Grosse Pointe FarmsJanuary 19, 2012
Power problems believed to be primary cause of sewage backups
By K. Michelle Moran
C & G Staff Writer
GROSSE POINTE FARMS — City leaders and residents are finally starting to get a clearer picture of what caused massive basement sewage backups last year and what it might take to prevent future incidents.
At a Jan. 9 City Council meeting, Hubell, Roth & Clark Executive Vice President Tom Biehl presented his company’s findings to date into what apparently led to the backups and what steps the city could take to improve its Kerby Road pump station. HRC is the Farms’ longtime engineering firm.
Although the two storms varied somewhat, Biehl said, their study determined that electrical problems caused by DTE Energy power outages appear to be the main cause of flooding in the city.
“The existing Kerby Road pump station is satisfactory in terms of operation at the present time,” Biehl told the council. “This is confirmed by (Anderson, Eckstein and Westrick), an engineering (firm) hired by the city, an independent third-party firm. … The primary issue, based upon the power interruption problems last year, is the electrical system at the Kerby Station. To address potential future power issues and provide a third source of power for the pumps, which exceed code requirements, we are recommending the installation of permanent standby generators at the station to power all of the pumps, including storm pumps seven and eight.”
2011 was a record year for rainfall in Southeast Michigan, with Wayne County receiving 47.7 inches of precipitation and beating the previous record, set in 1880, Biehl said. By contrast, average annual rainfall in Wayne County is 33.5 inches, he said.
Two strong storms May 25 and Sept. 10 led to hundreds of basement sewage backups, as well as street flooding, primarily in the city’s Inland District. After more than 4.2 inches of rain fell in 18 hours May 25 on ground already saturated from storms in the days before, Biehl said the storm tripped the high water alarms at the plant, causing the large storm pumps, seven and eight, to be activated. However, he said power fluctuations from DTE Energy caused some pumps to shut down temporarily; a downed tree was blamed. In the September episode, storm intensity “was not the primary issue,” but Biehl said power was interrupted on primary feed 32T, probably from a lightning strike, which resulted in a blown fuse in the main telemetry pump control panel, blown fuses in three ground potential transformers and tripping of the primary switchbreaker. In addition, a lightning and surge arrestor was blown, and the Detroit Water and Sewerage Department’s magnetic flow meter, which measures flow, experienced a blown fuse, he said.
“As a result, all of the pumps at the station stopped,” Biehl said.
Operators responding to the high water alarms had to manually reset the system, he said.
As to variations in flooding amounts from one house to another on the same street, Biehl said basement elevation could account for some of those differences. In other instances, especially for the May event, overburdened house leads may be to blame in some cases, he said.
The pump station — built in 1929 and upgraded several times since then, including the addition of large storm pumps seven and eight following basement flooding circa 1947 — can handle 358 million gallons of storm and sewage water per day, or nearly 15 million gallons an hour, Biehl said. It has two power feeds from DTE, 32T and 191T, so that if one is interrupted, the other should be available to serve the station. In addition, after a national power grid failure in 2003, the city installed an emergency backup generator for pumps one to three, which handle dry weather flow, he said. Operational codes require two power sources, so Biehl said the station meets those standards.
The electrical system recommendations include the purchase and installation of a diesel-powered standby generator system to provide power to all of the pumps during an outage, replacement of pump motor starters and wiring for all eight pumps, installation of supervisory control and data acquisition equipment to allow for remote pump reading and control, as well as improved backup power capabilities, and, as required by new codes, new lighting and gas detection and protection devices in the wet wells, Biehl explained.
Another HRC recommendation, said Biehl, is switchgear modification to alleviate the possibility of multiple switchovers during short-term power interruptions, meaning that if the station shifts to an alternate power source, it would stay on that source — for example, a generator — until it was manually reset.
“Of all of the recommendations that have been made, the emergency generator to serve all pumps is the highest priority in light of recent power issues,” Biehl said.
Mechanical system improvements include removal of an old boiler and related gas piping that are no longer used, review of the heating system, new ventilation equipment for the wet well and dry well, dry well sump pump replacement, and plumbing and backflow prevention, according to the report. The pump system itself needs to see refurbishing of raw sewage pumps five and six with new parts, including rotating assemblies; suction and discharge valve replacement on pumps one to six; and removal and replacement of the wet well dewatering pump for pumps seven and eight, Biehl said.
Permanent generators could be placed at the rear of the building in the southwest corner, and should be screened off and include sound-attenuating housings and critical silencing mufflers with hospital-grade noise suppression so that they’re compatible with the surrounding residential area, he said.
