This is the eighth lesson in the independent learning correspondence course on municipal solid waste (MSW) landfills. One lesson in this 12-part series will be published in Waste Age magazine each month throughout the year.
If you are interested in taking the course for two continuing education credits (CEUs), send a check (payable to the University of Wisconsin) for $149 to Phil O''Leary, Department of Engineering Professional Development, University of Wisconsin, 432 North Lake Street, Madison, WI 53706. Phone (608) 262-0493. E-mail: [email protected]. website: www.wasteage.com.
Course registration can occur at any time until December 2006. Previous lessons will be sent to you.
Even the world''s best-designed landfill will have problems if it is poorly operated. Small problems can lead to nuisance complaints from neighbors, increased inspections from regulators and difficulty in future siting or expansion. Poor operating techniques also can anger clients and decrease landfilling efficiency — which can result in losing money and good will. Because operations determine whether a landfill has community trust or faces continuous opposition, it''s important to follow an effective operating plan.
Landfill operating procedures are determined by many site variables. The operational plan is a primary resource because it provides the landfill''s technical details and procedures for constructing various engineered elements.
Because a landfill is constructed and operated over several years, personnel must continually consult the plan to assure long-term conformance. An accurate record of procedures must be maintained. Operational changes often need regulatory approval, and planning is necessary to transition to a revised plan.
After authorities approve a landfill design, site preparation and construction can begin [See “Site Preparation and Construction Steps” on page 53].
Developing a complete landfill may be divided into stages, some of which are completed years after the site''s opening. Work should be documented to help answer site construction questions. For instance, documentation proves to regulatory authorities and concerned citizens that design standards are being implemented. Also, good documentation can ease repairs, if they are necessary.
Monitoring Incoming Waste
Since the Sept. 11th terrorist attacks, interest in landfill security has grown. Federal law already requires solid waste landfills to have a program to detect and exclude hazardous waste and polychlorinated byphenyls (PCBs). To detect and exclude regulated hazardous wastes and PCBs from disposal, a landfill owner''s operating program should include:
Random inspections of incoming loads or other prevention methods;
Well-maintained inspection records;
Facility personnel training; and
Procedures for notifying appropriate authorities if hazardous wastes or PCB wastes are detected.
Inspections & Limitations
An individual who is trained and qualified to identify unacceptable wastes can conduct a visual inspection. An inspection is satisfactory if the inspector can discern whether all materials in the load are potentially regulated hazardous wastes.
Random inspections adequately control the receipt of inappropriate wastes. Inspection frequency may be based on waste type, daily quantity received, and the accuracy and confidence desired in conclusions drawn from inspections. Regulations don''t provide statistical pa-rameters, so use reasonable judgement.
The program may require inspecting every incoming load one day every month, or inspecting one or more loads from transporters of unidentifiable waste each day. Inspection frequency also can vary based on the nature of the waste. For example, waste received exclusively from commercial or industrial sources may require more frequent inspections than waste collected just from households.
Inspection priority can be given to haulers with unknown service areas, loads brought to the facility in vehicles not typically used for MSW disposal and loads transported by previous offenders.
To provide the facility operator with the opportunity to refuse or accept wastes, loads should be inspected prior to landfill disposal. Inspections can be conducted on transfer station tipping floors before moving the waste to the disposal facility, or at a tipping floor located near the facility scale house, inside the site entrance, or near the landfill''s working face.
Preventing the disposal of hazardous and PCB waste also may be accomplished while receiving household and processed (shredded or baled) waste, because it is screened before processing.
Public access to landfills must be controlled by artificial and/or natural barriers to prevent unauthorized vehicular traffic and illegal waste dumping. These barriers can include fences, ditches, berms, trees, etc. Access also should be controlled by gates that can be locked when the site is unsupervised.
Waste Handling & Placement
Waste movement usually is confined to spreading the waste on the working face with compactors or dozers after loads are deposited by trucks. Movement over long distances is inefficient with this equipment [See “Solid Waste Placement and Compaction” on page 54].
Typically, compacted waste is covered with earth daily, and a new cell is started. Manufactured foams or temporary blankets also can be used as daily covers. Foams must be sprayed on. Blankets can be lifted into place with a crane or tracked excavator, and then removed the following day prior to waste placement.
