4. **Volatilization**

450 Pesticides in the Modern World - Risks and Benefits

X-63 X-53 X-54 X-51 X-48 X-47 X-83

35

**Yun Long Lake** 

X-61 X-46

X-50

1. **Free-phase CCl4 existence in observation well**

X-43 X-42 X-44 X-60 X-41

X-59 <sup>水</sup><sup>6</sup> <sup>水</sup> X-39 X-58 <sup>2</sup> X-38 X-37 X-36 X-57 水4

30 30

X-80 X-81 X-82

X-32 X-28

X-88

X-84

X-72

30

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

20 25

X-14

X-23

25

X-33 X-34 X-65

35

<sup>a</sup>

**5.4 Factor analysis of CCl4 attenuation in the Karst aquifer** 

**Kuihe River**

X-90

X-20 X-19

X-56 X-24

> X-35 X-30 X-31

> > X-85

X-87

10

Groundwater sampling point Piezometic level Residential area Railway, highway River 0 1 Km 2Km

Fig. 17. Contours of the karst aquifer piezometric level ( a, 2009-8-30; b, 2009-12-30)

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

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

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

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

X-63 X-53 X-54 X-51 X-48 X-47 X-83

X-61 X-46

X-50

X-43 X-42 X-44 X-60 X-41

X-59 <sup>水</sup><sup>6</sup> <sup>水</sup> X-39 X-58 <sup>2</sup> X-38 X-37 X-36 X-57 水4

25

25

30

**Kuihe River**

X-80 X-81 X-82

X-32 X-28

X-88

X-84

X-72

30

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

X-14

X-23

X-33 X-34 X-65

20

X-90

X-20 X-19

X-56 X-24

> X-35 X-30 X-31

> > X-85

X-87

10

Groundwater sampling point Piezometic level Residential area Railway, highway River 0 1 Km 2Km

X-91 X-68 X-67

25

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

X-89

**Abandoned Yellow River**

X-16 X-15

X-27

30

X-40

X-83

X-45

X-69

X-49

**Yun Long Lake** 

X-66

b

**Pesticide Plant**

X-91 X-68 15.87 X-67

21.74

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

X-89

**Abandoned Yellow River**

X-16 X-15

X-27

30

X-40

X-83

X-45

X-69

X-49

X-66

main factors are as follows:

determine the CCl4 NAPL existence.

CCl4 concentration (Pei, 2009).

water flow from the aquifer around the well.

2. **Passive extraction** 

3. **Dilution** 

**Pesticide Plant**

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).
