Mark Sprouls Free-lance Writer Tucson, Ariz.

One of the highest-volume landfills in the United States has reduced soil use for its daily cover by 30 percent and has extended cell capacity using a computer-based grade control system, which relies on global positioning system (GPS) data.

The Olinda Alpha Landfill, Brea, Calif., operated by the County of Orange Integrated Waste Management Department, sees an average of 9,500 tons of material per day, with 7,000 tons of that buried in place. Concerned about grade control problems, the landfill decided to test Peoria, Ill.-based Caterpillar's Computer-Aided Earthmoving System (CAES) as a way to conserve valuable airspace and reduce soil use.

“Limiting soil use has been a priority for us because we did not have enough soil on site to meet our needs until the closing date of 2013,” says Dave Lowry site manager for Olinda Alpha. “This problem is compounded by the fact that purchasing and importing clean soil is very costly. We have been successful in using processed green material as alternative daily cover at the working face and for erosion control on slopes.”

To present and collect data, CAES relies on GPS, wireless mobile data communications, onboard computing and sensing, and computerized information management in the office.

Olinda Alpha wanted to test the system's effectiveness in grade control. Consequently, it was installed on four pieces of equipment — a Caterpillar 836 compactor, two D10R tractors and one D9R tractor — allowing the operator to view a color computer image of the landfill plan.

The real-time display shows how many passes the compactor has made and how much must be cut or filled by a tractor. The display also shows the location of the machine in relation to the site plan.

Equipment operators can view up-to-the-minute plans from their machines, and they can view current topography and cross-sections, with updates in real time as the surface is altered.

As each machine works, terrain updates are collected and transmitted back to the landfill office to maintain a single up-to-date model of the site. Such data can be exported to the original planning software when additional design work or plan changes are needed. The system accepts plans generated with conventional computer-aided-design software.

Overall, the system has helped Olinda Alpha create a daily cover with more uniform lift thickness, which saves airspace and translates to $1 million per year in savings at the current tipping fee.

“Our emphasis has been on proper grade control,” Lowry says. “The biggest waste of space here has been soil used as daily cover. Daily cover required in California is 6 inches of earthen material, but we sometimes used much more soil to smooth out areas where there was differential settlement. Building a tighter, flatter trash base helped reduce excessive soil use for grade control.”

Lowry also notes that the system reduced labor. With CAES, there is no need for a survey crew to spend time in the field conducting surveys on every lift. The system also eliminates the need to place grade stakes and vertical elevation markers.

Previously, survey stakes had to be placed on a 50-foot by 50-foot grid and replaced every three days of operation. The new system uses a 10-foot by 10-foot grid, which is automatically updated. This means the virtual stakes are more accurately placed and there are fewer obstacles to work around.

The engineering department also does not need physical surveys to complete as-built files.

Operators report the system reduces the amount of mental work. According to George Valenzuela, the compactor operator, “It takes away a lot of the stress by telling you when you have made the right number of passes. When the screen is green, I'm done.”

Wade Griffith, a veteran tractor operator says it took him about two days to adapt to the new system. “I could tell the difference right away. It made my job a lot easier, and the landings were a lot flatter. We also get our jobs done faster and can work on other things on the site.”

According to Lowry, operators rely on information about boundaries and obstacles, such as methane recovery and leachate lines. Because only four machines at Olinda Alpha are equipped with the new system, those four operators communicate grade and location information over voice radio to other operators.

The landfill continues to set a progressive pace, even though it opened in 1960. The 565-acre site has 420 acres designated for waste disposal. Total airspace capacity is about 123 million cubic yards — enough for Olinda Alpha to reach its 2013 closing date.

This will allow ample time for landfill staff to adopt more innovative techniques and equipment to reduce costs and improve efficiencies even further.