Proficiency Testing Requirements

Under the NC WW/GW LC Rule 15A NCAC 2H .0800, laboratories must demonstrate proficiency for all certified parameters (for which a proficiency testing sample is available) each year and the graded results must be received in this office by September 30. Proficiency Testing samples must be obtained from an accredited vendor as unknowns. If performance evaluation samples are not available for a parameter, certification for that parameter may be based on the proper use of the approved procedure as determined by an announced or unannounced on-site inspection.

North Carolina permittees will not be required to order Discharge Monitoring Report-Quality Assurance (DMR-QA) Study PT samples (see DMR-QA PT Study Exemption below). This exemption applies only to DMR-QA Proficiency Testing. All permittees must continue to provide environmental data pursuant to their permit on the monthly discharge monitoring reports. Permittees may order water pollution (WP) PT samples and must have the graded results reported directly to the NC WW/GW LC program. In addition, permittees will not be responsible for reporting data for their contract laboratories any longer. The contract laboratories will analyze PTs for all certified parameters and have data reported directly to the NC WW/GW LC program just as the permittees will do now.

Low-level Total Residual Chlorine PTs

The analysis of proficiency testing (PT) samples is designed to evaluate the entire process used to routinely report environmental analytical results. Therefore, PT samples must be analyzed in the same manner as environmental samples. For example, for colorimetric (i.e., DPD) procedures, Total Residual Chlorine (TRC) PT samples must be analyzed on the same spectrophotometric program (i.e., the sample wavelength) using the same procedure that is used for raw environmental sample analysis. There are two options for achieving this:

  1. If a regular level TRC PT sample is analyzed, it must be diluted to the verified range of the low level curve. The reported result must then be calculated using the dilution factor and the TRC value obtained.
  2. Since the dilution scheme in option 1 may introduce error, it is recommended that the low-level TRC PT sample be analyzed. These are currently available from many approved vendors. This sample should be within the range of your verified curve on the low-level program.

PT Study Requirements 

The following links describe proficiency testing requirements for field laboratories. The Proficiency Testing Requirements document serves as a guide to the PT sample requirements of the NC WW/GW LC program. In addition to clarifying the regulatory requirements for proficiency testing, this document answers many common questions concerning evaluation of PT sample results. Also included are important deadlines, penalties and corrective actions for proficiency testing sample failures. Highlighted changes and a condensed version can also be found in the links below.

Proficiency Testing Requirements Document (Revision 6.0) Effective January 2023

List of Parameters and PTs required for Field Laboratories (April 2022)

List of Parameters, Matrices and PTs Required **NEW for 2023 PT Calendar Year**

Field Proficiency Testing Checklist (September 2022)

Non-field Proficiency Testing Checklist (updated for 2023 changes)

Corrective Action Plan (CAP) example (2023) pdf format Word format

Corrective Action Report (CAR) example (2023) pdf format Word format

Proficiency Testing Providers 

The laboratory must obtain samples that are part of an official study obtained from a proficiency testing sample provider recognized by The NELAC Institute (TNI) and approved by the NC WW/GW LC program. A provider of PT samples must be accredited by a Proficiency Testing Provider Accreditor (PTPA) that meets the TNI requirements. A listing of organizations that are accredited to provide PT samples is available in the link below. Laboratories should check this list each time PT samples are ordered since the list changes periodically.

Link to current NC WW/GW LC and NELAC-approved  Accredited Vendors of PT Samples

EPA Lab Codes

Since different accreditation programs use a wide array of laboratory identification systems, the PT providers need a singular means of identifying participant labs when grading and reporting PT results. This singular system of identification is your EPA Lab Code. Each certified laboratory must have an EPA Lab Code and this code must be documented on the results to the proficiency testing provider. Without this EPA Lab Code, the NC WW/GW LC program may be unable to credit the PT results to the correct laboratory. The EPA Lab Codes are assigned by the US EPA. The EPA contact for Lab Code assignment for PT studies is:

Mr. Jeffrey Wilmoth ( Phone: 706-355-8623

U.S. EPA Region 4
980 College Station Road
Athens, GA  30605-2720

Please include the following information with your request for a new EPA Lab Code:

Contact name:
Laboratory or Facility Name:
Physical Address (with zip code):
PO address (if different):
Lab/Facility phone number:
Fax number (if available):
Contact individual’s e-mail address:
Type of Study (WP, WS, DMR-QA):


DMR-QA PT Study Exemption

In 2008, the NC WW/GW LC program appealed to the US EPA Clean Water Enforcement Branch, Water Protection Division for exemption from the National Pollution Discharge Elimination System (NPDES) DMR-QA PT program. After a thorough review of the NC WW/GW LC program, it was deemed that the NCDEQ [formerly NCDENR] proficiency testing program provides adequate quality assurance to replace EPA's DMR-QA PT study program. Therefore, all NC dischargers; classified as both Major and Minor, are exempt from the DMR-QA PT Study program as of May 13, 2009.  NC dischargers will no longer receive DMR-QA PT study reporting packages from EPA.

Click here to view the letter from EPA granting NC exemption from the EPA NPDES DMR-QA PT Study program.

For questions about Whole Effluent Toxicity (WET) DMR testing requirements, contact Ms. Cindy Moore at (919) 743-8442, NC Division of Water Resources, Water Sciences Section, Aquatic Toxicology Branch.

Chlorophyll a Round Robin Study

Currently there are no performance evaluation samples for chlorophyll a that can be carried through an entire method from extraction to instrumental analysis.  Consequently, laboratories currently certified for chlorophyll a will be required to participate in a round robin with other government, academic, and commercial laboratories pursuant to North Carolina Administrative Code 15A NCAC 2H .0805 (c) (3). The round robin studies are designed to provide a measure of laboratory performance in the absence of vendor-supported proficiency testing. The reports provide an illustration of intra-laboratory and inter-laboratory precision as well as a best estimate of the central tendency of data reported by laboratories currently engaged in chlorophyll a testing. Click here for a copy of the Chlorophyll a Round Robin Study Standard Operating Procedure (SOP).

Chlorophyll-a Round Robin Study Reports
2007 2011 2015 2019
2008 2012 2016 2020
2009 2013 2017 2021
2010 2014 2018 2022

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