Sanitation in Areas with Limited Soil Permeability

A reliable knowledge of the soil condition is important in sanitation planning and a key factor in the selection of appropriate technologies, especially where infiltration-based sanitation systems such as Single Pit Latrines or Soak Pits are to be used. Soils with a high infiltration capacity can be desirable from a technology perspective, but may be undesirable from a health and safety perspective, as they increase the risk of groundwater contamination. On the other hand, more compact, impermeable soils such as clay may severely limit infiltration and making drainage almost impossible. This has a direct impact on the filling rate of pits and will require a full sanitation service chain, consisting of the emptying of the pits, followed by transport, treatment and reuse or disposal of the feacal sludge.

Key Actions

Step 1. Conduct an infiltration test to understand the infiltration rate of the soil

The infiltration rate is the velocity or speed at which water enters into the soil. It is usually measured by the depth (in mm) of the water layer that can enter the soil in one hour. The infiltration rate can be measured through an infiltration test, find FAO guidelines on how to conduct an infiltration test here. For soakpits or pit latrines to functin correctly ,the infiltration rate for clean water should be at least 5mm/hour (ie 120 mm/day). However, low infiltration rates (<10mm/hour) might already cause challenges when pit latrines or soakpits will be used extensively by many people as shared latrines.

Step 2. Decide if a full sanitation service chain is required 

In areas with a low infiltration rates, sanitation facilities like pit latrines or septic tanks will fill up relatively rapidly. when full, these pit latrines or septic tanks will need to be emptied, and the collected faecal sludge will need to be transported and treated elsewhere, to be disposed of safely or reused.

You could decide to avoid using pit latrines or septic tanks due to the low infiltration capacity of the soil. Sanitation alternatives suitable for flood prone areas, like container based latrines, chemical toilet, or Urine diversion dry toilet can be considered. All these options need a full sanitation service chain as well.

Step 3. Plan accordingly

In some areas, local (public) sanitation service providers are active. Whenever, local service providers are available, try to partner with them. Working with existing services is generally cost-effective and provides the possibility to strengthen the capacities of these service providers.

If no (public) local service providers are present, it might be required to design, implement and run a system of deslduging, transporation and treatment of faecal sludge. This decision should not be taken lightly, as safe full chain sanitation services require significant resources, finances, skills and on-site follow up (see additional guidance under Strategic Planning).


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