The landfill course:
This months lesson focuses on sanitary landfill design steps, types of required design information and more. Next month: a continuation of landfill design.
When designing a sanitary landfill, your objectives are to provide
long -term environmental protection, ensure regulatory compliance, and achieve cost
-effective utilization of manpower, equipment, and space. This lesson and Lesson 7 will
present a design methodology to achieve these objectives.
The site selected for a sanitary landfill ordinarily has certain characteristic that are less than ideal. During landfill design, engineering techniques are used to overcome the site limitation and to meet design goals.
The design process is summarized in Table 1. Data collected during site selection will be incorporated into the site design, but changing conditions and the need for more detail may require re-evaluation and additions to previously collected data.
Federal, state, and local government standards generally are of two types: engineering
design standards and performance standards and performance standards.
Engineering design standards are essentially building codes which describe how the facility must be built: for example, a requirement that a new landfill have a six-foot-high fence -surrounding the facility. Compliance with these standards is evaluated by agency review of the building plans and on-site inspection of the landfill during construction.
Performance standards applicable over a facilitys life, and specify that a certain level of environmental control be achieved. For example, the state agency regulating groundwater quality may specify the maximum allowable concentration of a contaminant which may be present in the groundwater below or adjacent to the site. The site operator must incorporate the necessary control systems to achieve compliance with the groundwater standard. If the features initially designed do not achieve compliance, then the operator must install additional protective systems.
The U.S. Environmental Protection Agency, under the authority of the Resource Conservation and Recovery Act (RCRA), has regulations regarding: floodplains; disturbance of endangered species; surface water discharges; groundwater contamination; prevention of disease transmission; air pollution control; and safety concerns.
State regulations vary widely, but usually landfill engineering plans are submitted for review and approval. State standards are ordinarily more extensive than RCRA standards and address concerns that are specific to a particular geographic region.
Procurement of the various permits that may be required to open and operate a landfill may take several years, especially if there is public controversy regarding the site. State or local governments may require a Solid Waste Landfill Plan Approval, Zoning, Conditional Use Zoning Permit, Highway Department Permit for entrances on public roads and increased traffic volume, Construction Permit for landfill site preparation, Operation Permit for on-going landfill operation, Mining Permit for excavations, NPDES Permit for runoff discharge, Building Permit to construct buildings on the landfill site, Fugitive Dust Permit, Air Emission Permit, and Closure Permit (Conrad et al., 1981).
The regulatory standards should be viewed only as minimum requirements which specify a baseline standard of design and performance. Waste disposal facility owners are being held responsible for environmental damage and cleanup many years after the disposal site became operational, and even following closure. Claiming compliance with regulatory standards has not been an effective defense against pollution damage claims. Consequently, the landfill developer may find it a good strategy for build a facility that in some aspects exceeds the regulatory requirements. This may also be necessary in order to achieve public acceptanc
The landfill project's goals should be decided upon with input from the site owner and operator, potential landfill users, regulatory authorities, and residents or land owners near the site. Design goals for sanitary landfill could include:
.To protect groundwater quality by limiting the discharge of leachate;
.To protect air quality and conserve energy by installing a landfill gas recovery system;
.To minimize impact on adjacent wetlands by controlling and impounding surface runoff;
.To minimize dumping time for site users;
.To use the landfill space efficiently and extend site life as much as is practical; and .To provide for maximum use of land upon site completion.
The final use of the landfill must be considered during the design phase in order to
provide for the best use of the property. Good planning at the earliest possible stage
will minimize costs and maximize the site's usefulness after closure.
A landfill's final use should be compatible with nearby land use as well as the limitations of the landfill to support structures. Most full landfills are used for recreational purposes, such as golf courses, nature preserves, or ski hills. Consideration must also be given to compatibility with existing land forms, settlement allowances, and drainage patterns.
Waste characteristics provide important design information for determining operating
procedures; the waste type affects the handling techniques and waste quantity determines
site lifetime, daily operating procedures, and cover requirements. A waste
characterization study should precede the landfill siting work, but additional information
may be needed while the facility is being designed. For example, certain waste types may
be used as daily cover or on-site road base.
When preparing a profile of the wastes which will be received at the new landfill, special attention should be given to sources which may be unknowingly mixing hazardous waste with solid waste. In suspicious cases, hazardous waste testing procedures may be needed. Systematic load checking during site operation should also be planned.
The types and number of vehicles which will transport the solid waste to site should be tabulated also. Traffic information will be useful for later analysis of roadways and access points.
