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

2. Leachate Collection System (1)
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.

3. Leachate Collection System (2)
Refuse
Drainage tile
Drainage layer
Low permeability
barrier
Undisturbed
native material
Simple collection system
Refuse
Drainage tile
Drainage layer
Low permeability
barrier
Undisturbed
native material
Double liner system

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

5. Schematic of Various Leachate Discharge Pathways
Infiltration
Optional
toe drain
Leachate
seep
through
face
Toe
seepage
Leachate
collection
tiles
Toe
seepage
Leachate to
groundwater

6. Leachate Seep Remediation
Landfill cover
Granular toe-drainage collection
Refuse
Peripheral toe-drainage collection

7. Components of LCS French drain Refuse Tile drain Drainage layer
Low permeable
liner
Undisturbed
native material
K of drainage layer: min cm/sec; 10-2 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

8. Leachate Collection System Layouts
 130 ft
Clean-out access point
S = 1~5%
 1200 ft
S = 2~5%
Min. 2%

9. Schematic of Clean-Out System
Access manhole
Final grade
Refuse
Drainage blanket
Solid pipe
Perforated pipe

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

11. Storm Water Management in Area Type Landfill

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

13. Leachate Collection Facilities
Leachate collection and transmission vault
Leachate holding tank

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

15. Role of LCS Components (1)
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 10-3 cm/sec
Slope: to encourage lateral migration; min. 2% bottom final slope after long-term settling

16. Role of LCS Components (2)
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 10-4 cm/sec; 2 ft (0.7 m) thick layer to cushion the engineered system against damage and act as a filter
UC: Uniformity coefficient = d60/d10

17. Design Considerations for Tile Spacing
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.

18. Analytical Formulations for Tile Spacing
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.

19. Continuous-Slope Formulation (1)x L
D - L D P Z L A p e x z ( x ) y ( x ) L i n e r D r a i n S y o x D r a i n D

20. Continuous-Slope Formulation (2)
zx = sx + yx (10.1)
where: zx = static head at location x (m);
s = slope of the liner (radians);
x = horizontal distance (m); and
yx = depth of flow at location x (m).
where: K = hydraulic conductivity of the media (m/sec)
A = cross-sectional area of flow (m2);
W = width (m); and
dz/dx = gradient of static head (m/m).
At steady state, Qx = (L - x)·p·W (10.3)
where: p = rate of infiltration of moisture (m/sec).
(10.2)

21. Continuous-Slope Formulation (3)
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) = yo, yields three conditional cases:
(10.4)
(10.5)
Apex
Case I: 4 > s2
Case II: 4 = s2
Low permeable liner
Drain tile
Case III: 4 < s2

22. Continuous-Slope Formulation (4)
Case I: 4 > s2
Case II: 4 = s2
(10.6)
(10.7)
Case III: 4 < s2
(10.8)

23. Example
p = 15.2 cm/yr (6 inches/yr); K = 10-3 cm/sec; max. allowable mound depth = 0.3 m; drainage tile spacing 30 m; min. slope of the liner?
61 cm/yr
30 cm/yr
15.2 cm/yr
7.6 cm/yr
2.5 cm/yr

24. Flat-Slope Configuration (Worst Scenario)*
07/16/96
Flat-Slope Configuration (Worst Scenario)
When the slope of the liner system equals zero, Eq becomes:
ymax occurs at x = D/2. From Eq. 10.9, ymax becomes:
Ex. Determine ymax using Eq for a 30 m tile drain spacing, a drainage layer hydraulic conductivity of 10-3 cm/sec, a percolation rate of 7.6 cm/yr, and zero liner slope.
Solution:
(10.9)
(10.10)
= 0.23 m *

25. Sawtooth Formulation (1)
Apex
L=D/2
L=D/2 D P Z x
Q(x) d
Drain
Liner s
L=D/2

26. Sawtooth Formulation (2)
Based on the Dupuit assumption for unconfined flow, the differential equation governing the steady drainage on a sloping barrier is: This is equivalent to Eq with transformation of the origin (i.e., xsawtooth = L - xcontinuous). Transforming Eq by substituting the expressions xo = x/L, yo = y/L, and yo* = yo/L, defining u* = yo/xo, substituting u*x* for y*, and then separating variables leads to:
(10.11)
(10.12)

27. Sawtooth Formulation (3)
Case II
Case I
Case III
Alternative mathematical eqs. for determining ymax
(Moore, 1983)
(Richardson and
Koerner, 1987)

28. Sawtooth Formulation (4)
Case I: 4 > s2
(10.13)
Case II: 4 = s2
(10.14)
Case III: 4 < s2
(10.15)

29. Calculated Max. Mound Depth
Tile spacing, m
Slope, %
McEnroe, 1989
Moore, 1983
Richardson and Koerner, 1987
100 1 2 3 4 5
1.545
1.225
1.010
0.855
0.740
0.650
1.542
1.121
0.838
0.651
0.526
0.437
1.179
0.999
0.909
0.861
0.833 50 1 2 3 4 5
0.772
0.612
0.505
0.427
0.370
0.325
0.771
0.561
0.419
0.326
0.263
0.219
0.589
0.499
0.454
0.430
0.417
P = 30 cm/yr; K = 10-3 cm/sec; yo = 0

30. Max. Mound Depth vs. Slope
Continuous-slope configuration
Lower mound depth
Saw-tooth configuration
Better
p = 15.2 cm/yr; K = 10-3 cm/sec

31. Impact of Drain Tile Failure
Continuous-slope configuration
Greater mound depth: more problem
Saw-tooth configuration

32. Max. Mound Depth vs. Slope

33. Wisconsin Regulations
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

34. McEnroe Method R = p/Ksin2α < 1/4 R = 1/4 R > 1/4
p = percolation rate per unit surface area (cm3/sec/cm2);
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
ymax = Ymax (L tanα) = maximum saturated depth (ft).
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):

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

36. Breakthrough Time K = permeability coefficient, L/T;d
K = permeability coefficient, L/T;
ne = effective porosity;
d = liner thickness, L; and
h = leachate mound height.
Example: ne = 0.4; d = 4 ft; h = 1 ft;
K = 1ⅹ10-7 cm/sec = ft/yr

37. Clogging Problems
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 SO2 gas; some danger

38. Weeping Tile
Two types
Helical profile
Annular profile

39. Pipe Cleaning Method
Rodding equipment

40. 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.

41. Sewer ball
Snakes

42. Other Design Considerations
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 HDPE
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

43. Leachate Collection Pipe
Drainage Couplers and Fittings
Diameter: 4" ~ 36"
Length: 20"

44. 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.