Bill Sangster, landfill field service supervisor.
Thirty years ago, the city of Denton ECO-W.E.R.C.S. (Energy, Recycling, Composting and Solar) Landfill started with 32 original acres. About 13 years later, the city began expanding the landfill, and today, the landfill permit 1590-A now encompasses 152 acres.
The need for landfill expansions is crucial, especially during the past 15 years. The national 2010 Census showed that the city of Denton, Texas, increased in population by 40 percent during the 10-year period since the previous count was taken, expanding from just more than 80,000 to 113,383. The growth trend continues to point in an upward direction.
The most recent data, collected in 2013, showed the population at more than 123,000, and since 2006, the city has been among the nation’s top 25 fastest-growing cities with populations of 100,000 or more. In addition to a burgeoning number of individuals and families, the city is home to the University of North Texas and Texas Woman’s University.
“We handle all the trash for the city of Denton, as well as from the two large universities located here and some refuse from surrounding counties,” said Bill Sangster, field service supervisor of the Landfill Division of the Solid Waste Department. “We have about 700 tons of waste per day, 80 percent of which is commercial waste from businesses, and the rest is residential waste. Our goal is to recycle a large percentage and keep as much as possible out of the actual cells.”
The city’s curbside recycling program helps in that effort, as does a focus on sorting and diverting construction and demolition debris that comes in from contractors and through the city’s solid waste commercial roll-off service. It provides boxes at job sites and picks them up when they’re full. The city makes mulch from pallets and sells it and other wood products, as well as different colored mulch made from brush, leaves and small trees that the city collects throughout the year.
“Additionally, residents can contact us if they want to dispose of chemicals or paints,” Sangster said. “They can arrange for us to pick them up. If household chemicals or paint are not toxic and can be reused, we put the items in the reuse store and allow residents to take them for free. If they are toxic, we dispose of them properly. We don’t want those items going down the drain or into the landfill.”
Benefits of Water, Gas
Two components contribute to the city of Denton ECO-W.E.R.C.S.’s vision of sustainability. One is an enhanced leachate recirculation program. As water percolates through a trash cell, it’s collected at the bottom of the pit. Pumps send it back into the cell through a piping system that includes some perforated pipes. This allows the water to pass through the cell again.
“Normally, it would take about 30 years for the materials in a cell to fully decompose,” Sangster said. “Leachate recirculation speeds up the decomposition by half or more, in most cases. We can also add stormwater or effluent water to help with decomposition. Then we can go into an old cell, mine out the inert material and reuse the cell. In a city such as Denton that continues to grow, that’s a great benefit.”
Another advantage, and the second component of the landfill’s sustainability effort, is that it captures the methane that’s produced as the trash decomposes. The city of Denton ECO-W.E.R.C.S. program sends the gas to an onsite generator that produces electricity. The electricity is sent to the local power grid, and it is enough to power about 1,600 homes.
“We constantly monitor the methane, which also helps us determine if a cell is ready to be mined,” said Sangster. “Eventually, the methane level drops significantly. When that happens, we can mine the cell and reuse it.”
Moving Materials With Komatsu
Soon the landfill will begin mining an old cell. Sangster said the process will involve removing the cap, then digging out the dirt and removing any remaining trash, about 40 percent of which will be recycled.
The landfill will use four new pieces of Komatsu Tier IV Interim equipment that it recently purchased from Kirby-Smith Machinery, Inc. to dig and move the dirt and harmful materials. The list of machines includes a PC490LC-10 excavator, an HM400-3 articulated truck and a D65EX-17 dozer. The landfill rounded out its equipment package with a truck equipped with an 8,000-gal. (30,283 L) water tank that it uses to spray the cells and reduce the dust on haul roads.
“We’re extremely pleased with the Komatsu equipment from every standpoint,” said Sangster. “Our operators like the ease of operation and especially the comfort of the trucks. They have good power and efficiency, so our production is high and our costs are low.
“Something that really stands out to me is that Komatsu’s Tier IV engines regenerate automatically while the machines are operating, so we don’t have to pull them out of service to sit for half an hour or more. That allows us to keep working, which in turn means we’re maintaining production,” he added.
“KOMTRAX is another terrific feature. I like that we can track machine idle time and other critical information, such as hours. That keeps our services on track.”
The landfill worked with Kirby-Smith Machinery Inc. Governmental Sales Representative Sol Gieser to put the package together, including extra guarding on the dozer and excavator undercarriages and a thumb on the excavator.
“The decision to buy Komatsu equipment came down to a couple of things,” said Sangster. “One was price, and the other was the service backing the equipment. Sol and Kirby-Smith put together a nice package, and the fact that they cover the services complimentary through the Komatsu CARE program certainly helped when making the final decision. They track the machines and let us know when a service is due, then come and take care of it. We’re very happy with the relationship we’ve built.”