Sanitary Sewer System Bypass Pumping During May 17, 2020 Wet Weather Event

Due to wet weather on Sunday, May 17, the City experienced overflows at nine lift stations, which required bypass pumping of the sanitary sewer system.  Bypass pumping is used to reduce basement backups and limit potential private property damage. The times varied for each station, but the duration can generally be described from approximately 1:30 P.M. on Sunday, May 17 to 3:00 A.M. on Monday, May 18.   The following lift stations experienced overflows from the wet weather:

11101 River Road (LS C)
11750 River Road (LS D*)
2020 Ranch Road (LS E*)
12439 N. Circle Drive (LS F*)
12701 Fieldwood Road (LS G*)
3000 Riverland Road (LS H*)
515 Cedar Lane (LS J)
606 Juniper Court (LS L)
9729 Tamerlane Drive (LS O*)

*Six of these nine lift stations are located near the Milwaukee River or Little Menomonee River, and have a history of surcharging in major wet weather and flooding events.

During this wet weather event the rain fall intensity caused supersaturated soil conditions which is attributed to inflow and infiltration in the sanitary sewer system.  While the system is designed to accommodate an amount of clear water flow, on Sunday the amount of inflow and infiltration exceeded the capacity of the system.  MMSD also had multiple bypass locations, as did several adjacent communities.  The City is continuing its efforts to reduce the amount of inflow and infiltration with ongoing sewer lateral work plus rehabilitation of the sanitary sewer mains. 

The East Trunk Sewer was monitored and performed as designed to relieve wet weather flows for this event, where no backwaters were reported in that portion of the sanitary sewer collection system.  However, lift stations that are located upstream of the East Trunk Sewer had capacity issues. These lift station wet-weather capacity-issues have been identified in ongoing Lift Station condition assessments and has led to ordering pump replacements with increased capacity (LS J,Q,P,S).  Additional upgrades and improvements are planned this year (LS H,L,O,R) and anticipated for the 2021 budget (LS C,D,E,T).   The City appreciates the  Sewer Maintenance Crew and other DPW staff for their efforts during this challenging time.