All,

Further research on the topic of check valves has indicated that we made a mistake at the recent public meeting, and perhaps at a previous CAC meeting, as to the prevalence of check valves installed as part of the FDD program.

 

 

 

 

It was the intention of the original FDD Program to install check valves for all homes in Phase 1A and Phase 1B. (Note: Phase 1A included homes within the 5 study areas that had experienced basement backups or were identified as being at high risk for basement backups.  Phase 1B consisted of homes outside of the 5 study areas that had experienced basement backups or were adjacent to those homes and had potential for basement backups to occur.) Very roughly, this amounts to about 450-500 homes in phase 1A, and 200-250 in phase 1B. The rationale for installing check valves during phase 1 was that it was realized that sewer surcharging would only be partially addressed by the FDD work at these homes and that they would still be at risk for basement backups until the City also completed phase 2 homes (those in the same sanitary tributary area as the phase 1). The check valves were intended to provide temporary protection to high risk homes until the wet weather flows could be reduced to a point where the basement backup risk was essentially gone.

 

 

It should also be noted that the flow metering data collected in the priority districts during 2013 shows that the flow depths were contained within the pipes at these locations during all of the storm events. This means that the water did not reach a level where the check valves would activate. Therefore, the presence of check valves is not relevant to the evaluation of flows from the 2013 metering data.