Sanitary landfill (New York State Department of Health, 1969; Soil Survey Staff, 1971; Kansas State Department of Health, 1972; Figures 18-20) in trenches consists of dug trenches in which refuse is buried and compacted at least daily, and in which the refuse is covered with a layer of soil material at least six-inches thick. The material used in covering the garbage is the soil excavated in digging the trenches. When the trenches are full, a final cover of soil material at least two-feet thick is placed over the landfill.
Figure 18--No dumping sign near urban area. Garbage disposal is a problem in practically every county in Kansas. Sanitary landfill can provide a safe, efficient, and aesthetic method of burial and disposal at a site if soil and geologic conditions are favorable. Sites to be avoided include those with rapid permeability and high water tables, areas often subjected to devastating floods, steep slopes, stony soils, and soils with poor workability and trafficability. Good soils for sanitary landfill include the Altus, Clark, Cozad, Dalhart, Hord, Konawa, and Lubbock series (see Table 6).
Figure 19--Sanitary landfill site. Management of sanitary landfill is a critical factor influenced by soil and geologic conditions. At this site garbage is buried each day, but the standing and seeping water indicates a possible pollution hazard. Wells and sampling sites should be established around the landfill sites to monitor contamination movement into aquifers, and to provide additional data for soils and geological interpretation.
Soils of Kansas are rated for limitations for trench-type sanitary landfill in Table 6; Table 4 gives the criteria by which the ratings were made. Soil-drainage classes and depths to seasonal water tables in soils of Kansas are given in Table 1; free water in soils is a primary consideration in interpreting these ratings. The degree and duration of soil wetness can so affect earth-moving operations as to make a soil severely limited for sanitary landfill. In addition, the probable contamination of ground water by a landfill is closely related to depth to the seasonal water table.
Table 4--Ratings of limitations of soils for solid-waste disposal in trench-type sanitary landfills1 (Adapted from Soil Survey Staff, 1971
|Depth to seasonal water table||> 72 in||> 72 in||< 72 in|
|Soil-drainage class||Excessively drained, somewhat excessively drained, well-drained, and some3 moderately well drained soils||Somewhat poorly drained and some3 moderately well drained soils||Poorly drained and very poorly drained soils|
|Flooding||None||Rare||Occasional or frequent|
|Permeability4||Slower than 2.0 in/hr||Slower than 2.0 in/hr||Faster than 2.0 in/hr|
|Slope||< 15%||15-25%||> 25%|
|Dominant soil texture,5 to a depth of 60 in||Sandy loam, loam, silt loam, sandy clay loam||Silty clay loam6, clay loam, sandy clay, loamy sand||Silty clay, clay, muck, peat, gravel, sand|
|Depth to hard bedrock||> 72 in||> 72 in||< 72 in|
|Depth to rippable bedrock||> 60 in||< 60 in||< 60 in|
|Stoniness class7||0 and 1||2||3, 4, and 5|
|Rockiness class7||0||0||1, 2, 3, 4, and 5|
|1. Ratings based on soil depth of 5-6 feet commonly investigated in soil surveys. Additional geologic and engineering investigations should be made before landfills are established.
2. If probability is high that the soil material is similar down to a depth of 10-15 feet, this could be indicated by statements like "Probably slight to a depth of 12 feet" or "Probably moderate to a depth of 12 feet" as determined by the soil survey.
3. Soil drainage classes are related to depth to fluctuating water tables. The overlap of moderately well drained soils into 2 limitation classes allows some of the wetter moderately well drained soils to be given a limitation rating of moderate under certain conditions.
4. These ratings reflect the ability of a soil to retard movements of effluents leached from landfills. In arid and semiarid areas rapid permeability may not be a severe limitation.
5. Ratings of soil textures reflect ease of digging in soil, ease of moving soil, and trafficability of vehicles on soils in the immediate area of the trench where hard-surfaced roads are absent.
6. Soils high in montmorillonitic clays probably need to be given a limitation rating of severe.
7. Stoniness and rockiness class definitions are given in the Soil Survey Manual on pages 216-223 (Soil Survey Staff, 1951). Large numbers indicate more stones and rocks.
Permeability of soils is an important consideration in interpreting the limitation ratings for sanitary landfill (Soil Survey Staff, 1971). Soils with slow permeability are most desirable because in them the probability of polluting ground water by vertical or lateral seepage is minimized. If necessary, permeable horizons near the bottom of sanitary landfill trenches can be sealed by compacting (along the sides and bottom of the trench) a blanket of relatively impervious material at least two feet thick-of course, this is very expensive.
