By the time gasoline prices topped $4 per gallon this summer, it was obvious to people across the United States that our energy situation needed to change. Energy self-sufficiency became a much higher priority.
Conservation, off-shore drilling, biofuels, nuclear, wind and solar have all been put forward as solutions, and it seems likely all will play a role in time. In the short term, the leading alternatives appear to include more extensive use of abundant energy sources such as natural gas and coal. The nation already has infrastructure in place to harvest those products and deliver them to end users efficiently.
Natural gas seems most likely to cash in. The supply is there, and the wells are in place to get the natural gas out of the ground. End-user technology is in place to handle increased supplies, especially at numerous gas-fired powered plants.
The trick now is to deliver the gas from the wells to the end users. Pipelines are considered the safest and most efficient mode of delivery, and the United States has more than 180,000 miles of high-capacity natural gas pipelines in service. That's a lot of capacity. Most of the country's population centers have the infrastructure already in place to ramp up their use of natural gas.
A map of the nation's pipeline network reveals some large coverage gaps, however. Arizona, for example, has just two high-capacity lines. One enters the state from New Mexico in the southeast corner of Arizona. The other parallels Interstate 40 in Northern Arizona from New Mexico to California. Until recently, the southern line was the only natural gas pipeline feeding the state's two major population centers, Phoenix and Tucson.
That's been changing rapidly this year, thanks to construction of a 258-mile extension branching from the existing northern pipeline. The new line runs south from near Ash Fork, through West Phoenix. From there it turns west to near Buckeye and then southeast to near Coolidge. The segment from Ash Fork through Yavapai County has 42-inch pipe. Just after the line crosses into Maricopa County, the pipe diameter drops to 36 inches.
|This map shows the route of the Phoenix Lateral natural gas pipeline. Terry Ertter map. Click to enlarge.|
The Phoenix Expansion Project
The new line belongs to Transwestern Pipeline Co., the Houston-based company that owns the interstate pipeline across Northern Arizona. The northern segment is part of a 2,400-mile line that originates in West Texas, travels north to Oklahoma, then west through New Mexico and Arizona to the California border. Natural gas flowing through the pipeline comes from four primary sources:
- The Permian Basin in West Texas and Eastern New Mexico;
- The Anadarko Basin in Oklahoma;
- The San Juan Basin near the Four Corners area;
- The Rocky Mountain Basin in Colorado and Wyoming (through interconnections with TransColorado Pipeline and Northwest Pipeline).
Drillers in the Rocky Mountain Basin have tapped enormous reserves of natural gas in recent years, and pipeline builders have been scrambling to install delivery systems. The Phoenix Expansion Project is a key part of the network.
Construction on the Phoenix Lateral began March 5, 2008. As is always the case with pipelines, the construction phase followed months of studies to determine a route that would best suit the many needs of the land and people along the way.
"Transwestern worked closely with the Federal Energy Regulatory Commission to evaluate the impacts on geology, soils, water resources, vegetation, wildlife, land use, cultural resources, air quality, and noise," said company spokesman Jerry Hereden. Much of the northern half of the line travels through public land, including national forests. Wherever possible, Transwestern used existing rights-of-way for utilities such as power lines and roads.
Pipeline construction can appear to be a very disjointed process. If an environmental concern or right-of-way agreement in one area delays work, the construction companies will frequently work on each side of the disputed area until an agreement is reached. Generally, Transwestern's contractors worked from north to south, but with a 258-mile long project, it's common to have crews scattered along the length of the route.
Transwestern hired veteran pipeline companies as general contractors, including Rockford Pipeline Co. and Gregory Cook.
"When complete, the Phoenix Lateral will deliver 500 million cubic feet of natural gas per day. Most will go to existing generating stations in and around Phoenix for creation of electricity," Hereden explained. "The result will be that residences, businesses and other operations will benefit for traditional uses like cooking, heating air and water and powering machinery."
At its southern end, near Coolidge, the new line will tie into the existing El Paso Natural Gas pipeline that has long been the only source of natural gas for the Phoenix area.
The benefits for the Phoenix area and Southern Arizona are significant. 500 million cubic feet of gas per day can create 4,000 megawatts of electricity. That's enough to power 4 million typical American homes (1 megawatt per 1,000 homes).
