What slope percentage is deemed unsuitable for drainfield installation?

In the context of on-site sewage facilities, the slope of the land where a drainfield is to be installed is crucial for ensuring proper drainage and function of the system. A slope that exceeds 30% presents numerous issues.

When the slope is too steep, gravity can cause the soil to drain too quickly, preventing adequate treatment of the wastewater as it moves through the soil layers. This rapid drainage can lead to surface runoff, which can carry untreated effluent into nearby water bodies, posing environmental and public health risks. Furthermore, steeper slopes make it difficult to maintain and inspect the drainfield, and they can also increase the risk of erosion and sediment transport that can disrupt the integrity of the system.

The optimum slope for a drainfield is generally between 0% and 10%, as it allows for adequate absorption and treatment of wastewater. Therefore, any slope exceeding 30% is considered unsuitable for drainfield installation, thus making it a critical factor to evaluate during the site assessment process for OSSF.