Handpump drainage channels
I am on a WatSan project in Cuddalore, Tamil Nadu, India and I have a query about the drainage for handpumps. At present, all the handpumps in the area either have no concrete apron or the apron is very cracked and the drainage channel leads nowhere. I was wondering about the possibility of either directing the water into leach pits or recycling it for animal drinking water or irrigation. Is there a recommended distance between the leach pit and the handpump and are there any existing designs available for the recycling of spill water from the pump? Regards,
The most important is to ensure the apron is not cracked and various apron radii from 1 to 2m from the handpump are suggested. I would suggest a minimum of 1.5m from the edge of the handpump or well cover slab.
The next most important is to keep animals away from the wellhead.
There is, as far as I can see (and I have checked all the usual texts in our resource centre e.g. SPHERE, Env Health Engineering, ITDG books on Hand Dug Wells and Hand Pumps and others on handpump construction) no standard for distance from apron to soakaway. The soakaway here is different from that for pour flush latrines or household waste as the wastewater should be very lightly loaded with pathogens (unless people wash themselves/clothes at the wellhead or water animals). The soil characteristics are the most important in terms of polluting - a chalk or lime rock could allow very quick ingress of wastewater back into the well without filtration through cracks whereas a sand or loam would allow good filtration and so the soakaway could be placed nearby. A clay would allow very little wastewater to soak away and so other means of getting rid of the wastewater is important. The only books I can find with drainage channel lengths are Field Engineering which talks about several metres.
There is a nice design in Engineering in Emergencies p253 that has a 2% slope on the apron and drainage channel. The drainage channel is minimum 6.3m long, leading to a cattle trough of minimum 1.5m long then to a soakaway. This should allow plenty of distance between the soakaway and well, although the main reason for its length must be to keep animals from the well (if animals are watered nearby the well should be fenced).
If you are replacing aprons they really should be pretty strong as they will get plenty of abuse - good deep foundations and steel reinforcements over the well itself. If you want I can send you a design or two, especially if you give some more details of the well and handpumps.
It is often the way that the wastewater irrigates a vegetable garden kept by the handpump caretaker - a useful use for the waste. I have also seen it feeding a duckpond (a very small one). People often have very good strategies themselves to reuse the wastewater from a handpump.
The water from the handpumps is mostly contaminated with a faecal coliform count between 10 and 100. The water is not used for drinking as tap water is available for two hours each morning. The handpump water is used for bathing, washing plates and clothes and for animal consumption. Are these acceptable uses for contaminated water or should plate washing for example be restricted? Many of the handpumps are located near to Septic tanks which leak and contaminate the ground water so it would be very hard to protect the pumps from contamination without relocating them. The charity I'm working with has said that the concrete aprons are not really necessary due to the soil being sandy, so water does not pool around the pump for very long, and the pump water is not for drinking. Is this a correct assumption to make about the concrete aprons or would you suggest their construction anyway?
The groundwater is already contaminated, however, the apron slab can still prevent short-circuiting of contamination down the sides of the borehole casing, particularly if there is not already a good sanitary seal, and hence should prevent the water being contaminated further. The apron slab can also add support to whatever is holding the handpump in place.
The apron slab is also useful for preventing erosion of the soil around the pump which can also adversely affect the fixing of the handpump.
One needs to consider the rainy season when in addition to spilt water there is also potentially flow of contaminated surface water around the pump. I suspect that muddy conditions will soon develop as silt begins to block the sand, which will make water collection unpleasant.
10 - 100 e.coli/100ml far from ideal but is not an extremely high level of contamination. Often people are drinking water with much higher levels of e.coli. My personal feeling is that the risks from using it for bathing are minimal (as long as people don't ingest an water when they are washing themselves or children). I also feel that the risk from washing plates is also minimal. If the plates are dried on plate racks that are exposed to sunshine then I would expect the UV component of the sunlight to kill of most of the pathogens, reducing the risk even further.
Given the likely contamination in a sink of washing up near the end of the process, using slightly contaminated water for washing up would be unlikely to cause additional contamination of the plates. They should be air-dried thoroughly before being stacked and reused. If in doubt, uncontaminated water could be used for rinsing before drying.
One the aspect of apron I have mixed feelings, but I would really suggest putting it in and as Toby say make sure it is not cracked and seals up to the well. Irrespective of use it is desirable to minimise pollution from animal droppings, and other extraneous flow back water into the well.
Secondly without an apron it can rapidly become a chewed up bog, and in the right circumstances / environment cause ponding and even a breading ground for vectors (especially malaria, dengue mosquitoes and others) in the ponding / dampness, though if the soil is truly sandy that may be minimised
I would have thought with sandy soil there was a good chance of infiltration back into the well if excess water was not taken away by an apron .... that could well have the effect surely of washing back more coliforms into the well and actually concentrating them in the well.
