Start with the discharge permit, required pollutants, approved sampling point and reporting period, then agree on the sampling method with the control authority and qualified laboratory. Grab and composite samples serve different purposes. Record operating conditions and sample handling so the results represent the discharge being evaluated, rather than an unrelated drain or convenient time.
Which sampling method applies?
Federal pretreatment rule 40 CFR 403.12(g)(3) requires representative monitoring data. It specifies grab samples for pH, cyanide, total phenols, oil and grease, sulfide and volatile organic compounds. For other pollutants, the default is a 24-hour, flow-proportional composite unless the control authority authorizes an alternative. The rule also has specific conditions for compositing certain grab samples; do not assume every bottle can be mixed.
| Method | What the planning team must resolve |
|---|---|
| Grab | Required parameter, collection time and how many samples are needed |
| Flow-proportional composite | Sampling period, flow measurement and approved equipment setup |
| Authorized alternative | Written authority approval and why the data will be representative |
The number of samples can depend on the report and available historical data. Have the authority and laboratory confirm it rather than treating one bottle as a complete monitoring program.
Where and when should the sample be collected?
Identify the regulated stream and the approved sampling location. Establish whether pretreatment, other process flows or domestic wastewater enter before that point. A grease-interceptor sampling port is an access feature; its presence does not establish the industrial sample's required location or method.
Record production, cleaning cycles, discharge timing and any unusual condition during collection. If operations have changed, use the advance discharge-change notice before assuming the old plan remains suitable. Phoenix's industrial program reviews regulated processes and local discharge requirements; its permit guidance identifies the appropriate city program for permit questions.
What should accompany the laboratory result?
Ask the qualified laboratory to establish containers, preservation, holding times, analytical methods and custody documentation for the actual pollutants. These details are not interchangeable between tests. Keep the location, collection times, collector, operating notes and laboratory report together in the monitoring file.
Compare results with the applicable limit and averaging basis. If a result indicates a violation, follow the notification and repeat-sampling workflow. A plumbing repair invoice or a clear-looking sample does not establish discharge compliance.