Brian Lowe
Mowing the vegetative cover on a closed landfill cell is a vital component in the ongoing post-closure plan, but it also presents a challenge to the authorities and the contractors that are tasked with executing the plan. Most modern cells are designed with slopes shallower than 3 to 1 to minimize erosion from the elements. But older landfills and a demand for increased cell capacity without an increase in the footprint mean that cells with steeper slopes are a reality. While the construction of these steeper side cells has its own challenges, the post-closure control of vegetation for any cell has their own concerns that will span the next several decades.
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Proper Control of Vegetation
Establishing a healthy vegetative cover is important for long term 鈥榮urvival鈥� of a capped cell by reducing the effects of the environment and the associated erosion concerns. However, the vegetation cover must be managed so roots from woody plants and saplings do not penetrate the cap and reach and damage the geo-membrane. Similarly, proper control of vegetation is deemed an important component of a brush fire risk reduction plan. As a result, most post-closure management programs recommend semi-annual mowing to encourage growth of beneficial ground covers while discouraging the establishment of damaging shrubs and trees. This is viewed as a best management practice that strikes an optimal balance between vegetation control and ongoing cost. As every site is different and depending upon native vegetation, more frequent mowing may be required. This in itself adds to the challenge and cost of mowing on slopes.
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Slope Problems
Even on the more gentle slopes, uneven settlement of the cell cover over the first few years following closure can produce localized areas that exceed the operating angles of common mowing equipment. Zero Turn Radius mowers (ZTRs) are frequently used in grass cover/vegetation control as they are fast, efficient, and common, making them cost effective. However, they generally have a working angle limitation of 15脜茫 (or a slope of 3.7 to 1). If operated on steeper ground, theriding operator can be placed at risk for a roll-over, often with serious consequences. As most slopesare not uniform across the face, operating in an area perceived to be less than a 15脜茫 slope is noinsurance against a rollover. Exacerbating the problem, people are generally very poor judges of anactual slope. Can you tell a 17脜茫 slope from one that is 10脜茫 or 22脜茫? In a study conducted by U.S.Consumer Product Safety Commission, it was found that at least 42 percent of ZTR鈥檚 are operated onslopes in excess of 15.. The same concerns holds true for a crew using string trimmers and clearingsaws on slopes with overgrown vegetation. While the threat of equipment roll-over is removed, therisk of twisted ankles and other slip and fall injuries are very real. People do not perceive that thiscould be as hazardous as it is.
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Remote-Controlled Tracked Mowers
Since vegetation control on landfills is a challenge that will be present for decades to come, a remote controlled tracked mower is one solution that can combat the challenges that come with maintaining landfills鈥� slopes. A heavy duty, remote controlled, industrial mower is available that was designed for mowing slopes and other hazardous applications. At 2,600 pounds and a 52鈥� wide cut, it can easily mow more than 3/4 acres of sloped ground in just 1 hour and with only one person. Other considerations such as lower liability and workers鈥� compensation insurance costs and a smaller crew factor into a low cost of operation.
With an operating radius of 300 feet, the remote controlled mower significantly reduces the manual labour hours previously required. Running on rubber tracks, the mower has a low center of gravity and is capable of operating on side slopes up to 50脜茫, all without the need for external tie-offs or ground damaging steel spikes attached to the tracks. Making operations even easier, an operator simply can run the mower backwards rather than taking time to turn the unit around to make another pass.
But the main factor to highlight is that the operator is remotely positioned away from the mower. If a concealed washout is encountered or the ground suddenly gives way, the operator remains at a safe distance. The same holds true for natural hazards such as snakes and unseen bee hives hiding in the overgrowth. Keeping the operator at a safe distance from the mower is not possible with other means of mowing. Regardless of the conditions at hand, the site鈥檚 closure plan must be followed or partitioned to be changed. The latter is a daunting task in most cases so adapting to the stated vegetative control requirements is often the easier path. A remote controlled mower provides an additional tool to accomplish the plan.
For more information, contact Dave Burkhart, sales and marketing coordinator for
Tiger Corporation (Sioux Falls, SD), at (800) 843-6849, via e-mail at [email protected] or visit .
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Sidebar
Maintaining a Landfill in Iowa
Following an unfortunate incident that resulted in an injury to an operator, an 1,800 acre landfill in Iowa* needed a better way to maintain the vegetation growing on their site. Various mechanical means were tried, including tractors with dual tires and bat wing mowers, and ATV鈥檚 equipped with tracks pulling a small mower. Each method had its drawback鈥攖ractors were large and heavy with a high center of gravity, and an ATV offered no protection to the operator. The need to look for a better way to maintain the steep slopes became a priority.
Having seen the remotely controlled Prowler庐 mower at a recent industry trade show, the management at the landfill called the local Tiger dealer, Mid Country Machinery, to demonstrate the Tiger Prowler on their own site and conditions. The demonstration showed that the Prowler was easy to operate and capable of negotiating the steep slopes and terraces that surround both the active and closed cells of the complex. Although the season has been unusually dry, the Prowler was able to maintain the vegetation that had grown since the previous control cycle to the management鈥檚 satisfaction. In the spring of 2013 following a governing board鈥檚 decision, a Prowler Slope-Pro was purchased. With experience operating a wide range of track based rolling stock, the Prowler was soon 鈥榬ight at home鈥� at the landfill. From a management perspective, the remotely controlled Prowler addresses many issues that all landfills face: it not only offers increased employee safety, it helps to control costs associated with equipment maintenance and repair and the ever present insurance risk.
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*It is the policy of the landfill referenced that testimonials are not provided. Tiger Corporation respects their position. The landfill continues to use the Prowler Slope Pro since early this year to maintain their landfill.
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Sidebar
A Closed Landfill in Massachusetts
A closed landfill in Massachusetts situated within a valley, issued a post closure maintenance contract for a 20 acre site with 30 degree sloped cell walls. As is standard design practice, the site has a berm or terrace of riprap to control erosion about every 75 yards and an extensive methane collection system. The slope of the terrace was gauged at 40 degrees and approximately 8 to 10 feet wide. The contract called for twice per year vegetation control with a cut height of 4″ to 6″. While these are common site conditions, it very difficult to use conventional mowing equipment or a boom mower effectively and safely. The company that was awarded the contract initially used a 73 HP diesel compact track loader with a 72″ front mount mower and a tractor pulled 15′ bat wing mower for the flat, open areas. Augmenting the mowers was a crew of several string trimmers. While it 鈥榞ot the job done鈥� the methodology took its toll on both equipment wear and tear and the retention of manpower as it was tough work.
In late 2012, the contractor added a 鈥楶rowler鈥� Slope-Pro庐 as part of his fleet. As with all new equipment, there was a learning curve in how to best use the Prowler and extract the highest productivity. To date it has shown great results in this application and has replaced the string trimmer crew as well as their associated costs. While the company is now 鈥榮maller鈥� the Prowler has also opened up new opportunities (and reduced expenses) at other sites the contractor maintains, such as dams and other riparian zones, where mechanical mowing was previously prevented or consider too hazardous.