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Transport of Carbon Tetrachloride in a Karst
Aquifer in a Northern City, China
Baoping Han1,2, Xueqiang Zhu2, Zongping Pei2 and Xikun Liu3
1Xuzhou
Institute of Technology,
2China University
of Mining and Technology,
3Management Department of Urban Water Resource of Xuzhou,
China
1. Introduction
Carbon tetrachloride (CCl4) has been used as a grain fumigant, pesticide, solvent for oils and
fats, metal degreaser, fire extinguisher and flame retardant, and in the production of paint,
ink, plastics, semi-conductors and petrol additives (Agency for Toxic Substances and
Disease Registry (ATSDR), 1994). Its properties are shown in Table 1. CCl4 is classified by
the International Agency for Research on Cancer (IARC) and the US Environmental
Protection Agency as a Group B2 carcinogen and also listed on the CERCLA Priority List of
Hazardous Substances maintained by the Agency for Toxic Substances and Disease Registry
(ATSDR, 2008). CCl4 is a common contaminant in soil and groundwater. CCl4 is found in
approximately 20% of the US Superfund National Priority List sites (Ferguson & Pietari,
2000). But, there are limited published case studies of CCl4 contamination in karst aquifer.
Karst aquifers are distinguished by an abundance of large subsurface openings and are
therefore especially vulnerable to chlorinated-solvent contamination (CCl4, TCE, PCE). The
release of chlorinated solvents into karst aquifers presents a difficult challenge to
environmental scientists, managers, and regulators. The importance of karst aquifers to
Molecular weight 153.8 g/mol
Density(25 °C) 1.594 g/mL
Vapor pressure at 20 °C 12.2 kPa
Boiling point at 101.3kPa 76.72 °C
Melting point at 101.3kPa 22.92 °C
Critical pressure 4.6 Mpa
Critical temperature 283.2 °C
Solubility in water at 25 °C 785 mg/L
Henry’s law constant at 24.8 °C 2.3×10-2 atm·m3/mol
Heat of evaporation 194.7 kJ/kg
LogKow 2.64
LogKoc 2.04
Table 1. Physical properties of carbon tetrachloride (Fouw, 1999)
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554 Pesticides in the Modern World - Risks and Benefits
water supply and their vulnerability to contamination by chlorinated solvents are reasons to
seek improved understanding of how chlorinated solvents behave in karst aquifers (Wolfe
et al., 1997). This chapter discusses CCl4 transport and fate in a karst aquifer in a northern
city of China based on years of continuous monitoring of CCl4 concentrations.
2. Site characterization
2.1 Site location and pollution source
Karst aquifer investigated is located in the Northern China Plain. Karst aquifers provided
averagely 25.8×104 m3/d to urban public water supplies from 1981 to 2008 (Liu, 2010). As
illustrated in the Fig.1, the karst water is in a relatively confined groundwater system unit and
its east and west boundaries are coal seam water-resisting layers and the south and north are
groundwater watershed. The karst groundwater system is composed several relatively
independent aquifers. The CCl4 pollution occurs in the southern Qiligou water-bearing basin.
Fig. 1. Hydro-geological zonation of the karst groundwater system in the city
According to monitoring data obtained in November, 2000, it has been contaminated with
CCl4 in Qiligou water-bearing basin. The pollution source is a pesticide plant which
produced a pesticide that used CCl4 as a solvent and it has used more than 42 tons of CCl4 in
the past ten years. This plant is located at hill slope in southwestern recharge area of the
karst aquifer (Fig. 2). However, emergency measures were taken in 2001, including closing
the pesticide plant and intensive pumping from heavily polluted wells. Untill May 2001,
carbon tetrachloride was found in 53 wells (contaminated area is about 17.3 km2). The
highest CCl4 concentration in karst water was over 3900 μg/L in a water supply well
approximately 465m away from the pesticide plant. The concentration in Chinese standards
for drinking water quality is lower than 2μg/L (GB5749-2006) (China’s Ministry of Heatlth,
2006). Since then, the contaminated wells have not been used for dinking water. While, some
lightly contaminated wells have been pumping for agricultural and industrial production.
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 555
Fig. 2. View of the pesticide plant and its wastewater drainage
2.2 Geological and hydro-geological settings
As shown in the Fig.3, the contaminated site is a NE synclinal basin with area of
approximately 200 km2. Its southeastern and northwestern boundaries are two NE
mountain chains composed of Cambrian and Ordovician limestone with elevations from 100
m to 248 m above the sea level. Quaternary deposits in the central lowlying area of the basin
are composed of alluvium, proluvium, sand, sandyclay and subclay. The thickness of
Quaternary is from 5 to 30 m, and the elevation varies from 30m to 40m above the sea level.
Fig. 3. Bedrock geologic map of Qiligou water-bearing basin
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556 Pesticides in the Modern World - Risks and Benefits
karren and grooves in exposed karst area
Corrosion on the surface of limestone
Fig. 4. Surface karst formation in the site
Limestone cropped out along hills contains abundant karst landforms such as caves, blind
valleys and sinkholes, which provide pathways for the rapid transport of contaminants into
the aquifer. Fig.4 presents the surface karst landform in the studied region.
Fig.5 demonstrates the degree of development of karst in the subsurface. Karst caves and
fissures are the major structure of water storage. Especially, the honeycomb-like dissolved
solution pores are quite well-developed.
