Dear colleagues,

I am sure that the well established "50-days-rule" is a useful concept to come up with some initial guidance for separation distances based on an assumed E-coli inactivation time of 50 days.

However, given the increased knowledge about viruses and also about the stochastic nature of this contamination problem, authorities in New Zealand have come up with a number of lookup tables for seperation distances for different aquifer settings and different thicknesses of the vadose zone, based on some quite convervative stochastic modelling.

You find the new Zealand Guidelines here:
www.envirolink.govt.nz/PageFiles/31/Guid...virus_transport_.pdf

"Guidelines for separation distances based on virus transport between on-site domestic wastewater systems and wells"
I have replied in a different thread in a similar manner, but i discovered that the link was not working.

The look-up tables are provided at the end of the document. Of course, they do not replace some hydrogeologic expertise.

As already mentioned by Jürgen, good practices in well design, well construction (appropriate sealing), well disinfection & pumping after contaminating flood events and and taking care of the immediate surrounding of the wellhead seam to be good first measures.

Actually, i would think that it could be a good idea if SuSanA would gather some key information on well siting and seperation distances adapted to low tech environemnts in a kind of factsheet document

Kind regards,
Leif

Dear Mr. Juergen,

Thank you for sharing useful information. I'm particularly delighted to read the information about Sindh, you gave. Thank you for that. If you have more information/reports on Sindh, please share those as well.

Regards,

F H Mughal

Dear colleagues,

End 90's I used in South Africa a little computer based (on diskette) simple program from WRC, to determine possible contamination by VIPs before projects started. As fare I remember, one of the inputs been soil conditions. Unfortunately I lost the little program and the booklet by a flooding later on.

Maybe this little program it is still in use in South Africa as an improved version. Do anybody know this little WRC-program too?

Regards,
Detlef SCHWAGER

Hello Mr. Mughal,

usually, the distance between the point of pollution and the well should be equal to the distance corresponding to 50 days of groundwater flow. According to the aquifer, this may range from just a few meters to several hundred meters. Flow velocity of groundwater can be deduced from pumping tests or through tracer tests; however,

these norms were established based on results obtained from max. survival times of e. coli in groundwater in cool climates (N. America, Europe) and the survival of e. coli in regions as Sindh, where groundwater temperatures are generally above 25° C, are suspected to be different(longer), so greater distances would be needed. When water testing after the 2010 floods in Sindh, we found e. coli in almost all wells within the villages, at distances of > 100m, we frequently found NH4 (ammonium), which in field testing is usually attributed to bacterial activity in groundwater.

Due to the depths and poor design of almost all wells, we couldn't determine the source of pollution with certainty (animal faeces being found al around the wells) nor it's depth location within the aquifer (usually, pollution 'feathers' tend to extend laterally from the main direction of groundwater flow, but take much time / long distances to seep down into deeper sections of the aquifers).

Conventional 'good practices' in well construction might help to provide drinking water quality to the rural poor in Sindh in many areas.

Thanks, Mr. Makowka. I appreciate.

Best regards,

F H Mughal

Working download link:
www.sswm.info/library/7411

I recently came across with an interesting publication: Pit Latrines and Their Impacts on Groundwater Quality: A Systematic Review, Jay P. Graham and Matthew L. Polizzotto, dx.doi.org/10.1289/ehp.1206028, ehp.niehs.nih.gov/1206028/ (Ms. Elizabeth: it says open access; so I believe no violation of copyrights laws – Please check at your end. Have I provided the link correctly?).

In the rural areas of Sindh province (Pakistan), pit latrines are used extensively by the rural people. There are no yardsticks as regards their siting with respect to the location of wells. There are some reports of groundwater contamination, due to the close proximity of pit latrines. While, the distance between the pit latrines and the location of wells depends on the nature and type of soil between the pit latrines and the wells, I think there are some regulations, according to which the minimum distance between the pit latrines and the wells should be 100 meters.

It would be helpful, if someone could highlight the siting regulations – location of pit latrines with respect to wells; and also highlight some case studies. Thanks

F H Mughal