for such permits. Accordingly, all pertinent agencies shall be contacted early in the design phase to take the following steps:

identify regulations impacting on the prospective landfill
determine the extent, detail, and format of the application
obtain permit application forms and other background information.

4.2.6.7 Two permits relevant to landfills are identified and mandated by these criteria:

1.

NPDES (National Pollutant Discharge Elimination System) permit (402 and 404) required for location of a landfill in waters of the United States. It is also required for any point source discharges from sanitary landfills, such as from leachate collection systems.

2. Army Corps of Engineers permit required for the construction of any Tevee, dike, or other type of containment structure to be placed at a sanitary landfill located in waters of the United States.

4.2.6.8 Permit requirements of state and local regulations vary depending on jurisdiction. In some areas, only one permit is needed. Other states may require several separate permits or stipulate that a new sanitary landfill proponent coordinate with several agencies.

4.2.6.9 Sanitary landfill regulations can be the responsibility of one or more state agencies. Appendix D lists the various state agencies (including addresses and telephone numbers) responsible for solid waste disposal activities in those states.

4.2.6.10 Local regulatory agencies may include one or more of the

environmental and health departments
planning and/or zoning commissions

board of county commissioners
building departments

highway departments

fire departments.

4.2.6.11 The reviewing agency may require the submittal of information on standard forms or in a prescribed format in order to facilitate the review process. This process can take at least 1 month and usually 6 to 12 months or longer, depending on the degree of controversy and opposition. After a permit is issued, it can be valid for various durations, depending largely upon the submittal of monitoring results and performance reports and the results of periodic onsite inspections.

4.2.6.12 Site Selection. Selection of an appropriate site on the installation is the most critical step in establishing a sanitary landfill facility. Site selection criteria shall include cost, availability of land, availability of cover material, impact on natural resources (i.e., wildlife, endangered species, ecological sensitivities, etc.), topographic features and hydrogeologic considerations, environmental and pollution hazards, and social

and aesthetic consideration. The process of site selection shall involve specialists from military, local, state, and federal agencies as appropriate.

4.2.6.13 Site characteristics. Various sites on an installation may be available for sanitary landfill operations. These sites shall be screened by the facilities engineer to determine which is the most advantageous, using various site characteristics.

1. Land availability. Installation planning documents shall be consulted
in order to screen the sites. Also, legal considerations, including
the investigation of legal burdens, title restrictions, and other
possible jurisdictional blocks to the use of various sites for
landfill operations, shall be reviewed. Land area requirements vary
significantly with the type of landfill operation and characteristics
of land, compaction, and volume of waste generated by the

installation.

solid waste.

Figure 4-2-6A provides estimates of volume of compacted

2. Cover material availability. Consider the availability and suitability of cover materials. Most well-graded soils are suitable for daily cover, but not for intermediate or final cover and should exist at the site or be immediately available to the site. The quantity of cover material will vary with the design characteristics of the site. Typical waste: cover ratios of 4:1 to 2:1 are used.

3. Proximity. Landfill siting shall constitute a balance between

adequate distance from housing and work areas and economical hauling distances. The landfill shall be sited at least 750 ft from inhabited buildings and so that prevailing winds are away from living areas, where practical. Also, landfills must not be sited within 10,000 ft of any point of any airfield servicing jet aircraft or within 5000 ft of an airfield servicing only piston aircraft.

4. Roads. Sites shall be accessible to appropriate vehicles by all-
weather roads leading from the public road system.

5. Underground structures. Sites traversed by pipelines or conduits for sewage, stormwater, etc., shall be rejected unless the relocation or protection of the pipelines or conduits is feasible. These pipelines may serve as pathways for gas and leachate. Plans for maintenance and repair of protected pipelines must be developed.

6. Flood plains.

plain.

Landfills cannot be sited within the 100-year flood

4.2.6.14 Topography. Specialists shall evaluate alternative sites from the viewpoint of pollution hazards and possible environmental degradation. Military agencies and laboratories such as the Facilities Housing Support Agency, U.S. Army Construction Engineering Research Laboratory, Naval Civil Engineering Laboratory, Naval Energy and Environmental Support Activity, U.S. Army Waterways Experiment Station, U.S. Army Environmental Hygiene Agency, Air Force Engineering and Services Center, and others can provide additional technical guidance in these areas.

