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Pit Latrine Construction:Well Placement:Pro's & Con's:Kerala

I am writing from Kerala. Regarding the facts for constructing a pit toilet ( those found in rural areas).  The question is, is it good to dig a 20feet well in a sloppy area of 30 degree slanting, if a pit latrine(i.e. the toilet pit is not cemented, normal kacha pit of 5x5 dimension) is at a distance of 21 m above from the well.

Pradeep R S

drpradeeprs@gmail.com

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Comments

1.

Dear Pradeep,

Greetings from Plan!

Please note that in normal situation, horizontal distance between the leach pit and drinking water source should be minimum of 9 times of depth of your leach pit or in other wards approximately 30 mts.

Where as your case the horizontal distance is appearing to be bit less (21 mts). I assume both the leach pit and the proposed well is in sloppy terrain and the leach pit is located on higher elevation, in such condition, there is a higher probability of water contamination, especially during rainy season.

I would advise you to go for to seal the downside of your leach pit wall or a small sand barrier 1 to 2 meter down side of your leach pit . This sand barrier can be of 1 foot width, 8 ft length and 6 ft deep. In case you need any other technical details or drawing, please feel free to contact me.

Regards
Arumugam Kalimuthu,
Chairperson, WES-Net India
&
Technical Advisor - Water Supply & Environmental Sanitation,
Plan India
E12, Kailash Colony,
New Delhi - 110 048

Phone : +91-11- 46558482 (Direct)
+91-11- 46558484
Fax : +91-11- 46558443

http://www.plan-international.org
http://www.wesnetindia.org

2.

Dear Pradeep R S.,

Though the depth of ground water table is not given but 15 meter is considered to be a safe distance between the pit and water source. It would be better to terminate the pit excavation 10 feet above the ground water table.

Instead of square pit circular pit is a better option from structural point view. Kuchchaa pit- I don’t know the soil profile there, just Kuchchaa pit may collapse so it would be better to provide honey comb brick work lining. It can be avoided also, in case it’s a common practice there, means soil below can sustain.

Regards,

Lalit Mohan Sharma
(Program Leader - Water Management)
Institute of Rural Research and Development
A Sehgal Foundation Initiative
Plot No.34, Sector 44, Institutional Area
Gurgaon, Haryana - 122002

3.

Pradeep

There are a few factors that control thepossibility of contamination due to a pit latrine.

1) The amount of liquid in the pit. It shuld be kept to minimum

2) Nature of the unsaturated zone. Smaller the sediment size,lower the risk of contamination.

3)Distance between base of pit and water table.Greater the distance between base of pit and water table lower the risk of contamination.

4)Nature of saturated zone.Greater permeability of the subsurface material will increase the risk of contamination.

5)Horizontal distance between latrine and water point. Greater the distance lower the risk of contamination.

6)Direction and velocity of ground water flow. Greater the hydraulic gradient towards the water point (well) higher is the risk of contamination.

4.

Pradeep R S,

The horizontal distance of 21 meter is perfectly alright but check that the vertical distance between the bottom of pit toilet and ground water should be sufficient ( minimum 3 meter) otherwise chances would be that the ground water may be contaminated from pit latrine and seeped to the constructed well.

Prakash Kumar
Ecosan Consultant
EcoSanRes Program
Stockholm Environment Institute

5.

Dear Pradeep R S,

Warm Greetings from ENPHO, Nepal!

Normally, 21 meters is a fairly safe distance but a lot depends on the soil type. There are plenty of people / organizations in Kerala who are involved in pit latrines.

Regards,

Urmila Joshi
Environment and Public Health Organization (ENPHO)
Kathmandu (East)
Nepal

6.

Dear Pradeep R S,

The statement by Mr R. S. Pradeep is not clear. However, the understanding according to me is that the area has a considerable slope (30 deg) and construction of unlined toilet pit and also having normal dug well as water source at a distant place.

The depth of the toilet pit is 6 metre (20 ft). The elevation difference between toilet pit and the dug well is 21 metres. Considering the soil condition as mixed gravel - sandy soil, the soil permeability will be 0.005 cm/sec. Using Darcy's equation and 30 deg slope the velocity of leachate movement will be 249.44 cm/day i.e. 2.5 metres / day. Normally pathogen survival time is 10 days. Hence, pathogen travel distance will be 25 metres maximum. Therefore, the distance between toilet pit and dug well as per the statement of the question is safe.

But why 6 metre (20 ft) pit depth has been proposed? I feel it may be reduced to 1.2 or 1.5 metres (4 ft or 5 ft).

My experience from working for dug well water quality of Kerala, I found 99 % dug wells were bacteriologically contaminated. But Keralites drink boiled water; this is the plus point.

Regards,

Dr Arunabha Majumder
Chairman
Indian Water Works Association (IWWA)

7.

Dear Pradeep R S,

The safe distance varies with many factors and is not easy to decide without the advice of a hydrogeologist. It will depend on the time of travel of liquids from the pit to the water source. For no risk the times should be at least 90 days but where the time exceeds 25 days the risks are low.

For detailed coverage of the issues please refer the “Agross Manual”. See the manual available at
http://www.bgs.ac.uk/hydrogeology/argoss/manual.html

Sealing a latrine pit will adversely affect the performance of the pit since the pit will then become saturated and will malfunction because they are designed so liquids can soak away as the contents decompose partly aerobically (in the presence of air).

If the pit is watertight it will and become filled with smelly sludge and liquids very quickly and decomposition can only be more slowly by anaerobic processes. Such a pit will need regular emptying (and safe disposal of the contents somewhere where it does not create an environmental risk).

Regards,

Brian Skinner
Programme Manager
Water, Engineering and Development Centre (WEDC)
Loughborough University
UK

8.

Dear Pradeep R S,

The Manual on Sewerage & Sewage Treatment by Government of India. The Central Public Health and Environmental Engineering Organisation (CPHEEO), Ministry of Urban Dev., New Delhi has stipulated norms for keeping safe distance between toilet pits & water sources under chapter of ON SITE SANITATION (Pollution safeguards).
For details please visit at

http://cpheeo.nic.in/

With regards,

Harinder Bhardwaj
Assistant Engineer
Irrigation and Public Health Department
Himachal Pradesh

9.

Dear Pradeep R S

A 21 m distance between toilet and well is quite safe for contamination point of view. I understand that the soil condition is clay, sand or mix.

Regards,

Dr P K Jha
Technical Adviser
Sulabh International Academy of Environmental Sanitation
New Delhi

10.

Dear Mr. Lalith mohan

Any study details regrding your opinion that 15 meters is safe distance between drinking well and pit latrine ? sanil

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