Sources of excessively clear water in a sewer collection system include which of the following?

• A. A problem at the wastewater treatment plant
• B. A sanitary sewer leak
• C. Exfiltration from a high water table
• D. Infiltration from a high water table

Answer: (D)

Excessively clear water in a sewer system comes from groundwater seeping into the pipes when the local water table is high. This infiltration happens through cracks, joints, and around manholes, driven by the hydraulic pressure of the surrounding saturated soil. Groundwater is typically very clear and low in solids, so when it flows into the sewer, it dilutes the mix and makes the flow appear overly clear. Exfiltration, which would be water leaving the sewer into the surrounding soil, does not add water to the sewer system and thus doesn’t create excessively clear inflow. A problem at the wastewater treatment plant or a sanitary sewer leak could introduce other issues, but they don’t explain clean, clear water entering the sewer from groundwater.