ARTICLE

 EcoEng Newsletter No. 12, June 2006

Water from the Well - Still a Reality?

Content No. 12/06
  Title page / Index
  Editorial
Articles:
  Water from the well
  Phototrophic biofilms
  Cameroon:
  optimising waste flow
  India: Water supply
  schemes in a slum
  Austria: Sewerless city
  Composting: Ch. 5
  PNG: Ecosan project
IEES:
  Biopros project
  Ecosan curriculum CD
EcoEng News:
  Newsbits
Satire:
  Joe Swamp
Various issues:
  IEES Writers' Fund
  Calendar
  Mailing list
  Credits
  EE-Newsletter Flier

By Prof. R. Shanthini
EcoEng-Correspondent, Sri Lanka


Contact Prof. R. Shanthini
Head/ Dept of Chemical Engineering
University of Peradeniya
Peradeniya. Sri Lanka










Live chat event with Prof. R. Shanthini: July 5, 2006 at 10:30 UTC/GMT
on http://www.mynetworks.org
See www.timeanddate.com for your corresponding local time
 

It was being seated on the walls of the well that I first savoured the fruits of hospitality of my cousins from my father's side. The fruits were freshly plucked raw mangoes smashed into pieces by hitting them against the walls of the well. The mango pieces were garnished with the mixture of chilly powder and salt sneaked out from the kitchen. Though the whole episode was a lip-burning experience for a city girl like me, it was my first exposure to the well culture that prevailed in the homes of my Jaffna relatives. Their homes, as well as many other homes in the dry zone of Sri Lanka, obtain their water from the ground under their feet, and what is more, they also treated their wastewater in the ground under their feet.

A well, hand-dug well for that matter, is practically a wide hole in the earth reaching out to the water that is stored underground. One must dig down until one reaches an aquifer, where groundwater is found residing in permeable rock, sand, or gravel. An open aquifer, as shown in Figure 1, rests on an impervious layer, and the upper surface of the aquifer is known as the water table. To reach an open aquifer, one must dig through the aeration zone. This zone consists primarily of soil, which gets saturated with water following a heavy rainfall. However, no water will flow into the hole from this saturated soil since the water trapped by the soil is practically immobile. Only when the hole has been dug below the water table, water will rush into the hole since water in an aquifer could move at a rate of few inches a day (in sand) to few hundreds of feet per day (in gravel and permeable rock). The water enters the hole dug until its top surface reaches almost the same level as the water table surrounding the well, as shown in the case of the open aquifer well (the middle one) sketched in Figure 1.

Figure 1: Three
types of wells.
 

In the event of a severe draught, it is possible that the water table drops so much that a well dug into an open aquifer dries off. Therefore, such wells must be sunk much below the water table level anticipated during the dry season. A sub-artesian well or an artesian well, shown in Figure 1, is sunk into an artesian aquifer, where the groundwater residing in sand, gravel and fractured rock is contained by impervious layers of soil or rock. In an artesian well, water overflows from the top of the well since the top level of the well is lower than the level of water table in the artesian aquifer, as shown in the figure. Such wells are however a rarity, even though there is one in our neighbourhood.

In a sub-artesian well, even though water does not spill over owing to the ground surface being higher than the water table level, as shown in Figure 1, the amount of water found in it is in general much larger than that found in an open aquifer well. Therefore, these wells are ideal for irrigation of crops. The diameter of a well can vary from about 1.5 to 6 meters and its depth from about 6 to 20 meters depending on the geology, load and the degree of rainfall in the area. It is worth mentioning that community and irrigation wells of 10 meters in diameter and 60 meters in depth are also not uncommon in some parts of the eastern world.

I must not fail to mention here that community wells are great feasts for the mind and the soul. They are, however, used by the economically unprivileged group of people who could not afford their own water supply at their homes. It is a place where people come together to take baths and to wash their cloths. It is also a place where people talk about all sorts of things and socialise. It is usually a place of fun and laughter. The photograph of Figure 2 was taken in February 2006, and I pleasantly remember how those young ladies in their bathing costumes, wet cloths wrapped around them in styles not much unlike the Hollywood female stars in the Oscar night, readily obliged themselves to me, a total stranger to the village, when I requested permission to photograph them.

