**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.

Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 449

**Yun Long Lake** 

X-63 X-53 X-54

> X-63 X-53 X-54

2009-12-30; h, 2010-12-30)

X-66

**Pesticide Plant**

X-49

50 <sup>10</sup> <sup>3</sup> 1

X-61 X-46

X-41

X-51 X-48 X-47 X-83

X-50

X-43 X-42 X-44

X-59 <sup>水</sup><sup>6</sup>

X-80 X-81 X-82

X-38 X-37 X-36 X-57 水4

X-72

X-32 X-28

X-88

X-84

<sup>水</sup><sup>2</sup> X-39 X-58

g

1

**Kuihe River** X-35 X-30 X-31

X-85

X-87

10

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River 0 1 Km 2Km

X-91 X-68 15.87

21.74 3 1

3

X-40

X-83

X-45

X-69

X-26 X-29 X-64

X-56 X-24

X-20 X-19

X-60

X-49

X-41

**Yun Long Lake** 

**300**

X-70

**150**

**50**

**10**

**3**

X-66

**Pesticide Plant**

**Yun Long Lake** 

X-51 X-47 X-48 X-83 X-61 X-46

X-50

X-43 X-42 X-44

**50**

X-59

X-38 X-37

X-32 X-28

X-39 X-58

e <sup>0</sup> 1 Km 2Km

X-25

X-23

X-33 X-34 X-65

X-67

X-90

**10**

X-57

**3**

X-36

X-34 X-65

X-67

X-33

X-25

X-23 X-20 X-19

X-73 X-79

**3 10**

> X-35 X-30 X-31

X-68

**50**

X-75 X-74

X-26 X-29 X-64

X-17 X-18 X-21

**150**

**50**

X-56 X-24

X-22

**3 10**

X-27

**Abandoned Yellow River**

X-40

**3**

**Kuihe River**

**10**

**150**

X-45

10

X-22 X-18 X-17 X-21

X-89

**Abandoned Yellow River**

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River

X-27

X-63 X-53 X-54

**Yun Long Lake** 

X-63 X-53 X-54

50

X-61 X-46

X-41

X-49

X-66

Fig. 16.2 Change in CCl4 plume with time in the karst aquifer (e, 2004-12-30; f, 2008-12-30; g,

**Pesticide Plant**

X-51 X-48 X-47 X-83

X-50

X-43 X-42 X-44

3

X-59 <sup>水</sup><sup>6</sup>

X-80 X-81 X-82

X-38 X-37 X-36 X-57 水4

X-72

X-32 X-28

X-88

X-84

<sup>水</sup> X-39 X-58 <sup>2</sup>

10

<sup>0</sup> 1 Km 2Km h

1

**Kuihe River**

X-25

X-23

X-33 X-34 X-65

X-90

X-35 X-30 X-31

X-85

X-87

10

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River

X-91 X-68 15.87 X-67

21.74

10

3

X-40

X-83

X-45

X-69

X-26 X-29 X-64

X-56 X-24

X-20 X-19

X-60

X-66

f

**Pesticide Plant**

X-51

3

X-50

X-43 X-42 X-44

X-37

X-84

X-32 X-28

X-36

X-88

X-60 X-59

X-83 X-61 X-46

10 10

X-47 X-49

3

50 150

X-48

X-58 X-39 X-38

3

X-80 X-81 X-82

X-57

3

X-34 X-65

X-67

X-90

X-25 X-26 X-29 X-64

X-23 X-20 X-19

X-83

X-33

10

X-35 X-30 X-31

X-85

X-91 X-68

X-87

10

X-22 X-18 X-17 X-21

X-89

**Abandoned Yellow River**

X-27

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River 0 1 Km 2Km

X-22 X-18 X-17 X-21

X-89

**Abandoned Yellow River**

X-27

X-40

X-24

X-56

10

3

X-45

X-69

**Kuihe River**

X-69

X-60

**10**

**3**

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)

