"If you don't use a variety of fences at your landfill, yet your complaining about litter, you're not dealing with the problem, your chasing symptoms" (Who Says You Have a Litter Problem, Neil Bolton, MSW Management, July/August 2000)
Relying on one line of defence for managing your litter will help, but it won't solve the blowing litter issues. You need to look at a variety of fencing options. This includes, using perimeter fences, wind-break fences, and portable catch fences. You may need to erect temporary or semi-permanent lines of fences across your site between your action operations and the perimeter fences to catch litter. In some circumstances, you may need to use tall baseball netting.
Fencing systems must be designed to keep litter inside the landfill. You want to focus on keeping blowing litter to a minimum by using operating practices that include operation of small working faces, apply cover, and good compaction. In some wind conditions, you may even need to limit your landfill operations. Perimeter Fence
Perimeter fences serve more than one purpose. They provide site security, can limit animal access, and they are the last line of litter catchment before litter can escape the site.
Perimeter fencing is most commonly constructed as a chain-link fence mounted on steel post. Some designs include extension of the fence fabric below the ground surface and addition of electric fencing wire to discourage bear intrusion. To prevent human intrusion, the fences should be a heavy gauge mesh and mounted on sturdy fence posts. Some facilities will include barb-wire strands on top (as in the photo above). Signs should be posted that clearly state 'no entry', and if the fence is electrified.
To be effective as a litter catchment fence, the mesh wire should not be greater than 2 inches. A unique design that I've seen installed in a couple of location in Southern Alberta is a sloping perimeter fence. The fence is slope into the prevailing wind direction on the downwind side of the active landfill. The concept behind this design is to drive the blowing litter to the bottom of the fence for easier retrieval and to minimize plugging of the fence that can happen with vertical fences. With either a vertical fence or sloping fence design, it is essential that the fences be cleaned of any litter that is trapped by the fence for both aesthetic reasons and to maintain the fence. If litter is allowed to collect on the fence fabric, it may eventually plug the free flow of air through the fence and litter will then blow over the fence, or it may result in the fence being blown over.
Intermediate Fencing
What I mean by intermediate fencing is fencing that is placed at strategic locations between the active areas of the landfill and the site perimeter fences. Intermediate fencing may be temporary, semi-permanent, or even permanent when it makes sense to do so.
The purpose of intermediate fencing may be to establish fence boundaries for different operations on the landfill and to provide added security if needed. For purpose of this writing, it is fencing that is placed at location through the site to catch blowing litter. The more of this fencing that is used, there will be less litter collecting along perimeter fences, and by logic, the less litter that will escape the landfill property.
Intermediate fencing can consist of single rows of fencing or multiple rows. Of course this will be determined by blowing litter direction, wind conditions experienced at the site, site topography, and budget allowances.
When permanent fences are used, the fence could consist simply of a wire mesh fence (with no greater than a 2 inch mesh) mounted on angle iron posts, or it could be constructed similar to the chain-link perimeter fencing.
Using semi-permanent fences allows for the fencing to be easily moved as the landfill expands. The angle iron post design could be established as a temporary fence and used where it will be in that location for longer periods of time. Some fence designs marketed by fencing companies are intended to be even more temporary. Some vendor designs are simple fabric mounted on light weight posts and are anchored with wires. Others are designed to angle into the wind. The intent of the design is so that these fences can be easily and quickly moved.
The baseball netting fences, may also be considered as an intermediate fence. These fencing systems are usually a permanent installation, so their choice of location needs to be well planned out. they need to be placed where the litter blows and where they won't interfere with landfill operations and development. Some netting designs can be installed in a temporary location and be moved as the landfill operations move. See photo examples below.
Portable Catch Fences
Portable catch fences are used in close proximity of the active working face. The are designed to be quickly moved so they can move with the continually moving working face and when the wind direction changes.
Most designs consist of a heavy frame structure that is mounted on a skid frame. The fence mesh is typically a heavier gauge 2 inch wire mesh. The skid frame acts as the base to hold the fence erect. My view is that the base (or skid frame) needs to be 2/3 the height of the vertical fence frame. Ideally, at least 2/3 of the base should extend to the downwind site of the fence to reduce the potential for the fence blowing over. These fence designs are moved by pulling the fence sections with the landfill equipment.
Portable fencing sections can also be designed to slope into the wind. This helps contain the litter at the bottom of the fence and reduce plugging of the fence.
Some other innovative designs use a steel bar section on the vertical section of the fence that is built so the top of a loader bucket can hook under the bar to lift the fence and carry to the desired location
There are numerous manufacturers that market portable fence systems and can be easily found on an Internet search. Landfill operators often develop their own innovated designs and work with local welding shops.
What I think is important in portable fence design is:
- use heavy frames to reduce damages that occur with light frames
- use a wire mesh that is no greater than 2 inches
- design the fence with a substantial base to prevent it from blowing over
- design the fence so the ends butt up against each other, or even so they can over lap
Placing portable catch fences
The placement and use of portable litter catchment fences is just as important as their design. Poorly placed, they can be completely ineffective. The fences must be placed closed to the source of the litter and downwind. Some operators will place these fences in a circular pattern around their active working face.
Neil Bolton suggest using multiple rows of fences. With a single row, the fence can be plugged and the litter will then blow over the fence. Some litter may be trapped behind the fence if a sheltered zone is created by the plugged fence, but by placing a second row of fence, secondary trapment exists. A third row provides an even higher degree of litter trapment. A good example of this technique being applied is in the photo of the Lethbridge Regional Landfill at the top of this blog entry.
Ultimate Fencing Systems
If one searches around the Internet, you'll come across some fencing systems that entirely enclose the active working face under a mesh tent-like structure. One example is shown below.
No comments:
Post a Comment