Municipalities around the United States are gearing up for the next big battle in the war against aging infrastructure. This time the enemy is leaking water systems. While much attention has been placed on sewer replacement and Inflow and Infiltration, the battle lines have been drawn in what could promise to be an even bigger undertaking on the water utility side: unaccounted-for-water.
The Mammoth Community Water District (MCWD), Mammoth Lakes, Calif., serves as an example of a small water utility making a big difference in terms of the integrity of its water system. Plagued by tuburculated and deteriorating water mains and service lines, project superintendent Mark Busby has helped implement a district-wide water main replacement program. He said, “The system is deteriorating. The mains have a lot of pinholes in them that the crews have been plugging and fixing over the years. And it’s just getting to the point where our water losses and the cost associated with repairing these problems is becoming too great. It’s time to replace them.”
While conditions are favorable for open cutting most of the mains, services, however, pose more of a challenge. For service line replacement the District chose a pipe extraction method using a Grundomat piercing tool from TT Technologies, Aurora, Ill.
The Environmental Protection Agency has been very active in promoting and mandating the reduction of Inflow and Infiltration. The organization has also been actively pushing for the reduction of unaccounted-for-water. In its simplest terms, unaccounted-for-water equals the amount of water pumped by the utility minus the amount of water actually billed. In addition to a leaky system, several other culprits can be responsible for unaccounted-for-water. These include inaccurate meters, un-metered water and theft of water.
The EPA has set a goal of less than 10% for unaccounted-for-water nationally. Current estimates put annual percentage loss between 10% and 40%, with 10% to 12% considered acceptable. Worldwide the figure is even worse with some underdeveloped countries losing over half of their water before it reaches its destination.
It is easy to see that what is perceived as a minor problem can have a tremendous impact. For example, a typical 60-psi water system with a single leak of a 1/16 of an inch will lose approximately 74,000 gallons over a three-month period. A leak the size of a 1/4-inch will result in the loss of a staggering 1,181,500 gallons over a three-month period. In the water industry, small problems are big ones.
With such a valuable resource at stake, many communities are deciding to become accountable for their unaccounted-for-water. Identifying the problem is often the first step.
Some municipalities like the MCWD knew there was a problem even without completing a water audit. Busby said, “We knew our mains were leaking and we’ve had issues with the services from time to time. We also knew our mains and services were suffering from turburculation and would need to be replaced sooner or later.”
The Mammoth Community Water District
The MCWD is located approximately 8,000 feet above sea level in California’s Sierra Nevada Mountains. According to Busby, the town of Mammoth Lakes, (pop. 7,000) is a resort community, and can double and even triple in size during certain events and peak holiday periods. The District is home to the Mammoth Mountain Ski Area, and adjacent to Yosemite National Park, the Ansel Adams Wilderness and an endless variety of recreational opportunities.
Located on the eastern slope of the mountain range, the area receives over 30 feet of snow annually. This precipitation accounts for a significant portion of the MCWD’s renewable water resources. According to Busby there are two main water sources for the District. The first is run-off from the mountain snowmelt that supplies the area lakes. And the second is wells.
The District’s water system is still comprised of a large percentage of aging steel water mains and galvanized steel services. According to Busby, the system was installed in the late 1950s and early 1960s and is now starting to fail. Although the District has typically experienced unaccounted-for-water losses in the range of 15% to 20%, recent water audits had seen that figure exceed 30%.
Busby said, “That’s a lot of water. But it’s just not the water loss in and of itself. There are years when we have supply shortages and have to implement rationing. Four-and-a-half mgd [million gallons per day] or more through an old system with a 30 percent water loss, that’s a problem and it needs to be fixed.” With that in mind the District implemented an aggressive water main and service replacement program over the past few years and decided to accelerate this program earlier this year its annual during capital project budget discussions.
Water service replacement projects like the one at the MCWD are well suited for trenchless piercing tools. The piercing tool is easily one of the most versatile trenchless tools available. They have had an impact on almost every segment of utility construction. TT Technologies piercing tool specialist Davis Yates said, “The gas industry, wastewater industry and the water industry have not only been proponents of trenchless technology in general, they have been great supporters of piercing tools. With standard sizes ranging between 1 3/4 inches to 7 inches in diameter there is a piecing tool available for just about any application.”
The piercing tool is commonly used for horizontal boring. However, the tool can also be configured for various other applications including pipe ramming and pipe bursting. In the case of the MCWD, the tool was used for pipe extraction in addition to new service installation. Yates explained, “For new installations, the tool can pull in the new pipe during boring by utilizing a pipe pulling adapter. The new pipe can also be pulled in after the bore by attaching it to the air hose and pulling it into place after the bore.
“Pipe extraction adds another dimension. During extraction you have two objectives: one, remove the existing service and two, install the new one. This application really demonstrates the versatility of the tool. A pipe-pushing adapter is connected to the front of the Grundomat. The tool is used to drive the existing service out while pulling in the new service. This method is usually used for small diameter gas or water services.”
On The Job
For the first portion of the MCWD’s water main and service replacement project, a section of main paralleling a two-lane residential roadway was chosen. The 8-inch steel main was excavated and replaced with 8-inch ductile iron. As one crew was replacing the main, a second crew replaced the services. Busby said, “We decided to replace the services for two reasons. We figured that they were deteriorating as well. Also, we only wanted to go through this process once and since we were already replacing the mains, it seemed logical to replace the services at the same time.”
According to Busby, the trenchless application was chosen for the services because they ran underneath the roadway and the District did not want to disrupt traffic or incur the cost of restoring the road. Timesaving was also a factor in the selection of the pipe extraction method due to the region’s short construction season.
To extract the 1-inch diameter galvanized steel water services MCWD crews used a 185-CFM air compressor and a 3 3/4-inch diameter Grundomat-P 95 equipped with a pipe-pushing adapter. Yates explained the need for the 3 3/4-inch diameter tool. He said, “The services were located at a depth of four feet. We decided to go with a more powerful tool to overcome the weight of the existing services. The ground conditions are also tough in that area; made up of granite, decomposed granite, running sand and more granite. With the long-side services up to 80 feet long, we wanted to make sure we had the necessary power.”
Crews pulled the new 1 1/2-inch diameter High-Density Polyethylene (HDPE) services behind the tool using an air nipple. Yates said, “We decided to pull with the services using the air nipple to avoid contaminating them with an air hose. Using the air nipple allows us to use the new HDPE as the air hose. A tapered air nipple is attached to the back of the tool. The new HDPE service is then attached to the tool and the compressor and serves as the air supply. We also used a specially formulated, FDA approved, food-based tool lubricant called Grundosafe to avoid contaminating the new services.”
Crews excavated launch and exit pits using a vacuum excavator truck with a 500-psi water knife. Extraction of the old 60- to 80-foot services took approximately two hours each from start to finish. According to Busby, a crewmember positioned in the exit pit would bend the old service by hand as the old service was being extracted to keep it clear from obstacles.
For the first segment of the project, MCWD crews replaced 14 water services using the extraction method. District officials were very pleased with the results of the first phase. Busby said, “Using trenchless allowed us to keep the road open to traffic. Plus, asphalt paving up here is very expensive. If we open cut just three services, we’d be spending more than the piercing tool costs. So basically the tool paid for itself.”
More service line replacement is on the way. According to Busby, another 60 services are scheduled to be replaced by the end of this summer.
by Jim Schill
Trenchless Technology, July 2003