Fig. 5. Corrosion of rock core samples
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 557
According to borehole data, there are four well developed underground karst or paleokarst
zones and they are regarded as the horizontal runoff layers in the karst aquifer (Fig. 6). Of
them, the third karst zone with a depth from 90 m to 150 m is the most important runoff
layer of karst grounwater. Karst groundwater is recharged mainly from precipitation (about
835mm per year). Rain water seeps into karst aquifer from sinkholes, fissures in outcrop
areas or in covered karst area. It first infiltrates into Quaternary phreatic aquifer in lowlying
basin area, then infiltrates into underlying karst aquifer from recharge skylight. In middle
sub-area, there is a layer of igneous rock and the karst aquifer can be divided into upper
water-bearing zone and lower zone because of igneous rock watertight.
Fig. 6. Vertical zonation of karst development along the groundwater flow path in the site
(1. limestone; 2. dolomite; 3. igneous rock; 4. cave; 5. karst fissure;6. fault fracture zone; 7 water
table; 8 karst zone)
The variation in groundwater level from 2000 to 2008 is presented in Fig.7. Although the
range of groundwater fluctuation in different wells is different, the trend is similar. It
suggests there is a good hydraulic connection within the aquifer system, which makes the
aquifer more vulnerable to contamination. Many years of groundwater level observations
indicate that there is very little change in the karst groundwater flow field.
In conclusion, karst water-bearing medium in the site is distinguished as extreme
anisotropic and heterogeneous. Hence it can be classified as the combination of fissure
network and runoff zones type, which has unified hydraulic field. Tracer results indicates
that the karst conduits are well developed along the syncline basin axis and the velocity of
groundwater is fast in the runoff zone, which can attain 3027.8m/h when the water source
in the mining conditions (Pei, 2007). Therefore the convection is predominant in mass
transport of the pollutants in the aquifer. Hence the pollutant in the subsurface can move
faster and further with the groundwater flow.
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558 Pesticides in the Modern World - Risks and Benefits
40.00 X-72 X-36 X-33 X-49 X-39 X-24
30.00
Water level elevation (m)
20.00
10.00
0.00
-10.00
00-2-28
00-6-28
00-10-28
01-2-28
01-6-28
01-10-28
02-2-28
02-6-28
02-10-28
03-2-28
03-6-28
03-10-28
04-2-28
04-6-28
04-10-28
05-2-28
05-6-28
05-10-28
06-2-28
06-6-28
06-10-28
07-2-28
07-6-28
07-10-28
08-2-28
08-6-28
08-10-28
Dat a
Fig. 7. Variation in piezometric levels in the research region
3. Pollution pathway analysis
3.1 Leakage test
The pesticide plant is located in the hill slope of bedrock. When CCl4 was first found in
November 2000, the drainage ditch running off wastewater was not built. The effluent with
high concentrations of CCl4 could directly leak into the karst aquifer (Fig.8). Under the
intervention of provincial environment protection department, the plant built ditch in
partial section (Fig.9). Leakage research was conducted to investigate the CCl4 pollution
pathways. Spot S1 to S6 were arranged along drainage ditch for leak off tests (Fig.9). During
the flood period of 2001, two tests were performed and the results indicated that the
discharged water leakage rate reached approximately 22% and leakage mainly happened in
the bare limestone section, namely, effluent with high concentration CCl4 can flow directly
into karst aquifer (Table 2).
Fig. 8. Bare limestone along the wastewater ditch of the pesticide plant
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 559
N road X-47
S3
village
S2 abandoned
reservoir
farmland
pesticide plant S4
05-1
phreatic water well (X-70)
pit pesticide plant well᧤X-49᧤
05-7
K2 05-3 05-4
04-1
05-9 05-8 05-2 04-6
large calibre well
S1 S5 road
abandoned chloroactic acid plant
farmland village
effluent drain
farmland
04-5
Legend
ditch
1
2
3
4
05-6
5 S6 05-5
04-2
6 04-3
04-4 K3
7
0 50 100m
8 large calibre well (X-63)
Fig. 9. Boreholes and leakage observation spots location in pollution source sub-area
(1, lined ditch; 2, bared limestone; 3, karst groundwater well; 4, large calibre well; 5, phreatic
water well; 6, borehole; 7, village; 8, leakage observation spot.)
Discharge (m3/h) Leakage rate (%)
Observation spot Distance (m)
2001.7.22 2001.8.31 2001.7.22 2001.8.31
S1 45.82 45.34
1148.0 22.10 21.34
S6 35.66 35.66
Table 2. Results of the leak off tests
3.2 Soil pollution investigation
In order to investigate the feature of effluent leakage into karst aquifer, 17 soil sampling
boreholes numbered K2 and K3(2001), 04-1 to 04-6(2004) and 05-1 to 05-9(2005) were drilled
with auto-driller (Model: DPP100-3B) and a total 206 soil samples were collected(for
locations see Fig. 9). The quaternary deposits are 2.4-10.2m thick. CCl4 and chloroform were
detected in the soil (soil samples of K2 and K3 were analyzed only for CCl4). CCl4 was found
in the drilling soil along the drainage ditch and nearby the west part of well X-49, and the
highest concentration reached 47.1μg/kg (Table 3). The CCl4 content of soil in the boreholes
nearby well X-49, (e.g. 04-6, 05-2, 05-7 and 05-8) are much higher and their highest content is
34.0μg/kg, 42.2μg/kg, 33.5μg/kg and 47.1μg/kg respectively. In general, CCl4 was found in
the soil at depths than 3 meter, and the content increased with the increase of the soil depth.
CCl4 was not detected or was relatively low in the topsoil. Chloroform, the daughter
product of CCl4, was also detected, of which was in the range of 2.6 to 26.5μg/kg. For
borehole 04-2, 04-3 and 04-3, the chloroform distribution was larger than that for CCl4.
