Table 4.7 – Determination of Action and Limit Levels for Water Quality

Parameters	Action Levels	Limit Levels
Construction Phase Water Quality Monitoring
DO in mg/L (Surface, Middle & Bottom) ^2	Surface & Middle 5%-ile of baseline data for surface and middle layer. Bottom 5%-ile of baseline data for bottom layer.	Surface & Middle 4 mg/L or 1%-ile of baseline data for surface and middle layer. Bottom 2 mg/L or 1%-ile of baseline data for bottom layer.
SS in mg/L (depth-averaged ^1) ^3	95%-ile of baseline data or 120% of upstream control station’s SS recorded on the same day	99%-ile of baseline data or 130% of upstream control station’s SS recorded on the same day
Turbidity in NTU (depth-averaged ^1) ^3	95%-ile of baseline data or 120% of upstream control station’s turbidity recorded on the same day	99%-ile of baseline data or 130% of upstream control station's turbidity recorded on the same day

Notes:

1. “Depth-averaged” is calculated by taking the arithmetic means of reading of all three depths;

2. For DO, non-compliance of the water quality limits occurs when monitoring result is lower than the limits;

3. For SS and turbidity, non-compliance of the water quality limits occurs when monitoring result is higher than the limits.