Celebrating its 85th anniversary in 2011, the Consolidated Mutual Water Company (CMWC) in Lakewood, Colo., is continuing the pioneering spirit of the company founders who banded together to provide water for the growing population in the West.

Serving a population base of approximately 85,000 people in the communities of Lakewood, Wheat Ridge and unincorporated portions of Jefferson County, CMWC is in the midst of a pipe replacement program that is saving the community money while increasing water quality and reliability. Beginning in 2010, CMWC began a systematic program to replace aging water pipes using the trenchless replacement technique of pipe bursting.

Even though the program has been in place a short time, the results are already evident. CMWC is increasing its pipe replacement program in terms of footage installed per year with less cost and disruption to customers. Other utilities, including the neighboring communities of Denver, Aurora and Golden, have taken notice as well. In fact, CMWC has hosted some 1,000 visits to its jobsites over the past two years to see if the success can be replicated elsewhere.

Background

As the City of Denver grew in the early 20th century, so too did its suburbs. To the west of town, water was obtained by drilling deep wells that came with considerable costs. To help allay these costs, residents banded together and formed ?mutual water companies? that provided wells, pumps and distribution piping. In 1926, four of these companies ? the Oaks Mutual Water Company, the Glen Creighton Mutual Water Company, the Wadsworth Mutual Water Company and the North Wadsworth Mutual Water Company ? merged to form the Consolidated Mutual Water Company.

Through the years, CMWC expanded through additional mergers to its present service area of approximately 27 square miles and 400 miles of distribution. Instead of using the deep wells, which were not considered sustainable, CMWC acquires 70 percent of its water through the City and County and Denver. To help offset the effects of rationing and ensure adequate water supply to sustain growth, CMWC acquired surface water rights and constructed the Maple Grove Reservoir and Treatment Plant, which were completed in 1957. These facilities now provide approximately 30 percent of the water supply.

The CMWC piping network comprised mostly cast-iron pipe installed in the 1940s and earlier that was reaching the end of its useful life. The pipe was suffering from corrosion and tuberculation, which resulted in water main breaks and water quality issues. In the past, CMWC had relied on open trench replacement of water mains, which resulted in disruption to residents and businesses in addition to the high cost of surface restoration. Mike Queen, president of CMWC, estimates that open trench replacement cost the utility an average of $112 to $115 per foot.

Looking for a Better Way

After Queen was invited to view a pipe bursting program in Florida, he was intrigued by the process and initiated a pilot project in Colorado. After evaluating and testing bursting equipment and piping products, CMWC decided to proceed with a pipe bursting program to replace approximately 25,000 linear feet of water mains beginning in April 2010 targeting areas with antiquated and undersized lines. In total, CMWC crews replaced 27,000 linear feet of pipe in 2010.

While many cities hire specialty contractors for pipe bursting projects, CMWC elected to use its own crews. ?We?ve always done our own pipeline installation, so we?ve always had our own construction crew. And it is the opinion of the Board, and mine too, that if we?re going to own it and maintain it, we might as well install it so that we know what we are getting. We met with the construction crew prior to starting the pipe bursting program and said ?this is the direction we?re going, we need you on board,? and everybody bought into it,? Queen said.

CMWC purchased a TT Technologies 800G static pull pipe bursting system and McElroy fusion equipment to install DR 18 Fusible C-900 PVC pipe from Underground Solutions. CMWC enlisted the technical assistance from the manufacturers when it initiated the pipe bursting program and have been fully self performing the installations with efficiency ever since. Typical pipe bursting runs are in the range of 500 to 800 feet, but CMWC has successfully completed runs of 1,300 and 1,800 linear feet.

The pipe bursting process consists of digging an entry pit and an exit pit instead of trenching along the whole length of the pipe alignment. A temporary bypass is needed to keep water flowing to residents and businesses during the process.

Crews fuse the PVC pipe offsite and move it to the location when they are ready for the burst. The pipe bursting machine, which includes a series of rods that are strung through the pipe, attaches to a bursting head that is pulled through the existing pipe, breaking the pipe and expanding out into the soil while pulling in the new PVC pipe. Once in place, pits are dug to reconnect house connections.

