HAND DUG WELLS

( pick & shovel technology for large diameter holes )

Modified Chicago Method of safe well construction

The photo illustrates the use of a traditional temporary excavation support system for safe digging in open holes. Steel rings, wedges and timber boards ensure the safety of workers at any depth.

Having found good water - at 15 metres (50-ft) in this case - a variety of completion options are possible. These include brick lining or precast concrete rings, in situ concrete, shaped blocks, or a borehole casing. Whichever method is employed, the boards and rings are withdrawn as work progresses, to be used again in further wells, without waste or loss.

To give some scale to the picture, the steel channel rings are 4-ft (1.22 m) dia.

It took 4 weeks to arrive at the stage illustrated here in Togo, by hand labour in hard stoney ground just out of the flood plain. Only the upper 4 metres needed support. It would have taken longer but for the constant supervision & encouragement.

ALTERNATIVELY or IN ADDITION . . .

The same well pictured above could have been completed in a single day using the light cable percussion drilling machine shown below, powered by a 10 hp (7½ Kw) diesel engine and operated by 2 people. It will drill 30 metres per day in any material in which it would be practical to hand dig. The best that can be expected of hand digging using pick-and-shovel methods is 1 metre (3'-3") per day, with a team of 8 to 10 men. The single day's work would have illustrated that there was good water from 15 metres depth, and that there was at least enough to supply a hand pump. A decision could have been made to either case the hole as a borehole, or commence hand digging a large well, absolutely confident that it would be successful in all respects.

The drilling machine could also have drilled deeper than is possible by hand digging, and would have been able to access the full depth of water-bearing material. This would have enabled the completion of a well capable of providing a powered water supply, as an alternative - possibly as a future option to replace a hand pump.

It is difficult to motivate hand digging teams and local support if a high failure rate is experienced - perhaps due to boulders, the water being too deep for practical hand digging, water not being found within the overburden, or water of an unacceptable quality (salt, iron, or other high mineral content). Rates of failure as high as 60% in some places are typical. The cost of failure must be added into the overall cost of the successful wells and rates can be so high that wells dug at random become unaffordable. Knowledge that a well will certainly be successful acts as a motivation for both funders and communities. People will participate or contribute more willingly if they know their money or effort will not be wasted.

When a Forager-55 is used as a water prospecting tool in ground known to contain boulders, several holes at the same site can exactly, and quickly, determine if a hand dug well will be successful - or find a site where it will be so. The depth to water-bearing material can be discovered, together with a likely yield, and the water quality. No other drilling method provides such information before the hole has been fully cased and pumped out.

The ground that can be seen in the top picture, consisting of silty sand above a hard clay containing pebbles and larger stones, would have defeated a light rotary drilling rig, but not the cable percussion method of drilling. Stones would be broken, recovered whole or displaced by the tools, and the time taken would still have only been a day to drill the 15m to water.

CABLE TOOL (CABLE PERCUSSION) DRILLING

The photo shows a Forager-55 cable tool rig drilling at nominally 5-inch diameter using a bailer to clean out a hole being drilled in village in south-eastern Sierra Leone. Stones and boulders of up to 4-inch (100mm) size can be recovered by the clay cutter lying on the ground by the right wheel. The trailer tripod rig is powered by a 10 hp diesel and uses a tool string weight of 250 Kg. It is light enough to be wheeled between sites by hand, minimising the support needed for a continuous drilling programme.

The bailer being used with this machine can remove water from the hole at at faster rate than a hand pump. This effectively tests the output to see if there is enough, and also if deepening the hole increases the yield.

The Consallen Forager-55 cable percussion borehole drilling rig: Cable-tool drilling

HAND PUMP

The hand dug well in togo shown above was fitted with a Consallen hand pump.

The well was completed using a plastic borehole casing, and back-filled before the concrete slab was laid and the pump stand mounted. By selecting clean sand & gravel from the excavated material a good 'gravel pack' can be made in the water-bearing zone. This provides a good wide area for water flow to the screen section of the casing in addition to some storage volume. In this instance, storage was not a major requirement for this high yielding well. Bailing with a 100 litre bucket at 2000 litres per hour did not measurably depress the water level.

Details of the pump can be found at this link: http://www.consallen.com/handpumps

Home: http://www.consallen.com

Consallen Group Sales Ltd., P.O. Box 2993, Sudbury, Suffolk CO10 0ZB, United Kingdom.
Tel/Fax: +44-(0)1787-247770; e-mail: sales@consallen.com