Sewage treatment plant pushed to limit on days with no rain
No rain fell on the Milwaukee metropolitan area Thursday or Friday but the South Shore sewage treatment plant in Oak Creek was pushed close to its capacity.
There was no spike in sewage volumes flushed to the plant at half-time of the Wisconsin-Belmont game of the NCAA tournament, and no sustained surge from St. Patrick's Day revelers.
Melting snow draining into residential sanitary sewers Thursday and Friday boosted wastewater flows entering the plant to more than four times normal volumes, Milwaukee Metropolitan Sewerage District Executive Director Kevin Shafer said. The plant serves only the separated sanitary sewer area outside of central Milwaukee and eastern Shorewood.
Peak volume treated at the plant rose to a rate of 262.5 million gallons a day at 10 p.m. Thursday, a time of day when the rate usually is less than 60 million gallons a day, Shafer said. The plant's treatment capacity is a rate of 300 million gallons a day.
Flows to the plant remained above a rate of 225 million gallons a day for 19 hours, from 7 p.m. Thursday to 2 p.m. Friday, records show.
Volumes remained high Friday, a day with cooler temperatures and less snow to melt, because of delays in conveying wastewater in the system. It takes 13 hours for wastewater from Fox Point to reach the South Shore plant.
A rate of 205 million gallons a day at 1 a.m. Friday was the peak of flows reaching the Jones Island sewage treatment plant, which serves the combined sanitary and storm sewer area.
All the melting snow on streets and parking lots in central Milwaukee and eastern Shorewood that drained to the combined sewers was no match for leaks into private laterals in the separated sewer area.
The excessive volumes of water, not sewage, treated at the South Shore plant this week is among the reasons why MMSD approved a 10-year, $156 million plan to reduce the amount of stormwater flowing through private laterals to municipal sanitary sewers, officials said. Funding for the program might drop by nearly two-thirds, to a 10-year total of $54 million, under restrictions on local spending included in Gov. Scott Walker's proposed state budget.
Thursday's high temperature reached 60, melting much of the remaining snow cover, as well as snowbanks and parking lot piles.
Snow on rooftops and adjacent to exterior walls melts and flows to a foundation drain. At homes where the drains are connected to the sanitary lateral, the water enters the lateral where it is directed into the municipal sanitary sewer beneath a street.
As soils thaw in spring, melting snow on lawns also can leak into laterals and add to the volume of unwanted water flowing to street sanitary sewers.
MMSD's program would distribute funds to the 28 communities it serves to help pay for residential lateral upgrades, from repairing leaky laterals to disconnecting foundation drains from laterals.
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