What is likely to cause odors in long, sluggish-flow, flat grade sewer lines?

The likelihood of odors in long, sluggish-flow, flat grade sewer lines is primarily due to biological activity. In these types of sewer lines, the slow movement of wastewater allows for the accumulation of organic matter, which can lead to anaerobic conditions. This anaerobic process occurs when there is insufficient oxygen for aerobic bacteria to thrive, resulting in the breakdown of organic materials by anaerobic bacteria. This breakdown produces volatile organic compounds and gases such as hydrogen sulfide, which contribute to unpleasant odors.

In contrast, high pressure buildup is more closely associated with blockages or surcharges rather than odor issues directly. Excessive rainfall may dilute wastewater flows and potentially flush out some odors but isn't a primary cause of persistent odors in sewer lines with sluggish flows. Electrical malfunctions typically relate to pumps or treatment equipment failures rather than directly causing odors in sewer lines. Therefore, biological activity takes precedence as the primary culprit for odors in these situations.