5

BIOREACTOR LANDFILLS:GEOTECHNICAL ENGINEERING

CONSIDERATIONSby

Edward Kavazanjian, Jr., Ph.D., P.E.Research Professor

University of Southern Californiafor the

ASTSWMOState Solid Waste Managers Conference

Salt Lake City23 July 2003

7/17/2003 11:18:21 AM

Design Considerations

(INTERNET POLL)

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Design Considerations

Seeps Slope Stability Head On Liner / Flow Capacity Clogging of Leachate Collection System Gas Generation and Emissions Operating Temperature

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Geotechnical Considerations

Design Engineering Analyses Waste Mass Properties / Parameters

Monitoring and Reporting Measurements Interpretation Frequency

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Geotechnical Design

What is the Same? Most Performance Analyses Shear Strength (Effective Stress)

What is Different? Pore Pressures Fluid Volumes (Liquid and Gas) Temperatures (Aerobic Systems) Monitoring and Reporting (?)

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Properties(Same)

Shear Strength: No (or little) Difference in Effective Stress Parameters Drained (Static) Strength Depends

on Steady State Pore Pressure Undrained (Dynamic) Strength is

Unknown (Depends on Excess Pore Pressure Generation)

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Doña Juana

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Bioreactor Shear StrengthOII Direct Shear Testing

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92%

75%99%

84%

50%

76%

74%

73%

10%

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Bioreactor Shear Strength

OII Simple Shear Testing

90 100 200 300 400 500 600 700

Normal Stress (kPa)

300

200

100

0

Shea

r St

ress

(psf

)

Upper Bound Failure Envelope(c = 625 psf, φ = 59)

Lower Bound Failure Envelope(c = 340 psf, φ = 33)

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Bioreactor Shear Strength

WMI Bioreactor Direct Shear Testing

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Effective StressStrength Envelope

Low Pressure: 500 psf cohesion Higher Pressures: 33 degrees friction angle

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Bioreactor Shear Strength

Kavazanjian, E. Jr., Hendron, D. and Corcoran, G.T. (2001) Strength and Stability of Bioreactor Landfills, Proceedings, 6thAnnual SWANA Landfill Symposium, San Diego

Kavazanjian, E., Jr. (2001) Mechanical Properties of Municipal Solid Waste, Proc. Sardinia 01 - 8th International Waste Management and Landfill Symposium

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Properties / Parameters(Different)

Unit Weight Increase: Double (or More)

Pore Pressure Increase: Not Zero Anymore

Temperature (Aerobic Systems) Increase: Potentially Excessive

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MSW Unit Weight

Dry Landfilling 45 - 65 pcf at

surface 85 - 100 pcf at

depth

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MSW Unit Weight

OII In-Situ Unit Weight Measurements 100 pcf at

surface up to 130 pcf

for wet waste

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Boring BA-1Boring BA-2Boring BA-3

0

20

40

60

80

100

120

140

160

75 85 95 105 115 125 135 145Unit Weight (pcf)

Dept

h (ft

)

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MSW Unit Weight

OII Consolidation Tests

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CONDLCONDHCONMMCONMHSWCONDLSWCONDMSWCONDH

0

5000

10000

15000

20000

25000

Unit Weight (pcf)

Nor

mal

Str

ess (

psf)

60 70 80 90 100 110 120 130 140 150 160

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Bioreactor Unit Weight

Can be 100 pcf at Surface, 135 pcf at Depth 2 to 3 times conventional (dry

waste) values Can reduce some factors of safety

proportionally But NOT static stability !

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MSW Unit Weight

Kavazanjian, E., Jr., Matasovic, N., Stokoe, K.H., II, and Bray, J.D. (1996), In-Situ Shear Wave Velocity of Solid Waste from Surface Wave Measurements, Proc. 2nd International Congress Environmental Geotechnics, Osaka, Japan

Kavazanjian, E., Jr. (2001) Mechanical Properties of Municipal Solid Waste, Proc. Sardinia 01 - 8th International Waste Management and Landfill Symposium

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Performance Analyses(Same / Similar)

Geomembrane: Puncture, Tension Drainage / Filtration: Clogging,

Maximum Head / Flow Capacity Pipe Design: Capacity / Spacing,

Crushing Stability: Global (Waste Mass), Local

(Veneer)19

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Performance Analyses(Different)

Water Balance: Supplemental Liquid, Liquid Consumption /Generation

Liquid Distribution: Method, Schedule Settlement, Gas Generation: Softening (Temperature) : Pipes,

Geomembrane

(Stability - Including Pore Pressure)20

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Geomembrane Analyses

Puncture, Tension Depend on Unit Weight Increased Unit Weight Reduces

Factor of Safety

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Drainage / Filtration

Max Head / Flow Capacity New Cell: Design Accordingly Retrofit:

Max Head May Increase Additional Pumping Capacity May Not Mitigate

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Drainage / Filtration

Clogging Potential Low pH in Acid Phase May Induce

Precipitation Additional Flow May Increase

Flushing

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Pipe Design

Crushing Depends on Unit Weight Increased Unit Weight Increases

Load, Reduces Factor of Safety Spacing / Capacity

New: Design For It Retrofit: Must Evaluate Capacity,

Maximum Head 24

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Stability If Strength is Frictional, Static Stability

