What considerations are necessary when switching from time based to flow paced sampling?
Time based vs. Flow paced sampling
Review NPDES permit for requirements, and consider the following:
- Total volume of sample(s) needed to complete the analytical testing for the NPDES permit
- Discrete samples (multiple bottles) or Composite (combined into one container)?
- Bottle volume
- Time period in which samples are to be collected (example: 24 hours)
- Average/minimum number of samples in the collection time period
- Volume of sample needed for each sample event based on average/minimum flow to achieve the minimum sample volume necessary to complete the required analytical testing
- Make sure collection bottle volume is sufficient to accommodate more volume than the minimum required to complete the analytical testing
- Proper accessories for the sampler to accommodate the flow signal from the flow meter (examples: 4-20 mA output, 15 volt pulse, or contact closure)