LANDFILL GAS

LANDFILL GAS PRODUCTION •  Anaerobic diges.on is a process that decomposes organic ma3er in the absence of oxygen. •  Main product from this process is biogas which is a mixture of approximately 60% CH4 and 40% CO2. •  Anaerobic degrada.on of organic frac.on of municipal solid waste requires a few phases of highly ac.ve microbial popula.on.

There are five phases of biological process in a landfill. •  Phase I: ini.al adjustment phase; •  Phase II: transi.on phase; •  Phase III: acid phase; •  Phase IV: methane fermenta.on phase; •  Phase V: matura.on phase Flow rate and characteris.c of leachate change from .me to .me because of these processes. Aerobic and anaerobic degrada.on happens during these processes.

Main gas genera.on stage is Phase IV genera.ng gas composi.on of approximately 60% CH4 and 40% CO2. In this stage, methanogenic bacteria are present. Direct conversion of hydrogen and carbon dioxide to form methane and water due to the involvement of microorganisms. Might take six months to several years and the longest stage of waste degrada.on. Main chemical compounds categorized into saturated and unsaturated hydrocarbons, acidic hydrocarbons, organic alcohols, aroma.c hydrocarbons, halogenated compounds, sulfur compounds and inorganic compounds

Typical Constituents Found in MSW Landfill Gas

Component

Percent (dry volume basis)

Methane

45 -60

Carbon Dioxide

40-60

Nitrogen

2-5

Oxygen

0.1-10

Sulphides,disulphides, mercapans, etc.

0-10

Ammonia

0.1-1.0

Hydrogen

0-0.2

Carbon monoxide

0-0.2

Trace constituents

0.01-0.6

Source: Tchonobanoglous et al., 1993

Percentage Distribu;on of Landfill Gases Observed during the first 48 hours aEer the Closure of a Landfill Cell

Average, Percent by Volume

Time Interval since Cell Completion, Month

Nitrogen (N2 )

0-3

5.2

88

5

3-6

3.8

76

21

6-12

0.4

65

29

12-18

1.1

52

40

18-24

0.4

53

47

24-30

0.2

52

48

30-36

1.3

46

51

36-42

0.9

50

47

42-48

0.4

51

48

(Source: Tchonobanoglous et al., 1993)

Carbon Dioxide (CO2)

Methane (CH4)

Condi;ons affect landfill gas produc;on •  Waste composi;on. The more organic waste present in a landfill, the more landfill gas (e.g., carbon dioxide, methane, nitrogen, and hydrogen sulfide) is produced by the bacteria during decomposi.on. The more chemicals disposed of in the landfill, the more likely NMOCs and other gases will be produced either through vola.liza.on or chemical reac.ons. •  Age of refuse. Generally, more recently buried waste (i.e., waste buried less than 10 years) produces more landfill gas through bacterial decomposi.on, vola.liza.on, and chemical reac.ons than does older waste (buried more than 10 years).

•  Presence of oxygen in the landfill. Methane will be produced only when oxygen is no longer present in the landfill. •  Moisture content. The presence of moisture (unsaturated condi.ons) in a landfill increases gas produc.on because it encourages bacterial decomposi.on. Moisture may also promote chemical reac.ons that produce gases. •  Temperature. As the landfill's temperature rises, bacterial ac.vity increases, resul.ng in increased gas produc.on. Increased temperature may also increase rates of vola.liza.on and chemical reac.ons.

Explosion Hazards •  The following condi.ons must be met for landfill gas to pose an explosion hazard: •  Gas produc;on. A landfill must be producing gas, and this gas must contain chemicals that are present at explosive levels. •  Gas migra;on. The gas must be able to migrate from the landfill. Underground pipes or natural subsurface geology may provide migra.on pathways for landfill gas •  Gas collec;on in a confined space. The gas must collect in a confined space to a concentra.on at which it could poten.ally explode. A confined space might be a manhole, a subsurface space, a u.lity room in a home, or a basement. The concentra.on at which a gas has the poten.al to explode is defined in terms of its lower and upper explosive limits (LEL and UEL)

Volume of Gas Produced •  Generalized chemical reac.on for the anaerobic decomposi.on of solid waste; bacteria Organic ma3er + H2O Biodegraded + CH4 + CO2 + other gases (solid waste) organic ma3er •  Cossu et al present following reac.on represen.ng the overall methane fermenta.on process CaHbOcNd + nH2O xCH4 + yCO2 + wNH3 = zC5H7O2N + energy •  CaHbOcNd is the emperical formula for organic content •  C5H7O2N is the emperical formula for bacterial cell



