6002_Mecklenburg_HolbrooksRoad_MSWLF_LFGRequest_FID1642325_20220210

DocuSign Envelope ID: 583574A6-BD37-4391-8AB1-28B6468B9018
SMITH GARDNER
ADDRESS TEL WEB
14 N. Boylan Avenue, Raleigh NC 27603 919.828.0577 www.smithgardnerinc.con
February 9, 2022
Ms. Jaclynne Drummond
Hydrogeologist
NC Department of Environmental Quality
Asheville Regional Office
2090 U.S. Hwy 70
Swannanoa, NC 28778-8211
RE: Landfill Gas Monitoring Probe Modification/Evaluation — HP-9
Closed Holbrooks Road Landfill (Permit 60-02)
Huntersville, North Carolina
Dear Ms. Drummond:
On behalf of Mecklenburg County, Smith Gardner, Inc. (S+G) is requesting a modification of
landfill gas (LFG) monitoring probe HP-9 at the closed Holbrooks Road Landfill. The
proposed modification will assist in further evaluation of landfill gas migration at the site. A
summary of the modification is provided below.
Background
The Holbrooks Road Landfill is located in Huntersville, North Carolina. This facility is a
closed unlined "trench fill" landfill that operated between 1968 and 1986. In accordance with
the Landfill Gas Monitoring Plan', the site has 19 LFG monitoring probes and nine (9) LFG
vents. These monitoring locations are shown on the attached Figure 1.
In 2018 a Corrective Action Plan' was submitted and approved by the NCDEQ. This plan
included the installation of four (4) vertical LFG extraction wells with a flare skid,
approximately 250 feet of vent trench located along the southern edge of waste, and a
passive flare.
Proposed Modification
LFG probe HP-9 is located south/southeast of LFG well LFG-4. LFG-4 is connected to the
vent trench that was installed just outside the edge of waste. Ongoing landfill gas monitoring
at the facility indicates landfill gas (LFG) probe HP-9 continues to exhibit intermittent
concentrations of methane that exceed the lower explosive limit.
Due to the silty soils at the site, as well as the age of the waste, it is possible HP-9 is located
in an area of relict LFG that migrated over time and is beyond the effective radius of the vent
trench. To further evaluate whether the LFG concentrations in HP-9 are from relict LFG
migration or current migration, we request permission to modify this well as a passive vent.
A figure showing the proposed design is attached as Figure 2. This modification would
include a monitoring point and a valve to close off the vent for monthly LFG readings which
will allow further evaluation of LFG in this area.
Landfill Gas Monitoring Plan, Smith Gardner, Inc. June 2017
2 Corrective Action Plan Closed Holbrooks Road Landfill, Smith Gardner, Inc., November 2018

DocuSign Envelope ID: 583574A6-BD37-4391-8AB1-28B6468B9018
Ms. Drummond
February 9, 2022
Page 2of2
Mecklenburg County is prepared to modify this well upon approval. If you have any
questions, or require any additional information, please contact us at the email addresses
below. Thank you for your consideration of this modification.
Sincerely,
SMITH GARDNER, INC.
EsDocuSigned by:
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Spencer Hollomon, P.E.
Project Engineer
DocuSigned by: 21101
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Joan A. Smyth, P.G.
Senior Hydrogeologist
spencerlasmithgardnerinc.com [e-mail]
CC: Amber Grzymski, P.G. - Mecklenburg County
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REFERENCES
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1. TOPOGRAPHY FROM NCDOT GIS DEPARTMENT, BASED ON LIDAR DATA
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PROVIDED BY THE NC FLOOD MAPPING PROGRAM. TOPOGRAPHY IN
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ACTIVE AREAS FROM AERIAL SURVEY DATED FEBRUARY 27, 2018.
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2. PARCEL BOUNDARIES, STRUCTURE LOCATIONS, MONITORING WELLS,
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AND STREAM CENTERLINES FROM MECKLENBURG GIS DEPARTMENT.
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