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DMR FAQs on Average Flow

NOTE: This guidance is to be used if the permit does not include site-specific requirements.

General Guidance

Calculations for 7-day, weekly, 30-day, or monthly average flows shall use only values collected during days of actual discharges divided by the days of actual discharge during a monitoring period.

Examples

  1. Seasonal facility opens for cleaning/startup activities on the 15th of the month and begins full operation 5 days later. Facility only discharges for 15 days out of the 30 day monitoring period. The facility's permit has a 30 day arithmetic mean flow limit, and is required to monitor flow 1/day with a sample type of "instantaneous". The facility should report its flow value as the combined flows for the 15 days divided by the 15 days of discharge.
  2. Same scenario as above except the facility uses a totalizer or water meter readings to monitor flow. The facility should report its flow value as the total flow for the 15 days divided by the 15 days of discharge.
  3. School or other type of facility that is in operation for only part of the week or monitoring period. Let's use a school for the example. School is in session for Monday through Friday, and has activities at the school on Saturday. The facility's permit has a 30-day arithmetic mean flow limit, and is required to monitor flow 1/day with a sample type of "instantaneous". The facility should report its flow value as the combined flows for the 6 days per week during the monitoring period and divide that total by the total days of actual discharge during the monitoring period.
  4. Same scenario as above except the school has a nine day vacation during the monitoring period. The facility should report its flow value as the combined flows only on the days it had a discharge, and divide that number by the total days of actual discharge during the monitoring period.
  5. Industrial facility that operates only 5 days a week and only has a discharge 5 days a week. The facility's permit has a 30-day arithmetic mean flow limit, and is required to monitor flow continuously with a sample type of "recorder". The facility should report its flow value as the combined flows for the 5 days per week during the monitoring period and divide that total by the total days of actual discharge during the monitoring period.
  6. Same scenario as above except the industrial facility has a lagoon system that discharges continuously. The facility would then combine flow values for all 30 days of the monitoring period and divide by 30.
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    Facility Operations Assistance Section
    625 Broadway, 4th Floor
    Albany, NY 12233-3506
    518-402-8177
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