At some sites, waste may be deposited at the top of the working face, making it easier to spread. Litter may be more difficult to control with this procedure.
Compaction is critical to extending the landfill''s life. To achieve high, in-place waste densities, a compactor may be necessary. A minimum in-place compaction density of 1,000 pounds per cubic yard is recommended. The number of passes that the machine should make to achieve optimum compaction depends on wheel pressure, waste compressibility and compaction layer thickness. Generally, three to five passes are recommended [See “Waste Densities,” on page 59]. Although additional passes will compact the waste to a greater extent, the return on the effort diminishes beyond six passes.
Each site will have different compaction results, depending on waste layer thickness. However, there will be a de-crease in density above a compacted layer thickness of about 1 foot to ½ foot. The best compaction results from compacting waste in layers 1- to 2-feet thick.
The working face''s slope also affects compaction. As the slope increases, vertical compaction pressure decreases; the lower the slope, the higher the compaction. Nevertheless, the feasibility of a nearly flat working face has to be weighed against the larger area over which the waste and cover soil must be spread.
When shredding waste, incoming refuse is mechanically processed into small, uniformly sized pieces immediately before landfilling or at a transfer facility prior to transport. Shredding can occur as a sole process before disposal or as part of the mechanical separation process that removes recyclable or reusable materials from the waste stream.
After compaction, shredded refuse has a greater density than compacted, unprocessed MSW. This can preserve landfill space and reduce the amount of required cover material. Additionally, landfill settlement and stabilization may be more uniform over time. These benefits must be compared with the significant capital and operating costs of the shredding equipment, space required to process the waste, and historically significant potential for worker injury and equipment downtime. For instance, equipment can be damaged by explosions from crushing compressed gas containers and by the ignition of gases by sparking metal.
Baling Solid Waste
Baling MSW compacts refuse into high-density blocks that are stacked and covered with material in a landfill. Bale density can range between 1,000 to 1,900 pounds per cubic yard. In certain circumstances, baling waste before disposal may save landfill space as a result of increased compaction density and reduced cover material requirements. Baling waste also can reduce the amount of blowing litter.
Cover Material Requirements
The federal Resource Conservation and Recovery Act (RCRA) Subtitle D standards require landfill owners or operators to cover solid waste with 6 inches of earthen material at the end of each day. Alternative daily cover materials of varying thicknesses may be allowed in certain jurisdictions. Covers prevent waste exposure to birds, insects and rodents, which can transmit human disease. Covers also reduce the exposure of combustible materials to ignition sources, reduce odors and control litter. And, removing waste from sight reduces scavenging.
Environmental Factors Air Criteria
Subtitle D standards prohibit routine open burning of waste. Infrequent burning of agricultural and silvicultural waste, diseased trees, or debris from land clearing or emergency cleanup operations is allowed, but must meet air pollution control regulations. Burning areas should be far from the landfill to avoid igniting other waste.
The U.S. Environmental Protection Agency (EPA), Washington, D.C., has established New Source Performance Standards (NSPS) and Emission guidelines. As mandated by the Clean Air Act, these rules require landfills to collect landfill gas and prescribe design standards and performance limits for gas extraction systems.
Run-on and Runoff Control Systems
Site drainage is critical. As much water as possible should be diverted off the landfill to minimize operational problems and leachate formation. A run-on control system should prevent liquid from flowing onto the active portion of the landfill during the peak discharge from a 25-year storm event. The run-on system also should collect and redirect surface waters entering the landfill boundaries.
On the other hand, a run-off control system must be able to manage at least the volume of water that results from a 24-hour, 25-year storm over the active portion of the landfill. The run-off system should collect and control any water that may have contacted any waste materials and must comply with Clean Water Act point and nonpoint source requirements.
Small Vehicles and Safety
Allowing public access to the disposal face can interfere with operations and lead to unsafe conditions. Consequently, separate waste collection facilities (i.e. 40-cubic-yard containers) can be located near the entrance for citizens. This area should be inspected and cleaned regularly to prevent unsightly conditions.
