School of Civil and Environmental Engineering

Water Balance and the Influence of Soil Structural Changes on Final Covers for Landfill Closure

Melissa Salt, University of Adelaide Mark Jaksa, University of Adelaide Jim Cox, CSIRO Paul Lightbody, Tonkin Consulting

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The University of Adelaide

School of Civil and Environmental Engineering

Research Objectives

• Measure and compare the drainage to determine if phytocovers reduce drainage to the same extent as conventional covers • Correlate changes in drainage patterns over time from the phytocover and conventional cover changes with changes in bulk density, soil water characteristic curve and permeability • Assess the tendency for anthropomorphic soil to tend towards the natural profile of the borrow source or toward a new stable profile • Determine the effect of changes in bulk density, soil water retention curve and permeability on the predictability of the water balance as estimated from pre-construction laboratory testing

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The University of Adelaide Slide 1

School of Civil and Environmental Engineering

Water Balance

• P = ET + R + L + D + ΔS

Precipitation (P)

COVER

Evapotranspiration (ET) Runoff (R) Soil moisture storage (S) Drainage (D) Lateral flow (L)

WASTE

Leachate Life Impact

The University of Adelaide Slide 2

School of Civil and Environmental Engineering

Methodology – Field Scale

Earthen berms Runoff collection Soil cover layer Monitoring nest Root barrier Drainage layer 1.5 mm LLDPE geomembrane Interim cover Drainage collection not to scale • Precipitation - Weather station • Runoff - Flow meters • Drainage and lateral flow - Tipping bucket rain gauges • Soil moisture content – MP406 • Soil suction – CS229

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The University of Adelaide Slide 3

School of Civil and Environmental Engineering

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The University of Adelaide Slide 4

School of Civil and Environmental Engineering

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The University of Adelaide Slide 5

School of Civil and Environmental Engineering

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The University of Adelaide Slide 6

School of Civil and Environmental Engineering

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The University of Adelaide Slide 7

School of Civil and Environmental Engineering

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The University of Adelaide Slide 8

School of Civil and Environmental Engineering

Methodology – Small Scale

• 1 m x 1 m x 1.5 m deep • Replicate conventional and phytocover from Adelaide, including plants • Irrigation and measure drainage • Destructively sample 1 box of each cover type every 6 months • Analyse samples for bulk density, soil water characteristic curve and permeability

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The University of Adelaide Slide 9

School of Civil and Environmental Engineering

Methodology – Core samples

• To measure any change in permeability or bulk density as a result of alternate saturation and then drying the soil layers proposed to use in the Adelaide A-ACAP trial. • Prepared core samples at known bulk density of phytocover soil and clay barrier • Wet using falling head permeability apparatus until saturated and hydraulic conductivity measured • Dry in oven at 30 o C until equilibrated and observe shrinkage and cracking • Repeat process

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The University of Adelaide Slide 10

School of Civil and Environmental Engineering

Water Balance Modelling

0.5

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.05

0.1 m 1 m 0 200 400 600 800

Days since modelling commenced

1000 Moisture content at depth through conventional profile over first 3 years modelled 0.5 m 1.5 m 1200

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The University of Adelaide Slide 11

School of Civil and Environmental Engineering

Water Balance – Adelaide Site

P I ET R L D Water balance Phytocover (mm/yr & %) 1 m 1.5 m 2 m 515 117 (23) 349 (68) 0.7 (0.1) 0 48 (9) 515 123 (24) 357 (69) 0.7 (0.1) 0 34 (7) 515 123 (24) 364 (71) 0.7 (0.1) 0 28 (5) Conventional (mm/yr & %) As placed Dried 515 103 (20) 412 (80) 0.8 (0.1) 0.5

0.2 (0) 515 125 (24) 369 (72) 0.8 (0.1) 0 23 (4)

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The University of Adelaide Slide 12

School of Civil and Environmental Engineering

Water Balance Predictions

100 80 60 40 20 1000 800 600 400 200 0 1957 1962 1967 1972 1977

Year

1982 1987 1992 Conventional 1997 2002 Phytocover 0 Rainfall Predicted annual runoff volumes when surface soil permeability is reduced by one order of magnitude

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The University of Adelaide Slide 13

School of Civil and Environmental Engineering

Results – Adelaide Soil Moisture

40 35 30 25 20 15 10 5 0 31/10/20 07 0:00 2/11/200 7 0:00 4/11/200 7 0:00 6/11/200 7 0:00 8/11/200 7 0:00 10/11/20 07 0:00 Date and Time 12/11/20 07 0:00 14/11/20 07 0:00 16/11/20 07 0:00 18/11/20 07 0:00 upslope 150 mm upslope 700 mm upslope 1350 mm centre 150 mm centre 700 mm centre 1350 mm downslope 150 mm downslope 700 mm downslope 1350 mm RG201017 Life Impact

The University of Adelaide Slide 14

School of Civil and Environmental Engineering

Results – Adelaide Topsoil Moisture Content

500 450 400 350 50.00

45.00

40.00

35.00

300 250 200 150 30.00

25.00

20.00

15.00

100 50 10.00

5.00

0 17/07/2007 0:00 6/08/2007 0:00 Rainfall 26/08/2007 0:00 15/09/2007 0:00 5/10/2007 0:00 Date and time Phytocover 150 mm 25/10/2007 0:00 Conventional cover 150 mm 14/11/2007 0:00 0.00

4/12/2007 0:00

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The University of Adelaide Slide 15

School of Civil and Environmental Engineering

Results – Melbourne Soil Moisture

40 35 30 25 20 15 10 5 0 12/02/07 0:00 3/04/07 0:00 Phytocover 150 mm Conventional 150 mm Cumulative Rainfall 800 700 600 500 400 300 200 100 23/05/07 0:00 12/07/07 0:00 Date Time Phytocover 800 mm Conventional 500 mm 31/08/07 0:00 0:00 0 20/10/07 Phytocover 1550 mm Conventional 850 mm

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The University of Adelaide Slide 16

School of Civil and Environmental Engineering

Outcomes

• Water balance comparison of phytocaps for Australian environment • Variability of water balance predictions from selected models • Quantification of soil structural changes in the short to medium term • Impact of soil structural changes on sustainability of the phytocaps • Determination of best soil input parameters for pre-construction modelling

Life Impact

The University of Adelaide Slide 17