1. Surface water. Surface water that infiltrates the cover soil can
increase the rate of waste decomposition and eventually cause
leachates to leave the solid waste and create water pollution
problems. This problem can be minimized by rejecting sites containing
surface water features, diverting upland drainage, and designing
facilities with sufficient grade and slope to allow surface water
runoff. Sites shall be selected on the basis of a geohydrological
evaluation of surface water problems.

2. Terrain. A sanitary landfill can be constructed on virtually any
terrain; however, some land features require extensive site
improvements and expensive operational techniques. The best terrain
consists of flat or gently rolling land not subject to flooding.
While depressions such as canyons and ravines are more efficient than
flat areas, cover material may not be available. Also, special
difficulties may occur in depressions and control of surface waters
may be difficult. Such manmade features as strip mines, quarries, and
open pit mines can often be safely and economically reclaimed by the
government as sanitary landfills. Some offer excellent protection
against leachate pollution, while others require more extensive
improvements. Terrain features that shall exclude a site for
consideration include the following:

a. hilltops and other similar land forms

b. highly permeable and porous areas such as gravel beds

g.

land having karst features such as limestone formations which can lead to the formation of sinkholes and depressions

h. steep slopes.

4.2.6.15 Hydrogeological Characteristics

Both

4.2.6.16 Liner Systems: Soil and Membrane (Robinson 1986). the need to protect the environment and regulatory agency requirements have resulted in the installation of liners at the base of many landfills. The liner's purpose is to limit the movement of leachate through the base of the landfill and into the underlying formations. Many materials and techniques have been tried in an effort to prevent leakage at a reasonable cost.

4.2.6.17 The liner must endure chemical and physical attack mechanisms. Many chemicals found in leachate have the potential to damage liner materials. Also, the liner must not fail structurally during installation or from the strain of the solid waste.

4.2.6.18 Liner materials include soils and, in particular, clay soil, admixed liners, flexible polymeric membranes, sprayed-on linings, soil sealants, and chemical absorptive liners. The purpose of the liner is to prevent the movement of water and its associated contaminants through the base of the landfill and into the underlying formations. The liner may be fabricated in one of two ways. It may be constructed onsite, such as when soil materials are placed and compacted, or it may be a manufactured flexible membrane placed on the site during construction.

4.2.6.19 Many landfills have had clay liners placed at their base. Clay minerals may be kaolinite, illite, or montmorillonite. A typical clay will contain one or more of these clay minerals and possibly will be mixed with other fine-grained soil materials such as silt. Clay minerals have a low hydraulic conductivity and therefore will significantly retard the movement of any leachate through them. Permeabilities for most soils containing greater than 25% clay are in the range of 10-8 cm/s to 10-5 cm/s.

4.2.6.20 Clay liner thicknesses of 5 ft (1.5 m) or greater have been required at some sites. The success of the clay liner will not only depend upon its original characteristics, but also upon the method of liner installation. Best results are achieved by placing several individual layers or lifts. Each lift is compacted before the next layer is placed. The degree of compaction achieved will be a function of the compacting equipment, the thickness of the lift, and the moisture content of the soil. The soil moisture content is a significant factor. Soil that is either too dry or wet will be less than optimum for compaction.

4.2.6.21 Admixed liners are formed-in-place liners. These include asphalt concrete, soil cement, soil asphalt, and bentonite clay liners. The liners are formed by mixing the lining material with the natural soil at the base of the landfill. The resultant mixture hardens or modifies the characteristics of the soil material to provide a low-permeability barrier. Each of these approaches has been employed successfully in the lining of impoundments.

4.2.6.22 Flexible polymeric membranes are manufactured materials that are 0.020 to 0.120 in. (0.51 to 3.0 mm) thick. The liner material is manufactured in rolls that are 48 to 96 in. (1.2 to 2.4 m) wide and hundreds of feet long. A uniform bedding material, such as sand, is placed at the base of the landfill prior to the installation of the liner. The particle size of the subgrade material usually should be less than 3/4 in. (19 mm). The base grade on the liner should be a minimum of 2% if gas release from materials beneath the liner is anticipated. Gas vents may also be necessary in order to adequately allow release. The liner is installed by unrolling the sheets of plastic and then using specialized equipment to form bonded seams between the individual sheets. The liner is usually extended up the side of the landfill to the ground surface where it is anchored.

4.2.6.23 Soil sealant and chemically absorptive liners are two other approaches that have been used on a limited basis for retarding the movement of the materials through the base of impoundments. These approaches are also being tested for use in landfills.

4.2.6.24 Groundwater. Groundwater pollution hazards are determined by examining annual fluctuations in the depth of the water table. A site shall