7904_RockinghamCountyMSWLF_VOCASDResp_DIN27583_20170404

April 4, 2017

Sent Via Email – [e-mail]

Kathryn Jolly
Environmental Compliance Solid Waste Program Manager
P.O. Box 132
Wentworth, NC 27375

Re: Alternate Source Demonstration Addendum: Volatile Organic Compounds
Rockingham County, Rockingham County Landfill, Permit #7904
DIN 27583

Dear Ms. Jolly:

The Solid Waste Section (Section) has completed a review of the Alternate Source Demonstration
Addendum: Volatile Organic Compounds (DIN 27542) submitted on behalf of Rockingham County by
Joyce Engineering (Joyce). The addendum was submitted in response to detections of volatile organic
compounds (VOCs) above the standards established in 15A NCAC 02L .0202 (2L Standards) during the
March 2016 monitoring event, May 2016 confirmation sampling event, and the December 2016 monitoring
event.

Benzene and 1,2-dichloroethane (1,2-DCA) were initially detected in MW-19 during the October 2011
monitoring event and vinyl chloride was detected during the April 2012 event. Based on field observations,
Joyce thought the integrity of MW-19’s construction was compromised due to significant erosion around
the well, so MW-19R was installed as a replacement well prior to the October 2012 monitoring event. Joyce
submitted an alternate source demonstration (ASD) in April 2012 and an ASD addendum in February 2013.
Joyce concluded that the source of the VOCs stemmed from an isolated random release as opposed to an
ongoing release of leachate from the landfill since there was a sharp decline in VOC concentrations
following the initial detection. The Section decided to continue observing the monitoring results for two
additional monitoring events before issuing a decision on the ASD addendum. VOCs were only reported
above the 2L standards during two of the six monitoring events following the ASD addendum and prior to
the most recent exceedances beginning with the March 2016 monitoring event.

Joyce began investigative activities on September 26, 2016 by excavating the area where an outfall
sampling location (SMP-5) was inadvertently buried. The SMP-5 sample location is situated at the end of
the underdrain from Phase 3 and is also near MW -19 and MW-19R. Joyce sampled the outfall and collected
soil samples in its vicinity on September 27, 2016. SMP-5 sampling results indicated the presence of
benzene, vinyl chloride, and 1,2-DCA. VOCs were not reported above laboratory detection limits in the
soil samples. Joyce also compared the monitoring results for MW-19, MW-19R, and SMP-5 to the
historical leachate monitoring data and concluded that leachate could not be the cause of groundwater
impact since 1,2-DCA, benzene, and vinyl chloride have not been detected in leachate.

Joyce also investigated the potential for landfill gas to impact groundwater quality at the facility in the
vicinity of the Phase 3 underdrain. Joyce surmised that landfill gas was entering the 6 inch slotted HDPE
underdrain pipe and partitioning into the water present within the pipe. According to Joyce, the impacted
water was flowing through the underdrain and discharging near MW-19 likely causing the VOC detections.
Landfill gas odors were noticeable near the outfall of the underdrain so Joyce monitored the outlet for
methane and placed caps on MW-19, MW-19R, and MW-20 to monitor headspace. The maximum percent
volume concentration of methane measured at each location was 2.9 at the drain outlet, 4.8 at MW-19, and
0.1 at MW-19R. During the October 26, 2016 semiannual monitoring event, MW-19, MW-19R, and SMP-
5 groundwater samples were also analyzed for dissolved methane, dissolved ethane, and dissolved ethene.
Dissolved methane was reported at elevated concentrations of 562 ug/l in MW-19, 1240 ug/l in MW-19R,
and 1340 ug/l in SMP-5. Dissolved ethane and dissolved ethene were not reported above laboratory
detection limits in the samples. Based on the comparison of groundwater sample results with leachate
sample results and the field investigation, Joyce concluded that landfill gas instead of landfill leachate is
the source of the VOC contamination. Joyce proposes to install a concrete sump to collect discharge from
the SMP-5 outfall for laboratory analysis to determine impact. Impacted water will be pumped out and
placed in the leachate pond. Gas vents that will later be converted to extraction wells after landfill closure
are also proposed to be installed in the landfill to reduce the flow of landfill gas along the underdrain.

Based on the evidence presented by Joyce in the addendum, it appears that landfill gas may be impacting
groundwater in the vicinity of MW-19 and MW-19R. Rockingham County should proceed with the
concrete sump installation and landfill gas vent construction as outlined in the addendum. Engineered plans
and specifications related to the concrete sump and any gas vents installed within the waste mass should be
submitted to Larry Frost, SWS Engineering Project Manager, for review and approval prior to construction.
However, a successful alternate source demonstration must identify a ground water contaminant source
other than the landfill. While Joyce has provided evidence demonstrating the possibility of landfill gas
impacting groundwater quality, landfill gas is being generated by the waste mass within the landfill. Since
the groundwater contaminant source is still derived from the landfill, most likely in the form of landfill gas,
Rockingham County is required to initiate assessment monitoring. Rockingham County should begin
implementing assessment monitoring in accordance with 15A NCAC 13B .1634 during the next semiannual
groundwater monitoring event. A proposed schedule for the concrete sump construction and landfill gas
vent installation should be submitted to the Section within 30 days of receiving this letter. Please contact
me at [phone] or by e-mail at [e-mail] if you have any questions or concerns
regarding this letter. Thank you in advance for your anticipated cooperation with this matter.

Sincerely,

Ervin Lane
Compliance Hydrogeologist
Solid Waste Section

cc sent via email: Alex Everhart., Joyce Engineering
Jason Watkins, Field Operations Branch Head
Deb Aja, Western District Supervisor
Susan Heim, Environmental Senior Specialist
Ed Mussler, P.E., Permitting Branch Head
Larry Frost, Engineering Project Manager
Christine Ritter, Permitting Hydrogeologist