I'm attaching 2 more publications. While it is preferable to have a well upstream of a pollution source (e.g., a pit latrine), one should not automatically assume that the well water would be safe, in terms of water quality, because the well may be deeper than the elevation of the source of pollution, and depending on the soil characteristics, the contaminants may travel to the well.

F H Mughal

A bit older (2006), but this fact sheet from WELL sums up the various factors quite well:

www.lboro.ac.uk/well/resources/fact-shee...tm/Contamination.htm

In our project here in the Philippines it is very difficult to follow standard distances such as the Sphere recommendation of 25m, as the septictank/pitlatrine distribution is just too dense and wells installed far from the households are not used.

However due to the sandy soil conditions, fecal coliform indicator contamination is often rather low (<10MPN/100ml) even in wells only 10m from pit-latrines (which at least in the wet season often have a bottom submerged or very close to the ground water table).
Of course this does not give a good indication of virus transport (which are a major cause of diarrhea), but I think one has to look at the larger picture of both varying soil conditions and overlaying social-economic factors.

A well that is only lightly contaminated, but the water is actually used for personal hygiene and other domestic purposes, while the drinking water is bought from a more safer source or treated in the household (as quite common here), is in my opinion preferable to one that uncontaminated but rarely used.

This is an interesting review paper which I have just noticed, I don't think anyone has mentioned it before.

Pit Latrines and Their Impacts on Groundwater Quality: A Systematic Review by Jay P. Graham and Matthew L. Polizzotto

Open access and available here: ehp.niehs.nih.gov/1206028/#f2

...based on available reports, researchers who looked for groundwater contamination from pit latrines frequently detected it, and studies observed travel distances of up to 25 m, 50 m, and 26 m for unsafe concentrations of bacteria, viruses, and chemicals, respectively

Dear all

There is one report on Ground water pollution from on-site sanitation, by NEERI ( National Environment Engineering Research Institute) Government of India. It conducted analysis of Bacterial and Nitrate contamination due to on-site sanitation in 6 cities in India in 2005. It is available on the site of CPHEEO, Ministry of Urban Development , Government of India. It is uploaded chapter wise. Following is the link of site;
www.cpheeo.nic.in
Click on R&D activities , then click on the link of Impact of On-site Sanitation on the Quality of Ground & Surface Water Sources by NEERI Nagpur. There are links of different chapters and tables.
It has some useful information on nitrate and microbiological contamination from on-site sanitation.
Best

Pawan

Very interesting thread and discussion.
This topic needs to be brought into attention more not least when we are in a era of CLTS and pour flush latrines are constructed indifferently to the geohydrological conditions.

We did a global survey to try to better understand the trends in sanitation and the pit latrine is one of the fastest growing technologies in Africa (see attached document). The health risk complexities in densely poplulated areas in African cities with life-threatening diseases like malaria, severe diarrhoea, typhoid etc.

In this context to avoid this kind of contamination I believe that WHO Safe Sanitation Planning manual is really an excellent tool:
www.who.int/water_sanitation_health/publications/ssp-manual/en/

Keep the conversation going,

Madeleine

Dear Pawan,

With respect to your first post, I'm attaching 2 publications. One is by USEPA (Drinking Water from Households - see pp. 14), and the other one is titled: Guidelines for separation distances based on virus transport between on-site domestic wastewater systems and wells.

I trust, you will find them useful.

Regards,

F H Mughal

Here are some papers on movement on pathogens through soil, in case anyone is interested:

On movement in unsaturated soil:

www.americanalpineclub.org/uploads/mce_u...ough_soil%5B1%5D.pdf

Movement of the protozoan pathogen Cryptosporidium parvum through three contrasting soil types by Jane Mawdsley, Alison Brooks and Roger Merry

General conclusions: most of the spiked pathogens were found in the top 2cm of soil

On bypass flow:

www.researchgate.net/profile/Malcolm_Mcl...b2811697be000000.pdf

Regionalizing Potential for Microbial Bypass Flow through New Zealand Soils
by Malcolm McLeod, Jackie Aislabie, Janine Ryburn, and Alexandra McGill

Conclusion: Gley, Ultic, and Granular Soils have high potential for bypass flow of microbes.

