Chapter 16 Landfill Liners and Geosynthetics 연세대학교 지반공학연구실

16 Landfill Liners and Geosynthetics ▶ Waste materials can be classified into four categories : municipal waste, industrial waste, hazardous waste, and low-level radioactive waste

16 Landfill Liners and Geosynthetics ▶ Leachates are a main source of ground water pollution, therefore, they must be properly contained in all landfills, surface impoundments, and waste piles, within some type of liner system. TABLE 16.1 Waste Material Generation in the United States

16.1 Landfill LinersOverview ▶ Until about 1982, Liner material used in landfill – Clay ▶ In 1984, U.S. Environmental Protection Agency’s minimum technological requirement for hazardous waste landfill design and construction by U.S. Congress in Hazardous & Solid Waste amendments - double liner system ▶ Review the general properties of the component materials involved in the system – that is clay soil (6.9 & 6.10) and geosynthetics (given in the following sections)

16.2 Geosynthetics ▶ The term geosynthetics includes the following : Geotextiles Geomembranes Geogrids Geonets Geocomposites

16.2 Geosynthetics ▶ Five major function Separation Reinforcement Filtration Drainage Moisture barrier ▶ For further information, refer to a geosynthetics text such as that by Koerner (1994).

16.3 Geotextiles ▶ Geotextiles are textiles in the traditional sense ; - however, the fabrics are usually made from petroleum products. They may be woven, knitted, or nonwoven, or needle-punched nonwoven. ▶ Bonding processes : Chemical bonding Thermal bonding Mechanical bonding ▶ Geotextiles have four major uses : Drainage Filtration Seperation Reinforcement

16.3 Geotextiles ▶ Permittivity (16.1) where P = permittivity ( ) hydraulic conductivity for cross-plane flow ( ) t = thickness of the geotextile ▶ Transmissivity (16.2) where T = transmissivity ( ) hydraulic conductivity for in-plane flow ( ) (Figure 16.2)

16.3 Geotextiles FIGURE 16.1 Cross-plane flow through geotextile FIGURE 14.2 In-plane flow in geotextile

16.3 Geotextiles ▶ Hydraulic conductivity, ▶ Permittivity, P: - Nonwoven: - Woven: ▶ Transmissivity, T:

16.4 Geomembranes ▶ Geomembranes are impermeable liquid or vapor barriers made from continuous polymeric sheets that are flexible – thermoplastic or thermoset ▶ Hydraulic conductivity of geomembranes : ▶ Thickness of scrim-reinforced geomembranes :

16.4 Geomembranes ▶ List of tests for geomembranes Density Mass per unit area Water vapor transmission capacity Tensile behavior Tear resistance Resistance to impact Puncture resistance Stress cracking Chemical resistance Ultraviolet light resistance Thermal properties Behavior of seams

16.4 Geomembranes FIGURE 16.3 Configurations of filles geomembrane seams: (a) lap seam; (b) lap seam with gum tape; (c) tongue-and-groove splice; (d) extrusion weld lap seam; (e) fillet weld lap seam; (f) double hot air or wedge seam (after U.S. Environmental Protection Agency, 1989)

16.5 Geonets ▶ Geonets are formed by the continuous extrusion of polymeric ribs at acute angles to each other. ▶ The primary function of geonets is drainage ▶ Dimension of geonet : - witdth : 1.8 to 2.1m - length : 30 to 90m - aperture size : 30mm 30mm to 6mm 6mm - thickness : 3.8 to 7.6mm

16.5 Geonets FIGURE 16.4 Geonet

16.6 Single Clay Liner and Single Geomembrane Liner Systems ▶ Single clay liners - until about 1982, most landfill liners - thickness : 0.9m to 1.8m - hydraulic conductivity : ▶ Single geomembrane liners – Around 1982

16.6 Single Clay Liner and Single Geomembrane Liner Systems Figure 16.5 Cross section of single clay liner system for a landfill FIGURE 16.6 Cross section single geomembrane liner system for a landfill

16.7 Recent Advances in the Liner Systems for Land fills ▶ Since 1984, most landfills developed for solid and hazardous wastes have double liners. The two liners are an upper primary liner and a lower secondary liner. ▶ Between the primary and secondary liners is a system for leak detection, collection, and removal (LDCR) of leachates.

16.7 Recent Advances in the Liner Systems for Land fills FIGURE 16.7 Cross section of double-liner system (note the secondary composite liner) FIGURE 16.8 Cross section of double-liner system (note the primary and secondary composite liners)

16.7 Recent Advances in the Liner Systems for Land fills ▶ General guidelines for the primary leachate collection system and LDCR system : It can be a granular drainage layer or a geosynthetic drainage material such as a geonet. If a granular drainage layer is used, it should have a minimum thickness of 12 in. (0.3 m) The granular drainage layer (or the geosynthetic) should have a hydraulic conductivity, , greater than . If a granular drainage layer is used, it should have a granular filter or a layer of geotextile over it to prevent clogging. A layer of geotextile is also required over the geonet when it is used as the drainage layer. The granular drainage layer, when used, must be chemically resistance to the waste material and the leachate that are produced. It should also have a network of perforated pipes to collect the leachate effectively and efficiently.

16.8 Leachate Removal Systems ▶ The bottom of a landfill must be properly graded (2% or more) so that the leachate collected from the primary collection system and the LDCR system will flow to a low point by gravity. ▶ Leachate removal system for primary system. Low-volume sump High-volume sump ▶ Leachate removal system for LDCR system Pumping Gravity

16.8 Leachate Removal Systems FIGURE 16.9 Primary leachate removal system with a low-volume sump (after U.S. Environmental Protection Agency, 1989)

16.8 Leachate Removal Systems FIGURE 16.10 Primary leachate removal system with a high-volume sump (after U.S. Environmental Protection Agency, 1989)

16.8 Leachate Removal Systems FIGURE 16.11 Secondary leak detection, and removal (LDCR) system-by means of pumping. Note: The plastic pipe penetrates the primary geomembrane

16.8 Leachate Removal Systems FIGURE 16.12 Secondary LDCR system-by means of gravity monitoring. Note: The plastic pipe penetrates the secondary geomembrane

16.9 Closure of Landfills ▶ Cap will reduce and ultimately eliminate leachate generation. ▶ A schematic diagram of the layering system recommended by the U.S. Environmental Protection Agency and Koerner for hazardous waste landfills is Fig 16.14 ▶ Layering system consists : compacted clay cap geomembrane liner drainage layer cover topsoil ▶ EPA recommends this period to be about 30 years

FIGURE 16.13 Landfill with liner and cap 16.9 Closure of Landfills FIGURE 16.13 Landfill with liner and cap

FIGURE 16.14 Schematic diagram of the layering system for landfill cap 16.9 Closure of Landfills FIGURE 16.14 Schematic diagram of the layering system for landfill cap

16.10 Summary and General Comments Selection of material Stability of side slope liner Leak response action plan