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560 Pesticides in the Modern World - Risks and Benefits
Samples with the highest content chloroform were colleted from clay-limestone interlayer
(depth at 6.5 to 6.7m), intensive weathered igneous rock layer (depth at 9.0 to 9.2m) and
fissured clay layer (depth 7.8-8.0m) respectively.
CCl4 Chloroform
Borehole Borehole Depth of Depth of
Detected Content Detected Content
number depth (m) maximum maximum
depth (m) (µg/kg) depth (m) (µg/kg)
content (m) content (m)
K2 9.1 0.8-8.7 1.3-2.9 4.6-4.8 NT NT NT
K3 6.0 0.8-5.3 1.1-7.7 6.5-7.0 NT NT NT
1.5-1.7,
04-2 7.0 0.9-2.8 6.5-6.7 5.0-6.7 9.5-19.8 6.5-6.7
6.5-7.0
04-3 10.5 4.0-6.7 0.7-1.1 5.5-5.7 2.5-10.2 5.3-11.7 9.0-9.2
04-4 9.2 5.0-8.7 0.7-1.1 8.5-8.7 7.8-8.0 15.8 7.8-8.0
04-6 5.0 0.5-4.7 0.7-34.0 4.0-4.2 ND ND ND
05-1 8.1 ND ND ND 0.5-8.1 5.3-9.2 5.0-5.2
05-2 4.7 2.5-4.7 3.3-42.2 4.0-4.2 0.2-4.7 2.7-26.5 4.0-4.2
05-3 5.7 ND ND ND 1.2-5.7 2.7-7.3 1.0-1.4
05-4 6.7 5.5-6.2 1.0-1.8 5.5-5.7 1.0-5.7 2.6-8.0 3.5-3.7
05-6 6.2 ND ND ND 0.2-6.2 6.9-11.3 2.5-2.7
05-7 5.7 2.7-4.9 7.6-33.5 4.2-4.4 ND ND ND
05-8 5.4 3.2-5.4 1.8-47.1 5.2-5.4 ND ND ND
ND- Not detected, NT-Not test.
Table 3. CCl4 and chloroform contents in the soils
3.3 Pollution pathways
There are three pollution pathways of karst groundwater. Specifically: Wastewater directly
entering the karst aquifer in the pesticide plant area (Fig.10); Flowing into the aquifer
through bare section of limestone in drainage ditch; and Leaking under ditch by soil (Fig11).
Fig. 10. Generalized pollution pathway of direct seepage into the karst aquifer within the
pesticide plant (1. Intrusive igneous rock; 2. limestone; 3. clay; 4. silty clay; 5. cultivated soil;
6. sand; 7. Movement direction of CCl4)
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 561
Fig. 11. Wastewater with CCl4 seeping through the soil into the karst aquifer
4. Spatial distribution of CCl4 in the karst aquifer
4.1 Plane distribution of the CCl4 plume
The size and shape of the CCl4 plume in the aquifer was confirmed by multiple samples
from multiple water supply wells. In porous media aquifer or unconsolidated aquifer, the
plume concentration decreases with the distance from the pollution source. But the plume
distribution in the studied site was quite different. Karst conduits develop along preferential
pathways between areas of groundwater recharge and discharge. CCl4 in groundwater was
recharged from the southern pollution source and transported into northern supply wells
forming a long belt-like plume. Based on CCl4 concentration data, the contaminated area can
be divided into three sub-areas: southern pollution source sub-area, northern sub-area of
artificial discharge center and transition sub-area or middle sub-area. The CCl4 plume in the
karst aquifer was "dumbbell" shaped, with high contamination located in the southern and
northern sub-area and relatively light concentrations in the middle transitional sub-area, as
shown in Fig. 12.
X-17 X-17
X-18 X-18
Yun Long Lake X-21 Yun Long Lake X-21
X-88
X-88 X- X-19 X-22
X-20 X-22
19 X-20
X-23 X-24
X-89 X-23 X-56
X-24
X-89
X-25 X-25
X-56
X-26
3
X-90 X-27 3 10 X-27
10 X-90
X-29 10
X-31
X-28 X-29 X-28
X-31 X-64 X-30
X-33 X-64 X-30
X-33
X-32
X-32 X-65
X-65 X-35 X-67 X-35
X-84 X-84 X-91
X-34 X-91 3 X-34
X-68
X-83 X-68
X-83
X-85 X-36 X-85
X-36
X-57
X-40
X-57 X-40
X-37 10
X-37
X-38
X-38 X-87 X-39 X-87
X-58
X-39
X-58
X-82 X-80 X-82
X-80 3 10
X-59
X-69
X-59 X-81
X-81 X-69
X-44 X-44
X-41 X-42
X-60 X-60 X-42
X-45 X-45
X-75 X-43 X-43
X-68
3
X-67 3
Groundwater sampling Groundwater sampling
point 50 1.0 point
X-61
X-46 X-46
Groundwater flow X-61 10
Groundwater flow
X-83 direction X-83 direction
X-47 Concentration contour 150 Concentration contour
X-47 X-48
X-48
Residential area Residential area
X-49 X-49
Pesticide Plant
X-51 Pesticide Plant
Railway, highway 50 Railway, highway
X-51
X-63 X-66 X-63
X-50
X-66 3 X-50
River River
X-54
X-53
X-53 X-54
a 0 1 Km 2Km
b 0 1 Km 2Km
Fig. 12. CCl4 plume distribution in the karst aquifer (a. 2001-4-18; b. 2008-4-30)
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562 Pesticides in the Modern World - Risks and Benefits
Because of the obstruction of higher-level water in the southern and western parts of the
pollution source, polluted water could transport to northern sub-area along well-developed
karst conduits. Transition sub-area has formed an obvious depression cone by artificial
withdrawal and the water level was about 5.00 m lower than of the southern sub-area. Karst
fissures and caves are most well developed in both horizontal and vertical direction in the
northern sub-area. Water development experience in past fifty years has revealed this zone is
the most water-yielding section and also the most intensive pumping area in the water-bearing
basin. Consequently, northern sub-area is the centre of the depression cone and the CCl4 is
accumulated in this area. In the middle sub-area, there is a layer of diabase igneous rock
aquifuge at a depth from 100 m to 150 m, which separates the aquifer into two individual
layers without hydraulic connection. Because the depth of most wells in the middle sub-area is
less than 150 m, CCl4 concentration of the wells in this sub-area is relative lower.