Independent of Unit Weight Resistance Increases Proportional to

Driving Force (Weight) If Cohesive / Adhesive, Factor of Safety

Inversely Proportional to (Unit) Weight Double Unit Weight, Halve Factor of

Safety Impact of Seismic Load Complicated,

Generally Adverse with Increase 25

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Stability Depends on Pore Pressure

Analyze in Design Many Assumptions Needed

Water Balance Gives Global (Indirect) Indication

Can Simply Assume Max Value Monitor in Field

May be Cellular (Discontinuous)» Particularly w/ Low Perm. Daily Cover

Must Exceed Field Capacity 26

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Stability

Deformations, Seepage Generally Preceed Instability Indirect Monitoring Can Give

Warning Deformations for Waste Mass Seepage for Veneer Stability

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Stability

Other Strategies Reduce Waste Strength

Not Recommended) Increased Factor of Safety

No Rational Basis For Increased Value

Stabilized Zone Around Perimeter Pore Pressure Can Still Migrate

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Landfill Performance Modeling

Input:Waste StreamLiquid InjectionGeometric Design Factors

Output:LCRS Pumping RatesSettlementGas Generation Rate

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Performance Model Considerations

Site-Specific ConsiderationsWaste compositionWaste placement practices

Design of Piping NetworkTrench size and spacingInjection pressure and schedule

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Water Balance Analyses

Global Water Budget Initial Value + Recirculated and

Supplemental Liquids + Water Consumption / Generation (through decomposition)

Compare with Field Capacity Predict LCRS Collection Rates

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Liquid Distribution Analyses

Injection Schedule Injection Pressure

Pore Pressure in Waste Mass Trench Geometry

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Effects of Injection Schedule

Trench size: 3 ft x 3 ft

Kwaste = 0.001 cm/sec

Injection pressure = 7.9 ft

Injection schedule: 8-hr on, 16-hr off

t = 8 hr t = 24 hr

t = 32 hr t = 48 hr

G S CEO YNTEC ONSULTANTS

t = 8 hr t = 24 hr

t = 32 hr t = 48 hr

30

30

30

30

0

0

15

15

15

15

30

30

30

30

0

0

15

15

15

15

0

15

15

0

15

15

X (ft) X (ft)

Y (ft)

Y (ft)

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Effect of Daily Cover

Trench Size: 3 ft x 3 ftKwaste = 0.001 cm/sec; Klayer = 0.00001 cm/secInjection Pressure = 7.9 ftInjection Schedule: 8-hr On, 16-hr Off

t = 120 hr

30 300 1515X (ft)

t = 32 hr

30 300 1515

0

15

15

X (ft)

Y (ft)

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Effect of Waste Anisotropy

Trench size: 3 ft x 3 ft

Injection pressure = 7.9 ft

Injection schedule: 8-hr on G S CEO YNTEC ONSULTANTS

Kw,h = 0.005 cm/sec

Kw,v = 0.001 cm/sec

I = 490 gal/ft/8hr

KwI = 274 gal/ft/8hr

Kw,h = 0.005 cm/sec

Kw,v = 0.001 cm/sec

I = 490 gal/ft/8hr

Kw = 0.001 cm/sec

I = 274 gal/ft/8hr

30 300 1515 30 300 1515

0

15

15

X (ft)

Y (ft)

X (ft)

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Waste Permeability

1500

1000

500

0

2000

5 10 15 20 25 30Fluid Injection Pressure P(ft)

kw = 0.01 cm/seckw = 0.005 cm/sec

kw = 0.001 cm/sec

Flui

d In

ject

ion

Rat

e (g

al/ft

/8hr

)

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Trench Geometry

300

200

100

0

400

5 10Fluid Injection Pressure P(ft)

Flui

d In

ject

ion

Rat

e (g

al/ft

/8hr

)

1 x 9 Trench9 x 1 Trench

3 x 3 Trench

1 x 1 Trench

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Iterative Design Approach

Verify Design Assumptions w/ Monitoring Liquid and gas distribution and pressure profiles Efficiency of liquid distribution system Efficiency of gas extraction system

Update Modeling Parameters and Optimize Hydraulic properties of waste and preferential

paths Liquid injection schedule Gas generation potential and timelines Gas extraction requirements

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Monitoring and Reporting Requirements

What Data to Collect ? What Interpretation to Provide ? What Frequency to Monitor, Report ?

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Performance Monitoring and Reporting

Model Validation Liquid Balance Gas Generation Stability Model

Field Measurements Gas Flow Rate LCRS Pumping Rate Waste Moisture Content 40

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Liquid Collection / Removal Monitoring

Water Budget Analysis LCRS Pumping Rates Supplemental Liquid Volumes Water Consumption / Generation

from Decomposition (Gas Generation) Head Measurements

In Sump Elsewhere

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Stability Monitoring

Pore Pressures Direct (Pore Pressure Measurements) Indirect (Water Budget Analysis)

Deformations Visual Observations Surface Monuments Sunsurface Measurments

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Periodic Submittals Landfill Performance Modelling

LCRS Pumping Volumes LCRS Testing

Supplemental Liquid Injection Schedule Comprehensive Water Budget Evaluation

Stability Monitoring Pore Pressures

Liner Waste Mass

Deformations Visual Observations

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Discussion

Internet Poll Results

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