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Kansas Environment Technical Note KS-2

September 15, 1971

Subject: Sanitary Landfill Principles

Although the procedures involved in planning, design and operation of a landfill are not always complex, there are misconceptions concerning this method of waste disposal. SCS does not perform any of the design for such projects. The purpose of this technical note is to explain the basic concepts involved. It is not intended that this be sufficient data to design and operate a sanitary landfill.

What is a Sanitary Landfill?

The American Society of Civil Engineers has defined a sanitary landfill as "a method of disposing of refuse on land without creating nuisances or hazards to public health or safety, by utilizing the principles of engineering to confine the refuse to the smallest practical area, to reduce it to the smallest practical volume, and to cover it with a layer of earth at the conclusion of each day's operation, or at such more frequent intervals as may be necessary."

A true sanitary landfill is not an open dump.

Methods of Sanitary Landfilling

There are three general methods of landfills, which are: (1) area method, (2) trench method, and (3) ramp, or slope method.

The area method is best suited for flat or gently sloping areas where some land depressions may exist. The wastes are spread, compacted and then covered with material which may need to be hauled in from adjacent areas.

The trench method consists of an excavated trench into which the solid wastes are spread, compacted and covered. The trench method is best suited for nearly level land where the water table is not near the surface. Usually the soil excavated from the trench is used for cover material.

The slope or ramp is sometimes used in combination with the other two methods. The wastes are spread on an existing slope, compacted and covered. This variation may be suitable for most areas. The cover materials usually come from just ahead of the working face.

The landfill method can be adapted to suit almost any circumstances, but there is usually one best method for any specific instance.

Planning

A sanitary landfill is an engineering project. Therefore, an important consideration in preliminary planning is to select a competent designer knowledgeable in the subject. Proper planning and design is essential for a successful operation.

One of the first steps is to select a site. Some of the items to consider are:

  1. Nuisance Factors - Although an efficient sanitary landfill operation can be pleasing in appearance, there are certain inherent nuisance factors which require consideration, such as traffic to and from site, noise of mechanical equipment, and dust.
  2. Accessibility - Sites should be easily reached. Travel through residential areas should be avoided. Adequate all-weather roads are needed. More than one access should be provided in the event a route is temporarily closed. Collection and delivery of refuse to a disposal. site represents two-thirds or more of the total cost of refuse service. A location close to the area generating the refuse would be the most desirable site.
  3. Community and Area Development - The anticipated community growth factor should be considered involving the direction and magnitude of projected growth, redevelopment and consequent change in character and density of refuse, long range area development and commercial and industrial development. All zoning ordinances should be reviewed to determine legalities which may affect a project.
  4. Utility Services - A well operated sanitary landfill, depending upon size, requires utility services. Water supply is necessary for sanitary purposes, equipment washing, dust control, and fire protection. Electrical power for lights and equipment, telephone or radio communication, and sewer services may also be necessary.
  5. Land Requirement - The area of land necessary for a sanitary landfill will depend on such factors as quantity and character of the solid wastes, depth of fill, efficiency of compaction, and desired life of the landfill. About 15 acre-feet of space or volume per year per 10,000 population is generally needed. Cover material requirements are approximately 20 percent of compacted refuse volume and should be readily available, either on or near the landfill site.
  6. Soils Information - A workable soil is desirable for landfill sites. A well graded sandy loam soil has the good workability and compaction characteristics which are necessary. It is important that the cover material does not crack when it becomes dry. A CH soil would be very undesirable as cover material. Suitability of existing soil for cover material should be determined on the basis of engineering tests and evaluations.
  7. Ultimate Land Use - The ultimate land use, such as parks and playgrounds, industrial, agriculture, etc., proposed for the site will also influence site selection.
  8. Climate - Climate is an important consideration for design and operation of a landfill. Excavation of trenches and sources for cover material become a problem in winter months.. The wind and rain are two other factors which must be considered.
  9. Geology - Prior to final design of a landfill, a geological investigation of the site should be made. This will reduce the possibility of pollution of ground and surface waters. Items to consider are: (1) locate the site at a safe distance from streams, lake, wells and other water sources, (2) avoid site location above the kind of subsurface stratification that will lead leachate from the landfill to water sources, i.e., fractured limestone, (3) location of groundwater table, (4) using an earth cover that is nearly impervious, and (5) providing suitable drainage trenches to carry the surface water away from the site. It is recommended that the depth of investigation extend at least 10 feet below the lowest elevation planned for the operation of the landfill.

Design

A consultant who is knowledgeable and has had experience in sanitary landfills should be retained for proper design. The design phase will actually be the plan of operation. Good plans and specifications are essential for estimating costs, for obtaining bids, and operational control and inspection.

Plans

The detailed plans should show the existing contours or topography and the designed contours of the completed landfill. It should show the intended use of the completed landfill.