It won't take long for Arizona utilities and citizens to put that energy to good use. The area in and around Phoenix has added more than 40 generating stations since 2001. Current total capacity for those new stations is more than 8,000 megawatts, but they rarely work anywhere near their current capacities. The stations are intermediate load and peaking power generators that can ramp up quickly to supply power as needed.
Electricity demands for the Phoenix area are expected to climb rapidly for years to come. The generating capacity is already in place to cover the next few years, and the Phoenix Lateral will ensure the plants have a plentiful and reliable supply of fuel — all produced within the United States — into the future.
As noted earlier, it often takes longer to get ready to start building a major pipeline than it takes to perform the actual construction. Routes must be finalized, important vegetation must be carefully moved out of the way, existing underground structures and utilities must be located and mapped, and crossings of waterways and highways must be studied and planned.
When all the planning is done, the process is straightforward, according to Hereden:
- The route is cleared and graded;
- Strings of pipe sections are laid out along the right of way;
- Trenches are dug deep enough to allow at least three feet of cover, and the soil removed is set aside for backfilling;
- Pipe is bent to match the topography of the land;
- Pipe sections are welded into one continuous length, and welds are inspected;
- Uncoated areas of pipe, usually around welds, receive a coating of epoxy to prevent corrosion;
- Pipe is lowered into the trench and covered with dirt;
- Pipe and weld integrity is tested with water under pressure;
- The surface is restored to original condition or better if possible.
Those nine steps are essentially the same today as they were a few dozen years ago. A number of technological advances in the past couple of decades have made the process more efficient and the pipe more likely to retain its integrity over longer time periods.
"On this project, we used mechanized welding techniques. That's a fairly new process that's more efficient than traditional hand welding with a rod," Hereden noted.
The padding process has enjoyed advances as well — primarily in the mobility and versatility of the padding equipment. Pipe lasts longer underground if it's surrounded by fine dirt with no clumps, rocks or voids that can settle unevenly beneath the pipe. Modern padders are machines — often modified crawler tractors — with screens mounted on them. They can plow into a stockpile of dirt alongside a trench, scoop the dirt and rocks up, run the material through the screens to remove rocks and break up clumps, and deliver ideal fine dirt to surround and protect the pipe in the trench. The entire process requires just a single pass.
Custom shops also have developed padding attachments for excavators in recent years. With their superior reach, excavators can fill trenches without having to be right next to them.
Perhaps the biggest advance has come from the horizontal drilling equipment. Horizontal Directional Drills allow crews to carve tunnels under canals, highways, railroad tracks, and other obstacles where trenching is not an option.
Yet, HDD is not one-size-fits-all. For instance, at one point, this pipeline had to pass under the Waddell Canal. The canal is part of the Central Arizona Project that moves Colorado River water across the state from Lake Havasu through Phoenix and on to Tucson.
"Use of an HDD is predicated on the geotechnical conditions of the soil. The soil conditions at the Waddell Canal were not conducive to an HDD, so a bore was performed," Hereden said.
The most visually interesting construction site came at the crossing of the Verde River near Chino Valley. The crossing also presented several technical and environmental challenges. A small fleet of excavators and pipe layers set up just a few feet apart.
"Crews used a flume-and-dam method," Hereden said. "The method places a dam a few yards upstream from the crossing. A temporary pipe carries water from the dam to the downstream side of the crossing.
"On this particular crossing, we had biologists construct a special screen to clear debris and capture fish for release away from the crossing. They caught more than 300. Other crews strung pipe, bent it, welded it, and placed it in the river 11 feet deep. The pipe consisted of three 80-foot sections encased in concrete. Then, they removed the flume and dam to let the river flow."
By mid-August, pipe placement and covering work was complete on Stretch 1 (milepost 0 to milepost 114). Cleanup and testing phases were well under way. Crews began trenching on Stretch 2 (mileposts 114 to 255), including some delicate work around developed areas in Northwest Phoenix.
Two months later, nearly all the pipe was in the ground for the entire project. Contractors were installing metering stations near generating stations, and working under and around the last few obstacles.
"Our target has been to complete the project before the end of 2008 and have a new supply of natural gas flowing to our customers," Hereden said. "We are working diligently within this timeframe."