Since then, pipe installation has proceeded round the clock, with divers operating off a 250-ft by 50-ft barge replete with crew quarters, allowing dive superintendents and teams of five to participate in continuous shifts. In September, crews were nearing the site of a 60-in.-dia inlet located 1.25 miles offshore at a depth of 30 ft. Later this fall, they hope to proceed a quarter-mile farther, the site of a second inlet.
Operations also involve choreographing the movements of a 150-ft by 45-ft barge involved in excavation. Due to clouding caused by soft clay, movements of a Komatsu model 1250 excavator are guided by a GPS station located on shore. "Otherwise, we'd be digging blind," says O'Brien. Divers on the second barge verify trenches haven't been infilled by drift, then assist in connecting 20-ft-long sections of pipe. Operations involve a 275-ton Manitowac model 999 crawler crane equipped with a spreader bar, in addition to a pipe-fitted vacuum that "hydropulls" sections into place. After they are secured, divers disassemble the lifting mechanism and vacuum, then inspect joints to ensure they are leak-free. Next, a Volvo excavator performs backfill to return the bed to its original condition.
Once crews complete work on the first inlet, they will cap it with a 40-ft-long, 40-ft-wide screened wood crib to regulate water velocity, thereby impeding formation of frazzle ice, a slushy mixture that can hamper water flow. Constructed of Douglas fir timber, the crib will be floated to its site via barge, then will be weighted with stone to submerge it.
Though progress is subject to weather conditions, crews are installing up to eight sections—or 160 ft—of pipe per day. "Work started slowly in June, but conditions improved in July and August," says O'Brien. "The lake can grow choppy in September, but to date we've been lucky in timing our reloads of rock and pipe with bouts of bad weather. If conditions deteriorate, we may have to wait until spring to complete operations."
To expedite lake- and landside work, KWA broke the project into eight prime contracts. On land, five contractors, Zito included, each will install about 15 miles of pipeline—"about as much as you'd expect in a single season but spread over two," O'Brien says.
To accelerate the schedule, KWA contracted directly with Birmingham, Ala.-based supplier American Cast Iron Pipe Co. last fall to supply 67 miles of spiral-weld and iron pipe, additional fittings, bends, reducers and hydrant tees. With a May award date, Zito would not have begun work until fall had it procured the pipe itself.
The arrangement also allowed American Cast Iron to participate during the design phase, as project team members evaluated trade-offs between pipe diameter and pumping costs, and pipe thickness and pressures.
As engineered, 66-in.-dia pipe will extend 25 miles from an initial substation sited near Lake Huron to an intermediate station located on a 100-ft-high incline. From there, 60-in.-dia pipe will climb another 50 ft before beginning its descent along a 25-mile trajectory. Once it reaches Genesee County, the line will have deposited sufficient quantities of water in treatment plants and reservoirs to transition to 36-in.-dia ductile iron for the final leg of its journey.