Pipe sizes being replaced are 4-, 6- and 8-inch. One unique feature about pipe bursting is that it allows the option to upsize the pipe. In most cases, CWMC is upsizing the pipe by 2 inches, including some instances of upsize 4-inch pipe to 8-inch.

The first phase of the project started on April 26, 2010, and was completed on Sept. 10, 2010. Due to the success of the program, CMWC increased the footage installed in 2011 to 34,000 linear feet, with plans to replace 40,000 feet in 2012. Previously, CMWC had been able to replace an average of 12,000 feet of pipe per year through open-cut methods. CMWC purchased a second pipe bursting unit to allow crews to leap frog between job locations, which has helped increase production.

CMWC?s Queen stated: ?We saved $1.3 million using pipe bursting instead of the open-cut method on the first phase ? and we anticipate the same cost saving results [for future projects].? He said that pipe bursting has cut replacement costs in half.

Queen said that he sees resistance to pipe bursting at other utilities because of unfamiliarity to the method or a reluctance to try new technologies. ?At some point you need to toss tradition aside and do what is best for the organization,? he said. ?We are aggressively replacing our old cast-iron mains and in the next 15 years, our system will be in really good shape.?

Andy Seidel, CEO and president of Underground Solutions, said CMWC is an example for other utilities and municipalities. ?In a time of constrained municipal budgets and tight capital spending, Consolidated Mutual Water Company has shown that it is possible to do more with the same vs. settling for doing less,? he said. ?The key variables to this equation of success are courage, discipline and an open mind.

?This project is a call to action for utilities across the country ? that with trenchless technology, they can gain ground on their infrastructure problems vs. falling behind.?

Jim Rush is editor of UIM.

Advanced Water Treatment Technology

Pipe replacement isn?t the only area of innovation at the Consolidated Mutual Water Company. CMWC recently upgraded its Maple Grove Treatment Plant. The plant upgraded its capacity to 15 mgd (expandable to 18 mgd) and uses GE?s ZeeWeed Ultrafiltration membrane as part of its primary and secondary treatment process.

The membrane is a pressure-driven barrier to suspended solids, bacteria, viruses, endotoxins and other pathogens used to produce water with very high purity and low silt density. It can serve as a treatment for surface water, groundwater, and biologically treated municipal effluent (membrane bioreactor and tertiary treatment). It can also serve as a pre-treatment before reverse osmosis and other membrane systems.
Plant operator Chuck Conway said that turbidity regulations were the primary driver installing the membranes as the Maple Grove Plant. The plant uses the ZeeWeed 1000 system membrane for primary treatment and 500 system membrane for secondary treatment.

A full-scale ZeeWeed treatment facility is comprised of a given number of modular components: modules, cassettes, and trains.

A module is the basic building block and the heart of a ZeeWeed system. Each module contains thousands of horizontally strung membrane fibers that have millions of microscopic pores in each strand. Water is filtered by applying a slight vacuum to the end of each fiber which draws the water through the tiny pores and into the fibers themselves. The pores form a physical barrier that allows clean water to pass through while blocking unwanted material such as suspended solids, bacteria, pathogens and certain viruses.

Modules are joined together to form a cassette, which is the smallest operable unit of the filtration system. Each cassette can have a variety of module configurations depending on the amount of water that the cassette is required to treat.

Multiple cassettes are joined to form what is known as a process train. The train is a production unit containing a number of cassettes immersed in a membrane tank. Multiple process trains form a ZeeWeed treatment plant.

Feed water flows into the membrane tanks and treated water is drawn through the membranes during
Production by applying a vacuum to the inside of the membrane fibers. The water removed by permeation is replaced with feed water to maintain a constant level in the tank.

The particles that are rejected by the membrane pores remain in the process tank and are periodically removed by a process called a Backwash (BW). During a backwash, filtered water is reversed through the membrane fiber to dislodge any particles that may be physically lodged in the membrane fiber. Simultaneously, aeration scours any solids that are attached on the surface of the fibers.
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To prevent fouling of the ZeeWeed membranes operators are required to perform regular maintenance cleans (MC). Maintenance cleaning begins by draining the membrane tank and soaking the membranes in a cleaning solution for several minutes. The solution is then drained and chemical residues are flushed from the membranes before the system resumes normal operation.