4.2 Vertical distribution of CCl4 in the karst aquifer
The high density and low viscosity of CCl4 cause it to migrate downward until they
encounter openings too small to enter. The influence of well depth on the CCl4 concentration
in wells was studied. CCl4 concentration in Qiligou wells and Sanguanmiao wells increased
with the increase of the well depth (Fig. 13). The transport of CCl4 in the groundwater is
controlled primarily with gravity under similar hydro-geological conditions. Therefore, with
deeper the wells, there is higher CCl4 concentration of groundwater is.
30 240
y =0.0224x2 - 3.8283x +172.97
CCl4 concentration(μg/L)
y = 0.0044x2 - 0.9435x + 69.017
CCl4 Concentration (μg/L)
R2 = 0.9025 180 R2 =0.9615
25
120
20
60
15 0
90 100 110 120 130 140 150 160 90 110 130 150 170 190
A Well depth (m) B ell
W depth(m)
Fig. 13. Relationship between CCl4 concentration and the well depth (A: Sanguanmiao wells;
B: Qiligou wells)
Recharge area
Pesticide plant Discharge sub-area
Middle sub-area
Pollution source sub-area
0
-50
-100
-150
-200
-250
Quaternary loose Ordovician limestone Igneous rock Aquifuge Flow direction
Fig. 14. Conceptual model for CCl4 transport in the karst aquifer (Han et al., 2004)
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 563
According to geologic, hydro-geologic setting and monitoring data of CCl4 concentration in
the past years, transport of CCl4 in the complex karst aquifer can be generalized as shown in
Fig. 14.
5. Temporal change in CCl4 plume in the karst aquifer
5.1 Temporal change in CCl4 concentration in the aquifer
The changes in CCl4 concentration in typical wells are presented in Table 4 and Fig.15.
However, there is a general downward trend in concentration, CCl4 concentration in most of
the wells increased in 2010. This may be due to the decrease in groundwater exploitation.
Well 2001 2004 2005 2006 2007 2008 2009 2010
25%
1279.4 369.6 90.1 500.0 201.3 146.6 70.1 222.3
quantile
50%
X-49 n=16 1722.6 n=20 1662.6 n=52 104.6 n=29 815.0 n=27 264.5 n=19 218.3 n=12 119.6 n=49 272.5
quantile
90%
2584.3 2911.9 681.4 1313.6 620.5 587.9 193.8 627.6
quantile
25%
181.5 248.0 61.8 17.7 9.1 13.0 20.3 65.1
quantile
50%
X-61 n=12 907.7 n=20 325.2 n=54 96.0 n=32 52.2 n=27 19.0 n=25 21.6 n=12 30.4 n=55 108.5
quantile
90%
2241.5 609.0 212.7 168.1 163.7 104.0 122.4 152.0
quantile
25%
59.6 8.9 21.6 18.5 25.5 25.0 8.8 11.8
quantile
50%
X-47 n=14 69.0 n=20 29.3 n=52 68.5 n=28 53.4 n=27 74.5 n=23 48.5 n=11 18.4 n=49 15.3
quantile
90%
134.8 162.8 216.6 136.6 107.2 116.9 27.7 39.0
quantile
25%
6.3 17.8 14.5 16.2 10.4 15.5
quantile
50%
X-83 n=53 25.1 n=32 27.3 n=25 45.4 25 24.6 n=12 11.3 n=53 18.9
quantile
90%
204.0 115.8 78.8 75.7 21.4 29.2
quantile
25%
14.6 13.2 8.8 10.9 7.5 4.9 20.8
quantile
50%
X-59 n=21 24.2 n=56 23.1 n=30 14.0 n=27 14.2 n=25 11.3 n=12 6.5 n=53 23.6
quantile
90%
44.6 58.8 39.2 39.5 16.9 19.2 27.7
quantile
25%
30.0 22.4 16.0 14.4 11.9 8.2 29.8
quantile
50%
X-64 n=21 40.2 n=40 31.0 n=29 23.6 n=25 16.2 n=25 14.4 n=12 8.7 n=24 33.1
quantile
90%
115.0 67.5 81.2 31.1 28.2 17.4 37.2
quantile
25%
92.0 24.5 13.6 11.9 10.9 8.7 33.6
quantile
50%
X-56 n=20 115.8 n=56 43.2 n=32 23.8 n=27 18.1 n=25 13.5 n=12 9.9 n=48 37.8
quantile
90%
196.4 89.1 67.8 27.8 30.0 16.9 45.2
quantile
“n” is the number of the samples
Table 4. Summarizes of changes in the average CCl4 concentrations with time (μg/L)
The Fig. 15 shows that: (1) the CCl4 concentration in karst auifer has obvious seasonal
variation. In general, CCl4 concentration of groundwater during the drought period from
February to June is relative lower and during the rainy period from August to October is
much higher. (2) CCl4 changes rapidly with time, which is notably different from the
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Fig. 15. The variation of CCl4 over time in typical supply wells
564
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CCl4 (μg//L) CCl4 (ug/L) CCl4 (μg/L) CCl4 (μg/L) CCl4 (μg/L)
100
150
200
250
300
350
1000
1200
200
250
100
150
100
120
140
160
50
1000
1500
2000
2500
3000
3500
50
20
40
60
80
200
400
600
800
0
500
0
0
0
04-2-19 2004-2-19
0
2004-3-11
04-2-19 2004-2-1 9
2004-6-30 2004-6-10
2004-6-30 2004-4-2 9
2009-9-25 2004-7-16 2004-9-13
