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David Ball gravatar image
RedR

Bobby and Mujeed's answers draw your attention to the water table level.

The water table, or groundwater level, is not static, constant or horizontal. It is the level, below which all open pores or interconnected spaces in the subsurface are filled with water, at a particular moment in time. The water table or groundwater level fluctuates. When there is no rain soaking into the ground, water drains from the groundwater system (probably to the lake or marsh), and the water table falls. When rain soaks into the ground (groundwater recharge) the water table usually rises, because the rate at which the water is getting into the ground, is faster than the rate at which it is draining from the ground. The water table level can fluctuate by several metres between the end of a dry season and the end of a rainy season. You need to know the normal maximum and minimum level of the water table before you start siting and designing your latrines. You need to understand the geology and soils below the area before you start siting and designing your latrines. All of this is not very complicated and you could try researching it yourself, but the easiest way of getting an answer to your question would be to talk to, or engage, a qualified and experienced hydrogeologist who has worked in your area.

When you are constructing pit latrines you are potentially discharging effluent into the groundwater system. It would be wise to understand the groundwater system before you site and design your new pit latrines. Hydrogeologists are trained to understand the static framework of subsurface soils and rock and the dynamic fluid moving through this framework of soils and rock. A hydrogeologist who knows your area should be able to help you and answer you questions quickly.