Good housekeeping procedures are necessary. Subtitle D requirements and many state regulations mandate operation controls [See 40 CFR Part 258 and appropriate state regulations]. A well-planned and maintained landfill provides effective controls for:
Addressing aesthetics may include using fences, berms, plantings or other landscaping to screen landfill operations from roads or nearby residents. This also could encompass providing an attractive entrance with good roads and easy-to-read signs.
- Wind-Blown Paper
Litter can be controlled with fences, which stop blowing paper and plastic. Frequent manual or mechanical litter pickup also is needed.
Mosquitoes, flies and other insects are controlled by covering the waste daily and eliminating standing water, such as in appliances stored for recycling or in surface depressions.
- Wildlife and Rodents
Rats once were a problem at open dumps, but landfills should bury all food waste with daily cover, which usually eliminates rats.
Birds can be a nuisance or cause problems with planes if the landfill is near an airport. The Federal Aviation Administration (FAA) should be notified if the facility is within five miles of an airport runway used by jet aircraft. To discourage birds, operators can use noisemakers, wire grids and liberal use of cover soils, can keep the working face small and can provide adequate cover.
- Odors and Fires
Daily cover and compaction reduces odors. Daily cover also forms cells to prevent inadvertent fires from spreading throughout the landfill. Burning or smoking waste should be dumped off to the side and extinguished before placing it on the working face. Fire-fighting equipment and an emergency water supply should be available onsite or arranged for with local authorities.
Equipment should be operated behind berms to shield surrounding areas from noise. Access should be designed to minimize the impact that site traffic has on nearby neighborhoods.
- Dust and Tracking
Roads should be watered in dry periods to minimize dust. Roads also should be crowned and well-drained to reduce mud tracking. Adequate wheel cleaning and mud knock-off areas should be provided. Entrance roads should be paved or have all-weather surface concrete or asphalt to keep mud tracking onsite. Roads should be cleared whenever mud builds up.
While recycling at a landfill may be desirable, scavenging (or uncontrolled picking through waste to recover useful items) is not desirable. Scavengers can be injured while picking through waste, which is why it should be prohibited. Salvaging, which is the controlled separation of recoverable items, should be distinguished from scavenging. Salvage operations should be kept away from the landfill. These events usually are held at the gate area, and residues should not be allowed to accumulate.
- Gas and Leachate
Controlling gas generated by decomposition and leachate as water migrates through waste is important to protecting public health and the environment. Methods to control gas and leachate were detailed in earlier lessons.
Wet weather problems are serious with soils that have a high silt or clay content, as they can be- come muddy and slippery. Provisions should be made to continue operations in areas less susceptible to problems during inclement weather. During wet weather, procedures to minimize and clean mud tracking on roads are important.
Cold weather may create problems in starting and operating machinery, keeping employees comfortable, and obtaining cover material. Equipment manufacturers can recommend cold weather starting and operation tips. Excavation of well-drained and stockpiled cover soil can improve operations.
Windy conditions can require extra or specially placed fencing, and the use of a lower or more protected working face. The wind cannot pickup materials as easily at the bottom of the working face as it can when waste is deposited at the top.
In addition to fencing the active area''s perimeter, portable fences can catch litter downwind of the working face. The fenced area should be cleaned daily.
Dust can be a nuisance to employees and neighbors. Water wagons can be used to control dust. Calcium chloride also can be used to absorb moisture from the air.
Personnel and Safety
To maintain an efficient landfill operation, employees must be carefully selected, trained and supervised. Proper landfill operation depends on good employees. Along with equipment operators, other necessary employees may include maintenance personnel, scale operator, laborers, supervisor and employees to keep financial and operating records.
Good training and supervision must include attention to safety. Accidents are expensive and have hidden costs — often several times readily apparent costs.
Solid waste personnel work in all types of weather, with varied equipment and materials that present diverse hazards. Potential accidents include injury from explosion or fire, contaminant or dust inhalation, asphyxiation from poorly vented leachate collection system manholes or tanks, falls from vehicles, operating earth-moving equipment, attempting to repair equipment while engines are operating, exposure to extreme cold or heat, and traffic accidents.
Educational landfill safety films and written materials are available from the federal government and from equipment manufacturers. Safety program setup assistance also is available from insurance companies with worker''s compensation programs, the National Safety Council, Itasca, Ill., safety consultants, and federal and state safety programs.
