If the wastewater effluent in a gravity system tests at 7 DO, what could this indicate?

The presence of a wastewater effluent testing at 7 mg/L of dissolved oxygen (DO) in a gravity system can indicate that the system is experiencing some issues that might be allowing additional water to enter the septic system, leading to a dilution of the effluent.

When dissolved oxygen levels in wastewater are low, it often suggests that aerobic bacteria are using up available oxygen to decompose organic material, which can be a normal process in septic systems. However, a significantly low DO level could indicate problems such as groundwater intrusion, which introduces additional water that can dilute the concentration of oxygen and other constituents in the effluent.

In addition to groundwater intrusion, a running toilet and a leaking faucet can also contribute to excess water entering the system. A running toilet can continuously add water to the septic tank without allowing for proper treatment, which can reduce the effectiveness of the system and alter the oxygen levels. Similarly, a leaking faucet can introduce unnecessary water, further contributing to the dilution of effluent and affecting the system's balance.

Given that all these scenarios can lead to a diminished DO reading, the most comprehensive answer encompasses all possible causes, highlighting how they collectively signify issues within the system. Thus, identifying all potential contributing factors helps in diagnosing the problem more accurately.