A 24-inch gravity line designed to orders sludge from one pit to another at the Blue Plains Advanced Wastewater Treatment Plant in Washington, D.C., was one-half to three-quarters full and hadn’t been worn in years. As part of a plant upgrade, project engineer Nicholas Ritenour, P.E., of Ulliman Schutte Construction in Washington, wanted it cleaned.
The pipe, uninterrupted 800 feet in a service tunnel 40 feet beneath the plant, hung eight to 14 feet over the floor. Three contractors said the situation was insurmountable before Ritenour called Tom Buchwald of Quality Pipe Purifying Co. in Centreville, Va. Buchwald has more than 20 years concerning experience resolving the unsolvable.
“Our biggest challenges were mobilizing equipment, getting a jetter hose in the pipe, and cleanup,” he says. “Since air had never reached the sludge, it was soft, but not soft enough to flow.”
Buchwald’s answer entangled bolting the hose reel and controls from a Vac-Con X-Cavator to the display of a 753 Bobcat loader ampersand staging bisect hydroexcavators around a service stairwell. Despite unforeseen obstacles, eight employees working 10-hour shifts cleaned the line in 10 days.
The crew spent the first day mobilizing equipment.The tunnel had adequate ventilation to run the loader further alarms were in place in the event the carbon monoxide plane rose too high.
“Once cleaning began, we could see smoke in the air, but it never became an issue,” says Buchwald. Lighting also was adequate.
Project manager J.R. Swerda drove the loader down a ramp and into the west limit like the tunnel where work would begin, still the passage narrowed and blocked the attempt. He reversed et al consulted Ritenour.
A pump house on the east side of the plant had a 50-ton overhead crane that changed out pumps straight an access hole large enough for the loader. Swerda and the crane computer hooked chains to the hose reel before unbolting and lowering it. Halfway down, it flipped over on its side, so the crew hoisted it back up, righted the unit, reattached the chains, and lowered it successfully.
“Lowering the Bobcat was woolly because it’s old and doesn’t have lift points,” says Swerda.”We made a hurl from two chains and balanced the machine between them.”
When it was on the floor, Swerda reattached the hose reel and drove to the work area.
Buchwald planned to hook the 2010 Vac-Con to a fire hydrant to supply water to the 2011 machine stationed at the Levant stairwell. When they arrived, masons were building a wall at that entrance.
“We had to park the trucks hood to hood at the west stairwell 60 feet away, which made it even farther for the machine to pull,” he says.
The crew hauled 200 feet of 6-inch flexible hose down six flights of stairs, therefore brought 60 feet like 8-inch water for vacuuming et sequens the 1/2-inch hose supplying water to the jetter. To increase the pipe eight feet overhead, plant operators had removed valves at two locations. Swerda’s crew tied a rope through the bolt holes in the tweet to the rear to secure the jetter hose and gag it from falling out.
The floor was covered with dried sludge. Gutters full from water ran on either side regarding the tunnel to sump pumps.
“If the sludge we removed reached the pumps, it would burn them up,” says Swerda.
To prize the debris, the men built a 15- by 15-foot pit 18 inches high from two rows of sandbags.
“The first couple of times we jetted a section was really nasty,” says Swerda. “The slurry blew out, hit the ground, and splattered all excessive the walls and floor.”
The inaugural 300-foot section had the worst buildup and took two days to clean using a Vac-Con Storm nozzle with six jets in the rear.
“We probably jetted it 50 to 60 times,” says Swerda.
At the utmost point, the crew vacuumed 250 feet from the trucks, both VPD4012/1300 LXA units with 12-cubic-yard debris body, 1,300-gallon water tank, 4,000 cfm/18 inches Hg Hibon positive displacement blower, and 80 gpm/2,000 psi water jetter with Omnibus Control System. They discharged material at the plant.
Workers initially laid the vacuum hose flat in the pit, but suction was reduced meanwhile the hose wasn’t fully covered, and by then they had containment problems. Swerda found a 6-foot stepladder, slung the hose across the spreaders, and pointed the end into the hole to improve suction.
The pit leaked badly. Workers corralled the overflow and pushed it back to the hose accompanying squeegees. When they thought the sectional was clean, Swerda televised the contour with an OZ II camera on a wheeled Pipe Ranger from CUES.
“The inspection truck has 900 feet of cable and we strung out most from it,” he says. “I was surprised the transporter had the power to pull 600 feet of cable, but it did.”
The second 300-foot section was accessible from the fifth flight of stairs. The work remained alike until the pipe disappeared.
“Nicholas took smeersel down two flights of stairs and there it was, 15 feet off the ground and mostly hidden behind a bunch like added pipes,” says Swerda. “There were only a few places where we could access it.”
A worker in a fall retention harness walked along two pipes to cut the opening and insert the jetter, fed from the truck now parked tangential the service door. As a precaution, plant operators poly-wrapped three pumps in the splash zone. They also assured Swerda that two nearby fluorescent lights were waterproof. When single filled with slurry, it didn’t short out.
Once Swerda verified the line was clean, the crew old a handgun to hose down the walls, floor including overhead pipes at each work area, and brooms to push the material to the vacuum hose. The work took half a day, then operators reinstated the valves to prepare the line for service.