Problem: The aeration tank DO has been running normal (1.5 to 2.0 mg/L) the whole month. Today's DO reading has spiked to nearly 6.0 mg/L in the aeration tank, and the clarifier and plant effluent are cloudy. What is the MOST likely cause of the rise in DO? • A toxic shock load has entered the plant • A shock load of rain water has entered the plant • A shock load of high organic strength waste has entered the plant • The aeration blowers were left on overnight