MAKING SENSE OF PRIVATE RDII FROM FOOTING DRAINS

Total wet weather response is based on understanding of connected footing drains tributary to thesanitary collection system and supporting sewer metering and footing drain flow monitoring data. Footing drain contribution to private rainfall dependent inflow/infiltration (RDII) is important to the local conditions of the Ann Arbor sanitary collection system (Sanitary Sewer Overflow Study Task Force; Sherman et al.; Stonehouse et al.; Zawacki et al.). In Ann Arbor, an extensive Footing Drain Disconnection (FDD) program is currently underway. The characterization of the responses and site conditions could be used to prioritize FDD work.This paper provides some background regarding the footing drain monitoring information. This information discusses seasonal variation in response volume while exhibiting little seasonal differences for peak flow; thus, indicating that inflow responses are fairly consistent through the year and the infiltration response is what predominantly undergoes seasonal change. Also, discussed is a site characterization index (SCI) that may be used to assess likelihood of a range of footing drain responses based on a simple site assessment. Applicability of this index to other areas of the city is planned for future investigation.