3606_HardinUnitIIIMSWLF_EMPApproval_FID1840037_20240521

May 21st, 2024

Sent Via Email – mailto:[e-mail]
Dan Ziehm
Gaston County Public Works Director
P.O. Box 1578
Gastonia, NC 28053

Re: Environmental Monitoring Plan – Unit III
Gaston County Landfill – Hardin Site
Permit# 3606-MSWLF-1997
FID 1840037

Dear Mr. Ziehm:

The Division of Waste Management, Solid Waste Section (Section) has reviewed the Water Quality
Monitoring (FID 1837993) and Landfill Gas Monitoring (FID 1837994) Plans for the facility submitted by
Buxton Environmental, Inc. (Buxton) on behalf of Gaston County.

Water Quality Monitoring Plan
Existing monitoring well MW-1 will serve as the background well for Unit III. The remaining groundwater
monitoring network for Unit III will consist of recently installed downgradient monitoring wells MW-36,
MW-37S, MW-37D, MW-38S, MW-38D, MW-39, MW-40S, MW-40D, MW-41S, MW-41D, and MW-42.
These wells are primarily located on either side of the drainage swale downgradient of Unit III. Buxton
proposes to analyze samples from the newly installed wells for constituents listed in 40 CFR 258, Appendix
II plus 1,4-dioxane during the baseline monitoring period due to current Appendix II Assessment
monitoring at the adjacent closed MSWLF and Unit 1 Phases 1 & 2. The need to continue Appendix II
analysis will be determined at the conclusion of the baseline monitoring period. Groundwater samples
from the 11 monitoring wells will also be analyzed for PFAS constituents via EPA Method 1633 for at least
the first two consecutive monitoring events.

The monitoring network will also consist of two surface water monitoring locations (US-1 and DS-1). A
leachate sample (Leachate Unit III) will be collected from a gravity fed leachate sump located in the
southern corner of the site. Lastly, a French drain water sample (FD-III) will be collected from the
discharge pipe which daylights at the base of the toe-slope for Unit III. Surface water samples are
proposed to be analyzed for Appendix I constituents plus 1,4-dioxane. The Leachate Unit III sample will
also be analyzed for Appendix I constituents in addition to 1,4-dioxane, biologic oxygen demand, chemical
oxygen demand, sulfate, nitrate, and phosphate. The FD-III sample will be analyzed for constituents listed
in 40 CFR 258, Appendix II plus 1,4-dioxane during the baseline monitoring period. The need to continue
Appendix II analysis will be determined at the conclusion of the baseline monitoring period. Surface water

samples US-1 and DS-1 have already been analyzed for PFAS constituents, so Buxton proposes to analyze
Leachate Unit III and FD-III samples for PFAS constituents for at least two consecutive monitoring events.

Landfill Gas Monitoring Plan
The landfill gas monitoring network for Unit III will consist of existing monitoring well LFG-7 located
approximately 250 feet north of the Unit III northern waste boundary and newly installed wells LFG-8 and
LFG-9. The newly installed landfill gas monitoring wells are located approximately 50 feet southwest of
the Unit III southern waste boundary. Landfill gas monitoring will also be conducted at on-site structures
including the scale house, maintenance building, and bailing building. Landfill gas will be monitored on a
quarterly basis in accordance with guidelines established by the Section.

The Section approves the Water Quality and Landfill Gas Monitoring Plans as proposed. If you have any
questions or need further assistance, please contact me via email at [e-mail] or by phone
at [phone].

Sincerely,

Ervin Lane
Hydrogeologist
Solid Waste Section, Division of Waste Management
NCDEQ

Cc sent via email: Perry Sugg, P.G. – SWS Environmental Compliance Branch Head
Sherri Stanley – SWS Permitting Branch Head
John Nguyen – SWS Permitting Engineer
Allen Gaither, P.E. – SWS Permitting Engineer
Kim Sue – SWS Environmental Senior Specialist
Marcie Smith – Gaston County
Ross Klingman, P.G. – Buxton Environmental, Inc.
Emily Tucker, P.E. – HDR Engineering, Inc.