CSO solution

November 2013 » Features » PROJECT CASE STUDY
New pipe system separates stormwater from sanitary sewer system to relieve stress on treatment plant.
Stephen C. Cooper
To be able to work in a tight space next to buildings, the Gendron crew used an excavator without a counterweight on the back and shorter pipe lengths.

Lewiston, Maine's combined sewer overflow (CSO) separation initiative has continued with the successful completion of the Oak Street - Phase III segment. The job, however, was not without its challenges, which included a massive rock ledge, old buildings virtually on the edge of the trench, and an existing sewer that was unexpectedly found to be leaking effluent. As the third part of the city's CSO master plan, this new pipe system separates stormwater from the existing sanitary sewer system to relieve capacity stress on the treatment plant and meet Maine Department of Environmental Protection requirements. With a population of 37,000, Lewiston is the second largest city in Maine and is part of the Portland-Lewiston-South Portland, Maine combined statistical area.

Project
Oak Street – Phase III CSO Separation, Lewiston, Maine

Participants
City of Lewiston
Gendron & Gendron
Ted Berry Company

Product application

Versatility of Advanced Drainage Systems' SaniTite HP pipe helps overcome multiple problems in difficult installation.

"There are five phases to our CSO work," said Jeffrey D. Beaule, P.E., project engineer for the City of Lewiston. "We just finished Phase IV, but the Oak Street - Phase III portion was probably the most challenging. This is because of the location of the pipeline, the unexpected sewer rehabilitation, and the geological make up of the area."

During the course of installing the new pipe, an old 60-inch-diameter concrete sewer line was found to be leaking and needed to be replaced. As an alternative to replacing the sewer pipe, it was sliplined using the same type of pipe being used for the new stormwater line – SaniTite HP pipe from Advanced Drainage Systems, Inc. (ADS). Additionally, the company's N-12 corrugated high-density polyethylene (HDPE) pipe was used for some other sections of the storm drain pipeline and smaller-diameter SaniTite HP was used for new sanitary sewer piping.

To quickly fix a 60-inch concrete sewer line that was leaking effluent, the Ted Berry Company crew pushed the new 48-inch SaniTite HP pipe into the old pipe.

"Originally, this project went out to bid with concrete pipe for the project's storm drainage piping and SDR-35 for the new sanitary sewer piping," Beaule said. "ADS came to us at the pre-bid meeting and educated us on the benefits of utilizing the SaniTite HP after the great results Portland, Maine, has had with the product that meets and exceeds the performance specifications of RCP and PVC, plus the economic advantage and installation benefits. With this, SaniTite HP was allowed as an alternate and we ended up going with it for the project as the contractor bids came in. It turned out to be a really versatile pipe because it could be ordered pretty much any way we needed it, including lengths and fittings at virtually any angle."

Neighborly advice
A CSO separation project in nearby Portland, Maine, helped Lewiston gain comfort with the SaniTite HP pipe. The project used the polypropylene pipe to increase conveyance capacity, replacing a smaller, 100-year-old vitrified clay line. Completed in 2010, the new line used 5,600 feet of the 60-inch-diameter pipe to separate a parallel 10-foot-diameter combined sewer, which now solely conveys stormwater.

"The common thread is that both the Portland and Lewiston CSO projects were difficult jobs," said Bob Pelletier of E. J. Prescott, which provided the materials for both. "Basically, the Portland water/sewer separation and the project here in Lewiston found the ease of handling and assembling of the products made a big difference as far as cost savings in installation as opposed to concrete pipe. Plus this pipe is very durable and can be used in all these situations because it covers the full pH scale from 1.5 to 14."

SaniTite HP pipe, available in 30- to 60-inch diameters with triple-wall profile construction, meets ASTM F2764 specification requirements. It also provides a watertight joint, exceeding the requirements of ASTM D3212 with a dual-gasketed spigot design and banded reinforced bells. The smaller SaniTite HP diameters – 15 and 18 inches – that were used for new sanitary sewer applications, meet ASTM F2736 specification requirements and are made with dual-wall construction to provide performance ratings that exceed all of today's industry standards for gravity flow sanitary sewers.

