NC0081621_Split Samples Tox_20210901

DocuSign Envelope ID: 4D150FBB-020D-4D7A-8973-3E4BCB2E1E85
Division of Water Resources
August 11, 2021
MEMORANDUM
To: Corey Basinger
Water Quality Regional Operations, MRO
ADS
Through: Cindy A. Moor CM
Supervisor, Aquatic ToAcology Branch (ATB)
From: Lorimar S. Henning L,k
Environmental Specialist II, Aquatic Toxicology Branch (ATB)
Subject: Whole effluent toxicity test results
Muddy Creek WWTP
NPDES Permit # NC0081621/001
Cabarrus County
The aquatic toxicity test using flow -proportional composite samples of effluent discharged from
the Muddy Creek WWTP has been completed. Muddy Creek WWTP has a permitted effluent
discharge of 0.3 million gallons per day (MGD) entering Rocky River. Whole effluent samples
were collected on July 13 and July 15 by Roberto Scheller for use in a chronic Ceriodaphnia dubia
pass -fail toxicity test. The test passed. Toxicity test information follows.
Test Type 3-Brood Ceriodaphnia dubia chronic pass -fail
Test Result Pass
Test Concentrations 0.6%
Control Survival 100%
Control Mean Reproduction 21.5 neonates
Test Treatment Survival 100%
Treatment Mean Reproduction 21.1 neonates
First Sample pH 6.72 SU
First Sample Conductivity 721 micromhos/cm
First Sample Total Residual Chlorine <0.2 mg/L
Second Sample pH 6.57 SU
Second Sample Conductivity 715 micromhos/cm
Second Sample Total Residual Chlorine <0.2 mg/L
Test results for the above samples indicate that the effluent would not be predicted to have
water quality impacts. These samples were split and tested by Meritech, Inc. and Environmental
Testing Solutions, Inc. (ETS) labs. The test performed by ETS was invalidated due hold time
exceedances of the second sample. The test performed by Meritech, Inc. was completed;
however, after comparing the tests between the ATB and Meritech lab test, we noted that
Meritech performed the test at a concentration of 1.2% in comparison to ATB's test at 0.6%.
After investigating, we realized there was a modification to the facility permit changing the
chronic limit to 1.2%, effective on June 1, 2021; thus, making this a non -split test. ATB will count
this as a split for the EPA 106 Grant tally. The chronic Ceriodaphnia dubia pass/fail test run by
Meritech, Inc. resulted in a pass. Please contact us if you have any questions or if further
effluent toxicity monitoring is desired. We may be reached at [e-mail] and
[e-mail].