The price tag for just the electrical system upgrades is $2.689 million, according to HRC’s calculations. The mechanical system improvements add another $138,000, and the pump system upgrades are $714,000. Exterior and interior architectural improvements — which include an optional window replacement costing $99,000 for more energy-efficient new windows, and access to the wet well area for pumps one to six, along with underground service revisions, at a cost of $400,000 — are $651,500. Making all of the improvements would cost the city just over $5.24 million, while excluding the wet well access provision and doing it later would bring the cost to slightly more than $4.84 million, according to HRC. Biehl said some work could probably be done in-house, such as boiler removal, which would reduce the total price.
It would take roughly six to nine months from the bid award to have these upgrades and new pieces of equipment fully operational, Biehl said. He said the city has been told informally by a state official that the Farms should qualify for an S2 grant for some pump station improvements, not including anything the state considers routine maintenance. Whether or not the city receives an S2 grant, he said they could apply for a low-interest loan from the state’s revolving fund, which has an interest rate of about 2.5 percent. However, given the state’s schedule for such loans, the city couldn’t submit a plan for such a loan until next July and wouldn’t find out if they qualified for the money until late 2013, Biehl said.
Another issue that needs to be looked at is the Fox Creek enclosure in Detroit, Biehl said. All Farms flows go there, as well as flows from Grosse Pointe Park and City, and part of Wayne County. The enclosure is under the jurisdiction of the Wayne County Drain Commission and likely needs to be inspected; Biehl said it hasn’t been inspected in about 35 years. If there are a few feet of sediment in the pipe, that could create capacity issues during extreme storms, he said. Biehl told the council any community associated with the enclosure can request an inspection at any time, and that’s something that should be done in the winter, because it requires a walk-through. County officials have indicated they might be able to perform such an inspection in March.
“That’s what we were hoping for,” Biehl said.
Two areas of the Inland District, located on either side of the pump station, were particularly hard hit, and Biehl said those also happen to be areas of low elevation. He said elevation in those sections of the city is around 580 feet, with grades climbing to 610 toward Ridge and the Hill. By comparison, Biehl said the current level of Lake St. Clair is 574.5 feet. That means some of the basements in the Inland District are probably below lake level, “which can be a problem when you’re talking about trying to protect them from flooding,” he said.
Partial sewer separation in the Inland District could provide additional relief for homes in the lowest part of the city by reducing the load at the pump station, Biehl said. Such a project could take about 150-200 cubic feet per second off the system, which has a capacity of 550 cfs, he said. Because many homes in the district have their house leads connected to a lead that runs through the backyard, Biehl advised city leaders to consider building a new separate storm sewer instead of a new sanitary line for the district. The storm sewer would require a new wet well and storm water pumps, and an off-site force main to convey the flow through the Hill out to the lake, he said. Force mains can be directionally drilled 1,000 feet at a time without tearing up the streets too badly, although some construction disruptions need to be expected, Biehl said. The city would need two 36-inch-diameter force mains, he said. That would provide redundancy in the event one of them was out of service.
Downspout disconnection is another way to remove some water from the system. Around the time the Lakeside District sewers were being separated, City Manager Shane Reeside said the city waged a successful campaign to disconnect downspouts throughout the city. Although some downspouts remain connected, in most case it’s because disconnecting them would lead to safety hazards, such as sending water onto a driveway or walkway, he explained. The city still has an ongoing disconnection program and is going through the Inland District looking for connected downspouts to see if any were missed or if any can now be disconnected.
As of press time, officials said they were continuing to monitor the plant closely, although basement backups are unlikely in the winter. Reeside said one of the two primary electrical feeds into the station, which has been getting serviced and has been down since Dec. 7, was slated to be back online as of Jan. 11, according to DTE. Once it was back online, he said, the city planned to have an operator around the clock at the pumping station only when temperature was above freezing and precipitation was anticipated.
While the city has had operators at the plant 24 hours a day, he said they’ve been doing maintenance, cleanup and painting.
The council unanimously approved getting preliminary plans and cost estimates for the first phase of work, at the Kerby Road pump station. The council also approved approaching Wayne County and other related entities regarding inspection of the Fox Creek enclosure.
At press time, Biehl said HRC hadn’t prepared cost estimates for partial sewer separation, but could do so if the council wanted to move forward with that. City Council member Louis Theros said separation in the Lakeside District, which took place around 1999, cost about $20 million.
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