An SIU can be identified by having a flow of ___ gallons or more, or a flow that equals or exceeds ___ % of the POTW average daily flow, or contributes an amount of organic loading that equals or exceeds ___% of the POTW's average daily organic load.

• A. 25,000 / 5% / 5%
• B. 10,000 / 1% / 1%
• C. 50,000 / 10% / 10%
• D. 5,000 / 2% / 2%

Answer: (A)

Significant influence on a POTW comes from identifying a user that either discharges a large amount of wastewater, or contributes enough flow or organic load to affect the plant’s operation. An SIU is defined as a facility that either discharges 25,000 gallons per day or more of process wastewater, or has flow equal to or exceeding 5% of the POTW’s average daily flow, or contributes organic loading equal to or exceeding 5% of the POTW’s average daily organic load. The set of numbers 25,000 gallons, 5%, and 5% matches these criteria exactly, so it’s the correct choice. The 25,000-gallon threshold catches large contributors, while the 5% thresholds ensure that a facility can still trigger SIU status if its impact is substantial relative to the plant, even if its total volume isn’t enormous. The other options use lower volumes or different percentages, which would not align with how SIUs are defined in pretreatment programs.