According to the soil wetness criteria, unsuitability is determined by what observation?

Determining unsuitability based on soil wetness criteria involves the observation of lateral water movement. When lateral water movement is present, it indicates that water is not only moving downward but also laterally through the soil layers. This can lead to the soil retaining excessive moisture, which can create unsuitable conditions for septic systems.

In septic system design and installation, it's crucial that the soil has adequate drainage to prevent saturation, which can impair the system's function and worsen wastewater disposal problems. The presence of lateral water movement suggests that the soil is not adequately draining and can lead to issues like effluent backing up and increased risks of groundwater contamination.

While high organic matter content, shallow root systems, and high clay content can also be indicators related to soil suitability for septic systems, they do not specifically point to the immediate concern of unsuitability due to water retention and drainage issues.