The plans should also show the overall program for landfilling, site preparations, drainage requirements, groundwater table, location of cover material and the wet weather operation site. Other features to be included are: access roads, personnel and equipment facilities, scales, signs and utilities

The pan should include both permanent and portable fences to aid in the control of blowing paper.

Specifications

Specification for construction and operation should complement the plans. The construction specifications will include construction materials, workmanship and equipment. Operation specifications detail the method of operation, which includes weighing the wastes, cross sectioning of the site at definite time intervals, thickness of cover material, depth of lifts and cells, compaction, wet weather procedures, amount, type and size of equipment and personnel.

Operation

The appearance of the site is very important to maintain public acceptance. This can only be accomplished through proper planning and operational procedures.

Supervision

Constant supervision by competent and experienced or properly trained personnel is important. There is no substitute for competent and a sufficient number of employees.

Operation Records

Detailed records for evaluation and future planning should be kept. Weights, type and origin of material should be recorded as well as deviations from the plan of operations. Periodic surveys will be necessary to determine rate of space utilization. This information can be used to determine amount of compaction, efficiency, land use, operation efficiency and to estimate the degree of decomposition and eventual settlement.

Cost-accounting records including initial costs and all operational costs are necessary for budget planning, user cost rtes ad estimating efficiency of operation.

Compaction

Solid wastes are placed in layers, usually about two feet thick, and compacted to one foot thickness. Better compaction usually results if the wastes are spread and compacted from the base upwards. Usually 3 - 5 passes over the total working face will be adequate for normal compaction.

Working Face

The size of the working face is determined by the rate of unloading of incoming vehicles. The working face should be kept as narrow as possible. Deposit refuse at the bottom of the slope for best compaction and control of blowing litter.

Depth of Cell

As the wastes are placed and then covered regularly with soil, "cells" or layers of wastes are formed. The cell depth is the thickness of the solid wastes measured perpendicular to the working slope. The depth of cell is determined largely by the size of operation, desired elevation of the completed fill, depth of trench and other operational factors. Although these depths range from 2 feet to 15 feet, a maximum depth of 8 feet is recommended to prevent excessive settlement and surface cracking.

Cover

The solid wastes must be compacted and covered at the conclusion of each day, or more frequently if necessary, with a minimum of six inches of compacted earth. The cover is necessary to prevent insect and rodent infestation, blowing paper, fires, the attraction of wildlife and the release of gas and odors.

For lifts which will not have additional fill for periods of up to one year, a minimum cover of 12 inches is recommended. Final cover should be two feet or more in depth. If trees are to be planted ço the site, additional depth is required.

Miscellaneous Considerations

A properly designed landfill will include consideration of the following items:

  1. Large Objects - Large, bulky items such as car bodies, appliances and tree stumps may require special provisions.
  2. Blowing Paper - Prevailing winds must be considered. Fences, both permanent and portable, are important as well as prompt compaction and covering to provide control. Dumping at the bottom of the slope will help.
  3. Maintenance - Includes items such as public and private facilities, cutting of grass and weeds, access roads, control of dust, picking up of scattered wastes.
  4. Drainage - Proper drainage is necessary at all tims. As settlement occurs, additional fill may be required.
  5. Winter and Wet Weather Operation - During inclement weather, provisions need to be made for source of cover material, proper roads and adequate trench capacity.
  6. Salvage Operation - To insure clean and orderly sites, salvage operations at landfill sites should be prohibited.
  7. Burning - Burning will not be permitted at a properly operated landfill.
  8. Revegetation - Temporary and/or permanent grass cover will be planned along with necessary plantings of trees or shrubs for screening purposes and for natural beauty.

Equipment

The size and amount of equipment required will vary as to size and method of operation at the site. Small landfills can be successfully operated with one tractor, either of the rubber tired or crawler type, with either a dozer blade, trash blade or a front end loader. Large operations will require more equipment, many times of a specialized type.

Costs

The major portion of the initial investment will be for the purchase of land and equipment. Operating costs for small operations will vary with variations in the efficiencies attained. Costs range generally from $1.25 to $5.00 per ton. Operating costs for large landfills generally range from $0.75 to $2.00 per ton.

Completed Sanitary Landfills

The rate of decomposition within the landfill will normally be very slow. Many items, such as paper, have been found unchanged in landfills after 15 to 25 years.

Gases resulting from decomposition usually reach a peak within the first two years.

Settlement can be expected to occur. Approximately 90 percent will likely occur in the first five years with the remainder over a long period of time. The surface should be resloped if differential settlement takes place.

Underground fires rarely occur, but should be dug up and extinguished when encountered

Reference

The source of information for this data was the publication "Sanitary Landfill Facts" and Training Course Manual "Sanitary Landfill Principles"  by the U. S. Bureau of Solid Waste Management.

Prepared by:
J. D. Rector
Assistant State Resource Conservationist

/s/

DONALD R. ROBERTSON
State Resource Conservationist

DIST: AC-3, DC, FS(A), FS(A,B,R,PMS), PS, RC&DPO, PMC, ASCS, RDS