1. Determination of solid waste quantities and characteristics
2. Compilation of information for potential sites
a. Performance of boundary and topographic surveys
b. Preparation of base maps of existing conditions on and near sites - Property boundaries, topography and slopes, surface water, wetlands, utilities roads, structures, residences, land use
c. Compilation of hydrogeological information and preparation of location map
- Soils (depth, texture, structure bulk density, porosity, permeability, moisture, ease of excavation, stability, pH, CATION exchange capacity), bedrock (depth, type, presence of fractures, location of surface outcrops), groundwater (average depth, seasonal fluctuations, hydraulic gradient and direction of flow, rate of flow, quality, uses)
d. Compilation of climatological data
- Precipitation, evaporation, temperature, number of freezing days, wind direction
e. Identification of regulations (federal, state, local) and design standards
- Loading rates, frequency of cover, distances to residences, roads, surface water and airports, monitoring, groundwater quality standards, roads, building codes, contents of application for permit
3. Design of filling area
a. Selection of landfilling method based on:
- Site topography, site soils, site bedrock, site groundwater
b. Specification of design dimensions
- Cell width, depth, length, fill depth, liner thickness, interim cover soil thickness, final soil cover thickness
c. Specification of operational features
- Use of cover soil, method of cover application, need for imported soil, equipment requirements, personnel requirements
4. Design features
a. Leachate controls -
b. Gas controls
c. Surface water controls
d. Access roads
e. Special working areas
f. Special waste handling
i. Recycling drop-off
m. Monitoring wells
5. Preparation of design package
a. Development of preliminary site plan of fill areas
b. Development of landfill contour plans
- Excavation plans (including benches), sequential fill plans, - completed fill plans, fire, litter, vector, odor and noise controls
c. Computation of solid waste storage volume, soil requirement volumes, and site life
d. Development of final site plan showing:
- Normal fill areas, special working areas, leachate controls, gas controls, surface water controls, access roads, structures, utilities, fencing, lighting, washracks, monitoring wells, landscaping
e. Preparation of elevation plans with cross-sections of:
- Excavated fill, completed fill, phase development of fill al interim points
f. Preparation of construction detalls
- Leachate controls, gas controls, surface water controls, access roads, structures, monitoring wells
g. Preparation of ultimate land use plan
h. Preparation of cost estimate
i. Preparation of design report
j. Preparation of environmental impact assessment
k. Submission of application and obtaining required permits
l. Preparation of operator's rnanual
Source: Conrad, et al - 1981, with additions by the authors
the solid waste to the site should be tabulated also. Traffic information will be useful for later analysis of roadways and access points.
The design basis is a tabulation of the general performance requirements that the new
facility must satisfy in order to achieve project goals. It includes the facility's
capacity, waste flow rates, traffic counts, and principal environmental controls.
Tabulating the design basis in this manner communicates to the project design team end
others, such a regulatory review specialists, the nature and size of the proposed
Iandfill. An example is shown in Table 2.
The design basis may require later revision if unforeseen circumstances cause a significant change in the landfill plan.
Geotechnical information is used to begin the site layout. Geotechnical data includes information on the geology, hydrology and soils at and around the site. The data is usually collected during the site selection process, then supplemented during subsequent site investigations. The number,
Example Landfill Design Basis
Receive Waste 10 hours/day, 6 days/week
|Operating Schedule||Average (TPD)||Maximum (TPD)|
|Municipal Solid Waste
Industrial, non-hazardous sludges,.........................
|50% moisture ..................||
|Projected Total Quantities .||
(Note: Maximum waste loads for different waste types not expected to occur on same day.)
|Vehicle Count||40 Trucks/Day||50 Trucks/Day|
|Compacted waste density||1,000 pounds/cubic yard|
|Waste to dally soil cover ratio||4 cubic yards waste to 1 cubic yard dally cover|
|Minimum final cover thickness||2 feet of clay|
|Minimum separation distance landfill base to ground water||8 feet|
|Minimum distance to water supply wells||500 feet|
|Maximum methane gas||1.25%|
|Minimum distance to homes||500 feet|
|Estimated site life||12 years - final estimate will depend on site layout|
location, and depth of soil borings are determined by regulations and by the geological
conditions at the site, with more borings needed, at sites with irregular formations.
Soil boring logs, as well as other data describing subsurface formations and groundwater conditions, are diagrammed to present a picture of the underground conditions at the planned landfill site. Figure 1 shows a diagram of subsurface conditions that exist at a landfill under development. The soil boring logs are shown and the extent of each formation is extrapolated between the boreholes. The depths to bedrock and the groundwater table are also shown.
Using this data, the landfill designer can determine the suitability of the various soil layer for landfill construction and the eventual landfill cross - section. Of particular concern are the potential for gas and leachate migration and the suitability of the soil for landfill base and cover material.
