Albuquerque, N.M., evokes images of spectacular western panoramas, desert sunsets, and Native American culture. This natural beauty was put in jeopardy in the late 1980s. Population in the unincorporated areas of Bernalillo County had been growing steadily for years. The farms and ranches that used to dot the countryside were replaced by small communities. Most of the homes were beyond the reach of the city's services, so the families relied on septic tanks and well water. Over time, a number of these septic tank systems began to fail, increasing the amount of untreated wastewater discharge into the valley's groundwater. By 1990, the situation had gotten serious.
In 1993, the state legislature allocated $12 million to address the problem. However, there was an important stipulation—a commitment to spend the allocated funds within 12 months had to be made, which is a tight timeline for a major public works project. In 1994, the legislature followed through with an additional $15 million in funding.
“Typically it takes up to a year to get an engineer hired,” said Bill Zimmerman, P.E., of HDR Engineering, Albuquerque, a firm brought in by the city's public works department to handle the wastewater project. At the time of the project Zimmerman worked for Wilson & Co., the firm hired to manage the design and installation of the sewer system. “Greg Olson, P.E., city engineer and a leader in the development of the vacuum sewer system in the region, accelerated the advertising for the project and really got things moving,” he said.
“Realizing that time was of the essence, one of the first things we did was schedule a marathon meeting with city public works employees and engineers,” said Zimmerman. In a three-day meeting, the committee discussed gravity sewers, pressure sewers, vacuum sewers, and combination sewers. They created a matrix of options, assigned numbers to the alternatives, and reached a quick conclusion—gravity sewers would be a costly, time-consuming option. When all of the issues were considered, vacuum sewer technology came out on top.
Albuquerque's groundwater table is usually only 4 to 6 feet below the surface. A series of deep irrigation ditches cuts through the valley at various locations. These ditches are vital to the area's agricultural needs and could not be disturbed, posing yet another obstacle. And, because the area is flat, the collection lines would require deep trenches with numerous lift stations.
“Urbanization was occurring in a rural area that was dead flat,” said Bob Paulette, P.E., an engineer with Wilson & Co., who has worked on Albuquerque's vacuum sewer project for 10 years. “A 0.4% slope on the 8-inch collection line means the sewer is dropping 21 feet every mile just to meet the minimum slope requirements. It is difficult to install sewers 21 feet deep in high groundwater conditions. Factor in the difficult irrigation ditch crossings and the cost would be staggering. It also would take years to complete.”
“None of us had had any experience with vacuum sewers; we had only read about them,” said Zimmerman. “We made arrangements to travel to Rochester, Ind., to tour the AIRVAC test facility there. Then we went to Nashville, Tenn., to look at an actual installation. Once we came back from that trip we were convinced vacuum sewers were the way to go.”
Within a few months, work began on the installation of a new vacuum sewer system. Vacuum sewer technology not only made for a speedier installation, which was vital for this project, but it also solved a number of related problems that would have stalled the project and ballooned the budget.