**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

X-72 X-36 X-33 X-49 X-39 X-24


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**3.1 Leakage test** 

into karst aquifer (Table 2).

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**3. Pollution pathway analysis** 

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Fig. 7. Variation in piezometric levels in the research region

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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

Fig. 8. Bare limestone along the wastewater ditch of the pesticide plant

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Data

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0.00

10.00

20.00

Water level elevation (m)

30.00

40.00

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.)


Table 2. Results of the leak off tests