Four types of commonly encountered geologic conditions are diagrammed in Figure 2. The landfills layout will be strongly influenced by the geology. The formation in Type A are moderately impermeable and the water table is deep. Therefore, the primary concern is preventing excessive drainage of leachate form the landfill base in order to reduce its permeability.
If leachate accumulates at the landfill base, it can be removed with leachate recovery collection lines. A major asset of this type of site is the attenuative capacity of underlying soils which reduce the potential for groundwater contamination.
Type B conditions are similar to Tupe A but the water table is shallo. The landfill may be constructed above ground in a manner similar to Type D or a zones of saturation landfill may be constructed (as illustrated). The natural soils are used for final cover but the botton of the landfill is placed below the water table and the base soils are not compacted. Leachate in controlled by using drain tiles to induce groundwater flow into the site where the groundwater and any leachate are collected for disposal.
Construction below the water table is possible because the impermeable soil conditions
prevent rapid drainage of groundwater into the excavation, These types of sites are best
suited for groundwater discharge areas to ensure proper leachate removal and to limit
The primary concerns at sites with moderately permeable soils and deep groundwater tables (Type C) are the restriction of excessive infiltration through the landfill cover, and the need to install a liner to afford more protection of groundwater. Since many permeable soils will not provide a high degree of protection, importation of clay soil or the use of a geosynthetic cover or liner may be necessary. These soils will often be good-quality construction materials upon which to place the landfill base and liner material.
Constructing a landfill on Type D sites will be more difficult because they are moderately permeable and have shallow water tables which have the potential for rapid leachate movement. This necessitates controlling drainage from the landfill. Soils available at the site are probably not suitable for controlling cover infiltration or liner construction. The permeable formulation will restrict construction below the water table. If a site of this type must be utilized, the usual approach is to build the site almost entirely above the original ground surface and to import cover and liner materials. Soils required for intermediate cover and utility purposes such as roads can hopefully be obtained at or near the site.
Other conditions may exist at proposed landfill sites. The presence of bedrock can impede excavation and further complicate groundwater protection, Sites with multiple soil layers and formations will require careful assessment when designing time landfill. Many other site layout strategies have been proposed to overcome soil and ground water limitations.
The leachate control system elements are the landfill cover, surface water control
structures which prevent water from running into the site and, if installed the landfill
liner, collection pipes, leachate detection systems, and leachate disposal system.
Percolation through the proposed cover is estimated with the water balance equation (see Lesson 4).
Selection of the best alternative can be based on the cost and availability of the cover materials, the potential detrimental effect of leachate that drains from the base of the landfill, and leachate treatment cost. Regulatory constraints will also influence the alternative selected.
The slope and soil characteristics of the cover will establish the runoff characteristics of the site. Runoff quantities and peak flows can be predicted with standard drainage calculation techniques ("Urban Hydrology for Small Watersheds," 1975).
Water that percolates through the landfill cover is assumed to eventually
reach the base of the landfill as leachate. A variety of decisions is necessary on how to
best handle this leachate.
A small amount of leachate may not have a significant potential effect on groundwater. Making this determination is difficult; however, groundwater computer models are available to predict leachate flow and contaminant migration patterns. The difficulty arises in selecting the model's input parameters for leachate chemical characteristics, and in predicting the chemical reactions that will occur as the leachate moves through the soil.
The amount of leachate that drains from the base of the landfill will depend upon the type of liner, how successfully the liner is installed, and the procedures employed for removing leachate from the landfill. For soil liners, a liner efficiency can be calculated if data regarding soil permeabilities ms available. Am example of the results of a liner efficiency calculation, for a clay liner, is shown in Figure 3.
The projected liner efficiency of 81% indicates that 19% of the leachate will eventually drain through the liner. If this quantity is determined to be potentially detrimental to groundwater quality, then a more efficient liner can be designed. One possibility would be to incorporate a geosynthetic membrane into the liner system. Implicit in the design of the soil liner with the efficiency calculation is the slope of the soil liner at the base of the landfill and the spacing of leachate collection lines. The leachate retained by the liner must be removed for treatment or a portion recycled.
Geosynthetic liners may complement or be used in place of clay liners. The typical geosynthetic lining material is 40-to 80-thousandths-of-an-inch-thick flexible sheets which can be bonded to adjacent sheets with thermal or chemical bonding equipment. Many configurations are available for installing geosynthetic liners. Composite liners utilize a combination of geosynthetic and clay liners. The geosynthetic liner is placed immediately on top of the clay liner. Sand above the geosynthetic liner carries leachate to time collection system. Alternately the sand may be replaced by high-strength geosynthetic grid or mesh material which is less than one-half-inch thick and capable of transmitting large quantities of leachate to the collection pipes.