Also wash back down the well may also not be good for the longer term well maintenance and walls
On the question of washing plates I will give you the definitive insight from our own kitchen ... we live in Cambodia and all parties accept the local piped water is not safely drinkable ... even my rural Cambodian wife will not drink it without extensive boiling and only then if bulk bottled water is not available that we have delivered to our flat every three or four days (boiling water only kills coliforms it does not remove metals etc)..... We have no water heater or hot taps in our flat but hygiene is one of the highest priorities. we survive in the same way I have in remote parts of Afghanistan and Pakistan and even recently in South Sudan ......................
1.) keep water as clean as possible for washing dishes etc ... i.e. change it 2.) obviously use soap / detergent or or other surfactant to break down grease etc 3.) air dry the plates in racks or similar until they are completely dry - then remove them 4.) do not allow wet plates to drip onto dry plates / cutlery 5.) if possible store the dried and drying plates with a cloth (a dry clean cloth or piece of muslin) over to try and avoid vectors such as flies
this is on the advice of several doctors and so far I have found it very successful ant home and on assignment in many places over many years
.... THE KEY, as doctors point out, is the plates and cutlery must be completely dry ...... germs do not survive well on a dry surface .. they survive in droplets and damp films ....... dot them well and thoroughly air dried and many of your risks are very significantly removed if not removed.....
Also depending where you are you may want to think about guinea worm nets for the water
Also as a point of reference it is worth noting (I extract below from a recent project report I wrote where we had similar issues of at least partially ... (more)
I have informed the charity about your recommendations and we are going to design and build a concrete apron for an existing pump that channels the spilled water towards a small garden which will be maintained by the children that attend a child care centre in the area. I am unsure about how to go about designing the apron as all the current slabs are broken, probably due to the lack of ground stability as the soil is sandy. Are there any standards for concrete apron dimensions in sandy soils cast insitu that would be more durable than the precast slabs already in place?
Before I comment on the technical aspects of this I have a public health orientated question, and this is not a criticism. Can you guarantee that the water will not be used for drinking, say for example by kids when they are collecting water or watering their animals? Or if your piped supply breaks down for a couple of days? If you can’t then there is a public health risk posed by the contamination. And if you can then I want to know where you are working because it is far more straightforward that anywhere I have ever been.
Faecal coliform are used as indicators of faecal contamination as they are ubiquitous in the guts of humans and animals. According to the WHO counts of by 0 per 100 mil represent no risk. Counts of 1-10 are considered to indicate low risk and counts of 11-100 are considered high risk. Anything above that is considered Russian Roulette.
The acceptable use question is kind of hard to answer. The problem is that the risk of getting sick is different to the risk of contamination. The former depends on the bacteria that are doing the contaminating. For example a low dosage of bacillary dysentery is relatively harmless while a single giardiasis occyst may make you very ill. What constitutes a low disk depends on the body mass of the individual and the infectiousness of the bug. So I can’t say objectively for what purposes the water could be used for. I personally would not use it for preparing food, bathing or washing utensils unless it had been boiled. I would definitely not let young kids near badly contaminated water unless it had been boiled.
The primary purpose of an apron around the well is to provide a sanitary seal to prevent contamination entering the well. Prevention of standing water is secondary, except when the standing water could re-enter the well and contaminate the water. A major concern in your case is that a sandy soil allows rapid drainage back into the well. If this water is contaminated with faeces then there will be insufficient contact time for the soil matrix to purify the water. As the water travels through the soil, bacteria are removed by adsorption onto the soil matrix and by predation. So if there are large amounts of faecal contamination around the well, as there quite often are, the water that is not being collected and is seeping back into the well could be the primary source of your contamination. Environmental Health Engineering in the Tropics, by Cairncross and Feachem, quotes 15-20 m as a minimum distance between a source of faecal contamination and water well. At least I think it does, I don’t have a copy handy, but it is an excellent and accessible resource, and you should get a copy if you are going to be dealing with these sorts of questions.
If the septic tanks are working properly there should be large amounts of ... (more)
The fact that the soil is sandy seems to me to indicate a
greater, rather than a lesser need for a good concrete apron. While it is true that water will not
pond around the well, it is soaking downwards and taking any contamination back into the well
I do not have any experience in India but from what I have seen in many countries in Africa, it makes little difference what engineers and public health officers say about not drinking water from a particular source, it will be drunk anyway if the "safe" water is only available for a very limited time. I would also question the safety of a piped water supply that runs dry. This creates a negative pressure in the pipes and tends to draw water in from the surrounding soil which may be contaminated from adjacent septic tanks.
Going back to the question of apron and drainage design, I would support Toby's suggestion of keeping animals, clothes and body washing away from the area surrounding the well head. A fence could be provided with a concrete channel taking water to clothes washing basins and/or animal troughs. I have seen variations on this in several countries, also channels taking drainage water to small gardens. There is often a low level of faecal contamination in well water. In remote rural communities people have a level of immunity to the diseases in the area but there may be a problem if here is a large number of people travelling from outside the area.. Washing plates should not e a problem if they are left to drain dry before re-use. As a rule of thumb, wells should not be dug within 30m of latrines but there is not much you can do if you are improving existing wells
I also am away from most of my literature .... If someone can check the Helvetia Guide for Wells (Sri Lanka) that will help.
This thread is public, all members of KnowledgePoint can read this page.