Infiltration and inflow (I/I) are common problems in sanitary sewer systems. While inflow typically gets most of the attention in wet weather, groundwater infiltration can also be a big problem in dry weather, silently stealing sewer capacity 24 hours per day, 7 days per week, 365 days per year. Groundwater infiltration cannot be measured directly but is often estimated from sewer flow monitor data using a variety of empirical methods.
The authors provide an overview and comparison of four methods, including the % Minimum Method, the Wastewater Production Method, the Stevens-Schutzbach Method, and the Mitchell Method. Examples of each method are provided using actual flow monitor data to further explore the performance of these methods and provide guidelines for proper application.