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Crew begins deep tunnel video inspection
Jan 27, 2012 (Milwaukee Journal Sentinel - McClatchy-Tribune Information Services via COMTEX) --
An eight-wheeled vehicle began slowly cruising the cross-town segment of the deep tunnel Friday at a top speed of 30 feet per minute as its three-person crew videotapes the inside of the underground wastewater storage cavern for a once-a-decade inspection.
The speed of this tunnel crawl is governed by national standards for videotaping sewers, said Scott Royer, general manager for Veolia Water Milwaukee. The company operates two sewage treatment plants, regional sewers, deep tunnels and Milorganite sewage sludge fertilizer factory under contract with the Milwaukee Metropolitan Sewerage District.
Shortly after 10 a.m. Friday, a crane lowered the diesel-powered transport vehicle -- equipped with video camera, generator and lights -- more than 300 feet down an access shaft off W. Seeboth St. to the cross-town tunnel. The crew was lowered separately while standing in a metal basket.
The transport vehicle will carry its crew the entire length of the cross-town over the next few weeks. This tunnel segment extends west from downtown to Miller Park then northwest to Milwaukee County Grounds in Wauwatosa, generally about 300 feet beneath the Menomonee River corridor.
The cross-town is one of three major segments of the original 19.4-mile-long tunnel system in use since 1994. All of it will be inspected this winter, as it was in 2002. No structural problems were found 10 years ago.
The start of inspection was delayed a few weeks ago after a surveillance crew on foot and driving an excavator equipped with snowmobile-like tracks got a first-hand look at a short stretch of the tunnel both east and west of the Seeboth St. shaft, Royer said. Their excursions were the first time people had been in the tunnel system since 2002.
A loose layer of sediment west of the shaft was several inches thick at that time -- too high for the eight-wheeled vehicle to traverse. Much of the muck was washed down the tunnel during a recent storm.
Subsequently, the green light was given this week to lower the transport and begin the televised inspection west of the shaft.
Before the storm, however, the scouts encountered an even deeper layer of loose sediment -- made up of sand, grit and sewage -- on the tunnel floor east of the shaft.
This is not a permanent layer and has not reduced the 30-foot diameter tunnel's capacity in the past, Royer said.
The scouts' slow progress down the tunnel was called off after walking between 2,000 and 2,500 feet when they measured at least eight inches of wastewater atop the sediment, Royer said.
For that reason, a proposed cleaning at the bottom end of the tunnel beneath Jones Island likely has been postponed a few more weeks, he said. There is an estimated 800 cubic yards of plastic trash -- bottles, jugs, bags -- and other floatable debris at the low end of the tunnel that was to be removed concurrent with the inspection.
Unless another rain storm comes along in early February to help push some of the sediment out of the east end of tunnel, neither inspectors nor cleanup crews will be able to drive in there, Royer said.
How could they inspect 6,000 feet of tunnel between the W. Seeboth St. shaft and Jones Island?
Boats are being considered, according to Royer. Flat-bottomed boats powered by electric trolling motors could float inspectors and video cameras down to the east end of the tunnel if Veolia allowed water levels to rise several inches higher just in this stretch.
Around 8 million gallons of ground water seeps into the tunnel each day and it is pumped out to provide full capacity for wastewater storage in storms, Royer said. Halting pumps for a few days during dry weather would provide enough water to float a small boat and complete the inspection, Royer said.
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