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Jae K. (Jim) Park Dept. of Civil and Environmental Engineering University of Wisconsin-Madison 1

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Designed as containment facilities due to concern with the environment impact of landfills Needed to prevent landfill gas and leachate from migrating from the site in significant quantities Purpose: to collect leachate for treatment or alternative disposal and to reduce the depths of leachate buildup or level of saturation over the low-permeability liner. Underdrain system: constructed prior to landfilling and consists of a drainage system that remove the leachate from the base of the fill. Peripheral system: installed after landfilling, constructed around the edge of the disposal area, and used to control leachate seeps through the face of the landfill. 2

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Refuse Drainage layer Low permeability barrier Undisturbed native material Simple collection system Refuse Undisturbed native material Low permeability barrier Drainage layer Double liner system Drainage tile 3

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4 Leachate collection pipe (see detail below) Sloped intercepting leachate collection pipe Sloped terraces Leachate movement Liner Perforated leachate collection pipe Protective soil layer Geotextile filter fabric Sand drainage layer Extra geomembrane (optional) Geomembrane liner Compacted clay layer Washed gravel (1½~2 in.) Geotextile filter fabric

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Infiltration Optional toe drain Leachate collection tiles Toe seepage Leachate to groundwater Toe seepage Leachate seep through face 5

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6 Landfill cover Granular toe- drainage collection Peripheral toe-drainage collection Refuse

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French drain Tile drain Refuse Drainage layer Low permeable liner Undisturbed native material K of drainage layer: min cm/sec; desirable Drainage layer gravel should be washed to remove fines; no limestone-based aggregate French drain: used in the event of pipe failure or clogging; gravel pack Additional containment and/or leak detection system 7

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8 Clean-out access point 1200 ft 130 ft S = 1~5% S = 2~5% Min. 2%

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9 Access manhole Final grade Perforated pipe Solid pipe Drainage blanket Refuse

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10 Slotted leachate collection pipe Clay berm First cell to be developed Slotted pipe connected to leachate removal system Leachate collection line Stormwater collection line Solid waste Clay berm (2 ft) Sand layer GeomembraneClay liner (3 ft) Slotted leachate collection pipe

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Pipe passed through side of landfill Leachate removed with a pump 12 Potential leakage: Not recommended Most widely used

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Leachate collection and transmission vault Leachate holding tank 13

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14 Leachate Collection Facilities Above grade Below grade Used in cold regions

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Barrier layer: a very low-permeability synthetic or natural soil liner to restrict and control the rate of vertical downward flow of liquids Drainage layer: a high permeability gravel drainage layer to laterally drain the liquid to the collector drain pipes; at least 30 cm thick with a min. K of cm/sec Slope: to encourage lateral migration; min. 2% bottom final slope after long-term settling 15

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French drains and tiles: maximize the amount of leachate diverted to, and collected by the tile drains; subangular gravel with UC < 4 and max. of 2 in.; two or more rows of holes at the 2 and 10 o’clock positions; min. slope of 0.5% and min. of 6 in. Filter layer: granular or synthetic, used above the drainage layer to reduce the potential for migration of fines into the drainage layer Fine soil or refuse: K of cm/sec; 2 ft (0.7 m) thick layer to cushion the engineered system against damage and act as a filter 16 UC: Uniformity coefficient = d 60 /d 10

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Why? To control the height of a mound of leachate Design considerations Flow rate or flux of leachate impinging on the barrier layer Spacing between the tiles Slope of the liner Thickness and hydraulic conductivity of the drainage layer If the tiles are separated by too large a distance, the leachate mound will penetrate back up into the refuse, resulting in increase in the hydraulic gradient and consequently increase in leachate seepage. 17

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Mathematical models to examine a series of design considerations including: Depth, hydraulic conductivity, and slope of the drainage layer Thickness of the low-permeability barrier layer Two measures of hydraulic performance: max. saturated depth over the barrier and amount of leakage through the barrier Leachate mounding: function of liner slope, leachate infiltration rate, permeability of drainage and barrier layers, and drainage tile spacing Assumptions in mathematical formulation Flow is one direction (lateral). Saturated steady-state flow conditions exist. The drainage media are homogeneous and isotropic. 18

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19 L D - L D Apex Apex D x y(x) y o Drain Liner Drain L S Z z(x) P

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20 z x = sx + y x (10.1) where:z x = static head at location x (m); s = slope of the liner (radians); x = horizontal distance (m); and y x = depth of flow at location x (m). where:K = hydraulic conductivity of the media (m/sec) A = cross-sectional area of flow (m 2 ); W = width (m); and dz/dx = gradient of static head (m/m). At steady state, Q x = (L - x)·p·W(10.3) where:p = rate of infiltration of moisture (m/sec). (10.2)

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21 Assuming a unit width of aquifer and combining Eqs and 10.3 yields: where = p/K, w = L - x, and y = vw. Solving the preceding equation and invoking the boundary condition y(0) = y o, yields three conditional cases: Apex Case I: 4 > s 2 Case II: 4 = s 2 Case III: 4 < s 2 Low permeable liner Drain tile (10.4) (10.5)

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22 Case I: 4 > s 2 Case II: 4 = s 2 Case III: 4 < s 2 (10.6) (10.7) (10.8)