Equipment falls into three functional categories: waste movement and compaction, earth cover transport and compaction, and support functions. Selecting the type, size, quantity and combination of machines required to move, spread, compact and cover waste depends on:
Waste amount and type;
Site and soil conditions: topography, soil moisture and difficulty of excavation;
The distance the cover material must be transported;
Amount and type of soil cover;
Compaction requirements; and
Supplemental tasks, such as maintaining roads, assisting in vehicle unloading, and moving other materials and equipment around the site.
The amount of waste influences the appropriate machine size [See “Equipment Needs” on page 56]. Heavier equipment provides more compaction and flexibility in handling a variety of materials using thicker compaction lifts. However, the condition in which the waste is received may affect equipment choice. For example, landfills accepting only shredded waste may need less daily soil cover. It also will be easier to compact shredded waste. Bales being landfilled often are moved with forklifts, and no compaction equipment is necessary.
Waste Compaction Equipment
Steel- wheeled compactors feature wheels studded with load concentrators of various designs. They maximize compaction and are suited to medium or large sites, which can support more than one machine.
Track-type tractors or dozers may handle or compact waste, as well as assist in cover excavation and compaction. They can be used for site preparation, road construction and maintenance. These are versatile units and are preferred for small operations in which one unit must perform a variety of functions.
Rubber-tired loaders or dozers provide more speed and maneuverability than track-type units, and can haul cover, applying it up to approximately 1,000 feet from the working face. Rubber-tired scrapers are efficient for excavating and transporting cover soil when it is more than 1,000 feet from the working face. Where the soil is hard to excavate (e.g., clay or frozen soil), scrapers can be pushed with a bulldozer.
Draglines are efficient earth-movers but are only able to deposit soil within the area reached by the boom and are not suitable for transporting cover. Backhoes are suited for small, specialized excavation, such as for a leachate collection system. Dump trucks can be used with excavation equipment to move cover material. Motor graders are useful for road construction and maintenance, for berm and drainage construction, and for landscaping.
Maintenance and Backup
Regular equipment maintenance reduces breakdowns and identifies equipment problems early — before more costly and time-consuming repairs are needed. Provisions also must be made for backup equipment, perhaps by keeping additional equipment available.
Phil O''Leary and Patrick Walsh are solid waste specialists with the University of Wisconsin-Madison.
Remove and stockpile topsoil.
Install drainage improvements.
Excavate fill areas.
Stockpile daily cover materials.
Install environmental protection facilities (as needed):
a. Landfill liner with leachate collection system;
b. Groundwater monitoring system;
c. Gas control equipment; and
d. Gas monitoring equipment.
Prepare access roads.
Construct support facilities:
a. Service building;
b. Employee facilities;
c. Weigh scale; and
d. Fueling facilities.
Install utilities (electricity, water, sewage and telephone).
Construct fencing (perimeter, entrance, gate and entrance sign, and litter control).
Prepare construction documentation (continuously during construction.
Steps do not have to follow exact order shown.
|Approximate Population||Daily Wastes Tons||Equipment Number||Equipment Type||Equipment weight, lbs||Accessorya|
|0-20,000||0-50||1||Tractor, crawler||10,000-30,000||Dozer blade, Front-end loader, (1-2 cu/yd), Trash blade|
|20,000-||50-150||1||Tractor, crawler||30,000-60,000||Dozer blade, Front-end loader, (2-4 cu/yd), Bullclam, Trash blade|
|1||Scraper or dragline|
|50,000||150-300||1-2||Tractor, crawler||30,000+||Dozer blade, Front-end loader, (2-5 cu/yd), Bullclam, Trash blade|
|1||Scraper or draglineb|
|>100,000||300c||1-2||Tractor, crawler||45,000+||Dozer blade, Front-end loader, (2-5 cu/yd), Bullclam, Trash blade|
|1||Steel wheel compactor|
|1||Scraper or draglineb|
|a. Optional, depends on individual needs.|
|b. The choice between a scraper or dragline will depend on local conditions.|
|c. For each 500-ton increase add one more of each piece of equipment.|
|Source: G. Tchobanoglous, Integrated Solid Waste Management: Engineering Principles and Management Issues, 1993|