4903_IredellMSW_ASDResponse_DIN28506_20171031

S t a t e o f N o r t h C a r o l i n a | E n v i r o n m e n t a l Q u a l i t y | W a s t e M a n a g e m e n t
1 6 4 6 M a i l S e r v i c e C e n t e r | 2 1 7 W e s t J o n e s S t r e e t | R a l e i g h , N C 2 7 6 9 9 -1646
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ROY COOPER
Governor
MICHAEL S. REGAN
Secretary

MICHAEL SCOTT
Director
October 31, 2017

Sent via email – [e-mail]
Mr. David Lambert, Director
Iredell County Solid Waste Department
354 Twin Oaks Road
Statesville, NC 28625

RE: Alternate Source Demonstration - Request for Additional Information
Iredell County Subtitle D MSW Landfill
Permit 4903-MSWLF-1993
Iredell County
DIN 28506

Dear Mr. Lambert:

The Solid Waste Section (Section) has completed a review of the July 26, 2017 Alternate Source
Demonstration-Total Metals (DIN 28361) for the referenced facility submitted on behalf of Iredell County
by Municipal Engineering Services Company (MESCO). The Alternate Source Demonstration (ASD)
addresses groundwater compliance exceedances of arsenic, beryllium, cadmium, chromium, cobalt, lead,
and vanadium above the Interim Maximum Allowable Concentration (IMAC) and/or 2L standards
established in 15A NCAC 02L .0202. Elevated metal concentrations have historically been detected and
reported in both pre-operation baseline samples and during Detection Monitoring since 1993 for the five
phases of landfill development.

The ASD submittal included an interwell background evaluation, an intrawell baseline evaluation, leachate
evaluation, and a dissolved versus totals metals evaluation. The ASD also proposes new site specific
groundwater protection standards using statistical analysis of historical groundwater monitoring data
from site background wells. The groundwater monitoring data for each of the seven inorganic
constituents referenced above were evaluated applying statistical methods in accordance with .1632(g)(3)
and USEPA Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities-Unified Guidance,
March 2009. Statistical methods used in this ASD included data transformation, distribution testing,
outlier screening, trend analysis, and seasonality testing.

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Based on our review of the ASD, the Section is requiring additional information to be submitted, in a
phased approach if applicable, as an ASD Addendum. The Section is requesting Iredell County to address
the following in the ASD Addendum:

• Review and provide turbidity data for groundwater monitoring data used to evaluate and
calculate the statistical background values for arsenic, beryllium, cadmium, chromium, cobalt,
lead, and vanadium. In calculating background levels, groundwater sample data with
documented or suspected turbidity (measured at greater than 10 NTUs) should be removed from
the dataset and calculations rerun. Background levels derived from turbid samples do not
accurately represent background conditions for constituents that are mobile in groundwater. For
samples with excessive turbidity, it is difficult to differentiate between sediment that represents
formational material versus mobile particulates or precipitates (May 13, 2013 Aquifer Protection
Section Memorandum, Subject: Aquifer Protection Section Policy for Metals Determinations
Required by Title 15A, NCAC, Subchapter 2L). Statistical background levels must be calculated
using monitoring data from a minimum of ten groundwater samples where the turbidity values
are less than 10 NTUs. If there is an insufficient number of previous background samples with
turbidity values less than 10 NTUs or no field notes to verify the turbidity values, Iredell County
must establish a temporary groundwater monitoring schedule to collect the required number of
non-turbid samples from the background well within a two-year period. Include the temporary
groundwater monitoring schedule in the ASD Addendum.

• Recalculate background values using only valid, non-turbid data from the four shallow background
wells. Based on the data presented in Table 4, it appears statistical background values for
inorganic constituents were calculated using combined data from all five facility background wells:
four screened within the surficial regolith aquifer (MW-1B, MW-1C, MW-17, and MW-37); and
one screened in the deeper bedrock aquifer (MW-1A). Only background data from the four
surficial wells should be used when calculating site background values to compare to
downgradient compliance wells also screened within the surficial aquifer.

Within 120 days of receipt of this letter, please submit an ASD Addendum that addresses Section
comments above and meets the criteria described in the guidance document titled NC Solid Waste Section
Guidelines for ASD Submittals for Solid Waste Management Facilities. Upon submittal of the requested
information, the Section will evaluate the ASD addendum and make a determination on the ASD request.
Be advised that additional information or analyses may be requested to fully evaluate and support an ASD
for the constituents of concern. Additional requirements consistent with the ASD Guidance may include,
but are not limited to, collection of valid background samples to establish site background levels, statistical
analyses, trend analyses, review of sampling procedures, or other means necessary to establish the landfill
has not contributed to groundwater standards exceedances.

Please note that if Iredell County decides not to submit an ASD Addendum within 120 days, the facility
will be required to initiate Assessment Monitoring in accordance with 15A NCAC 13B .1634.

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If you have any questions or concerns regarding this letter, please feel free to contact me by email at
[e-mail] or by phone at 919.707.8258. Thank you for your continued cooperation with
this matter.

Sincerely,

Perry Sugg, PG
Permitting Hydrogeologist
Solid Waste Section, Division of Waste Management
NCDEQ

Cc: Ellen Lorscheider, Solid Waste Section Chief, NC SWS
Jason Watkins, Field Operations Branch Supervisor, NC SWS
Ed Mussler, Permitting Branch Supervisor, NC SWS
Allen Gaither, Permitting Engineer, NC SWS
Ervin Lane, Compliance Hydrogeologist, NC SWS
Kim Sue, Environmental Senior Specialist, NC SWS
Jonathan Pfohl, Municipal Engineering Services Company