Field-based assessment of the design of lysimeters for landfill final cover seepage control

Figures & data

Figure 1. Views of the field-test plot at St-Nicephore, Drummondville, Canada (a) Aerial view (enclosure plan); (b) Cross section A-A Lysimeter 1 (L1); (c) Cross section B-B Lysimeter 2 (L2).

Figure 2. Linear method.

Figure 3. (a) SWRC and (b) k-fct.

Table 1. Soil properties.

Property	Cover material	Sand	Gravel
USCS Classification	SM	SP	GW
D10 (mm)	0.002	0.258	4.943
D50 (mm)	0.052	0.563	5.700
D60 (mm)	0.065	0.913	7.900
Cu	33	4	2
Cc	2	1	1
Specific Gravity	2.68	2.77	-
ρd max (kg/m^3)	2,117.2	2,213.5	-
Optimum Water Content (%) for Standard Proctor Effort	7.93	7.64	-
Saturated Hydraulic Conductivity (m/s)	2.3 x 10^−5	1.8 x 10^−4	1.2 x 10^−2
van Genuchten (1980) parameters
α (1/kPa)	0.130	0.408	-
n	7.094	5.572	-
m	0.859	0.823	-
θs (m^3/m^3)	0.30	0.27	-
θr (m^3/m^3)	0.09	0.03	-

Figure 4. (a) L1 section; (b) L2 section.

Table 2. Probe location designation.

Symbol	$\theta$ – Moisture sensor (5TM by Meter Inc.)
	$\psi$ – Tensiometer T4e (Meter Inc.)
Location	Base – Probe installed at the base (bottom) of the lysimeter. Number 1 corresponds to the one closer to the sand layer, installed at 0.25 m from the bottom of the lysimeter, whereas number 2 is located 0.1 m above, i.e., 0.35 m from the bottom of the lysimeter.
	Drain – Probe installed at the drainage layer
	Top – Probe installed at the top of the formwork
	Surf – Probe installed near the surface. One is installed in the topsoil (ts) layer and another at the interface of the topsoil and the cover material.
Position	Int – Interior of the lysimeter wall
	Ext – Exterior of the lysimeter wall

Figure 5. Evolution of percolation collected in L1 and L2.

Table 3. Precipitation, percolation, and field measurements for the different lysimeters.

Year	Total (mm)	Percolation (mm)			Number of days
		L1	L2	L2/L1	Temp. Max > 30°C	Rain > 20 mm
2018	1060.8	185.8	118.0	63.5%	11	11
2019	1001.1	372.7	389.8	104.6%	5	9
2020	1057.5	481.8	467.6	97.1%	9	13
2021	476.6	171.2	149.0	87.0%	18	3
Total	3243.5	1211.5	1124.4	92.8%	43	36

Figure 6. Evolution of suction and volumetric water content at the mouth of L2.

Figure 7. Evolution of suction and volumetric water content at the base of L1.

Figure 8. Evolution of suction and volumetric water content at the base of L2.

Table

Acronym/Symbol	Definition
ACAP	Alternative Coverage Assessment Program
HDPE	High Density Polyethylene (geomembrane)
Hlys	Lysimeter wall height
k	Hydraulic conductivity or permeability
k-fct	Hydraulic conductivity function
ksat	Saturated hydraulic conductivity
L1	Lysimeter 1
L2	Lysimeter 2
qss	Design steady-state seepage rate
Δψ	Difference in the total head suctions
ψint	Intern suction elevation of the mouth of the lysimeter
ψext	Extern suction elevation of the mouth of the lysimeter
ψbase1_int	Tensiometer installed 25 cm above the cover/drain
ψbase2_int	Tensiometer installed 35 cm above the cover/drain
ψdrain	Tensiometer installed cover/drain interface
ψtop_int	Tensiometer at the intern elevation of the mouth of the lysimeter
ψtop_ext	Tensiometer at the extern elevation of the mouth of the lysimeter
θ	Water content
θsat	Saturated water content
θbase1_int	Water content probe aligned to ψbase1_int
θbase2_int	Water content probe aligned to ψbase2_int
θtop_int	Water content probe aligned to ψtop_int
θtop_ext	Water content probe aligned to ψtop_ext
θbase_ext	Water content probe installed outside of the base (bottom) of the lysimeter
SWRC	Soil Water Retention Curve

van Genuchten, M. T. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44 (5):892–98. doi:10.2136/sssaj1980.03615995004400050002x.

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Data availability statement

The authors confirm that the data supporting the findings of this study are available within this paper.