2601_CumberlandCoMSW_MetalsASDResp_DIN28120_20170721

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July 21, 2017

Sent Via Email – [e-mail]

Mr. Jeffry Brown
Cumberland County
130 Gillespie Street
Fayetteville, NC 28301

Re: Appendix I Inorganic Constituent Exceedances
Cumberland County Landfill
Solid Waste Permit Number 2601-MSWLF-1997
DIN 28120

Dear Mr. Brown:

The Solid Waste Section (Section) has completed a review of the Alternate Source Demonstration (DIN
27005) submitted on behalf of Cumberland County by CDM Smith (CDM) for the Cumberland County
Landfill, Solid Waste Permit Number 2601. The report was submitted in response to correspondence from
the Section titled Appendix I Inorganic Constituent Exceedances dated August 8, 2016 (DIN 26548) and in
accordance with 15A NCAC 13B .1633.

The monitoring network consists of one background well (MW-E) and compliance wells MW-F, MW-I, and
MW-J. CDM conducted a statistical analysis to determine if the contaminants of concern were reported
at statistically significant concentrations related to background sample concentrations. The results of the
statistical analysis indicated that arsenic in MW-F and MW-J was present at statically significant
concentrations. Additionally, cobalt was also reported at statistically significant concentrations in MW-I
and MW-J. CDM conducted further data evaluation and determined that the maximum and average
reported concentrations for arsenic and cobalt in the downgradient wells were equal to or less than the
maximum and average concentration in the background well. Dissolved groundwater samples were also
collected to determine if turbidity impacted groundwater analytical results. Suspended sediment seems
to impact groundwater monitoring results since metals concentrations in the dissolved samples were less
than the total metals concentrations.

Based on the results of the ASD, it appears that the metals reported in groundwater samples are naturally
occurring and turbidity may also impact analytical results. Cumberland County should determine if
modification to sample collection methodology and/or establishing a monitoring well re-development
schedule is necessary to reduce the impact of suspended sediment. Statistical background concentrations
should be calculated for the constituents of concern, arsenic, beryllium, chromium, cobalt, lead, thallium,
and vanadium in accordance with 15A NCAC 13B .1634 (g)(5) to determine if any future elevated
concentrations are a result of landfill impact.

Since it appears that turbidity has impacted groundwater analytical results, statistical background
concentrations should not be calculated using previous monitoring data unless field notes indicate that
turbidity values were less than 10 Nephelometric Turbidity Units (NTUs). Statistical background
concentrations derived from turbid samples may not accurately reflect background conditions, so
Cumberland County should calculate statistical background concentrations using analytical data from a
minimum of ten groundwater samples with turbidity values 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, Cumberland County should establish a temporary groundwater monitoring schedule
to collect 10 or fewer non-turbid samples from the background well within a two-year period. If a
temporary monitoring schedule is necessary, Cumberland County should submit the schedule to the
Section within 90 days of receiving this letter. Turbidity values should be recorded and submitted to the
Section during the temporary monitoring period. If Cumberland County declines to calculate statistical
background concentrations, additional assessment activities may be necessary.

Additional guidelines for calculating statistical background concentrations are listed below:
 If utilizing Upper Tolerance Limits, determine the new groundwater protection standards for the
metals of concern by the distribution hierarchy normal, gamma, lognormal, and nonparametric;
 Identify the outliers. Screen the data sets visually for potential outliers using the box-and-whisker
and Q-Q plots. Then screen the data sets quantitively using Dixon’s or Rosner’s Outlier tests as
specifically identified within the USEPA March 2009 Unified Guidance. If statistical outliers have
been detected, review the values to determine if they should be removed from the data set or
are representative of background and should be retained for statistical analysis. Provide technical
reasons why a statistical outlier should be included or excluded from either groundwater
background data sets;

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 919.707.8288. Thank you for your continued cooperation with this
matter.

Sincerely,

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

cc sent via email: Ellen Lorscheider, Solid Waste Section Chief
Jason Watkins, Field Operations Branch Head
Drew Hammonds, Eastern District Supervisor
Amanda Freeman, Environmental Senior Specialist
Ed Mussler, P.E., Permitting Branch Head
Elizabeth Werner, Permitting Hydrogeologist
Donna Wilson, Permitting Engineer
Aaron M. Weispfenning, P.E., CDM Smith