7803_Robeson_SubtitleDMSWLF_LeachateReleaseResponse_DIN28589_20171031

October 31, 2017

Sent Via Email – [e-mail]
Mr. Gene Walters
Robeson County Interim Solid Waste Director
246 Landfill Road
St. Pauls, NC 28384

Re: Leachate Release Assessment Report Response
Robeson County Subtitle D MSW Landfill
Solid Waste Permit Number 7803-MSWLF-1997
Robeson County
DIN 28589

Dear Mr. Walters:

The NC Department of Environmental Quality, Solid Waste Section has completed a review of the
Leachate Release Assessment Report dated October 9, 2017 (DIN 28588) and submitted on behalf of
Robeson County by Joyce Engineering for the Robeson County Subtitle D MSW Landfill, Solid Waste Permit
Number 7803-MSWLF-1997. The report was submitted in response to the approved Sampling Plan for
Leachate Release Assessment dated July 28, 2017 (DINs 28359 and 28360) as a result of the leachate
release near Phase II of the landfill in July 2017. The closed and unlined Phase I area consisting of a C&D
landfill on top of a MSW landfill is currently implementing groundwater corrective action.

Soil sampling, surface water sampling, and groundwater sampling were conducted on August 14th and 15th,
2017 to evaluate the extent of the potential environmental impacts from the release. All samples were
analyzed for Appendix I of 40 CFR Part 258 constituents (volatile organic compounds and metals).

The analytical soil results indicated no volatile organic compounds exceeded the Preliminary Soil
Remediation Goals (PSRGs). However, arsenic, barium, beryllium, chromium, copper, lead, mercury,
nickel, vanadium, and zinc were detected above the laboratory’s reporting limit. In addition, arsenic,
cobalt, and vanadium were detected above their Preliminary Soil Remediation Goals (PSRGs) for the
Protection of Groundwater and the Residential Health Based Goals.

The analytical surface water results indicated detections of barium and zinc below the 2B NC regulatory
surface water standards.

Groundwater samples from MW-17R (adjacent to Phase II) and SB-1 (a temporary well) were collected
close to the location of the leachate release. The analytical results indicated that arsenic, cobalt,
chromium, lead, and vanadium exceeded the NC regulatory groundwater standards (2L and IMAC).
However, during the most recent May 2017 routine semiannual water quality monitoring event, only
cobalt exceeded the NC regulatory groundwater standard (IMAC).

Also, the analytical groundwater results indicated that the volatile organic compounds ethylbenzene,
toluene, and xylenes were detected in the groundwater samples but below the NC regulatory
groundwater standards (2L and IMAC). These volatile organic compounds were not detected during the
most recent May 2017 routine semiannual water quality monitoring event in monitoring well MW-17R.
However, they are detected in the landfill’s leachate.

During the November 2016 monitoring event, MW-17R associated with Phase II showed an exceedance
of the NC regulatory groundwater standard for the volatile organic compound tetrachloroethene (PCE).
The volatile organic compound benzene exceeded the NC regulatory groundwater standard in monitoring
well MW-16, also associated with Phase II, during the following monitoring events: September 2012,
October 2013, October 2014, and November 2016.

In the County’s Leachate Release Assessment Report, the County is recommending to continue monitoring
well MW-17R for only the Appendix I metals for the next four quarters. If there is no significate increase
from the historical mean during those four quarters, the sampling will return to its regular sampling
schedule and constituents.

Based upon the soil, surface water, and groundwater assessment conducted in response to the leachate
release and based upon the routine semiannual monitoring results for the Phase II area since 2012,
additional assessment is required at this time.

Within 90 days of receipt of this letter, in accordance with 15A NCAC 13B .1633(c)(3) and 15A NCAC
13B .1634, Robeson County is required to initiate an Assessment Monitoring Program for Phase II of this
landfill. In addition, Robeson County will be required to address the metal exceedances within the soils
based upon the County’s Leachate Release Assessment Report.

If you have any questions or concerns regarding this letter, please feel free to contact us by email at
[e-mail] or by phone at 828.296.4706 or [e-mail] or by
phone at 919.707.8253. Thank you for your anticipated cooperation with these matters.

Sincerely,
Jaclynne Drummond Elizabeth Werner
Compliance Hydrogeologist Permitting Hydrogeologist
Solid Waste Section Solid Waste Section
Division of Waste Management Division of Waste Management
NCDEQ NCDEQ

cc sent via email: Jason Watkins, Field Operations Branch Head
Ed Mussler, Permitting Branch Head
Drew Hammonds, Eastern District Supervisor
Amanda Freeman, Environmental Senior Specialist
Ethan Caldwell, Permitting Engineer
Van Burbach, Joyce Engineering
Miguel Vazquez, Joyce Engineering