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p = 15.2 cm/yr (6 inches/yr); K = cm/sec; max. allowable mound depth = 0.3 m; drainage tile spacing 30 m; min. slope of the liner? 2.5 cm/yr 7.6 cm/yr 15.2 cm/yr 30 cm/yr 61 cm/yr 23

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When the slope of the liner system equals zero, Eq becomes: y max occurs at x = D/2. From Eq. 10.9, y max becomes: Ex. Determine y max using Eq for a 30 m tile drain spacing, a drainage layer hydraulic conductivity of cm/sec, a percolation rate of 7.6 cm/yr, and zero liner slope. Solution: (10.9) (10.10) = 0.23 m 24

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25 P x Q(x) Drain d Liner s L=D/2 Z Apex L=D/2 D

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Based on the Dupuit assumption for unconfined flow, the differential equation governing the steady drainage on a sloping barrier is:Dupuit assumption This is equivalent to Eq with transformation of the origin (i.e., x sawtooth = L - x continuous ). Transforming Eq by substituting the expressions x o = x/L, y o = y/L, and y o * = y o /L, defining u * = y o /x o, substituting u * x * for y *, and then separating variables leads to: (10.11) (10.12) 26

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Case I Case II Case III Alternative mathematical eqs. for determining y max (Moore, 1983) (Richardson and Koerner, 1987) 27

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Case I: 4 > s 2 Case II: 4 = s 2 Case III: 4 < s 2 (10.13) (10.14) (10.15) 28

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P = 30 cm/yr; K = cm/sec; y o = 0 29 Tile spacing, m Slope, % McEnroe, 1989 Moore, 1983 Richardson and Koerner,

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p = 15.2 cm/yr; K = cm/sec Continuous-slope configuration Saw-tooth configuration 30 Lower mound depth Better

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31 Continuous-slope configuration Saw-tooth configuration Greater mound depth: more problem

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NR (5)(a) Wisconsin Administrative Code (WAC): 12 inches of average leachate head over the liner < 130 ft drain spacing NR (3) WAC: Open conditions: p = 6 inches/yr = 0.5 inch/month Closed conditions: p = 1 inch/yr = inch/month Factors affecting the leachate mount height Percolation rate into the drainage layer Hydraulic conductivity of the drainage layer Leachate flow distance from the upstream boundary to the leachate collection pipe Slope of the landfill liner 33

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R = p/Ksin 2 α < 1/4 R = 1/4 R > 1/4 p = percolation rate per unit surface area (cm 3 /sec/cm 2 ); S = tan α = slope of liner (ft/ft); α = slope angle; K = hydraulic conductivity (cm/sec); A = (1-4R) 0.5 ; B = (4R-1) 0.5 ; L = drainage distance, measured horizontally (ft); and y max = Y max (L tanα) = maximum saturated depth (ft). 34 McEnroe, B.M. (1989). “Steady Drainage of Landfill Covers and Bottom Liners,” Jour. of Envion. Eng., ASCE, 115(6): McEnroe, B.M. (1993). “Maximum Saturated Depth over Landfill Liner,” Jour. of Envion. Eng., ASCE, 119(2):

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Residence Time, T where s’ = slope approximated by the bottom slope, m/m. Efficiency of Capture d: Thickness of low permeable layer y max : Max. height of leachate mound Undisturbed native material 35

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K = permeability coefficient, L/T; n e = effective porosity; d = liner thickness, L; and h = leachate mound height. d h Example: n e = 0.4; d = 4 ft; h = 1 ft; K = 1 ⅹ cm/sec = ft/yr 36

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Occur in agricultural irrigation, weeping tile systems, sanitary landfills, septic system leachate fields, and the like. Remedial measures Smaller-diameter lines (15~30 cm): cables > 30 cm lines: rodding equipment Max. 300 m between access ports or manholes Removal mechanisms Mechanical procedures: roto-routers, pigs, sewer balls, snakes, and buckets Low-pressure jets: 70 to 140 psi at nozzle High-pressure jets: 410 to 1300 psi at nozzle Chemical methods: such as SO 2 gas; some danger 37

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Two types Helical profile Annular profile 38

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Rodding equipment 39 Pipe Cleaning Method

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Bucket Machines - the only sure way to remove sand, solids, or sludge from storm & sanitation pipelines. Needs no water to create a vacuum slurry. Cost-effective. 40

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Snakes Sewer ball 41

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Collector sizing and type: at least 15 cm diameter; min cm, preferably 30 cm to reduce the effects of silting and to facilitate inspection and cleaning; schedule 80 PVC or HDPEschedule 80 PVC Collector slope: 2% if practical but not < 0.5% Collector perforations: at 2 and 10 o’clock positions French drain around the collector pipe: 38 to 50 mm washed stone Attention to field construction practices: within pipes, accumulation of deposits may occur in areas of hydraulic perturbation such as where pipe joins have been poorly installed 42

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Diameter: 4" ~ 36" Length: 20" Drainage Couplers and Fittings 43

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AdvanEDGE ® is a panel shape pipe offered in 12" and 18" heights, and in coils up to 400 ft. The primary benefit of its panel design is quick drainage response after introduction of water, making it ideal for time-critical applications such as high-traffic road and track beds. 44

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