For the overall project, the city contracted with Gendron & Gendron, a local construction company with a 42-year history of working with the city. "They usually save the ‘best' for us," said Todd Gendron with a smile. "The Oak Street job was the middle part of the city's separation initiative and we had to match up the elevation with what had been done a few years before, which stopped when they hit the rock ledge. And that's where we started....in the ledge. There was a 60-inch concrete sewer two feet away from where we were to put in the 42-inch and 48-inch SaniTite pipe and it was three feet deeper than the bottom of the concrete sewer. We also had other utility lines, so they wouldn't let me blast. We brought in a drilling company to drill holes 8 inches on center in an area 20 feet wide by 300 feet long and then we hammered out rock with a hydraulic hammer.

"On Oak Street, the buildings were right on the edge of the hole," Gendron said. "We were in a high-visibility, high-traffic area and had a dead end street to contend with as well as dealing with gas mains, telephone lines and conduit, water mains, and the 60-inch concrete sewer main that takes care of half the city."

It took the Gendron six-member crew from April until November 2012 to install 800 feet of pipe. Typically, a "normal" project of this size would take just a few days.

The new stormwater line (bottom) was installed close to an existing concrete sewer line, which was sliplined using the same 48-inch-diameter pipe.

"We used different lengths of ADS pipe, 13 and 20 feet and some others," Gendron said. "The 13s gave me the reach so I didn't have to have such a big excavator and we could use a 20-foot trench box instead of a 24-foot box. The job was originally designed for concrete pipe and structures but for all the things that had to be done, if we were trying to do it with concrete, there would be no way to complete the project. The ADS products gave the flexibility needed on the length of the pipe and the fittings no matter what the angle needed to be. When we designed the T-bases, ADS made the elbows specifically for us with the holes on the top and we just poured around them."

At the insertion pit, the new pipe was sliplined into the old concrete line upstream in the middle of a busy street and then sliplined downstream and connected in the middle.

"The CSO project was very challenging and time consuming, and when Gendron and his crew got near an old 60-inch concrete transmission sewer main, they found the joints were leaking so we ended up having to install another 400 feet of the 48-inch SaniTite HP pipe to segmentally slipline and rehabilitate the sewer pipe," said Beaule. "As the crew was digging alongside that old concrete pipe, the effluent was just pouring out of all the RCP pipe joints. We needed to do something quickly and sliplining seemed to be the best option since we already had a big hole opened. Matt Timberlake of the Ted Berry Company headed up that operation. Gendron helped with the excavation. Since we were installing a second storm drain for the CSO, we didn't need the full 60-inch capacity of the old sewer, so the 48-inch SaniTite HP pipe that we already had onsite worked perfectly; they just slipped it right through, and it worked out great."

The unexpected repair to the old sewer line was declared an emergency. "Within 72 hours from the time it was discovered we were putting pipe in," said Timberlake. "The city could have dug it up and replaced it or do a cured-in-place liner, which is not something that you're going to turn around in 72 hours, and this had to be done quickly."

A total of 400 feet of SaniTite HP, 48-inch-diameter pipe was sliplined into the old concrete pipe with connections to 10 service laterals, including two 18-inch service lines using Inserta Tee connections. The pipe's triple-wall profile design reduces friction and along with its engineered bell and spigot joint allows for longer, uninterrupted pushing distances with lighter construction equipment.

"We were able to insert in two different directions from one pit," Timberlake explained, "and then bring those pipe sections together with a final connection in that pit. Essentially, we lined upstream into a manhole and then downstream into a manhole. The pit was about 30 feet long by about 12 feet wide at the bottom so that we could use the 20 footers of the SaniTite HP pipe to minimize joints.

"Generally, a city can't get everything it wants," offered Timberlake. "They want it done quickly, they want it done correctly, and in a cost-effective manner. It's very hard to get all three. In this case, however, Lewiston got it done right with a very quick turn around and from an economic standpoint, they ended up with a new pipeline. And I know, all things considered, the city is very happy with the final install cost."

"As far as the pipe is concerned, if it wasn't for the ADS pipe, I would have never had the flexibility to do what we did," said Gendron. "It wouldn't have gotten done that fast."

According to Lewiston's Beaule, "We have to complete all the projects for our CSO master plan by the end of 2014 in order to stay in compliance with our permit from the Maine DEP. We expect to be installing at least 10,000 feet of SaniTite HP pipe this year, and perhaps more."

Stephen C. Cooper is the lead writer of SCA Communications in New York.


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