TABLE 6.
Coverage of each sampling area under different layers.
| Sampling point | 1 | 2 | 3 | 4 | 5 |
| Upper layer/100% | 75.2 | 69.5 | 46.5 | 59.4 | 60.3 |
| Middle layer/100% | 50.7 | 33.9 | 43.3 | 58.5 | 45.2 |
| Lower level/100% | 79.2 | 43.5 | 27.5 | 56.5 | 51.4 |
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