Landfill Case Study
Good Machine Management Cuts Operating Expenses, Extends Landfill Life for Yakima County
Caterpillar’s CAT 627G Scraper has proved the most cost-effective machine for moving obstinate materials at Yakima County’s landfills, in turn saving space and time.
Millions of years past, according to geologists, volcanic eruptions in the Cascade Mountains left widespread deposits of volcanic debris around the southcentral Washington towns of Ellensburg and Yakima. One such deposit, the Ellensburg Formation, has over time become a dense, stubborn soil composed of clay and abrasive rock. For Wendy Mifflin, solid waste manager for Yakima County, and Dan Brulotte, operations manager for the county’s Terrace Heights and Cheyne landfills, the Ellensburg Formation is both benefit and annoyance.
A benefit, says Mifflin, because the soil’s characteristics meet Washington’s regulations for “arid-design” landfills, which require no liner system. The landfill cells are underlaid with clay, she says, and the depth of the area’s ground water is at least 350 feet—and more than 700 feet in some areas. On the other hand, says Brulotte, excavating a new cell or excavating cover material is difficult, typically requiring a ripper tractor to first loosen the soil. Plus, he says, the rocky, abrasive nature of the soil accelerates wear on machines that handle it.
The chore of moving this tough soil falls primarily to Caterpillar’s (Peoria, IL) Cat® 627G scraper, which loads and transports the material after a Cat dozer (either a D9T or D8T) makes a pass with a single-shank ripper. The twin-engine 627G, which develops 630 net horsepower, can self-load in all conditions and hauls cover material up to 2,500 feet to create a stockpile berm that a dozer will later use to cover the face at day’s end.
The scraper works primarily at the 110-acre Terrace Heights site, the county’s principal landfill, located four miles from Yakima. Periodically, the machine is transported 25 miles south to the town of Zillah, where it works on the 125 active acres at the 960-acre Cheyne location. According to Mifflin and Brulotte, the scraper has proved the most cost-effective machine for moving this obstinate material at the landfills, and Yakima County has used such a machine almost from the opening of the sites in 1972.
The county purchased its first scraper for landfill duty in 1975—a Cat 613, which used an elevator-type loading system. The 613 served for seven years; then was replaced in 1981 with an International Harvester 433 dual-engine, open-bowl model. A few years later, the IH was traded on the county’s first 627 (a B Series model), and a 627 has been consistently onsite since.
Managing Operating Costs
Keeping the scraper working productively at low costs in its demanding environment requires careful machine management—a strategy that has evolved over time. Early on, the county recognized the benefit of purchasing on a total-cost-bid basis, which means that the selling dealer performs all preventive maintenance and all repairs for a set per-hour fee, while also guaranteeing a set level of availability.
The contract also establishes a trade-in value up front, based on the machine being used 6,500 hours. According to Mifflin, 6,500 hours typically equates to about three years’ use. “The 6,500-hour mark was established through trial and error over the years,” says Bill Moore, sales rep for NC Machinery, the local Caterpillar dealer that has placed most of the machines used at the two landfill sites. “Working in partnership with the county, we’ve collectively determined that after 6,500 hours in this application, we still have a machine that has incurred no power-train issues, has high availability and an acceptable resale value.”
The resale value of the scraper, in fact, may be higher than for comparable machines in the area—for several reasons. First, the machine has been under the watchful eye of the dealer from the day it was placed into service, resulting in it having been conscientiously maintained and assuring that needed repairs were performed in a competent, timely fashion. Also, the heavy-equipment operators at the Yakima County landfills take great care with the machines they run, helping to keep repairs to a minimum. Yet another reason for potentially higher resale value results from the extensive modifications NC Machinery performs on each 627 before its goes to work at the county’s landfills.
When a 627 destined for landfill service arrives at NC Machinery, the dealership’s technicians remove the apron from the bowl, then line the bowl with abrasion-resistant T-1 steel, along with lining and reinforcing the apron. Also, rubber belting is installed to protect the hydraulic cylinders and to prevent rocks from lodging between moving parts, for instance, between the bowl and draft arms. In addition, the machine is fitted with Caterpillar’s best seat, air conditioning, premium tires and a cold-weather-start kit. “These modifications are the result of experimenting over the years—and over many scrapers—with ways to avoid premature wear and damage,” says Moore. “We’ve concluded that we get the lowest overall cost of operation when we make the modifications up front, typically an investment of $25,000 to $28,000. The 627 is a heavy-duty machine, but repair costs resulting from handling the material in this application can run up expenses if you don’t protect the machine from the start.”
So successful has been the management of the county’s landfill scraper, that all machines in the landfill fleet are handled in a similar fashion—total-cost bid purchase and trade-in at a specified number of hours (usually 6,000 to 6,500). Again, says Moore, this “sweet spot” (the optimal time for replacement) has been determined through experience with the machines.
At present, in addition to the current 627G scraper, the county uses two Cat dozers at Terrace Heights (D8T and D9T), plus a Cat 826H landfill compactor and two Cat 950H wheel loaders. At Cheyne, a D8T and Cat 816F compactor are at work. Another 950H loader works at the country’s Lower Valley transfer station, and a Morbark horizontal grinder is used to process yard waste.
Right Equipment Yields Space (and Time)
Another aspect of Yakima County’s landfill-machine management is a willingness to keep an open mind toward more efficient ways of handling solid waste. For example, until several years ago, says Mifflin, compaction of waste deposited at Terrace Heights was handled by the D8T dozer and 816F compactor. But what would happen if large versions of these two basic machines were used? “We brought in the heavier D9T and the larger 826H compactor,” says Mifflin, “and our compaction rate increased from around 800 to 1,100 pounds per cubic yard. We’ve calculated that increase from flyovers, which give us the data to determine how much space we’re saving (or gaining) with better compaction. At Terrace Heights, we estimate we’re gaining a year of landfill life for every two years of future operation.”
The 816 compactor, formerly used at Terrace Heights, was transferred to Cheyne, where, before its arrival, trash was compacted only with a D8T dozer. These two machines now working together, says Mifflin, have yielded results proportionate to those at Terrace Heights. “Landfill space is a precious commodity in Yakima County,” says Mifflin, “so the longer we can preserve it, the longer disposal fees can remain reasonable. We figure that we paid for the upsizing of equipment at Terrace Heights within a year of purchase.”
Managing Space Wisely
In 2009, the Terrace Heights site accepted 161,000 tons of municipal solid waste, and the tonnage at Cheyne for the same period was 71,000. These are the numbers after an average 30 percent recycle diversion and after the diversion of yard waste and construction debris, most of the latter being processed at two private landfills in the area.
According to Brulotte, Terrace Heights will remain the county’s primary site until its closure, estimated to be around 2019. The site, at current usage rates, actually has the capacity to remain viable until 2024, he says, but the capacity remaining after 2019 will be used only for emergency fill.
In 2019, Cheyne will become the county’s primary site, having a permitted remaining life of 50 years. Cheyne presently is used only for accepting waste from the area’s Lower Valley region, but when it becomes the primary site, says Brulotte, the existing transfer station near Yakima will be enlarged, and all waste will be hauled to the site with a fleet of county-owned trucks.
As Yakima County adjusts its landfill operation to suit future requirements, one aspect of its operation likely will remain constant—the use of a modified, twin-engine, open-bowl scraper as the most economical method for moving cantankerous soil.
Walt Moore is a freelance writer for Caterpillar. For more information about Caterpillar, call (309) 675-1000 or visit www.cat.com.
*CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow” and the “Power Edge” trade dress, as well as corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission.