MMSD states that emergency measures were taken to reduce the risk of basement backups after storms dropped more than two inches of rain in about one hour at several locations on June 18. Rain fell so quickly that it added an additional 100 million gallons of stormwater and wastewater to the Deep Tunnel in 12 minutes. One District rain gauge measured five inches of rain between June 17 and 20. Several others showed four inches or more for the same period. One inch of rain on the MMSD’s service area equals 7.1 billion gallons of water.
The estimated volume of the combined sewer overflow is 336.2 million gallons. Two isolated separate sewer overflows occurred on June 18. The estimated volumes are 140,000 gallons at Greentree Road and the Milwaukee River in River Hills and 660,000 gallons at 35th Street and Roosevelt into Lincoln Creek in Milwaukee.
MMSD also took emergency steps to increase treatment capacity and reduce the volume of overflows by conducting combined sewage treatment at the Jones Island Water Reclamation Facility on June 18 and 19. The treatment procedure reduced combined sewer overflows by 60 million gallons. Combined sewage treatment pumps water directly out of the Deep Tunnel into disinfection chambers at Jones Island. The District has never violated its permit for fully treated effluent while conducting combined sewage treatment.