10th Asian Regional Conference of IAEG (2015)

Migration Behavior of Life Source Contaminants in a Landfill Site
Liwen CAO*, Dongmei WU, Yong WANG, Ke HAN, Xue QU and Pan HUO
School of Resource and Earth Science, China University of Mining and Technology, China*Corresponding author, E-mail:caoliwen@cumt.edu.cn
Abstract
The author establishes a generalized model of a landfill in China according to theactual sectional view. Such ions as Ca2+, Mg2+, CO32-, Na+ and Cu2+ with high concentrationof life source contaminants in landfill are used to research their migration in landfill site.
Under the water pressure with 10m, 20m and 30m, such migration characteristics ineach year as depth, breadth and concentration when Ca2+, Mg2+, CO32-, Na+ and Cu2+
seeping for 20 years in the landfill site are obtained based on the concentration as well as
the permeability coefficient of the five ions in the stratum. With the water pressure
increasing, the concentration of Ca2+, Mg2+, CO32-, Na+ and Cu2+ at the same monitoring sitein landfill are rising in varying degrees. Migration rate in descending order is
Na+,Cu2+,Mg2+,Ca2+,CO32-. The concentration growth rate of the five ions in descendingorder is CO32-,Ca2+, Mg2+,Cu2+,Na+. With the compaction degree of clay increasing, theconcentration decrease rate in descending rate is CO32-,Ca2+,Mg2+,Na+,Cu2+.
Particularly in terms of Mg2+ average concentration variance, it is 70% in the 0-10
years of migration in landfill site, but it reduces to 8% in the 10-20 years of migration.
During the 20 years of migration, for 4.5m depth, the concentration of Ca2+, Mg2+ and CO32decreases from 186ppm to 0.007ppm, from 414ppm to 3.8ppm, and from 1.241×104ppm to
9.89×10-9ppm, respectively. The concentration decreases faster in the 2m clay layer area
than that in other landfill sites, especially the concentration of Zn2+ and Cu2+ can reduce tozero after migration by degrees. Comparative study of the measured data and numericalsimulation results are carried out. Furthermore, the proposed compaction degree of clay inthe research is not less than 93.00%.
Keywords: life source contaminants; ion migration; landfill; numerical simulation
1.

Introduction

and contaminant migration is established (Zhang etal., 2009; Hu et al., 2010). Currently, the research
results rarely involve in the migration of life source
contaminants in clay. However, it is imminent tostudy the migration of life source contaminants due tothe fact that life source contaminants have alreadybecome a main pollution source on soil properties.
In this study, the numerical simulation method
was adopted to simulate the seepage of life source
contaminants in clay liner layers of Yanqun landfill in
Xuzhou, in order to calculate and predict the spatial
and temporal distribution characteristics of different
ion concentrations.

The migration of contaminants in soils
experiences a long and complex evolution, and its
migration law are researched by some scholars. The
migration and transformation of contaminants in soils
are investigated using centrifuge model tests(Mitchell, 1994a, 1994b; Zhang et al., 2002; Kumar
et al., 2012; Yu et al., 2014). The migration of suchheavy metal ions as Pb2+ and Cd2+ in unsaturated soils
and clay liners is studied through tests (Zhang et al.,2013; Sui et al., 2013; Chen et al., 2014). The
diffusion coefficient of contaminant ions in clay ismeasured (Xi et al., 2003). Meanwhile, such softwareas MODFLOW is implied to predict the spatial andtemporal distribution of contaminant concentrationand seepage parameters (Liu et al., 2008). The
migration characteristic on concentration of leachate
contamination components in soils are simulated (Diet al., 2008). A coupling model of soil consolidation

2.

Engineering Geological general situation of
Yanqun Landfill Site and Generalized Model

2.1 Geological general situaionzai of landfill site
Yanqun landfill site is located in Dapeng Town,
Tongshan District, Xuzhou City, and the first phase1

10th Asian Regional Conference of IAEG (2015)of the project covers an area of about 802.64mu, with

Fig. 1 Soil layer distribution of Yanqun landfill
National Road 310 on the north and 720m away fromthe site. The elevation of the northeast site is higher
ranging from 41.00m to 43.50m than that of thesouthwest site ranging from 34.00m to 35.50m, withthe total area about 50,000m2 and the depth 5-8m.
The geomorphic unit of the site is fluvial facies. In
the first phase of the project, the total landfill storage
capacity is 3,500,000m3, with the design total landfill
amount 3,100kt, the design maximum height of thewaste body 36m, as well as the maximum and mean
excavation depth 13.25m and 6m. The soil layers
under the landfill site can be divided into 11 layers
from top to bottom: cultivation soil, mild clay, clayey
silt, sandy loam, clay, mild clay, sandy clay, mildclay, as shown in Figure 1.

shown in Figure 2.

