What is the maximum infiltration/exfiltration limit expressed as a value per diameter inch of pipe per mile per 2 hours?

• A. 60 gallons per diameter inch of pipe per mile per 2 hours
• B. 50 gallons per diameter inch of pipe per mile per 2 hours
• C. 40 gallons per diameter inch of pipe per mile per 2 hours
• D. 30 gallons per diameter inch of pipe per mile per 2 hours

Answer: (B)

Infiltration/exfiltration in a sewer system is limited by a standardized cap that scales with pipe size and distance, measured as gallons per diameter inch of pipe per mile per 2 hours. This means for every inch of pipe diameter and every mile of sewer, only a certain amount of groundwater entering (infiltration) or wastewater leaving (exfiltration) is allowed in a 2-hour period. The commonly used maximum is 50 gallons per diameter inch per mile per 2 hours, so a mile of 8-inch pipe could have up to 400 gallons infiltrating in that 2-hour window (50 × 8). If infiltration exceeds this limit, it indicates excessive I/I sources to investigate. The other numbers simply represent lower or higher thresholds, but 50 is the standard maximum for this measure.