Type of Sample

There are two basic types of samples: grab samples and composite samples. The type of sampling that will be undertaken at the industrial user must be understood clearly and should be outlined in the facility’s Sampling and Quality Assurance Plan. It is very important that the facility establish specific procedures for collecting grab and/or composite samples. According to 40 CFR 403.12(g)(3), grab samples must be used for pH, cyanide, total phenols, oil and grease, sulfides, and volatile organic compounds. For all other pollutants, 24‐hour composite samples must be obtained through flow‐proportional composite sampling techniques unless time‐proportional composite sampling or grab sampling is specified in the protocol. Where time‐proportional composite sampling or grab sampling is recommended in the protocol, the samples must be representative of the discharge and the decision to allow the alternative sampling must be documented in the file for that facility or in any control mechanism.

The correct sample type for each regulated parameter must be included in the industrial user’s permit or control mechanism and for compliance determination purposes the inspector must collect the specified type of sample. Any problems noted with the type of sample specified in the industrial user’s permit or the control mechanism should be documented. If necessary, the permit or other control mechanism may need to be revised or amended.