•  The maximum theore.cal landfill gas yield (neglec.ng bacterial cell conversion) may be es.mated as: CaHbOcNd + ( 4a – b-2c + 3d)H2O 4 (4a + b – 2c – 3d) CH4 + (4a – b + 2c + 3d) CO2 + dNH3 8 8

•  Tchobanoglous 1993, also had developed emperical formulas for typical MSW for rapid decomposable and slowly decomposable categories 1.  Rapidly decomposable = C68H111O50N 2.  Slowly decomposable = C20H29O9N

Example 8 •  Calculate the volume of methane and carbon dioxide gases from organic waste with the following characteris.cs

Example 9 Table 1 shows the major component of MSW. Determine the chemical composi.on and the amount of gas that can be derived from the rapidly and slowly decomposable organic cons.tuent given in Table 1. It was assumed 60% of the yard waste will decompose rapidly. Specific weights of methane and carbon dioxide are 0.0448 and 0.1235 lb/j3 respec.vely.

1. Table 1. Percentage distribu.on of the major elements composing the waste Component

Wet weight, lb

Dry weight, lb

Composi;on, lb C

H

O

N

S

Ash

Rapidly decomposable organic residue Food waste 9.0

2.7

1.30

0.17

1.02

0.07

0.01

0.14

paper

34.0

32.0

13.92

1.92

14.08

0.10

0.06

1.92

cardboard

6.0

5.7

2.51

0.34

2.54

0.02

0.01

0.29

Yard waste

11.1

4.4

2.10

0.26

1.67

0.15

0.01

0.20

Total

60.1

44.8

19.83

2.69

19.31

0.34

0.09

2.55

Slowly decomposable organic cons;tuents Tex.les

2.0

1.8

0.99

0.12

0.56

0.08

-

0.05

Rubber

0.5

0.5

0.39

0.05

-

0.01

-

0.05

Leather

0.5

0.4

0.24

0.03

0.05

0.04

-

0.04

Yard waste

7.4

3.0

1.43

0.18

1.14

0.10

0.01

0.13

Wood

2.0

1.6

0.79

0.10

0.69

-

-

0.02

Total

12.4

7.3

3.84

0.48

2.44

0.23

0.01

0.29

2. Compute the molar composi.on of the elements

neglec.ng the ash C H O N S lb/mole 12.01 1.01 16.00 14.01 32.06 Total moles Rapidly 1.6511 2.6634 1.2069 0.0241 0.0028 decomp. Slowly 0.3197 0.4752 0.1525 0.0164 0.0003 decomp. 3. Determine approximate chemical formula without sulfur.



Component

Mol.ra;o (nitrogen = 1) Rapidly decomp.

Slowly decomp.

Carbon

68.5

19.5

Hydrogen

110.5

29.0

Oxygen

50.1

9.2

Nitrogen

1.0

1.0

The chemical formulas without sulfur are Rapidly decomp. = C68H111O50N Slowly decomp. = C20H29O9N



4. Es.mate the amount of gas that can be derived from rapidly and slowly decomp. In MSW a)  i. Rapid decomp. C68H111O50N + 16H2O 35CH4 + 33CO2 + NH3 (1741) (288) (560) (1452) (17)

ii. Slowly decomp. C20H29O9N + 9H2O 11CH4 + 9CO2 + NH3 (427) (162) (176) (396) (17)

b) Determine the volume of methane and carbon dioxide produced. i.  Rapidly decomp. Methane = (560 x 44.8 lb) / (1741 x 0.0448 lb/j3) = 321.7 j3 at STP Carbon dioxide = (1452 x 44.8 lb) / (1741 x 0.1235 lb/j3) = 302 j3 at STP ii. Slowly decomp. Methane = (176 x 7.3 lb) / (427 x 0.0448 lb/j3) = 67.2 j3 at STP Carbon dioxide = (396 x 7.3 lb) / (427 x 0.1235 lb/j3) = 54.8 j3 at STP

c) Determine the total theore.cal amount of gas generated per unit dry weight of organic ma3er destroyed. i)  Rapidly decomp. Vol/lb = (321.7 j3 + 302.5 j3) / 44.8 lb = 13.9 j3/lb

ii)  Slowly decomp. Vol/lb = (67.2 j3 + 54.8 j3) / 7.3 lb = 16.7 j3/lb

•  Varia.on of gas produc.on with .me

•  Total gas produced, j3/lb = ½ (base,year) x (al.tude, peak rate of gas produc.on, j3/lb.yr)



