Dear Julian,

If I have understood part 1 of your question correctly, you are checking, lined pits, if abandoned why should they become unsafe. Sharing my two cents: the answer lies in potential of ground water pollution by the system in use, if the pit while in use or in abandoned stage has the potential to pollute the ground water and considerable number of people in the vicinity use ground water for drinking purpose then the system is being unsafely managed throughout whether it is T2A5C10 or T2B7C10. In case the lined pits are not polluting then in that case the systems will be safely managed whether it is T1A5C10 or T1B7C10. Another thing one needs to keep in mind is that SFD checks safe management at each stage of the sanitation chain, and one should read the SFD not just with respect to final numbers but how the city performs at each stage. So to answer part 2 of your question if a system is showing red at containment stage that just means there is an intervention required at that stage to ensure the arrow turns green at that stage. If an arrow turns green in the latter stages of the chain it only reflects that the excreta is being managed well at those stages, so in the graphic that you have shared the city is managing the emptying and treatment well but interventions are required at the containment stage, hope I have clarified and not confused you further.

Regards
Bhitush

Dear Julian

That's an interesting question.  I am part of a team which is about to adapt the SFD manual for South Africa and I expect we will encounter the same debate.

Emptying an unlined pit toilet is quite dangerous, depending on how far down one empties.  Up to 1 m deep may be ok (depending on the soil), but I would not advise people to empty deeper than that in case the toilet collapses.  

As you intimate, it is more common for toilets with unlined pits to be abandoned and replaced.  If the pit is covered over with soil it is safely managed.  There is only a risk to the groundwater if there are wells fairly close to the pit.  How close is too close is another debatable point, but in most circumstances 15 m horiizontal distance will provide good protection.  

Any risk there might have been to the groundwater diminishes once the toilet in no longer in use.  Most pathogens do not survive that long outside the human host, and the ones that do survive longer (like Ascaris) are too big to travel through soil.  Leachate moves extremely slowly through soil, which is why the risk diminishes with distance.  If you go back to an old pit toilet and dig up the contents after a few years, you will find it like a peaty soil, and you will not find any viable pathogens.

In my view the risk posed by pit toilets and soakpits to the groundwater is generally greatly overestimated.  If you read some of the papers published on the subject you will see that often the "groundwater" being sampled has come out of wells which are not protected from contamination, either by the users of the well or from the ground surface.  To sample groundwater you need a dedicated sampling well which is sealed and used for nothing else, and you need correct sampling technique.

Attached is a presentation I made on this topic at the WISA Conference in South Africa in 2022.  This contains further information and some useful references.  

Regards

Dear Forum,

In the course of producing and SFD for Wobulenzi, Uganda, I stumbled across two things that I could not explain myself, neither experts I asked:

·    Abandoning pits: ·   If we have fully lined pits without any outlet,they will be contained, regardless of their vicinity to a groundwater source. However, if this lined pit is then (adequately) covered with soil and abandoned, all over sudden it does matter whether it is at significant
groundwater risk or at low groundwater risk (T2B7C10 and T1B7C10). The reasoning, that the pits will deteriorate after they are abandoned, but not during operation is not very consequent. On the other hand, we could also specify that the lined pits are never emptied, which results in FS being contained and never emptied (safely managed). Naturally, a lined pit, which is safely containing faecal sludge during operation should also safely contain faecal sludge after it is properly covered with soil and abandoned. One could argue, that lined pits are rarely abandoned, since they require higher investment costs due to the liner. However, in contexts where emptying services are very
expensive, the option to abandon the lined pit and build a new one could be feasible.   

·      Unlined pits being emptied: While containment,unlined pits if at significant groundwater risk are unsafely managed. However,
when they are eventually emptied, they become safely managed, even though during containment they were could percolate to the groundwater, which is likely to be consumed by nearby users. The attached .png belongs to this question.

I could not find any topic that covers the above mentioned issues and thought it might be interesting to highlight. 

Best,
Julian