Double geosynthetic lined landfills utilize two layers of liners and leachate collection systems. The upper layer is the leachate collection liner. The lower layer acts as a leak detection liner, should the upper liner develop a hole.
Liner systems, clay, geosynthetic. or combination, cost hundreds of thousands of dollars per acre. An interesting design consideration is the reduced volume that a geosynthetic liner system occupies within the increased volume of the landfill, A 367-foot-thick clay liner system may, depending on regulatory controls, be replaced by a geosynthetic liner system that is less than one foot thick. The geosynthetic liner system will cost more per acre but the added cost may be more than offset by the additional revenue which results from having a larger volume available for landfilling. Similar considerations apply to landfill covers constructed with geosynthetics.
When the design concepts for the leachate control system are completed, laying out the landfill on maps and engineering plan-sheets can begin. .
Preparation of the first map usually shows the landfill location in relation to surrounding communities, roads and other features. A topographic map of the area published by time U.S.
Geological Survey can be used as a base map. Note, however, that some features such as
buildings, roads, and stream Iocations may have changed since this map was produced. A
recent air photo, which may be obtained from a state or local zoning, transportation, or
other agency, will help to update these maps.
Next, a detailed site map with a scale of one inch equaling 200 feet is prepared. Contour lines are drawn at two- or five-foot intervals, the property Iine is determined accurately, easements and rights-of-way are indicated. Utility corridors, buildings, wells, roads and other features are located, drainageways are marked, and neighboring property ownership and land use are shown.
Detailed design follows with the selection of landfill base elevations, top elevations, and slopes. Development is usually planned so that the landfill can be constructed and operated in phases. T he site plans should describe landfill development in sequence, showing the chronological order in which the features are to be developed (Figure 4). Dividing the project into phases minimizes the amount of open landfill surface, thus reducing the potential for the accumulation of rainwater within the site that would require special handling. As each phase is completed, that portion of the landfill can be closed and final cover placed over the waste.
A final advantage of phasing is that premature closure of the landfill is more practical and economical in the event of an environmental problem. In a well-planned phase development, the landfill's end use can be implemented in the completed sections while other areas are still being utilized for disposal purposes.
Some regulatory agencies will mandate the construction of screening berms or fences around the active areas of the landfill. The extra soil needed for berm construction must be accounted for when planning excavation work. The height of time berms will depend upon the lines of sight into the landfill from adjacent areas.
Concurrent with the development of plans for liners, covers, service roads, and embankments soil cut and fill balances must be calculated. The best designs provide for earth-moving procedures that minimize soil movement. Substantial volumes of earth will be required for cover and possibly liners. When practical, the phases should be laid out so that earth excavated is immediately used as cover. When stockpiling is necessary, the work should be organized so that stockpiled soil may be heft undisturbed until needed.
After the completion of the phasing diagrams and earth work balances, a table is prepared which summarizes the waste each phase of the landfill.
The next lesson will describe how gas controls, roads, drainage structures, and support facilities are integrated into a complete landfill design.
lesson 6 and 7 - Sanitary Landfill Design Procedures
Robinson, W. D.; The Solid Waste Handbook, A Practical Guide, Jhon Wiley and Sons, 1986.
Articles and Technical Reports
Bourdimos, E. L.; Demetracopoulos, A. C. ; Karfiatis, G. P.; "Modeling for Design of Landfill Bottom Liners," Journal of Environmental Engineering, December 1984, pp. 1084- 1098.
Miller C. P.; Wright, S. J.; "Predicting Leakage Through Clay Landfill Covers," Environmental Engineering, 1984, pp. 708-710
Coffman, Glenn N.; "The Finer Design Process for Landfills and Surface Impoundments, "National Conference on Environmental Engineering, 1983, pp. 350-357.
Conrad, E. T.; Walsh, J.J.; Atcheson, J.; Gardner, R. B.; "Solid Waste Landfill Design end Operation Practices. "EPA Draff Report Contract N°. 68-01-3915, 1981.
Kemt, Peter; Quinn, Kenneth J.; Slavik, "Análysis of Design Parameters Affecting the Collection Efficiency of Clay Lined Landfills." Presented at the Fourth Annual Madison Conference of Applied Research and Practice on Municipal and Municipal and Industrial waste, September 28-30, 1981, University of Wisconsin-Extension, Madison, Wisconsin.
Siting, M.; "Landfill Disposal of Hazardous Wastes and Sluges." Noyes Data Corporation, 1979.
"Urban Hydrology for Small Watersheds" Technical Release # 55, SCS, USDA, January 1975.