MOVEMENT OF LANDFILL GAS •  Gases produced in soils are released to the atmosphere by means of molecular diffusion •  In an ac.ve landfill the internal pressure is greater than atmospheric pressure •  Landfill gas will be released by convec.ve (pressure driven) flow and diffusion •  Other factor influencing the movement include the sorp.on of the gases into liquid or solid component and the genera.on or consump.on of a gas component through chemical reac.on or biological ac.vity

Movement of principal landfill gases •  Upward migra.on of landfill gas –  CH4 and CO2 can be released through landfill cover into atmosphere through convec.on and diffusion –  Effec.ve diffusion coefficient

Dz = D (αgas )10/3 2 α

Dz = effec.ve diffusion coefficient, cm2/s (j2/d) D = diffusion coefficient, cm2/s (j2/d) αgas = gas-filled porosity, cm3/cm3 (j3/j3) α = total porosity, cm3/cm3 (j3/j3)

- assuming the concentra.on gradient is linear; αgas = α

-  Assuming dry soil condi.on introduces safety factor in any filtra.on of water into landfill cover will reduce gasfilled porosity and thereby reduce vapor flux from landfill NA = - Dα4/3 ( C Aatm – C Afill )

L

NA = gas flux of compound A, g/cm2 . S (lb . Mol/j2 . d) C Aatm = concentra.on of compound A at the surface of the landfill cover, g/cm3 (lb . Mol/j3) C Afill = concentra.on of compound A at the bo3om of the landfill cover, g/cm3 (lb . Mol/j3) L = depth of landfill cover, cm (j)

- Typical value for coefficient diffusion for CH4 0.20 cm2/s and CO2 is 0.13 cm2/s

•  Downward migra.on of landfill gas –  Ul.mately, CO2 because of its density can accumulate in the bo3om of a landfill –  Movement of CO2 can be limited with the use of geomembrane liner –  Carbon dioxide soluable and react in water and will form carbonic acid –  The reac.on will lower the pH, which in turn will increase the hardness and mineral content of groundwater –  Henry’s Law used to compute the par.al pressure of gas above the liquid

•  Mole frac.on of gas dissolved in liquid; Pg = H x g

Pg = par.al pressure of gas, atm H = Henry’s Law constant xg = equilibrium mole frac.on of dissolved gas = mol gas (ng) mol gas (ng) + mol water (nw)

Henry’s Law constant for common landfill gases

•  Movement of trace gases Ni = - Dα4/3 ( C iatm – C is Wi ) L Ni = vapor flux of compund i, g/cm2 . S D = diffusion coefficient, cm2/s Α = dry soil porosity, cm3/cm3 C iatm = concentra.on of compound i at the surface of the landfill cover, g/cm3 C is = satura.on vapour concentra.on of compound i, g/cm3 Wi = scaling factor to account for the actual frac.on of trace compound i in the waste C is Wi = concentra.on of compound i at the bo3om of the landfill cover , g/cm3 L = depth of landfill cover, cm

•  By assuming C iatm is zero, assump.on made because concentra.on of the trace cons.tuent reaching the surface of landfill will be quickly diminished by dispersal and diffusion into air, the equa.on is simplified Ni = Dα4/3 ( C is Wi ) L

Selected physical proper.es for 12 trace compounds found in landfill

Measured and satura.on gas phase concentra.ons of 10 trace compounds

Example 10 Determine the concentra.on of carbon dioxide in the upper layer of a groundwater in contact with a landfill gas at one atmosphere and 50oC (122oF). Assume that the composi.on of the landfill gas is 50% carbon dioxide and 50% methane that the gas is saturated with water vapour. (atmospheric pressure = 101.325 kN/m2 , vapour pressure = 12.33 kN/m2 )

Solu.on

1. Determine the par.al pressure of the CO2 by correc.ng for the vapour pressure of water Par.al pressure of CO2 = 0.50 x (101.325 – 12.33) kN/m2 101.325 kN/m2 = 0.44 2. Determine xg, from Henry’s Law constant for common LFG, at 50oC, H = 0.283 x 10-4 , Pg = H x g xg = pg = 0.44 H 0.283 x 10-4 = 1.55 x 10-4