2004-10-19 2004-7-8
2004-11-29 2004-11-1 2004-12-15
2004-9-1 6
05-2-21 2005-2-16 2005-2-28
05-2-21 2004-11-25
2005-3-22 2005-3-28
2005-4-14 2005-2-3
2005-4-28 2005-4-14
2005-5-17
2005-5-31 2005-4-1 4
2005-6-11 2005-5-31 2005-7-5
2005-6-2 3
2005-7-18 2005-7-15
2005-7-21 2005-7-29
2005-9-1
2005-8-11
2005-8-22 2005-8-25
2005-9-6 2005-9-1 2005-11-10
2005-10-8
2005-10-13 2005-10-18 2006-1-1 9
2005-10-27
2005-11-22
2005-11-30 2006-3-3 0
2005-12-6
2005-12-21 2006-1-6
2006-1-11 2006-6-8
2006-2-8 2006-2-22
2006-3-2 2006-2-22 2006-8-1 7
2006-4-7 2006-4-11 2006-4-11 2006-10-26
2006-4-18
2006-7-18 2006-6-1 2007-1-4
2006-6-26
Dat a sample co llect ed
Dat a sample collect ed
2006-8-1
Dat a samp le collect ed
Data samp le collected
Dat a sample collect ed
2006-9-27 2006-9-27 2007-3-1 5
2006-10-10 2006-11-14
Pesticides in the Modern World - Risks and Benefits
2007-2-13 2007-2-13 2007-5-2 4
2007-3-28 2007-5-12 2007-4-27 2007-5-12 2007-8-2
2007-8-5 2007-8-13 2007-10-11
2007-7-11 2007-8-13
2007-9-17 2007-9-24 2007-12-20
2007-9-24 2007-11-28 2007-10-17
2007-12-11 2008-2-2 8
2008-1-23 2008-3-24 2008-3-14 2008-5-8
2008-5-13
2008-7-1
2008-6-13 2008-7-11 2008-8-1 2008-7-1 7
2008-9-5
2008-10-17 2008-9-2 5
2008-9-17 2008-11-27 2008-10-17
2009-2-20
2008-12-4
2009-1-19 2009-4-21 2009-3-20 2009-2-1 2
2009-8-28
2009-10-27
2009-9-28 2009-11-22 2009-4-2 3
2010-4-28
2010-5-4
2009-7-2
2010-5-7 2010-5-19 2010-5-12 2010-5-14
2009-9-1 0
2010-6-8 2010-6-4
2010-5-26 2010-6-8
2009-11-19
2010-7-6 2010-7-2
2010-7-2 2010-7-13 2010-1-2 8
2010-8-6 2010-7-30
2010-8-20 2010-4-8
2010-8-10 2010-9-3
Well X-61
2010-9-3
Well X-47
Well X-59
Well X-49
2010-6-1 7
2010-9-30 2010-9-27 2010-9-30
2010-9-17
X--56
2010-8-2 6
2010-11-12 2010-11-12
2010-12-7 2010-11-17 2010-11-4
2010-12-17
Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 565
common porous media aquifer. This may be due to the facts that: (1) The groundwater
velocity in the aquifer is much higher than that in the porous media, which can reach
131.9m/h-3027.0 m/h. As a result, the advective flow dominates the movement of pollutant;
(2) Local groundwater flow regime changed frequently. It was one of the important water
supply source with over 80 wells owned by different departments for different purposes.
Pump stopping and starting at different wells caused change in local flow field and
subsequently cause change in CCl4 concentration; and (3) CCl4 transport channel is complex.
5.2 Mann-Kendall trend tests
The non-parametric Mann-Kendall test was used to detect monotonic (increasing or
decreasing) trends in time-series of CCl4 concentrations for the eight typical wells during the
period 2004-2010. The Mann-Kendall test is widely used in environmental science for the
detection of trends in time-series data. A 5% significance level was used to indicate statistically
significant trends in the current study. The Mann-Kendall trend statistics (Z) indicates
significant decreasing (Z <–1.96, p <0.05) and increasing (Z >1.96, p <0.05) trends. Table 5
presents that there are a highly significant decreasing trend in CCl4 in the karst aquifer and the
decreasing trend in pollution source sub-area and the north sub-area area are more significant.
Well Time Z Trend
X-49 2004.02-2010.09 -4.35532 Decreasing, Significant
X-62 2004.02-2010.09 -5.72119 Decreasing, Significant
X-47 2004.02-2010.09 -4.74661 Decreasing, Significant
X-83 2005.02-2010.09 -2.35838 Decreasing, Significant
X-43 2004.02-2008.12 -3.38838 Decreasing, Significant
X-59 2004.02-2010.09 -2.80019 Decreasing, Significant
X-74 2004.02-2010.08 -4.67132 Decreasing, Significant
X-56 2004.02-2010.09 -5.11015 Decreasing, Significant
Table 5. The Mann-Kendall trend statistic (Z, p<0.05) in CCl4 concentration in typical wells
5.3 Temporal change in CCl4 plume distribution
The Fig. 16 gives the change in CCl4 plume over time. In almost ten years, there was very
little change in the distribution of CCl4 in the range of 3-10μg/L or 10-50 μg/L. There was a
major reduction in the volume of groundwater containing concentrations between 50 and
300μg/L. The plume extended westward and eastward in northern sub-area to in the flood
period every year. It should be noticed that the plume expanded eastward.