Fig. 2 Grid division for generalized model of Yanqun
landfill site
2.3 Major ions of contaminants and theparameters of the numerical simulation
According to the water quality test results of life
source contaminants, CO32-, Ca2+, Mg2+, Cu2+ and Na+with higher concentration are selected as the main
migration ions. The initial concentration andpermeability coefficient of the five ions in clayey silt
and clay are determined as illustrated in table 1.

2.2 Generalized model of Yanqun landfill site
A two-dimensional generalized model of Yanqun
landfill site is established, with the unit of verticaland horizontal coordinate m and the model scale
1:100. The upper part represents waste layer, and the
middle 2m part compacted clay liner layer, the lower
5-8m part simplified clayey silt layer. The
generalized model is divided into grids, most ofwhich are triangular and quadrilateral elements, asion
speciesCa2Mg2+
CO32Na+Cu2+

Table 1 Migration model parameters of five ions of leachate
initialpermeability coefficient
permeability
concentrationof clayey silt
coefficient of clayboundary conditions
(ppm)
(m/d)
(m/d)
186
0.000100.0000010
Total water head of
the top of waste layer: 64m;
414
0.000300.0000030
the top of clay layer:
12410
0.00001
0.0000001
29m, 39m, 49m, 59m;
3319
0.00100
0.0000100
the bottom of sandy loam
0. 02
0.00100
0.0000100
layer: 0m

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10th Asian Regional Conference of IAEG (2015)

3.

Ion migration in landfill compacted clay layer

3.1 Variation of pollution plume with migrationtime
The pollution plumes of the five ions after 20
years of migration under 20m water pressure areshown from Figure 3 to Figure 7. The Na+ pollution
plumes pass through the clayey silt layer. Meanwhile,
concentration increases caused by boundary effect,and symmetric pollution plumes gradually form.
Moreover, the formation speed of Na+ pollution
plume is equal to the migration velocity of Na+.
Furthermore, the five ions in descending order of
migration velocity are Na+, Cu2+, Mg2+, Ca2+, CO32-.
Additionally, it is worth emphasizing that thepollution plumes of Na+, Cu2+, Mg2+ and Ca2+ passthrough the slope clay layer preferentially.

Fig. 6 Pollution plumes of Cu2+ after 20 years of
migration under 20m water pressure

Fig. 7 Pollution plumes of CO32- after 20 years of
migration under 20m water pressure
3.2 Variation of ion concentration with migrationtime
The point with the coordinates (12, 6) on the soil
layer of the landfill model (as shown in Figure 2) isselected to extract the concentrations of Na+ atdifferent migration time, as shown in Figure 8.

Fig. 3 Pollution plumes of Na+ after 20 years of
migration under 20m water pressure

2.800
2.100
1.400

H=0m
H=10m
H=20m
H=30m

+

3

Na concentration (kg/m)

3.500

Fig. 4 Pollution plumes of Ca2+ after 20 years of
migration under 20m water pressure

0.700
0.000
0

5

10
15
migration time (a)

20

25

+

Fig. 8 Variation of Na concentration with migrationtime
The results show that with the migration timeincreasing, the concentration of Na+ gradually
increases at the point (12, 6) by a decreasing speed.
During the 20 years of migration, for 4.5m depth,
Ca2+ concentration decreases from 186ppm to
0.007ppm, Mg2+ concentration from 414ppm to3.8ppm and CO32- concentration from 1.241×104ppm
to 9.89×10-9ppm. Meanwhile, the concentration
change rate of Mg2+ gradually declines. Specifically,
the change rate of Mg2+ concentration is 70% in theformer decade but 8% in the latter decade. Moreover,Fig. 5 Pollution plumes of Mg2+after 20 years of
migration under 20m water pressure3

