Ontario Operator-in-Training (OIT) Practice Exam

What is a source of excessively clear water in a collection system?

1. Stormwater runoff

2. Infiltration from a high water table

3. Backflow from treatment plants

4. Surface runoff

The correct answer is: Infiltration from a high water table

The best choice for identifying a source of excessively clear water in a collection system is the infiltration from a high water table. When the groundwater level rises, it can lead to an increase in clear, uncontaminated water seeping into the collection system through cracks or imperfections in the sewer pipes. This clear water, often termed 'infiltration,' can dilute sewage flows, making the water appear excessively clear. Stormwater runoff and surface runoff typically contain various pollutants, debris, or sediments, which would not lead to overly clear water. Backflow from treatment plants can introduce treated effluent that might be clear but can also contain residual contaminants depending on the treatment efficiency. Therefore, infiltration from a high water table is the primary cause of clear water entering a sewage or collection system.