What is the holding time for NPDES whole effluent toxicity samples?
The holding time is thirty-six (36) hours. When twenty-four (24) hour composite samples are collected, the sample holding time starts at the time the compositing of the sample has been completed. In cases where NPDES permits require a series of four grab samples to be collected every six (6) hours over twenty-four (24) hours, the sample holding time starts at the time the last sample is collected.
