Sewer Installation Encounters Obstacle Course

By James McRay, Efficiency Production | September 28, 2010

A new sanitary sewer interceptor for the southeast quarter of Mason was recently completed by Jule Swartz and Sons Contractors, of Jackson. Swartz installed 1,500 linear feet of new SDR-26, 24-inch pipe in 14-foot lengths, plus seven new manhole structures. The new sanitary sewer replaces an existing 10-inch sewer that had been running at near full capacity and was in need of an upgrade. Wolverine Engineers and Surveyors, Inc. was the engineering firm hired by the city of Mason to oversee the project.

The new sewer line starts at the Mason skate park, and then runs across a softball field to Rayner Creek. It progresses along the south bank of the creek and then turns south between homes to Columbia Street. After turning at a manhole, the line continues east underneath Columbia Street where it ties into another 1,500 linear feet of new 24-inch SDR pipe (not part of the city contract).

The circuitous route of the pipeline wasn't even the most challenging aspect of the project. On several occasions, the pipe-laying crew encountered various obstacles both foreseen and unexpected. In each instance, Swartz and Wolverine's ingenuity was critical in keeping the install on track.

On the turn south from the creek to Columbia Street, Swartz encountered a cluster of seven duct banks that were 5 feet deep, rather than the blueprint's indicated 3 feet. This prevented the crew from continuing to shore the trench with a set of trench boxes that they had been using. In the trench were two stacked 8-foot by 24-foot and 4-foot by 24-foot HT6 (6-inch. thick sidewalls) trench shields manufactured by Efficiency Production. Even with just one trench box, they could not position the trench shield under the conduits.

Rather than risk endangering anyone in an unshored trench, Al Swartz, president and co-owner of the company, contacted Efficiency Production, Inc., a manufacturer of trench shielding and shoring, to brainstorm possible shoring solutions. Conveniently headquartered in Mason, Efficiency supplied Swartz a modular aluminum Build-A-Box™ trench shielding unit, which could be assembled by hand and easily positioned under the cross-utilities and directly against the trench boxes.

"The Build-A-Box comes in very handy a lot of times when we encounter a variety of obstacles, because it's designed to be assembled into a variety of configurations," said Swartz.

It was planned that the new sewer line was going to punch through a 60-inch by 92-inch storm culvert located under the intersection of Columbia and Matthews Streets. "But when we started excavating, we found a water main running exactly where we needed to put in the shoring," Clint Martinez, project supervisor for Wolverine, said. "The water main completely surprised us due to the fact that it went underneath the culvert but turned a little bit going under the culvert. If it wasn't for that slight turn, we wouldn't have had a problem with it."

The storm culvert had also deteriorated and was filled almost 2/3 full with silt. Again, ingenuity prevailed and Swartz and Wolverine decided to cut the culvert and pour in place a 14-foot by 16-foot by 9-foot bypass vault that they could run the new sewer line through. However, there was still the problem of the water main that was in the way of the shoring. "We decided to reroute 150 feet of the water main around where we were working with 8-inch iron ductile pipe. That put us back one week," Martinez said. Additionally, the new potable line needed a 6-inch tie-in running north and a 4-inch tie-in running south.

A second, smaller storm culvert (42 inches by 65 inches) was also identified a few yards east of Matthews Street, and it was decided to pour in place a second, 10-foot by 22-foot by 9-foot bypass box culvert. Both new box culvert vaults were set 18 feet deep in the ground and contained access chimneys up to street level.

However, there was still the issue of shoring both excavations for the pour-in-place vaults. "We needed a different size shoring system than what was planned, and we were lucky that Efficiency was right in town, and could swap out the components with a different size," Martinez added.

Swartz rented from Efficiency their Slide Rail — Shore-Trak™ Sheeting Guide Frame System. Efficiency's Shore-Trak is the industry's only pre-fabricated, custom-engineered, cross-utility shoring system that integrates seamlessly with Efficiency Production's Universal Slide Rail System. The system allowed the crew to safely shore the pit around where the bypass vaults were poured-in-place, but also to shore closely around the existing corrugated metal storm culverts that ran through the pit on two sides.

"Without the Slide Rail System, we would have had to drive regular sheeting, which would require renting a crane at $150 an hour to vibrate-in the sheeting," Swartz said. "It probably would have taken twice as long, and the slide rail is just so much easier; it is just so much more flexible and consistent."