Based on observed trends in the development of a plume, plumes can be grouped as four
categories: expanding, stable, shrinking and exhausted (Rice at al., 1995). In this study, the
length of pollution plume of CCl4 in the water-bearing aquifer was found to be stable while
concentration is shrinking, which indicates that the plume decreased faster in concentration
than in length.
Dynamic groundwater flow field is one of the most important factors controlling the CCl4
plume (Han et al., 2006). CCl4 plume in the aquifer is similar with the groundwater flow
field, which is shown in Fig. 17. CCl4 diffusion was confined by higher water level around
the plume (Zhu et al., 2008). The scope of seriously polluted wells was similar with the
center of cone of depression. CCl4 concentration in the center of the local cone of depression
was higher than that in the wells outside of the center.
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566 Pesticides in the Modern World - Risks and Benefits
X-17 X-18 X-17
X-18
X-21 X-21
Yun Long Lake Yun Long Lake
X-88 X-19 X-88
X-19 X-22
X-20 X-20
X-22
X-24
X-23 X-24
X-23 X-56
X-25 150 X-89
X-25
X-56
X-26 X-26 50 X-27
10
X-90 3
10 X-90
3 X-29 X-31
X-29 X-28
X-28 X-64 X-64 X-30
X-30 X-31
X-33 X-32 X-33
X-65
X-65 X-67 X-35
X-32 X-35 X-84 X-91
X-34
X-34
X-68
X-83
X-83 X-85
X-36
X-36
X-57 X-57
X-40 X-40
X-37 X-37
X-38
X-38
X-39 X-87
X-58
X-40 X-39
X-58 3
3
X-80 X-82
10
X-59 X-81
X-59 X-69
X-44 X-44
X-42
X-41 10 X-42
X-60 X-60 X-45
X-45 X-43
X-43
3 10
50
Groundwater sampling
Groundwater sampling
point
point
X-46
X-61 X-83 X-46
Groundwater flow X-61
Groundwater flow
direction X-83 direction
10
X-48 Concentration contour 300 150 50 3
X-47 Concentration contour
X-47 X-48
Residential area
Residential area
X-49 X-49
Pesticide Plant Pesticide Plant
Rail way, highway
X-51 X-51 Railway, highway
X-63 X-63
X-70 X-50
X-66 X-66
Ri ver
X-53 X-54 Ri ver
X-53
X-54
a 0 1 Km 2Km
b 0 1 Km 2Km
X-17 X-18 X-17
X-18
X-21 Yun Long Lake X-21
Yun Long Lake
X-20 X-88
X-19 X-22 X-19
X-20 3 X-22
X-73
X-79
X-23
10 X-23 X-24 10
X-89
50 X-24
X-25
X-56 X-56
X-25
X-26 X-27 X-26 X-27
3
X-74 50
X-90
X-29 10 X-31
X-28 X-31 21.74
X-29
X-75
X-64 X-30 3 1
X-33 X-28 X-64
X-32 X-30
X-65 X-84 X-32 X-33
X-67 X-65 X-35
X-35 X-67
X-34 X-84
X-34 X-91
X-68
X-83 X-68
15.87
3 X-83
X-36 X-85
X-36
X-57 X-72
X-80
X-40
X-57
X-81 X-40
X-37 X-37
X-38 X-38
X-58 X-39 X-87
X-39
X-58 王山
X-80 X-82
X-59 1
X-59 X-69 X-69
10 3 X-81
10
X-41 X-44
3 X-44
X-42 X-41
X-42
X-60 3 X-45 X-60 10
X-43
X-43 X-45
50
50
Groundwater sampling Groundwater sampling
X-46 point
point
X-61 X-46 X-83
X-61
Groundwater flo w
X-83 Groundwater flow
direction
150 direction
Concentration contour Concentration contour
300 X-48 X-48
X-47 50 X-47
Residential area Residential area
X-49 X-49
X-70
Pesticide Plant X-77
X-51 Pesticide Plant X-51
X-63 Railway, highway X-63 Railway, highway
300
X-50 X-66
150 X-71 X-50
50
X-66 10
3 River River
X-53 X-53
X-54
X-54
c 0 1 Km 2Km
d 0 1 Km 2Km
Fig. 16.1 Change in CCl4 plume with time in the karst aquifer (a, 2001-8-30; b, 2004-8-30;
c, 2005-8-30; d, 2009-8-30)
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 567
X-17 X-18
X-17
X-18
Yun Long Lake X-21
X-21
X-20 Yun Long Lake
X-19 X-22 X-88
X-19 X-22
10 X-20
3
X-73
X-79
X-23 50
X-24 X-24 3
X-56 X-23 X-51 0
6
X-89
X-25 3 10 X-25
X-26 X-27 X-26
X-27
X-74
X-90
X-28 X-29 X-31
X-29 X-75 X-28 10
X-33 X-64 X-30 X-31 X-64 X-30
X-32 X-33
X-65 50 X-32
X-67 X-65
X-35 X-67 X-35
X-84 X-91
X-34 X-34
X-68
X-83 X-68
X-36 X-36 3 X-85
X-57
3 X-57
3 X-40
10 X-40
X-37 X-37
X-38 X-38
X-58 3 X-39 X-87
X-39
X-58
X-80 X-82
X-59 X-69
X-59 X-81
X-69
3
X-41
10 X-44 X-44
X-42
X-60 X-60 X-42
X-45 X-45
X-43
X-43
50
Groundwater sampling 3 10
Groundwater sampling
X-46 point point
X-61
X-61 X-46 10
150 X-83 Groundwater flow X-83 Groundwater flow
direction direction
300 50 50