Figure 2: Young girls using a community well.
 

Choosing a spot to dig for a well is the riskiest part of making of a well, since one cannot be very sure of how far down to go before one reaches an aquifer. If there are wells in the neighbourhood then one could make a good guess of the depth required to find groundwater. Presence of certain kinds of trees can also indicate the presence of aquifers. In Sri Lanka, trees named "kumbuk" and "Attika" in the dry zone are sure signs of finding groundwater at a reasonable depth since the existence of these trees depends heavily upon their roots reaching the water table. Today, electrical resistivity and seismic refraction measurements are used to locate the depth of water table with certain degree of success.

Having located the spot, sinking a hole in the earth to reach out for groundwater could be carried in many different ways. If one chooses to make a hand-dug well then one must take all precautions to follow the established technology in making a hand-dug well so as to avoid the possibility of well diggers getting killed during the well excavation or the beneficiaries getting killed during its use. Sinking a hole however is only the fist step in the engineering of well-making. The second step is to line the sides of the well to prevent the sidewalls of the hole from collapsing under their own weights. It is accomplished by use of brickwork, masonry, or concrete. If the well is sunk through hard rock or stone, one may omit lining the sidewalls. However, the top three meters or so of a well must be lined practising waterproof construction in order to protect the water contained in the aeration layer from slowly seeping into the well and contaminating its water. The bottom of the well is never lined since the groundwater enters the well through its bottom.

Figure 3 shows a well having a cement-on-brick lining, and water is drawn from this well using a bucket-rope-pulley system. It is the well at our home in Kandy situated among the hills 500 m above the sea level. To prevent rainwater runoffs entering the well and contaminating its water, a wall along the periphery of the mouth of the well, known as the wellhead, is raised above the ground level. Figure 4 shows the wellhead clearly. The wellhead also protects people and animals from accidentally falling into the well. Figure 4 also shows the drainage apron which is designed to remove the water spilled around the well during bathing and washing activities away from the well. It is also not uncommon to direct this water to water the plants in the garden by an intriguing mini-irrigation system which uses only gravity not energy.

Figure 3: A well with cement-on-brick lining.
Figure 4: A well with wellhead and drainage apron.
 

Figure 5 shows a well where the water is drawn using a bucket tied by a rope to a shaft made up of the truck of a palm tree, known as the "palmyra" tree. This shaft is pivoted on a cross bar that rests on the two supporting walls shown in Figure 5. This whole arrangement for lifting water is known as "shaduf", which is a very efficient system to irrigate crops. A man stands holding the rope as shown in Figure 4. Another man stands on the "shaduf" shaft at its pivoting point. When he moves to the well side of the "shaduf" shaft from the pivoting point, the bucket lowers down to fetch water. When he moves away on the "shaduf" shaft, his weight helps to raise the bucket filled with water from the well. The man shown in the picture gets hold of the bucket as it reaches his hands and empties the water into the drainage apron shown in Figure 5. The water emptied into the drainage apron reaches the crops by gravity via the mini-irrigation system. This sustainable irrigation system has been increasingly replaced by the fossil-fuel-burning water pump, which is seen as a symbol for the affluence of the well owner today.

Figure 5: A well with a "Shaduf" system for lifting the water from the well.
 

Having made a perfectly engineered well does not however guarantee a reliable supply of water. If, for instance, water is drawn at a rate higher than the rate at which groundwater moves into the well, then the well will dry off. Not only that, when an aquifer situated close to a sea is made to loose most of its fresh water content by excessive tapping of groundwater via the wells, salt water level could rise in the aquifer so as to enter the wells. It is therefore essential that a reliable system to recharge the groundwater is in place in an area where groundwater is the major source of freshwater supply.

In Jaffna, which is a dry zone receiving rains only for few months an year, this has been done by excavating into the aquifers and building large ponds, known as "kulam", that are sunk below the water table, as shown in Figure 6. The rainwater runoffs collected in these "kulams" seep into the aquifers replenishing the groundwater. Even though water in the "kulam" may be contaminated, when it reaches the well seeping through the sand, gravel and fractured rock found in the aquifer, it gets purified by the natural filtration action offered by the media.

