harriger, DEQ BRS
NORTH CAROLINAD_E QI__A
Aj
Oepamnam or Eimmamamai Quail
North Carolina Department of Environmental Quality I Division of Waste Management
217 West Jones Street 1 1646 Mail Service Center I Raleigh, North Carolina 27699-1646
919.707.8200