**Yun Long Lake** 

X-88

X-25 X-26 X-29 X-64

X-90

1

0

3

10

<sup>a</sup>

3

X-23

X-33 X-34 X-65

X-83 10

X-63 X-53 X-54

**Yun Long Lake** 

X-63 X-53 X-54

X-66

**Pesticide Plant**

c, 2005-8-30; d, 2009-8-30)

X-61 X-46

X-41

X-49

**300**

**150**

**150**

**10**

**3**

X-51 X-48 X-47

X-83

X-71 X-77X-70 **300**

X-50

**50**

**50**

**3**

**10**

X-43 X-42 X-44 X-60

**50**

X-59

**3**

**10**

X-80 X-81

X-36

X-38 X-37 X-57

X-32 X-28

X-39 X-58

**Kuihe River**

<sup>c</sup>

X-34 X-65

X-67

**3**

X-33

X-23 X-20 X-19

X-25

X-83

X-35 X-30 X-31

**10**

X-26 X-29 X-64

X-74 X-75

X-84

**50 10**

X-56 X-24

X-79 X-73

**50**

**3**

X-68

X-17 X-18 X-21

X-40

X-45

10

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River 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;

**X-69**

X-66

**Pesticide Plant**

X-49

300

X-70

X-61 X-46

150

50

X-41

**Yun Long Lake** 

X-51 X-48 X-47 X-83

10

3

X-43 X-42 X-44 X-60

X-59

1

0

3

X-32 X-28

X-40

X-58 X-38 X-37 X-36 X-57

X-39

**Kuihe River** X-35 X-30 X-31

3

10

5

0

150

3

00

3

X-18 X-17 X-21

> X-20 X-19

> > X-56 X-24

X-22

**Abandoned Yellow River**

X-40

X-45

10

X-22

**Abandoned Yellow River**

X-27

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River 0 1 Km 2Km

X-63 X-53 X-54

**Yun Long Lake** 

X-63 X-53 X-54

X-66

**Pesticide Plant**

X-49

50

X-61 X-46

X-41

X-51 X-48 X-47 X-83

X-50

X-43 X-42 X-44

X-59

X-80 X-81 X-82

3 10

<sup>0</sup> 1 Km 2Km d

X-38 X-37 X-36 X-57

X-72

X-32 X-28

X-88

X-84

X-39 X-58

1

X-35 X-30 X-31

X-85

X-87

10

X-91 X-68 15.87 X-67

21.74

3 1

X-40

X-83

X-45

X-69

X-26 X-29 X-64

X-56 X-24

X-20 X-19

X-18 X-17 X-21

> 10 3

X-60

X-66

**Pesticide Plant**

X-51

**3**

X-50

**10**

**300 150 50**

X-47 X-49

X-43 X-42 X-44

**10**

X-60 X-59

**3 10**

**50**

X-37

X-84

**3**

X-32 X-28

X-36

**3**

**10**

X-88

X-48 X-83 X-61 X-46

b <sup>0</sup> 1 Km 2Km

X-25

X-23

X-33 X-34 X-65

X-90

X-58 X-39 X-38

X-80 X-81 X-82

X-57

X-34 X-65

X-67

**3**

**Kuihe River**

X-90

X-25 X-26 X-29 X-64

X-23 X-20 X-19

X-83

X-33

X-35 X-30 X-31

**150**

X-24

X-56

X-85

X-91 X-68

**50**

X-87

10

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River

X-27

X-89

**Abandoned Yellow River**

X-22

王山

Groundwater sampling point Groundwater flow direction Concentration contour Residential area Railway, highway River

X-18 X-17 X-21

X-22

**3 10**

X-89

**Abandoned Yellow River**

X-27

X-40

X-45

X-69

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)

Transport of Carbon Tetrachloride in a Karst Aquifer in a Northern City, China 451

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).

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

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

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

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

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

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

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.

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).

connection. CCl4 concentration was generally decreasing over time.

4. **Volatilization** 

5. **Adsorption** 

influence on decrease of CCl4. 6. **Biological degradation**

aquifer can be ignored.

and artificial exploitation.

**7. Acknowledgment** 

extremely heterogeneous.

middle transitional sub-area.

**6. Conclusions** 

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. Highlyconcentration 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.