10th Asian Regional Conference of IAEG (2015)

the decrease of Mg2+ concentration is slower than thatof Ca2+ concentration in the migration process, due tothe fact that the exchange adsorption capacity of
Mg2+ is smaller than that of Ca2+. Similarly, thedecrease of CO32- concentration is faster than that of
Mg2+ and Ca2+ concentration because the exchange
adsorption capacity of CO32- is larger than that of
Mg2+ and Ca2+.
The migration velocities of the five ions indescending order is Na+, Cu2+, Mg2+, Ca2+ and CO32-,
which is consistent with the migration velocities
determined indirectly by pollution plumes. The
concentrations of Na+ and Cu2+ vary from fast to slow
with migration time, and that of Mg2+, Ca2+ and CO32vary from slow to fast. The reason is that the small
migration velocities of Mg2+, Ca2+ and CO32- in clay
layers are greatly affected by clay saturation;
Furthermore, the saturation and unsaturated hydraulicconductivity of the clay gradually increase with theincreasing migration time, resulting in the increase of
the migration velocities of Mg2+, Ca2+ and CO32-.

3.4 Influence of water pressure on ion migration
Compared with the concentration variation of
Ca2+, Mg2+, Cu2+, Na+ and CO32- under the waterpressures with 0m,10m, 20m and 30m expressed as
H0, H1, H2 and H3, the concentration growth rates ofthe five ions are calculated respectively under thewater pressure difference with ΔH1=H1-H0=10.0m,
ΔH2=H2-H0=20.0m, ΔH3=H3-H0=30.0m, as shown in
Figure 10.
160.00%2+

concentration
growth rate

120.00%depth (m)

20.0

25.0

2+

Ca

2+

Mg

240.00%2

concentration
growth rate

CO3 2+

Cu+

Na

160.00%80.00%

0.00%
0.0

5.0

10.0
15.0
migration time (a)

20.0

25.0

(b) ΔH2=20.0m
480.00%
2+

Ca

2+

Mg

concentration
growth rate

360.00%2

CO3 2+

Cu+Na

240.00%120.00%

0.00%
0.0

5.0

10.0
15.0
migration time (a)

20.0

25.0

(c) ΔH3=30.0m
Fig. 10 Influence of water pressure on growth rate ofion concentration[1] With the migration time increasing, the growth
rates of the ion concentrations gradually decrease
under the different water pressure.
[2] Under the same migration time and different
water pressure, the descending order of the five ionsin concentration growth rate is: CO32-, Ca2+, Mg2+,
Cu2+,Na+; In other words, the five ions in descendingorder of migration velocity sensitivity to the variationof water pressure are CO32-, Ca2+, Mg2+, Cu2+ and

0.0
3.000

10.0
15.0
migration time (a)320.00%

H=0m
H=10m
H=20m
H=30m

1.000
1.500
2.000
2.500
+
3
Na concentration ( kg/cm )5.0(a) ΔH1=10.0m

3.0

0.500

+

Na

80.00%

0.0

4.0

0.000

2+

Cu

0.00%

5.0

1.0

2

CO3 -

40.00%

3.3 Variation of ion concentration with migration
depth
The point with the coordinates (12,7) on the soil
layer of the landfill model (as shown in Figure 2) isselected as the initial depth in order to extract thevariation of Na+ concentration after 20 years of
migration, as shown in Figure 9. With increasing
migration depth, Na+ concentration remains constantat the beginning, but then gradually decreases. The
descending order of the five ions in vertical migration
capability is Na+, Cu2+, Mg2+, Ca2+ and CO32-.
Furthermore, the ions whose concentrations
drastically reduced with increasing depth have
weaker migration capacity, such as CO32-, while Na+
has stronger migration capacity conversely, which
proves that clay has different barrier capability as todifferent ions. The variation rates of theconcentrations of different ions with increasing
depths are different. Specifically, the concentrationsof Na+ and Cu2+ vary from slow to fast, while Mg2+,
Ca2+ and CO32- varying from fast to slow, which isjust contrary to the ion migration characteristics withtime, but both based on the same reason.

