IL Update - E.C. identified cause of flooding last weekgreenspun.com : LUSENET : Grassroots Information Coordination Center (GICC) : One Thread
Pump activator failed at Indiana Harbor station.
BY BOB TITA Times Staff Writer
EAST CHICAGO -- The inability of the city's sewer system to handle last week's deluge of rain has been traced to a malfunctioning control sensor that kept storm relief pumps from activating at an Indiana Harbor pumping station. The half-hour delay in clearing stormwater from the Michigan Avenue station resulted in sewage-laden stormwater backing up into homes through basement toilets, sinks and floor drains. The Harbor and the North Side of the East Chicago section appeared to have the most reports of flooding. Residents there tried to stem the flow of water by jamming plungers and other devices into toilets and sinks.
The storm last Monday, which dumped more than 2 inches of water in 20 minutes in some areas, was particularly frustrating for Sanitary District administrators who have spent millions of dollars in recent years upgrading pumping stations to eliminate chronic drainage problems.
"We're investigating where the faults came in," Utilities Director Michael Suty said.
As in most of the region's older urban communities, sanitary sewage and stormwater share the same network of sewers in East Chicago. Stormwater and sewage alike are treated at the city's wastewater plant at 152nd Street and Indianapolis Boulevard.
A handful of pumping stations throughout function as collection sites for wastewater. The three largest are the Alder Street, Magoun Avenue and Michigan Avenue stations. Water flows into the stations' underground wells and is then pumped to the treatment plant. The stations are outfitted with regular service electric pumps as well as storm relief pumps capable of moving as much as 200,000 gallons of water per minute.
The pumps are designed to be activated through control sensors that measure the water volume in the wells and adjust the pumping speeds accordingly. The computerized sensors also allow Sanitary District operators to remotely monitor conditions at the stations.
Last Monday at the Michigan Avenue station, one of the two control sensors in the station's well malfunctioned. While one sensor issued accurate information on the well's water level, the other did not. Suty said when such a conflict occurs, the pumps are programmed to shut down and issue a default signal to operators at the treatment plant. Suty said Sanitary District Manager Daniel Olson received the default signal about 3:30 p.m.
"When Mr. Olson became aware of the pumps shutting down, he immediately dispatched an operator" to the Michigan Avenue station. Although the pumps at the station were manually activated before 4 p.m., the storm sent so much water into the station that even the relatively short delay was enough to cause a drainage mishap throughout the city.
"Water does find it's own level and as the level in the wet well increases, that head pressure causes the backups through the whole system," Suty said.
Records from the Michigan Avenue station indicated the level of water in the station's well increased from 50 inches at 3:26 p.m. to 30 feet by 3:40 p.m., Suty said. Once the storm relief pumps were activated, the water level plunged from about 36 feet to 19 feet within 11 minutes.
Suty said the control sensors are difficult to monitor in non-storm conditions because duplicating the extreme amounts of water needed to activate the relief pumps is nearly impossible.
"We don't have the opportunity to run these pumps in a test mode," Suty said.
Suty, however, said he was pleased with performance of other upgrades and improvements to the city's sewer system, particularly the operation of a new pumping station at Columbus Drive and Indianapolis Boulevard that collects only stormwater from the North Side of the city.
"There were isolated instances (of flooding) all over, but with us putting in a North Side (pumping) station, that helped us immensely," he said.
-- Doris (firstname.lastname@example.org), September 19, 2000