When should a trench be backfilled with a clay mix or bentonite mix dam?

The correct scenario for backfilling a trench with a clay mix or bentonite mix dam is when there are site conditions that may lead to groundwater movement towards the drainfield. This is crucial for maintaining the integrity and effectiveness of the septic system. If groundwater is allowed to flow towards the drainfield, it can dilute and contaminate the effluent, causing treatment failure and potential environmental hazards. The clay or bentonite mix acts as a barrier to prevent this unwanted movement of groundwater, ensuring that the septic system functions properly and effectively.

In other scenarios, such as deep trenches or installations during winter, while certain precautions may be necessary, the specific need for a clay or bentonite mix dam is not directly linked to those conditions. In the case of sandy or loose soil, alternative solutions might be more appropriate to ensure stability and functionality, but the primary concern regarding groundwater movement is what necessitates the use of a clay or bentonite mix dam.