5103_JohnsonCoMSW_ASDResp_DIN28357_20170807

August 7, 2017

Sent Via Email – [e-mail]

Mr. Rick Proctor
Johnston County
680 County Home Road
Smithfield, NC 27577

Re: Appendix I Inorganic Constituent Exceedances
Johnston County Landfill
Solid Waste Permit Number 5103-MSWLF-
DIN 28357

Dear Mr. Proctor:

The Solid Waste Section (Section) has completed a review of the Inorganic Constituent Alternate Source
Demonstration Report (DIN 28356) submitted on behalf of Johnston County by Smith Gardner, Inc. (Smith
Gardner) for the Johnston County Landfill, Solid Waste Permit Number 5103. The report was submitted
in response to correspondence from the Section titled Appendix I Inorganic Constituent Exceedances
dated August 8, 2016 (DIN 26567) and in accordance with 15A NCAC 13B .1633.

The alternate source demonstration identified the inorganic constituents of concern to be antimony,
arsenic, chromium, cobalt, lead, and vanadium. Smith Gardner compared turbidity measurements to
laboratory analytical results and observed that samples with high turbidity measurements yielded
sampling results with elevated metals concentrations. Filtered sample analysis was conducted during the
November 2016 groundwater monitoring event to further evaluate the influence of suspended solids on
laboratory analytical results. Most of the constituent concentrations were reported at lower
concentrations in the filtered samples compared to the samples analyzed for total metals. The antimony
concentration in MW-15D was the only constituent reported at a higher concentration in the filtered
sample. In addition, antimony and cobalt were the only constituents reported at concentrations above
the 2L standard in dissolved samples. Smith Gardner also presented data from the National Uranium
Resource Evaluation database which indicated the presence of arsenic, chromium, cobalt, lead, and
vanadium in local stream sediment.

Based on the results of the ASD, it appears that the metals reported in groundwater samples may be
naturally occurring in the landfill vicinity. Due to elevated turbidity measurements, additional information
is needed to determine if the reported concentrations are a result of natural occurrence or landfill impact.
Statistical background concentrations should be calculated for the constituents of concern: antimony,
arsenic, chromium, cobalt, lead, and vanadium in accordance with 15A NCAC 13B .1634 (g)(5) to
determine if future constituent concentrations are a result of landfill impact. Johnston County should also

determine if a modification to sample collection methodology and/or establishing a monitoring well re-
development schedule is necessary to reduce the impact of suspended sediment.

Since 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, therefore, Johnston County should calculate
statistical background concentrations using analytical data from a minimum of ten (10) 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, Johnston
County should establish a temporary groundwater monitoring schedule to collect the required number of
non-turbid samples from the background well within a two-year period. If a temporary monitoring
schedule is necessary, Johnston 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 Johnston County declines to calculate statistical background
concentrations, additional assessment activities may be necessary.

Guidelines for calculating statistical background concentrations are listed below:
 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 the groundwater background data sets.
 If utilizing Upper Tolerance Limits to establish new background levels for the constituents of
concern, calculations should follow the distribution hierarchy preference.

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
Liz Patterson, Environmental Senior Specialist
Ed Mussler, P.E., Permitting Branch Head
Christine Ritter, Permitting Hydrogeologist
Madeline German, P.G., Smith Gardner, Inc.