Which of the following is considered excessive during the mixing process?

Excessive mixing during the mixing process can lead to negative outcomes in surface water treatment. When mixing is too vigorous, it can result in the breakdown of delicate floc, which is critical for effective sedimentation and removal of contaminants. This disruption can reduce the efficiency of the water treatment process, making it difficult to achieve the desired purification levels. Moreover, excessive mixing can cause turbulence that re-suspends settled particulates, leading to increased turbidity in the water. Therefore, maintaining appropriate mixing intensity is essential for achieving optimal treatment results without compromising the integrity of treated water.

The other options describe conditions that are either beneficial or neutral to the mixing process. Normal flow and proper stirring intensity contribute positively to the mixing of chemicals and pollutants, ensuring effective treatment without causing harm to the floc structure. Slow mixing may be less effective in achieving thorough dispersion but is not considered excessive like vigorous mixing would be.