Efficiency's Universal Slide Rail is a component shoring system comprised of steel panels (similar to trench shield sidewalls) and vertical steel posts. The versatile system can be used in a variety of configurations, such as small four-sided pits; large unobstructed working pits as big as 50 feet by 50 feet with Efficiency's ClearSpan™ System; or in a linear multi-bay configuration to install lengths of pipe over 40 feet.

The configuration of the Slide Rail was a 16-foot by 32-foot by 12-foot pit (benched down 8 feet) in "two bays" with one pair of linear posts and parallel beams pinning-in-place a set of two 14-foot standard trench box spreaders as cross members. Shore-Trak Sheeting Guide Frames replaced panels on the opposite sides of each of the bays to accommodate the sharp angle of storm culverts.

Martinez commented that, "This was the first time I've seen an Efficiency Slide Rail go in the ground, and I was very impressed with the system. I really liked the Shore-Trak Sheeting Guide Frame, because we could put in the stab-sheeting around the culverts and still be integrated with the rest of the system."

A 30-inch diameter, 3/8-inch-thick steel casing ran inline through both bypass vaults, then 80 feet of 24-inch high density polyethylene (HDPE) bore pipe was snaked through the casing in both bypass vaults and tied into manholes on both ends. "We really did the things that no one wanted to do," said Swartz of his crew and of the project.

"Everyone worked very well together, and we had very good coordination and communication," said Martinez. "When it got frustrating and we wanted to throw our hands up and walk away, it was really a collaborative effort to come up with the solution for whatever new challenge we were dealing with." About the Swartz team, Martinez added, "I can't say enough about them. Everything is done right, and everyone is very safe on the job. And, they really try to minimize the impact on the community and the neighborhood."

The job started in June, and it was completed by the end of July. Swartz had on-site a Komatsu PC 200 excavator and a Komatsu PC 300 excavator. They also used a Cat 314 with rubber tracks and a JCB 214 S wheel loader.


Sediment Tank Cleans Up Water

Swartz Construction and Wolverine Engineers faced one additional obstacle before completing the new sewer interceptor for the southeast quarter of Mason. The Ingham County Drain Commissioner had put in place very strict guidelines about the groundwater that could be pumped out from the new sewer pipeline and discharged into nearby Rayner Creek or the city's run-off storm sewer system. The water needed to be filtered and cleaned to almost drinking-water quality before going into the creek or sewer.

"Normally, we would use a 300-micron reusable water filter bag; however, that wasn't getting the water clean enough for the drain commission's standards," said Al Swartz. "In order to get the water that clean, we had to switch to a 100-micron filter bag. Those bags are non-reusable, and cost about $125 each." Swartz needed a better plan to filter the groundwater. Again, Swartz called Efficiency Production for ideas and assistance.

"We've been approached by other contractors facing similar problems with requirements to filter groundwater, so we suggested using our new flow-through Silt-Separator™ Sediment Trap tank," said Ken Forsberg, president of Efficiency Production, Inc. "The groundwater is pumped into the tank where it cascades through six baffle chambers, which slow the water flow, allowing the silt to settle at the bottom of the chambers. Each chamber has a removable tray at the bottom so the silt can be removed and dumped out and hauled away with the other non-reusable backfill."

The sediment tank was delivered on-site and the groundwater pumped into it. The discharge from the tank was then run through the 100-micron filter bag. Present on-site representing the drain commission was Kenneth J. Kolanowski from Ledy Design Group. "(The tank) really worked; it took a lot of the silt out of the water," he said. "Instead of using multiple filter bags that would have needed to be changed often, Swartz used only one or two filter bags on the tank discharge for the remainder of the project."

Efficiency's sediment tank was also very helpful when a torrential downpour one afternoon filled a good portion of the 10-foot deep pit where the pour-in-place bypass vault was set to be installed. "They ran all that dirty, muddy rainwater through the (sediment) tank, and were able to clean up the site very quickly to begin working again," Kolanowski added.

"Without the sediment tank, we would probably have gone through three or four of the non-reusable 100-micron bags per day," concluded Swartz. "Instead, after running the groundwater through the Efficiency Sediment Trap tank, we needed to use only a couple of filter bags for the entire project."