10 Concentration contour Concentration contour
X-47 X-48 X-47 X-48
3 150 3
X-49 Residential area X-49 Residential area
Pesticide P lant X-70 Pesticide Plant
X-51
X-63 Railway, highway X-51 Rail way, highway
X-66 X-63
X-50 X-50
X-66
X-53 X-54 Ri ver Ri ver
X-53
X-54
e 0 1 Km 2Km f 0 1 Km 2Km
X-17 X-17
X-18 X-18
X-21
un Long Lake X-21 Yun Long Lake
X-88 X-88
X-19 X-19
X-20 X-22 X-20 X-22
X-23 X-24
X-23 X-24
3 X-89
X-89
X-25
X-25 X-56
X-56
X-26 X-27
X-26 X-27
X-90
X-90 X-31
X-31 21.74
21.74 X-29
X-29
X-28 X-64 10
X-28 X-64
3 1 X-33
X-30 3
X-30 X-32
X-32 X-33 X-65
X-65 X-35
X-35 X-67
X-67 X-84
X-84 X-91
X-91 X-34
X-34 X-68
X-68 15.87
15.87 X-83
X-83 X-85
X-85
X-36
X-36 X-72 水4
X-72 水4 X-40
X-40 X-57
X-57
X-37
X-37 X-38
X-38 X-87
X-87 X-58 水2 X-39
X-58 水2 1 X-39
X-80 X-82
X-80 X-82
10
X-59 水6
X-59 水6 X-69
X-69 X-81
X-81
X-41 X-44 1
X-44 X-42
X-41
X-42 X-60
X-60
X-43 X-45
X-43 X-45
Groundwater sampling
Groundwater sampling
point
point X-61
X-46 X-83
X-61
X-46 X-83 Groundwater flo w
Groundwater flow 50 direction
direction
10
3 X-47 X-48 Concentration contour
Concentration contour
X-48
50 X-47
3
Residential area
X-49
1 Residential area X-49
Pesticide Plant X-51
esticide Pla nt X-63 Railway, high way
X-51 Railway, highway X-66
X-63 X-50
X-66
X-50
X-53 River
Ri ver X-54
X-53
X-54
0 1 Km 2Km h 0 1 Km 2Km
g
Fig. 16.2 Change in CCl4 plume with time in the karst aquifer (e, 2004-12-30; f, 2008-12-30; g,
2009-12-30; h, 2010-12-30)
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568 Pesticides in the Modern World - Risks and Benefits
X-14 X-15 X-16 X-15
X-14 X-16
X-17 X-17
X-18 X-18
Yun Long Lake X-21 X-21
Yun Long Lake
X-88 X-19 X-88
X-19
X-20 X-22 X-20 X-22
X-23 X-24 X-23 X-24
X-89 X-89
X-25 25 X-25
X-56 X-56
X-27 X-27
X-26 X-26
X-90 X-31 X-90
21.7 X-31
4
X-29 X-29
X-28 X-64 30 X-28 X-64 30
X-30 X-30
X-32 X-33 X-33
X-32
X-65 X- X-65 X-
X-84 X-67 X-84 X-67
35 35
25 X-34 X-91 X-34 X-91
X-68 X-68
15.8 20
X-83 X-83
20 7 X-85 25 X-85
X-36 X-36
X-72 水4 X-72 水4
30 X-57 X-40
X-57
X-37 X-40 X-37 X-38
X-38
X-87 X-87
X-58 水2 X-39 X-58 水2 X-39
30 X-80 X-82 X-80 X-82
X-59 水6 X-59 水6
X-69 X-69
X-81 X-81
30
X-41 X-44 X-41 X-44
X-60 X-42 X-42
X-60
25
35 X-45 X-45
X-43 X-43
35 25 30
X-61 X-46 X-61 X-46
X- Groundwater X- Groundwater
83 sampling point 83 sampling point
X-47 X-48 Piezometic level X-47 X-48 Piezometic level
Residential area Residential
X-49 X-49 area
Pesticide Plant X-51 Pesticide Plant X-51
X-63 Railway,
X-63 Railway,
X-66 highway X-50
X-50 X-66 highway
X-53X-54 X-53X-54
River
River
a 0 1 Km b
2Km 0 1 Km
2Km
Fig. 17. Contours of the karst aquifer piezometric level ( a, 2009-8-30; b, 2009-12-30)
5.4 Factor analysis of CCl4 attenuation in the Karst aquifer
Concentration of CCl4 decreased in the karst aquifer because of the influence of CCl4 fate
(volatilization, dilution, adsorption, chemical reaction, biological degradation) and it’s
difficult to describe CCl4 attenuation in karst aquifer because of shortage of parameters. The
main factors are as follows:
1. Free-phase CCl4 existence in observation well
Most organics exist as the NAPLs which are the long-term sources of dissolved-phase
organics in the aquifer. The EPA found the NAPL was the main-factor that affects the rate of
pumping and it’s important to determine its existence in the reservation well. Highly-
concentration dissolved-organics are barely measured due to the low solubility of NAPL
and dilution of reservation well. EPA presents an indirect way to measure the NAPL (1%
principle): NAPL will exist if the concentration of chemical materials that related with
NAPL was exceeded pure-phase or 1% of valid solubility. The pure-phase CCl4 solubility is
785 mg/L at 25ºC. The CCl4 has been measured in groundwater at about 3909.9 μg/L, which
is approximately 0.5 percent of its solubility, suggesting that there is no evidence to
determine the CCl4 NAPL existence.
