Related Experiment Video
Updated: Jun 5, 2026

Watershed Planning within a Quantitative Scenario Analysis Framework
Published on: July 24, 2016
Using risk analysis to predict design flow exceedance of decentralized wastewater management systems
Patrick A Dobbs1, Chris D Cox, John S Tyner
1AMEC Earth & Environmental, Nashville, Tennessee, USA.
Abstract:
In small communities, the number of residential units is a more stable indicator of wastewater volume than population. Large communities benefit from averaging because the likelihood of having concurrent large flows from all users is small. In contrast, a single septic system connected to a single residence must be designed to accommodate large flow variations. The objective of this study was to determine the risk of assigning various daily wastewater volumes to residential units. Risk was based on the probability of underestimating daily volume and, therefore, exceeding the capacity of the system. This study concluded that assigning a value of 950 L/d per residence (250 gpd per residence) is appropriate for communities with 15 or more residences, and that assigning a value of 850 L/d per residence (225 gpd per residence) is appropriate for communities with 30 or more residential connections.
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