An illegal discharge of 4.1 million gallons of wastewater from the Jones Island treatment plant in into Lake Michigan was caused by an operator error, according to the Milwaukee Metropolitan Sewage District. It is unknown the amount of untreated sewage contained in the water.
According to the Journal Sentinel, the discharge permit for the district authorizes diversions of wastewater around routine treatment processes only under extreme flows during heavy rain that threatens to flood portions of the plant. Since there was no storm at the time of the spill, the incident clearly violated the permit.
United Water, the utility behind the spill, violated other conditions of its contract by not reporting the incident to district officials until a few days after the spill.
John Jankowski, the district's contract compliance manager told the Journal Sentinel that all of the diverted wastewater was disinfected with chlorine to kill most disease-causing organisms before the flow was discharged to the lake.
The volume equals 4.3% of the estimated 95 million gallons treated that day at Jones Island. According to test of the discharged wastewater, the diversion did not increase the pollutant concentration beyond the limit of the plant’s permit.
The incident occurred when United Water employees were doing maintenance on two separate facilities at the plant. United Water has received 18 other notices of contract violation since it began operating the regional sewers in 1998.
John Cheslik, the United Water’s general manager in Milwaukee, speculated that the spill occurred when a gate designed to block flow from the plant's preliminary treatment building to a diversion channel malfunctioned.
United Water executive director Kevin Shafer has recommended installing a gate at the end of the diversion channel that would prevent any diverted flows from unintentionally reaching the disinfection facility and entering into Lake Michigan.