2. Passive extraction
Passive extraction is the main factor decreasing the concentration of CCl4 due to the fact that
research area was the water supply source in the city with extraction of 2000×104 m3/a. The
groundwater exploitation has decreased dramatically since 2001, however, there are several
irrigation wells and industrial wells situated within the contaminated area still in use. It is
estimated that the discharge of CCl4 for 2001, 2004, 2005 and 2008 were 5.42, 1.27, 0.26 and
0.14 tons respectively according to the groundwater exploitation volume and the average
CCl4 concentration (Pei, 2009).
3. Dilution
Convection is one of the most important processes leading to dissolved-phase of
contaminants transport in saturation area and concentration decrease. The trace experiment
illustrates that convection is the dominant rather than dispersion during CCl4 transport
because of the high flow rate of karst water. Funnel-shape water levels were generated
during pumping and the concentration of CCl4 in reservation wells changed due to the
water flow from the aquifer around the well.
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Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 569
4. Volatilization
Contaminants distribution in liquid-gas phase is governed by Henry’s law. The trend
between liquid phase and gas phase is determined by the Henry’s constant. Volatile
organics in groundwater could volatilize into atmosphere via soil. The volatilization should
be considered if Henry’s constant > 1x10-5 atm·m3/mol and molecular weight < 200 g/mol.
Thus the volatilization is dominant in the CCl4 decrease according to Henry’s constant of
CCl4 (2.76x10-2 atm·m3/mol) and molecular weight (153.82). It is estimated that CCl4
volatilization for 2004, 2005 and 2008 were 5.38, 9.06 and 4.44 kg respectively (Pei, 2009).
5. Adsorption
Organic matters and clays are the most important factors which contribute to adsorption in
aquifer and organic matters are dominant. The adsorption equilibrium of CCl4 is associated
with concentration of organics and KOC. Silva (Silva et al., 2000) indicated that pore filling
was main factor in solute distribution. The aquifer in Qiligou has the characteristics of high
runoff, intense flash and less pore fillings, due to the high burial depth, long-term
exploration and large production, which is shown in Fig.5. Therefore, adsorption has less
influence on decrease of CCl4.
6. Biological degradation
The CCl4 was transformed into chloroform by biological degradation in the soil. It was
manifested by the fact that CCl4 and chloroform both existed in the soil samples around the
pesticide plant and only CCl4 was founded in the pore water (Zhu et al., 2006). Chloroform
was not detected in the wastewater discharged from the pesticide and the karst
groundwater. This suggests that the CCl4 bio-degradation for its attenuation in the karst
aquifer can be ignored.
6. Conclusions
In this chapter, the spatial distribution and temporal evolution of CCl4 in the karst aquifer of
a northern city in China were studied through groundwater and soil sampling and testing,
groundwater level observation, analysis of water-bearing media, hydrodynamic conditions
and artificial exploitation.
1. The water-bearing media is characterized as the multi-system of karstific apertures,
fissures and caves. By the control of lithological and geological structure, the karst is
extremely heterogeneous.
2. The CCl4 plume in the karst aquifer was "dumbbell" shaped, with high contamination
located in the southern and northern sub-area and relatively light concentrations in the
middle transitional sub-area.
3. The concentration of CCl4 in the aquifer is changed rapidly with time, which is different
from the common porous medium aquifer because of the high groundwater velocity in
the aquifer and migration channel, complex local flow field and good hydraulic
connection. CCl4 concentration was generally decreasing over time.
4. The length of pollution plume of CCl4 in the water-bearing aquifer is stable while
concentration is shrinking. The attenuation of CCl4 in the water-bearing aquifer is
controlled by passive pumping, volatilization, convection dilution and biodegradation.
7. Acknowledgment
We would like to thank the National Natural Science Foundation of China and Jiangsu
Provincial Water Resources Bureau for financial support (40373044, 2007006 and 2009006).
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570 Pesticides in the Modern World - Risks and Benefits
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Pesticides in the Modern World - Risks and Benefits
Edited by Dr. Margarita Stoytcheva
ISBN 978-953-307-458-0
Hard cover, 560 pages
Publisher InTech
Published online 03, October, 2011
Published in print edition October, 2011
This book is a compilation of 29 chapters focused on: pesticides and food production, environmental effects of
pesticides, and pesticides mobility, transport and fate. The first book section addresses the benefits of the pest
control for crop protection and food supply increasing, and the associated risks of food contamination. The
second book section is dedicated to the effects of pesticides on the non-target organisms and the environment
such as: effects involving pollinators, effects on nutrient cycling in ecosystems, effects on soil erosion, structure
and fertility, effects on water quality, and pesticides resistance development. The third book section furnishes
numerous data contributing to the better understanding of the pesticides mobility, transport and fate. The
addressed in this book issues should attract the public concern to support rational decisions to pesticides use.
How to reference
In order to correctly reference this scholarly work, feel free to copy and paste the following:
Baoping Han, Xueqiang Zhu, Zongping Pei and Xikun Liu (2011). Transport of Carbon Tetrachloride in a Karst
Aquifer in a Northern City, China, Pesticides in the Modern World - Risks and Benefits, Dr. Margarita
Stoytcheva (Ed.), ISBN: 978-953-307-458-0, InTech, Available from:
http://www.intechopen.com/books/pesticides-in-the-modern-world-risks-and-benefits/transport-of-carbon-
tetrachloride-in-a-karst-aquifer-in-a-northern-city-china
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