Table 2 National quality standards for surface waters in China (GB3838-2002).
Parameters | Mean | Minimum | Maximum | Standard Deviation | Environmental Guides | ||||
|---|---|---|---|---|---|---|---|---|---|
First Level | Second level | Third Level | Fourth Level | Fifth Level | |||||
pH | 7.50 | 6.02 | 8.95 | 0.25 | 6 ~ 9 |  |  |  |  |
DO | 6.84 | 0.25 | 15.2 | 1.72 | ≥7.5 | 6 | 5 | 3 | 2 |
CODMn | 4.38 | 0.33 | 15.8 | 0.73 | ≤2 | 4 | 6 | 10 | 15 |
BOD | 3.17 | 0 | 23.2 | 1.68 | <3 | 3 | 4 | 6 | 10 |
NH3-N | 1.08 | 0.01 | 8.91 | 0.56 | ≤0.15 | 0.5 | 1.0 | 1.5 | 2.0 |
ArOH | 0.001 | 0.001 | 0.008 | 0.00 | <0.002 | 0.002 | 0.005 | 0.01 | 0.1 |
Petroleum | 0.09 | 0.005 | 1.88 | 0.05 | <0.05 | 0.05 | 0.05 | 0.5 | 1.0 |
DTP | 0.16 | 0.003 | 2.24 | 0.13 | <0.01 | 0.025 | 0.05 | 0.1 | 0.2 |
TN | 3.61 | 0.27 | 17.2 | 0.76 | 0.2 | 0.5 | 1.0 | 1.5 | 2.0 |
