The information posted to this page is meant to assist laboratories in reporting data to DHEC. But keep in mind that the ultimate authority for what is acceptable and what is not acceptable resides with the DHEC program area receiving and reviewing the data. Should information contained within this site differ from permit requirements or specific instructions provided by the program area to laboratories or clients, the program area's directions take precedence over the information found on this site.
Practical Quantitation Limits (PQLs)
DHEC has come up with a list of Practical Quantitation Limits (PQLs) to be used for NPDES reporting. This comes from Regulation 61-68. The PQL is defined as "the concentration at which the entire analytical system must give a recognizable signal and acceptable calibration point. It is the concentration in a sample that is equivalent to concentration of the lowest calibration standard analyzed by a specific analytical procedure, assuming that all the method-specific sample weights, volumes, and processing steps have been followed." In other words, the PQL is equal to the lowest non-zero standard on your calibration curve.
DHEC has come up with standard PQLs that every laboratory reporting compliance data is expected to achieve. If the laboratory meets the PQL as defined by DHEC and the sample has a concentration below that PQL, then the facility may report zero as the result on the DMR form.
Please see the following examples:
- " Reasonable potential exists ": If the permit limit is 1mg/L and the DHEC PQL is 0.5mg/L and the sample result is <2mg/L, the facility is out of compliance because it cannot be determined that the sample is below 1mg/L. A zero cannot be reported on the DMR because the laboratory's PQL is 2 which is higher than 1.
- " Complies with permit ": If the permit limit is 1mg/L and the DHEC PQL is 2mg/L and the sample result is <2mg/L, the facility may report zero on the DMR because the laboratory's PQL is equal to the DHEC PQL of 2mg/L. The comments section of the DMR must indicate that a PQL of 2mg/L was used in order to report the zero.
- " Out of Compliance with Permit ": If the permit limit is 0.011mg/L and the DHEC PQL is 0.05mg/L and the laboratory reports 0.02mg/L, the facility is out of compliance because the laboratory reported a number greater than the permit limit which means the laboratory PQL is lower than the DHEC PQL. This means that the laboratory can accurately detect a sample concentration of 0.02mg/L which documents that the facility sample has exceeded the 0.011mg/L permit limit. Because of this, it is always best to use DHEC PQLs when the laboratory reports data to the facilities.
What is the facility's responsibility?
Make sure that you use a certified laboratory that can meet the published PQLs. There are many certified laboratories and they may use different equipment which would allow some to meet the PQL and others not. Make sure that the DMR form is completed properly with the certified lab ID number beside each analysis performed by the contract lab. Make sure that the correct number is reported as the result on the DMR form.