3. Determine the concentra.on of CO2 in mol/L. 1 L of water contains 1000/18 = 55.6 g/mol, thus; ng = 1.55 x 10-4 ng + nw ng = (ng + 55.6) 1.55 x 10-4 Because the qua.ty (ng x 1.55 x 10-4) is very much less than ng, ng ≈ 55.6 x 1.55 x10-4 ≈ 8.62 x 10-3 mol/L CO2 4. Determine the satura.on concentra.on of CO2 expressed in mg/L Cs ≈ (8.62 x 10-3 mol/L) (44g/mol)(103 mg/g) ≈ 379 mg/L

Example 11 •  Es.mate the emission of toluene, 1,1,1trichoroethane and vinyl chloride from the surface of a landfill due to diffusion. Assume the following condi.on apply; –  Temperature = 30oC –  Landfill cover material = clay-loam mixture –  Porosity of landfill cover material = 0.20 –  Landfill cover thickness = 2 j (0.6 m) –  Scaling factor to account for actual frac.on of trace compound present below landfill cover = 0.001

Selected physical proper.es for 12 trace compounds found in landfill

Solu.on 1. Es.mate the concentra.on of the compound just below the landfill cover From table, satura.on of these compound are Toluene: 180.4 g/m3 = 180.4 x 10-6 g/cm3 1,1,1-Trichloroethene: 1081 g/m3 = 1081 x 10-6 g/cm3 Vinyl chloride: 11090 g/m3 = 11.090 x 10-6 g/cm3

Es.mate the concentra.on of the compound just below landfill cover, CisWi, by mul.plying the satura.on concentra.on values by the scaling factor 0.001 Toluene: = 180.4 x 10-9 g/cm3 1,1,1-Trichloroethene: = 1081 x 10-9 g/cm3 Vinyl chloride: = 11.090 x 10-9 g/cm3

2. Es.mate the mass emission rate and the diffusion coefficient a)  Toluene; Ni = - Dα4/3 ( C is Wi ) L = (0.068 cm2/s)(0.20)4/3(180.4 x 10-9 g/cm2) 60 cm = 2.39 x 10-11 g/cm2. s b) 1,1,1-Trichloroethane Ni = (0.071)(0.20)4/3(1081 x 10-9) 60 = 1.5 x 10-10 g/cm2. s c) Vinyl chloride Ni = (0.098)(0.20)4/3(11.090 x 10-9) 60 = 2.12 x 10-9 g/cm2. s

3. Convert the mass emission rates to units of g/m2.d a)  Toluene Ni = (2.39 x 10-11 g/cm2.s) x (0.864 x 109) = 0.02 g/m2.d b) 1,1,1-Trichloroethane Ni = (1.5 x 10-10 g/cm2.s) x (0.864 x 109) = 0.13 g/m2.d

c)  Vinyl chloride Ni = (2.39 x 10-9 g/cm2.s) x (0.864 x 109) = 2.06 g/m2.d

Passive Gas Collection Systems

Passive Gas Collection Systems •  use existing variations in landfill pressure and gas concentrations to vent landfill gas into the atmosphere or a control system. •  can be installed during active operation of a landfill or after closure. •  use collection wells, also referred to as extraction wells, to collect landfill gas. •  The collection wells are typically constructed of perforated or slotted plastic and are installed vertically throughout the landfill to depths ranging from 50% to 90% of the waste thickness. •  If groundwater is encountered within the waste, wells end at the groundwater table. •  Vertical wells are typically installed after the landfill, or a portion of a landfill, has been closed. •  may also include horizontal wells located below the ground surface to serve as conduits for gas movement within the landfill. •  Horizontal wells may be appropriate for landfills that need to recover gas promptly (e.g, landfills with subsurface gas migration problems), for deep landfills, or for active landfills. Sometimes, the collection wells vent directly to the atmosphere. •  Often, the collection wells convey the gas to treatment or control systems

Active Gas Collection System



Active Gas Collection System •  the most effective means of landfill gas collection (EPA 1991). •  include vertical and horizontal gas collection wells similar to passive collection systems. •  wells in the active system have valves to regulate gas flow and as a sampling port. •  Sampling allows the system operator to measure gas generation, composition, and pressure. •  include vacuums or pumps to move gas out of the landfill and piping that connects the collection wells to the vacuum. •  Vacuums or pumps pull gas from the landfill by creating low pressure within the gas collection wells. •  The low pressure in the wells creates a preferred migration pathway for the landfill gas. •  The size, type, and number of vacuums required in an active system to pull the gas from the landfill depend on the amount of gas being produced. •  system design should account for future gas management needs, such as those associated with landfill expansion.