As with all these things, the solution is to ask a soil scientist about specific conditions

From the Sphere Handbook on disaster relief, the specify as minimum standard for latrine distance from water source as 30 m horizontal distance, and 1.5 m vertical distance to water table.

(www.spherehandbook.org/en/excreta-dispos...e-from-human-faeces/)

One problem is that this is highly dependent on the nature of the latrine; type of soil and nature of the water source (as I'm sure you are well aware). But these numbers would seem to agree with a fairly conservatively sized soakage field for a septic tank system.

Nigel Langdon
BE (Natural Resources)

I have just caught up with this discussion after a few weeks when other concerns have kept me from looking at recent topics on SuSanA. One thing that interests me is how contamination from leach pits and septic tank soakaways penetrates down into groundwater. Clearly, there is a high risk of contamination where the water table is high and a pit latrine or leach pit is located close to a shallow well. But what is the situation when the water supply is drawn from a greater depth via a tubewell. In some parts of the World, household tubewells with a depth of 30 metres or more are not uncommon.

The relevant facts on this seem to be:

Groundwater movement below the water table is predominantly horizontal so the only vertical movement under 'natural' conditions is likely to be by diffusion.

However, vertical movement is presumably induced when water is drawn from tubewells, so that water must be drawn towards the tubewell to replace that which has been extracted.

There is likely to be vertical movement down the sides of poorly constructed tubewells - I would guess that this is an important cause of contamination.

Chemicals will be more persistent than bacterial pollution but I assume that the latter is more important.

I have been able to find very little discussion of the topic of likely water flows below the water table and the consequences for leach pit and groundwater source planning. Does anyone have any information on this?

I will try and get my colleague Paramasivan to write something. There are several villages in Tamil Nadu that he knows of that implemented pit toilets and it destroyed the ground water source from which they used to collect their drinking water. He's been promising me he will do it for a long time and I will now give him an extra nudge when I see him on Tuesday!!

Dear Joe, Christoph and Elisabeth

Thanks for your quick response. I compiled report from 7 nos. of research papers/ review article. There is one good paper from India. Review article from Graham and Polizzotto is very informative. Manual of CPHEEO,( 2013) Ministry of Urban Development, GOI is also important.
Yesterday there was an important discussion on this aspect in a meeting where I raised this issue. There is a planning of the Government to make Villages ODF, located near the bank of Ganga River by implementing twin pit household toilets. I had to submit documentary evidence of ground water pollution from leach pit toilet particularly for areas having high ground water table.
Elisabeth, I am putting reply of your queries on respective topic.

best regards
Pawan

I am so pleased to see from Christoph's reponse that the search function of the discussion forum worked well for him! (for those who don't know where the search function is: see at the top right, to the left of the manifying glass symbol)

I have also decided that it's high time that "groundwater pollution/protection" gets its own sub-category on the forum. So far it had been hidden under "working group topics" - see the blue round icon at the top right. But I don't think many people browse there. So it now has its very own sub-category (this one) which is also where I have moved the existing threads on this topic.
Let's give groundwater the recognition that it deserves!

Coming back to Pawan's question, I think Joe and Christoph have already given you good pointers.

From my side: if you are looking for a rule of thumb value for a safe setback distance, then the rule of thum is: "there is no such value, the further away the better, and ask your local geohydrologist for advice".

I also recommend the excellent new factsheet of the SuSanA Working Group 11 on this:
forum.susana.org/forum/categories/193-gr...f-sanitation-systems

And for anyone looking for a quick overview on the topic of groundwater pollution, I can also recommend the Wikipedia page (which I have edited together with others):
en.wikipedia.org/wiki/Groundwater_pollution

Pawan: if you find out more about groundwater pollution from leach pit toilets in India, or the local discussions around this topic, or specific examples of pollution incidences, please tell us more in this this thread. Thanks.

Regards,
Elisabeth

P.S. By the way, just wondering: was groundwater pollution not an aspect included in the handbook (Handbook on Technical Options for Solid and Liquid Waste Management in Rural Areas, released by the Ministry of Drinking Water and Sanitation, Government of India) which you posted about here
forum.susana.org/forum/categories/89-new...tation-govt-of-india ?