Dawn asked me to prepare a lunch and learn meeting over Skype with my colleagues at Golder in Vancouver (Canada), so as I think this is a great idea and really exciting opportunity, I decided to write this post for them. Although, I’ll try to make it interesting for everyone else who wants to learn about the drilling/pumping challenges encountered here in Malawi.
My actual work with EWB is not really directly involving the followings topics but I made it a side project as I get asked a lot of questions on different hydrogeological issues by people from the district and different NGOs. Hopefully you guys can help us find solutions or push our understanding.
Every district here has a main town, called a BOMA in which the water is distributed by the Water Board. Some districts have a few other cities with water distribution and electricity. The rest of the district depends on boreholes, shallow wells or gravity fed pipes (taps and protected springs) to get safe water.
The shallow wells, as their name states, are pumping the shallow source of water using different types of pumps, like the elephant pump (rope and washer system). These shallow sources of water are obviously more susceptible to surface contamination from latrines located nearby, livestock or fertilisers. This is what my village is using right now, and the latrines are located about 20 meters from the well I’m fetching water from. Nobody knows if the latrines are up or down gradient from the well as there is no hydrogeological mapping done here.
The boreholes are in general drilled by a drill rig but can also be done using manual percussion drilling when the time and soil conditions permit it. They are often installed in fractured rock, with a maximal depth of 40-60m as the Afridev Pumps (the pump that needs to be used in borehole) won’t withdraw water over this depth. The Afridev started life in Malawi in early 1981. From the start, the aim was to produce a deep well hand pump that was very easy to maintain at village level and could be manufactured in countries like Malawi, where industrial resources are limited.
The problem is not the actual pump, but the contractor doing the work or in many cases, the drillers. They cut corners short and somehow, they are able to get away with it; they don’t do proper pumping tests, they often install the pumps during the wet season and do not take into consideration the water drawdown in the dry season which can sometimes be lower than the pump capacity, so even if the community were to add extra rising main pipes and metal rods (which is rarely done) during the dry period, the pump wouldn’t be able to withdraw water. The rising main is made of PVC pipes that are clued (solvent) together using a connector as the pipe are not threaded and can’t be screwed together. This means that to do maintenance of the rising main or when it brakes and needs to be fixed, the pipe sections are cut and clued back together afterward using new connectors. This is a complicated process.
Aside from siting the waterpoints (well/borehole) in the right location and where they’d be needed, other problems that are encountered are the access to good filter pack, the development method, the pumping test and water quality test.
Filter pack
A filter pack is the material that surrounds the well screen to filter the water coming from the aquifer in the PVC pipe. It is supposed to be fine enough to filter the smaller soil particles of the surrounding aquifer, but coarse enough to not be washed away through the screen. To get filter pack here is complicated. The contractor needs to go buy it from a quarry or get it directly from the river bank (cheaper). The material is often too angular, not uniform enough in size. Good contractors will sieve it to get the adequate size, but must won’t and the filter pack will wash away or clog the screen preventing water from being pumped.
Development
The development of the well and borehole is done to wash out the sediments that were created during drilling in order to bring the conductivity and connectivity of the aquifer back to its original (pre-drilling) status. This is a really important step that is often not done properly, if at all. The drilling is done with mud, the lithology is often clay and silt, and the gravel pack contains varying amounts of fines, thus the need for proper development.
The development is normally conducted using a rope and washer pump. This type of pump is only targeting one section of the screen and does not disrupt the aquifer enough to get rid of the unwanted sediments. There is no electricity near the waterpoints to be able to use an electric pump to develop the well and generators function with fuel, so it makes them non reliable due to fuel shortage, and expensive to use as fuel or diesel is expensive.
Pumping test
As I just mentioned for the development, the use of electric or fuel pumps to do the pumping test is not possible in most cases. The pumping tests are done to ensure that the waterpoint will be able to supply sufficient amount of water per day for the number of users. In Canada, the pumping tests are done using a powerful pump that pumps for an extended period of time (12 to 48hrs), more water, at a faster flow rate than needed in reality. The pumping test is usually followed by a recovery test, which gives an idea of the recharge rate. The pumping tests here are done using a hand pump, meaning that someone has to pump by hand for hours. Therefor they are often just run for an hour or two and there are no real analysis of the data to make sure the well will produce enough water. There are no loggers or water levels available to check the drawdown or the recovery.
Any ideas on how we could do the pumping test more efficiently or at least get data on the water level. Remember: lack of fuel, lack of electricity, no western pumps, water level or logger available. Please help me on this one!
Water quality test
A lot of boreholes in Malawi have brackish water or dissolved metals in the water. The contractor should do a water quality test to ensure that the water is potable. The shallow wells often have pathogens and fecal bacteria problems associated to them. The water quality tests could prevent a lot of diarrheal diseases. Most contractors skip this step as they don’t want to have to redrill the borehole. The water analyses in Malawi are pricey and there are not that many labs that run them.
Ok, I think this is it for now. I hope some of you will be interested to help us find solutions or at least throw some ideas out there. Let me know your thoughts and feel free to send the link to everyone who might be willing to help.
Bye and thanks
Ge
4 comments:
Hi Ge! how many people rely on one of these wells? I.e how many are in your village?
Hi Ge,
for the pumping tests, those are really challenging conditions....I have to think about it, I'll let you know if something comes up or I'll see if someone else has any idea. Cheers from Italy
Ary
Hi Genevieve. For measuring water levels can you make something like a measuring tape with fabric that would be a slightly different color when it got wet? You'd need a weight on the bottom. Something along the lines of water/product paste - if you've ever used those.
Linda
Thanks Linda, I'll see what we can do with that idea, it's simple and cheap enough that it could work.
Amber, the boreholes are normally located to accomodate 250 people, and shallow wells for 125 people. This is often not respected by NGOs when they come and install the new ones, and even when it is, the breakdown of the waterpoints makes villagers use other's waterpoints. I think my village has 350 households (average of 5people/HH). They have more than one shallow well. They apparently get their drinking water from a borehole a couple KM from the house. Hope this answers your question.
Thanks
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