A shallow buried trench system is the only system that can be used when the percolation time of the soil is between

A shallow buried trench system is the only system that can be used when the percolation time of the soil is between

• A. 0.1 and 0.5 minutes per centimetre
• B. 1 and 125 minutes per centimetre
• C. 130 and 200 minutes per centimetre
• D. 60 and 120 minutes per centimetre

Answer: (B)

The key idea is how fast soil can accept and move wastewater, which is what the percolation time measures. A shallow buried trench works best when the soil drains at a middle ground: not so fast that effluent escapes treatment too quickly, and not so slow that it can’t infiltrate adequately. When the percolation time is between 1 and 125 minutes per centimetre, a shallow buried trench provides enough infiltration area and a shallow excavation height to dispose of effluent safely while still allowing some residence time for initial filtration and dispersion. If the soil drains faster than this (very low minutes per centimetre), the trench wouldn’t offer enough treatment time and other designs or additional treatment steps are needed. If the soil drains much slower (very high minutes per centimetre), a trench wouldn’t provide sufficient infiltration area or would require a different configuration with more surface area, such as another system type. So, soils with percolation times in that 1 to 125 minute range are the ones for which a shallow buried trench is the appropriate, and often the only, practical option.

The key idea is how fast soil can accept and move wastewater, which is what the percolation time measures. A shallow buried trench works best when the soil drains at a middle ground: not so fast that effluent escapes treatment too quickly, and not so slow that it can’t infiltrate adequately.

When the percolation time is between 1 and 125 minutes per centimetre, a shallow buried trench provides enough infiltration area and a shallow excavation height to dispose of effluent safely while still allowing some residence time for initial filtration and dispersion. If the soil drains faster than this (very low minutes per centimetre), the trench wouldn’t offer enough treatment time and other designs or additional treatment steps are needed. If the soil drains much slower (very high minutes per centimetre), a trench wouldn’t provide sufficient infiltration area or would require a different configuration with more surface area, such as another system type.

So, soils with percolation times in that 1 to 125 minute range are the ones for which a shallow buried trench is the appropriate, and often the only, practical option.