2.0

2+

Ca

Mg

3.500

Fig. 9 Variation of Na+ concentration with migration
depth

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10th Asian Regional Conference of IAEG (2015)

Na+.
[3] Under the water pressure with 10m, 20m, 30m,
the concentration growth rates of CO32- are105.56%-133.75%, 239.59%-279.17% and 390.51%450.00% respectively, which indicates that thepromotion of each additional 10m water pressure toCO32- migration become increasingly obvious.
[4] The promotions of water pressure to the migrationof Ca2+, Mg2+ and CO32- have the similar effects withthat of CO32-, but converse effects with that of Cu2+
and Na+, that is to say, the promotion of each
additional 10m water pressure to the migration of
Cu2+ and Na+ become increasingly weak. In summary,under the same water pressure difference, the higher
the absolute water pressure is, the stronger thepromotion to the migration ability of Ca2+, Mg2+ andCO32- becomes, instead of that of Cu2+ and Na+.
[5] The measured data in Yanqun landfill shows thesimilar regulation with that of numerical simulation
results.

the carbonate precipitation can be created by thechemical reaction between CO32- in life source
contaminants and ions on the surface of clay particles,
which can reduce clay porosity and inhibit the
migration of contaminants. Additionally, a large
amount of organic matters with macro molecular andtheir intermediate metabolites existing in the
degradation process can produce CH3COOH andrelease H2O and CO2 finally. The gas produced can
reduce the soil saturation degree, thus inhibiting the
migration of contaminants. However, CO2 dissolvedin H2O can produce H2CO3, declining the solution pH,
which increases the solubility of the insoluble salts
and chemical reaction rate. Consequently, themigration of life source contaminants can bepromoted.
5.

Based on the generalized model of Yanqun
landfill site, the migration of Na+, Cu2+, Mg2+, Ca2+,and CO32- in clay liner layer is simulated under
different clay compaction degrees and waterpressures. Furthermore, the variation of the pollution
plume and concentration with migration time anddepth are predicted. The results show as follows.
[1] The descending order of the five ions in migration
velocity is Na+, Cu2+, Mg2+, Ca2+, and CO32-.
[2] The descending order of the five ions inconcentration growth rate is CO32-, Ca2+, Mg2+, Cu2+
and Na+ with the increase of water pressure, which
can greatly promote the migrations of such ions as
Ca2+, Mg2+ and CO32- with slow initial velocity.
[3] The descending order of the five ions inconcentration decrease rate is CO32-, Ca2+, Mg2+, Na+
and Cu2+ with the increase of clay compaction degree,which can greatly inhibit the migrations of such ionsas Ca2+, Mg2+ and CO32- with slow initial velocity.
[4] The migration mechanisms of contaminants inclay layer are revealed from such perspectives as ion
exchange, complex reaction, biochemical reaction
and inorganic sediment. Finally, the proposed clay
compaction degree is not less than 93.00% according
to the technical code for sanitary landfill.

3.5 Clay compaction degree influence on ion
migration
The effects of clay compaction degree on ion
migration are shown as follows.
[1] At the same migration time, when the clay
compaction degree increases from 78.55% to 89.83%,
the descending order of the five ions in concentration
decrease rate is CO32-, Ca2+, Mg2+, Na+ and Cu2+.
[2] Compared with the promotion of water pressure to
ion migration, the inhibition of clay compaction
degree to ion migration is more obvious, which
proves that the higher the clay compaction degree is,the stronger the interception capacity becomes.
Combined with the regulations about thecompaction degree of clay layer in the bottom ofreservoir area in the Technical code for sanitary
landfill of municipal domestic refuse, the compaction
degree of the clay liner layer of Yanqun landfill issuggested as not less than 93.00%.
4.

Conclusions

Mechanisms of Migration of Life Source
Contaminant in Compacted Clay Layer

With the migration of life source contaminants insoil layer, the exchange of such ions as Na+, Ca2+ andCO32- with the ions adsorbed on the surface of clay
particles reduces the thickness of the electrical double
layer, leading to the cohesion for the gravitation
enhancement among the particles, thus causing theincrease of pore size and then promoting the
migration of contaminants in clay layer. Such metal
ions as Cu2+ in contaminants react with NH3·H2O can
produce the precipitation Cu(OH)2. Subsequently,[Cu(NH3)4]2+ can be produced through complex
reaction, which can increase the ion concentration oflife source contaminants and clay porosity, thus
promoting the migration of contaminants. Meanwhile,

Acknowledgements
This research is jointly supported by the National
Natural Science Foundation of China No. 41372326,
No.41072236 and project funded by the Fundamental
Research Funds for the Central Universities(2014ZDPY27) and the Priority Academic Program
Development of Jiangsu Higher Education
Institutions.
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