Despite the significance of these "kulams" in ensuring a reliable groundwater supply even during long dry seasons, they are the first causality of economical development activities in which villages turn to towns, and towns turn to cities. In a fragmented, compartmentalised approach to infrastructure development, the civil engineers have overlooked the importance of the "kulams", and they close them down in order to build high rising and other intimidating structures. These activities have not only contributed towards lowering the water table, but also have caused floods in cities during heavy rains since the drainage system that takes the stormwater to the river or sea is unable to handle large volumes of stormwater which has in fact been sent down to replenish groundwater, so to speak.

Figure 6: "kulam" collecting rainwater and replenishing the aquifers.

 

Almost all homes that take water from wells for their daily use also have installed septic systems to biologically treat the heavily polluted water leaving their toilets. The septic system consists of three underground tanks separated by leak-proof walls. The organic matter found in the water flushed down the toilets reaches the first tank, and is broken down there to methane, ammonia, hydrogen sulfide, phosphates and water by naturally occurring anaerobic microorganisms. These are microorganisms that thrive when no oxygen is present as in the case of the almost airtight, watertight septic tanks built underground. All products of anaerobic digestion dissolve in the partially treated wastewater that leaves the first tank and enters the second tank, making room for new wastewater to enter the first tank. The walls of the first and the second tanks are sealed such that they are entirely leak-proof. The liquid leaving the second tank, when it gets filled, is sent to the top of the sand-filled tank, the last one of the three tanks.

This third tank contains larger sand particles on the top and smaller sand particles at the bottom. The bottom of this tank is not sealed so that water could seep out of the tank into the surrounding soil through the bottom. The third tank indeed acts as a sand filter. It filters pathogens, harmful to human and other living creatures, that may be present in the water leaving the second tank of the sptic system. Pathogens, all of whom have protein coats, that pass through the sand filter get attached to sand, which are in fact tiny pieces of stones, owing to the minute electric charge that the stones possess. The pathogens are parasitic in nature, and therefore once they are separated from their host, which is wastewater, they die quickly. It is known that a mere 4 ft (ca. 30 cm) of sand bed is adequate to effectively disinfect the liquid passing through it. It is therefore the depth of the third tank is only 4 ft. The liquid seeped into the soil after passing through the sand filter in the third tank is further broken down by the aerobic microorganisms into stable compounds, most of which are essential for the healthy growth of plants.

The "filtered" and "disinfected" water replenishes groundwater stored in an open aquifer by sinking downwards from the leach field surrounding the septic tank. Even though, in theory, 4 ft of soil cleanses the water, a minimum of 50 ft (ca. 15 m) is maintained in practice between a septic tank and a well, which is in fact more than adequate to clean the water as good as or even better than what is expected of a sophisticated wastewater treatment process. What more is this entire system requires no energy to maintain it, and does not give out the deploring smell that emanates from most large-scale sewage treatment plants. Besides, the entire process is a golden example of an ecologically sound sustainable technology.

Getting back to the well, I must mention that it is also very common to maintain a mini ecosystem in the well by permitting the fish to populate the well water. You must, of course, bring the fish from your neighbour's or relative's or friend's well and place them in your well by lowering them in the bucket that is used for drawing water. Bear is mind that it is not at all necessary to feed the fish living in a well since the fish could feed themselves on the water plants growing in a seasoned well and also the beneficial natural microorganisms that come to populate the well water. The wells that support mini ecosystems require sunlight reaching out to the flora and fauna of the wells.

The gold fish that demanded bigger and bigger tanks from my brother's family in Trincomalee are now happily living in their well. Even though they use the bucket-rope-pulley system shown in Figure 3 to draw water from their well, they also use an electric pump to pump water from the well to an overhead tank from which they maintain their own running water system. The gold fish seem to know how not to get sucked into the pump" intake. And, it is fun to take a bath at their well looking down at the gold fish when drawing the water from the well using the bucket-rope-pulley system. The presence of healthy fish in the well water is a very clear indication that the well water is perfectly safe for consumption, perhaps much safer than the chlorinated water that we get from the municipal water supply system, a fish placed in which die almost at once owing to the presence of residual chlorine, the very purpose of which is to kill small lives.

© 2006, International Ecological Engineering Society, Wolhusen, Switzerland