What type of soil is suitable for backfill in an ET system?

The suitable type of soil for backfill in an Evapotranspiration (ET) system is sandy loam due to its ideal balance of particle size and permeability. Sandy loam consists of a mix of sand, silt, and clay, which provides adequate drainage while still retaining enough moisture to support the evaporation process crucial to an ET system.

In ET systems, proper soil characteristics are essential for the effectiveness of the treatment process. Sandy loam allows for quick percolation of water while minimizing anaerobic conditions, which can occur in heavier soils like clay. Clay tends to hold water and can lead to saturation, causing treatment inefficiencies. Gravel, while well-draining, may lack the moisture retention needed for evaporative processes to function effectively. Silt, although it can hold moisture, may also compact too much and reduce drainage.

Thus, sandy loam's combination of drainage and moisture retention makes it the ideal backfill material for ET systems, ensuring optimal conditions for sewage treatment through evaporation and transpiration.