Schema.c diagram of the major components of biogas treatment process

LEACHATE

•  Leachate produc.on is the result of precipita.on, evapora.on, surface runoff, infiltra.on, storage capacity etc •  Leachate from a landfill varies widely in composi.on depending on the age of the landfill and the type of waste that it contain •  usually contain both dissolved and suspended material •  In a landfill that receives a mixture of municipal, commercial, and mixed industrial waste, but excludes significant amounts of concentrated specific chemical waste, leachate may characterized as

–  Water based solu.on of four groups of contaminants; dissolved organic ma3er (alcohols, acids, aldehydes, short chain sugars etc), inorganic macro components (common ca.ons and anions including sulfate, chloride, iron, aluminium, zinc and ammonia), heavy metals (Pb, Ni, Cu, Hg) and xenobio.cs organic compounds such as halogenated organics (PCBs, dioxins, etc)

•  The physical appearance of leachate when it emerges from a typical landfill site is a strongly odour black, yellow or orange colour cloudy liquid. The smell is acidic and offensive and may be very pervasive because of hydrogen, nitrogen and sulfur rich organic species such as mercaptans

Table 1. Constituents in leachates from MSW landfills (after EHRIG, 1990 and KRUSE, 1994) Parameter

Medium

Range

Medium

-

4,5 - 7

6

7,5 - 9

8

COD

mg/l

6.000 - 60.000

22.000

500 - 4.500

BOD5

mg/l

4.000 - 40.000

13.000

20 - 550

TOC

Acid phase Range

Leachate from MSW landfills (KRUSE, 1994) Intermediate phase Methanogenic phase

Medium

6,2 - 7,8

7,4

Range

Medium

6,7 - 8,3

7,5

Range

Medium

7,0 - 8,3

7,6

3.000

950 - 40.000

9.500

700 - 28.000

3.400

460 - 8.300

180

600 - 27.000

6.300

200 - 10.000

1.200

20 - 700

2)

2)

2)

2)

230 2)

300 - 1.500

880

150 - 1.600

6602)

260 - 3.900

1.545

195 - 3.500

1.725

1.500 - 25.000

7.000

200 - 5.000

1.300

350 - 12.000

AOX

µg/l

540 - 3.450

1.674

524 - 2.010

1.040

260 - 6.200

org. N1)

mg/l

10 - 4.250

600

10 - 4.250

600

NH4-N1)

mg/l

30 - 3.000

750

30 - 3.000

750

TKN

mg/l

40 - 3.425

1.350

40 - 3.425

1.350

NO2-N1)

mg/l

0 - 25

NO3-N1)

mg/l

0,1 - 50

SO4

mg/l

70 - 1.750

500

Cl

mg/l

100 - 5.000

2.100

100 - 5.000

2.100

315 - 12.400

2.150

315 - 12.400

2.150

315 - 12.400

2.150

Na1)

mg/l

50 - 4.000

1.350

50 - 4.000

1.350

1 - 6.800

1.150

1 - 6.800

1.150

1 - 6.800

1.150

1)

K

mg/l

10 - 2.500

1.100

10 - 2.500

1.100

170 - 1.750

880

170 - 1.750

880

170 - 1.750

880

Mg

mg/l

50 - 1.150

470

40 - 350

180

30 - 600

285

90 - 350

200

25 - 300

150

mg/l

10 - 2.500

1.200

20 - 600

60

80 - 2.300

650

40 - 310

150

50 - 1.100

200

Ca 1)

0,5

0 - 25 0

0,5

3

0,1 - 50

3

10 - 420

80

2.600

2.500

mg/l

1)

2.400

17- 1.650

740

17- 1.650

740

17- 1.650

740

250 - 2.000

920

250 - 2.000

920

250 - 2.000

920

35 - 925

0,1 - 30

6

0,1 - 30

6

0,3

0,3 - 1,6

0,3

0,002 - 0,52

Fe

mg/l

20 - 2.100

780

3 - 280

15

3 - 500

135

Ni

mg/l

0,02 - 2,05

0,2

0,02 - 2,05

0,2

0,01 - 1

Cu1)

mg/l

0,004 - 1,4

0,08

0,004 - 1,4

0,08

0,005 - 0,56

Zn

mg/l

0,1 - 120

0,03 - 4

0,6

0,05 - 16

As 1)

mg/l

0,005 - 1,6

0,16

0,005 - 1,6

0,16

0,0053 - 0,11

0,0255

0,0053 - 0,11

0,0255

0,0053 - 0,11

0,0255

Cd1)

