NC0026051_WET Split Test Letter_20210608

June 8, 2021

Amy Moore
Durham Co. Triangle WWTP
5926 Highway 55 East
Durham, NC 27713

Subject: May 12, 2021 Toxicity Test
Durham Co. Triangle WWTP
NPDES No. NC0026051/001
Durham County

Dear Ms. Moore,

Thank you for submitting the supporting information requested for the May 12th, 2021
effluent toxicity test for Durham Co. Triangle WWTP. All relevant information has been
reviewed by the Aquatic Toxicology Branch (ATB) staff. Please see the details of our
analysis below.

Composite samples (~24hrs) from Durham Co. Triangle WWTP’s effluent were collected on
May 11, 2021 and May 13, 2021 for toxicity testing. The composite samples were collected
to perform the self-monitoring NPDES compliance requirement for the facility. Durham Co.
Triangle WWTP practice is to perform a split test between two commercial labs every
quarter as part of their QA/QC protocol. The composite samples were split between the
containers of the contract labs and transported/shipped to the commercial labs,
Environmental Testing Solutions, Inc. (ETS) and Meritech, Inc (Meritech) for toxicity
testing. The tests performed at each lab lead to disagreeing results, in where ETS’s test
resulted in a pass, and Meritech’s test resulted in a fail.

To investigate the disagreeing split results obtained from the two tests, documentation
concerning sampling, testing, and lab procedures were examined. There were no
irregularities noted between the chain-of-custody forms submitted. All quality assurance
documentation from both labs was in order. The conductivity values for the second
effluent sample measured in both labs showed a percent difference of 14.7%, however, this
difference is not large enough to be a problem.

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The ATB staff members (Zach Thomas, Lorimar Henning and myself) met with you and
your facility’s sample collector, Kelley van de Kamp via a Teams meeting on June 3, 2021 to
discuss sample collection in order to identify potential causes of the split test discrepancy.
During this meeting, Ms. van de Kamp described the process used to collect the samples for
each of the labs. Ms. van de Kamp described that a cleaned 20L plastic carboy is used for
toxicity samples collection and that the container is used solely for this purpose. Ms. van de
Kamp indicated that after collection the 20L carboy is hand mixed and a subsample is
poured into a smaller container that is more manageable to fill the toxicity sample bottles.
Then after the sample is in a smaller container, then the sample is well mix, rinsing the
toxicity bottles and then filling each bottle one quarter each time as recommended by the
NC DWR. Ms. van de Kamp also described the process of handling the samples after
collection. ETS sample was shipped via FedEx, while Meritech’s sample was placed in a
refrigerator until picked up by Meritech’s driver that afternoon.

During our meeting, ATB recommended that Durham Co. Triangle WWTP rinses all carboys
and bottles three times with the effluent before pouring the effluent sample.

After our meeting, ATB reached out to Meritech to obtain their QA/QC documentation (ETS
already provided this in their package) and everything falls within their acceptable ranges.
Their observations noted that the organisms in the effluent sample were pale as compared
to the control indicating that an effect in their organisms was observed. Their test met the
Control Acceptability Criteria as stated in the NC Ceriodaphnia Chronic Whole Effluent
Toxicity Procedure (https://deq.nc.gov/about/divisions/water-resources/water-
resources-data/water-sciences-home-page/aquatic-toxicology-branch/downloads#pro)
and is a valid test.

Unfortunately, at this time, we cannot pinpoint the specific reason for this disagreeing
result. Both labs have successfully pass the recent Performance Evaluation Test we
performed on February 2021, and have successfully passed our audit. Based on the
information described above, the results of each of the labs will remain as reported.
However, ATB will accept the Pass result from the ETS test for the May 2021 NPDES
compliance requirement for Durham Co. Triangle WWTP. Please let us know if you have
any questions, or need further assistance.

Sincerely,

Cindy A. Moore, Supervisor
Aquatic Toxicology Branch

Ec: Jim Sumner, Environmental Testing Solutions, Inc.
Mike Reed, Meritech, Inc.

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