NickBoerema wrote: In a study of wells in Cambodia, it was found that the shallow wells often had microbial contamination, meaning that treatment of pathogens across the shorter distances was not effective (unfortunately the deeper wells often had chemical contamination!).
Study (and see attached picture)
[attachment:1]C:\fakepath\Latrine Contamination Diagram.jpg[/attachment]
: Characterisation of the water quality from open and rope-pump shallow wells in rural Cambodia.

This study talks about open wells and rope-pumps, both of which are very prone to contamination from surface water. While it is true that there is a risk of "short circuit" ground-layers, shallow tube-wells with a proper sanitary seal and a regular suction pump are usually much less micro-biologically contaminated because they ensure that the water at least has to pass through some meters of soil.

Here in the Philippines the "open wells" (which do have a cover, but no water tight lining and the water is fetched with a bucket attached to a long bamboo stick) usually show a similarly high contamination, while a not much deeper shallow tube-well 10 meters next to it has often 2 logs less fecal coliforms.

NickBoerema wrote: I did not as yet find any information for flooding (or rather "pooling" might be a better description), or information on pit latrines close to rivers. For the pooling case, it is likely that the water still ends up contaminated-it would be interesting to know though how much of an improvement is achieved over open defecation.

There are two main issues with "flooding":
1. Overflow of pits, and thus spilling of feces into the flood-water and on the surface. This is really bad, but only happens with real flooding and not partial pooling.
2. Water intrusion into the pit and thus increased water infiltration through the pit bottom. This is problematic because the quantity of pathogens transported into the groundwater is strongly correlated with the quantity of water infiltrated. This is also why non-flush pit-latrines are preferable to pour-flush pit-latrines when it comes to possible ground-water contamination.

Hi JKMakowka, F H Mughal and Marikin,

Thank you for your posts.

From the references in your link Mughal, I was able to find some good reports that talk more about pathogen movement in the saturated zone (the case for when the ground water level rises above the base of the pit).
Assessing Risk to Groundwater from On-site Sanitation
And the guidelines that were developed from this:
Guidelines for Assessing risk to Groundwater from On-site Sanitation
WHO report: Protecting Groundwater for Health

The conclusions seem to be that more reliable protection is achieved through vertical separation where there is more chance of different layers creating a barrier. This is really for the non-saturated case-which is why the 2m distance to groundwater from the bottom of the pit is specified.

For the high ground water case, where the ground is saturated, the protection is predominantly from the horizontal distance to the water resource. In the horizontal case, treatment can occur but there is a much greater risk that there will be a layer that allows rapid movement of the contaminated water across to the water resource. So perhaps it is also the case of "all bets are off" for high ground water cases (water above the recommended 2m distance from the base of the pit to the ground water).

In a study of wells in Cambodia, it was found that the shallow wells often had microbial contamination, meaning that treatment of pathogens across the shorter distances was not effective (unfortunately the deeper wells often had chemical contamination!).
Study (and see attached picture)
[attachment:1]C:\fakepath\Latrine Contamination Diagram.jpg[/attachment]
: Characterisation of the water quality from open and rope-pump shallow wells in rural Cambodia.

I did not as yet find any information for flooding (or rather "pooling" might be a better description), or information on pit latrines close to rivers. For the pooling case, it is likely that the water still ends up contaminated-it would be interesting to know though how much of an improvement is achieved over open defecation.

Regards,
Nick

Dear Nick,

There have been a few treads on ground water pollution from pit latrines on this forum in the last years. For example:

forum.susana.org/forum/categories/193-gr...ty?limit=12&start=12

If you use the search function on the forum, I am sure you will find many more. Having said that, I do not remember coming across your specific questions in any of these threads. I think for most soil scientist, a situation where the pits (and surrounding areas) are flooded would present a scenario in which "all bets are off".

regards

Marijn

Dear Nick,

Please have a look at the attached paper.

Regards,

F H Mughal

That really depends on many factors and also at what pathogens or other contaminants you look at.

Here in the Philippines under what I assume similar conditions, but relatively well filtrating soils (fine sand and loamy sand), we did some (not very scientific) tests and I was quite surprised by the relatively high water quality as measured by fecal coliforms.

What we see is a sharp drop off in fecal coliforms found in shallow tube wells (<10m) at around 10 to 15 meters distance and many wells that do not have any major contamination sources within 30-50m are at or very close to 0 CFU for fecal coliforms.

At the same time there seems a strong overlapping plume effect in regards to nitrate, so in denser settlements you find some wells that are at 0 CFU coliforms but at very high nitrate levels (which seemingly does not originate from artificial sources like fertilizer).

I also suspect that when it comes to viruses, most of these wells have severe issues as these are much smaller and can travel further in the ground. But we lack a way to test this.

Maybe this gives you an idea, and the SuSanA library and this forum has additional background literature on the topic. But basically it is really hard to tell as there are so many factors influencing this.

Flooding and surface spilling of latrine pit contents is obviously a different story...

Dear Readers,

In rural Cambodia, the most common latrine design is a single pit connected to either a drop toilet or a pour-flush toilet . In the pit, urine and water percolate into the soil through the bottom of the pit and wall.
My question is: Does anyone know of any reports documenting the pathogen levels that occur either:
1. Above the ground surface near to the pit (and at a distance of say 30m) during longer term flooding
2. At a given distance for high ground water cases (say 30m)?

In Cambodia, the ground water level will rise above the bottom of the pit on a majority of these systems (the recommended 2m spacing between the bottom of the pit and the water level is often ignored), and in many cases the water will rise to be above ground level (flooding-but assume below the level of the toilet). This means that water will enter the pit and the ground around the pit will be saturated. This means that pathogens will be able to travel greater distances without the same level of treatment through this saturated ground. The level of treatment that is actually realised is what I would like to know about.

Best Regards,
Nick

Nick Boerema
SCE Project Facilitator
Sanitation in Challenging Environments (SCE)
Engineers Without Borders-Australia
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