mg/l

0,0005 - 0,14

0,006

0,0005 - 0,14

0,006

0,0007 - 0,525

0,0375

0,0007 - 0,525

0,0375

0,0007 - 0,525

0,0375

Hg1)

mg/l

0,0002 - 0,01

0,01

0,0002 - 0,01

0,01 0,000002 - 0,025

1)

mg/l

0,008 - 1,02

0,09

0,008 - 1,02

0,09

parameter more or less independent from the biochemical degradation phase DOC

0,008 - 0,4

0,155

2 - 120

36

0,19

0,01 - 1

0,09

0,005 - 0,56

2,2

0,06 - 1,7

0,0015 0,000002 - 0,025 0,16

0,008 - 0,4

0,3 - 54

240

0,03 - 1,6

0,002 - 0,52

6,8

25 - 2.500

mg/l

0,155

0,3 - 54

90

mg/l

Pb

6,8

20 - 230

Cr1)

5

0,3 - 54

200

tot. P

1)

2)

Leachate from MSW landfills (EHRIG, 1990) Acid phase Methanogenic phase Range

pH-value

1)

Unit

0,002 - 0,52

6,8 0,155

4 - 125

25

0,19

0,01 - 1

0,19

0,09

0,005 - 0,56

0,09

0,6

0,09 - 3,5

0,0015 0,000002 - 0,025 0,16

0,008 - 0,4

0,6

0,0015 0,16

Water balance and leachate genera.on in landfills •  Descrip.on of water balance components for a landfill cell –  Water entering from above, moisture in the solid waste, moisture in cover material, moisture in sludge

•  Water entering from above –  Precipita.on that has percolated through the cover material –  Where geomembrane is not used, amount of rainfall percolates through landfill cover can be determine using hydrologic evalua.on of landfill performance (HELP) model –  HELP modeling provides es.mated values for runoff, infiltra.on, precipita.on, evapotranspira.on, and storage for a set of input parameters –  Therefore, leachate genera.on can be es.mated from HELP modeling (Hydrologic Evalua.on of Landfill Performance) Leachate Genera.on = Runoff + Infiltra.on Leachate Genera.on = Precipita.on – Evapotranspira.on – Storage

•  Water entering in solid waste –  Moisture inherent in the waste material as well as moisture has been absorbed from atmosphere or rainfall

•  Water entering in cover material –  Depend on type and source of cover material and season of the year

•  Water leaving from below –  Water leaving from the first cell is leachate –  Water leaving second and subsequent cells corresponds to water entering from above for the cell below

•  Water consumed in the forma.on of landfill gas –  Water is consumed during anaerobic decomposi.on of organic frac.on in waste

•  Water loss as vapour –  Determine by assuming the landfill gas is saturated with water vapour and applying perfect gas law pvV = nRT

Landfill field capacity •  Water entering landfill and is not consumed or exit as water vapor may held within landfill •  The quan.ty of water that held against the pull of gravity refer as field capacity •  FC varies with overburden weight FC = 0.6 – 0.55 ( W ) 10000 + W FC = field capacity( the frac.on of water in the waste based on the dry weight of the waste W = overburden weight calculated at the midheight of the waste in the lij

•  Prepara.on of landfill water balance ΔSSW = WSW + WTS + WCM + WA(R) – WLG – WWV – WE + WB(L)

ΔSSW = change in the amount of water stored in solid waste in landfill, lb/y3 WSW = Water in incoming solid waste, lb/y3 WTS = Water in incoming treatment plant sludge, lb/y3 WCM = Water in cover material, lb/y3 WA(R) = water from above (for upper landfill layer), lb/y2 WLG = water loss in the forma.on of landfill gas, lb/y3 WWV = water loss as saturated vapor with LFG, lb/y3 WE = water loss due to surface evapora.on, lb/y2 WB(L) = water leaving from bo3om of element, lb/y2

Movement of leachate in unlined landfills •  The rate of seepage of leachate from the bo3om of a landfill can be es.mated using Darcy’s Law Q = KA dh dl Breakthrough Time •  .me in years for leachate to penetrate a clay liner of a given thickness can be es.mated using following equa.on t = d2α K(d + h) t = breakthrough =me, year d = thickness of clay liner, B α = effec=ve porosity K = coefficient permeability h = hydraulic head

Control and treatment of leachate in landfills •  Liner systems for MSW –  To minimize the infiltra.on of leachate into subsurfae soils below landfill