Wet Weather Alternatives Analysis
City of Millbrae, California

Faced with tight deadlines under a Baykeeper consent decree to complete multiple capacity upgrades, West Yost helped the City evaluate its options for implementing a long-term plan to reduce infiltration and inflow (I/I) through collection system rehabilitation and private lateral programs. The analysis included identifying and prioritizing subbasins within the collection system with the largest I/I levels by analyzing flow monitoring data and hydraulic model calibration results. I/I sources within each subbasin were identified by conducting a thorough analysis of: existing asset properties such as pipe material and installation year, surrounding soil conditions and the locations of creek crossings; operation and maintenance information from the City’s CMMS records including recent repairs, preventative maintenance frequencies and historical sanitary sewer overflow records; and Recent CCTV data (coded to NASSCO standards) to identify defects that indicate higher potential for I/I. The results of this analysis were then used to conduct an alternatives analysis of multiple I/I reduction scenarios, including capital costs.