MILWAUKEE - The Milwaukee Metropolitan Sewerage District began a combined sewer overflow Saturday afternoon following excessive rainfall that began in the area Friday, July 31.
What we know:
Several MMSD rain gauges show parts of the Milwaukee area have received more than three inches of rain since Friday. You can view the latest MMSD rain gauge data here.
Instead of treating the water and releasing it back into rivers and Lake Michigan, the combined sewer overflow sends a combination of untreated rainwater and wastewater directly into the nearest streams, rivers and lakes.
That happens because the district's two water treatment facilities, Jones Island and South Shore, don't have the capacity to take on more water. The South Shore plant is currently operating at 50 percent capacity, only able to hold 150 million gallons of water per day due to construction.
An MMSD map of affected waters includes the Menomonee River as far as west as the stadium freeway, the Milwaukee River as far north as Capitol Drive, the Kinnickinnic River as far south as Baran Park, and Lake Michigan between McKinley Beach and Bay View Park. Boat launches and beaches in these areas are also affected.
Under federal law and its state permit, MMSD is only allowed to initiate six combined sewer overflows per year before the district would face a regulatory review. MMSD averages 2.2 combined sewer overflows a year, largely because of the deep tunnel system, which opened in 1994. Before its construction, MMSD saw between 50 to 60 combined sewer overflows per year.
The Wisconsin DNR requires MMSD to inform the state of the overflow impacts within the next five calendar days, including an estimate on exactly how much untreated water was released.
MMSD is able to track this with a complex computer model that can run calculations based on the amount of water moving through the system.
This is MMSD's second combined sewer overflow this year. The first, which lasted six days during heavy rains in mid-April, sent 2.7 billion gallons of untreated water into the streams, rivers and lake.
The Source: Information in this story was gathered from the Milwaukee Metropolitan Sewerage District, the Wisconsin Department of Natural Resources and FOX6 News' prior reporting.