Soil slope also (Table 4) is an important consideration in interpreting the limitation ratings. More grading generally is required for the roads that lead to and from landfills located on sloping-to-steep soils than is required for roads leading to and from landfills on nearly level soils. Also, more care is needed on sloping-to-steep soils to provide for the proper disposal of surface water including that from adjacent higher elevations. In landfill operations, the bottom should be kept as nearly level as possible because the bottom tends to serve as a seepage plane; the solid waste layer offers little obstacle to the movement of water. Sloping trench bottoms are likely to cause difficult seepage problems in completed landfills. Trenches for sanitary landfill should be placed on the contour with bottoms level or nearly level,
Soil texture (Table 4) also is important for trenches for sanitary landfill. Textures listed in Table 4 are defined in the Soil Survey Manual (Soil Survey Staff, 1951). The case with which the trench is dug and with which a soil can be used as daily and final cover is based largely on texture and consistence of the soil. From knowledge of texture and consistence of a soil, degrees of workability of the soil in both dry and wet conditions can be determined. Soils that are plastic and sticky when wet are difficult to excavate, grade, and compact. To place a uniformly thick cover of wet clayey soil material over a layer of refuse is extremely difficult.
Because trenches (Soil Survey Staff, 1971) as deep as 15 feet or more are used for many landfills, geologic investigation is needed to determine the potential for pollution of ground water as well as to ascertain the design needed. These investigations include examination of stratification, rock formations, and other factors that might lead to the conducting of leachates to aquifers, wells, water courses, and other water sources. Hard nonrippable bedrock, creviced bedrock, and coarse strata in and underlying the proposed trench bottom are undesirable for excavation and hazardous due to the potential pollution of ground water.
The uppermost part of the final cover should be soil material that is favorable for the growth of plants. Surface layers of most soils have the best workability and highest content of organic matter. Thus, in the trench-type landfill operation, it is desirable to stockpile the surface layer for use in final blanketing of the fill.
Because of soil limitations (like shallowness to bedrock), refuse can be placed on the surface of the soil in successive layers in an area-type sanitary landfill (Soil Survey Staff, 1971). Table 5 outlines the criteria for determining limitations for this type of landfill; notice particularly that depth to bedrock is not important because only fill (and not excavation) is made in this area landfill. Information on soil characteristics used in Table 5 are given in Table 1; limitation ratings made from Table 5 are listed in Table 6 for soils of Kansas, along with the major limitations.
Table 5--Ratings of limitations of Soils for Solid-waste disposal in area-type sanitary landfills (Adapted from Soil Survey Staff, 1971).
|Depth to seasonal water table1||> 60 in||40-60 in||< 60 in|
|Soil drainage class2||Excessively drained, somewhat excessively drained, well-drained, and moderately well drained soils||Somewhat poorly drained soils||Poorly drained and very poorly drained soils|
|Flooding||None||Rare||Occasional or frequent|
|Permeability2||Slower than 2 in/hr||Slower than 2 in/hr||Faster than 2 in/hr|
|Slope||< 8%||8-15%||> 15%|
|1. Depth to water table and soil-drainage class reflects influence of wetness on operation of heavy-wheeled or crawler equipment.
2. These ratings reflect the ability of a soil to retard movement of effluents leached from landfills. In and and semiarid areas rapid permeability may not be a severe limitation.
In the area-type sanitary landfill, refuse is placed on the surface of the soil in successive layers. The daily and final cover material generally must be imported from other soil areas. A final cover of soil material at least two-feet thick is placed over the fill when it is completed. Although excavations are not made for this type of landfill, soil and geologic materials under the proposed site should be investigated so as to determine the probability that leachates from the landfill can penetrate the soil and thereby pollute water supplies.
For cover material (Soil Survey Staff, 1971), soils with very friable and friable consistence are good (classes of consistence and other soil properties can be obtained from the soil profile descriptions; Olson, in press). Soils with loose and firm consistence are fair; soils with very firm and extremely firm consistence are poor for cover material. Good soil textures include sandy loam, loam, silt loam, and sandy clay loam; fair textures include silty clay loam, clay loam, sandy clay, and loamy sand; poor textures include silty clay, clay, muck, peat, and sand. Thicker soil material, of course, is more desirable if excavation and hauling is to take place. Soils with gentler slopes, without coarse fragments, and with good drainage are better as a source of cover for sanitary landfill than are steep soils with stones or than soils in wet areas.
Figure 20--This photograph of a gate at a sanitary landfill site illustrates the importance of control and operation at the disposal area. Equipment must move soil every day in burial operations, whether the weather is wet or dry, hot or cold. Silty clay, clay, gravel, sand, and organic soils have severe limitations for sanitary landfill; sandy loam, loam, and sandy clay loam soil textures have slight limitations if other soil and geologic characteristics are also good (see Table 4). Dikes and other water-control structures can improve some sites for landfill operations.
Kansas Geological Survey, Geology
Placed on web Aug. 7, 2009; originally published March 1974.
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