Scramble to sink boreholes has experts worried

Experts are warning against the mass sinking of boreholes in Nairobi to deal with water shortage. The stability of some buildings in the metropolitan area could be compromised if drilling is not controlled, say hydrogeologists.

There are also concerns about the safety of borehole water, according to a recent World Bank report titled The Role of Ground Water in the Water-Supply of Greater Nairobi.

The report says there is the possibility of the ground caving in, putting buildings at risk of collapsing and the aquifers could also dry up. With high mineral content such as fluoride, the ground water has also led to tooth loss, says the report.

Cancer and death

It recommends the use of alternative sources of water for domestic purposes. In North Eastern Province, residents blame the underground water for cancer illnesses and deaths. In Marsabit alone, a number of human and livestock deaths have been reported. A report by the Water Resource Management (Warma) released in April this year said the water from boreholes and wells in the area was hazardous.

“It is evident that parameters, namely conductivity, sodium chloride, nitrate and total dissolved solids, are still above the World Health Organisation recommended values and pose human health risks if ingested,” reads part of the report. The desert has no piped water and people rely on boreholes and shallow wells. Records from a health centre in Kargi Location show that 38 people have died of cancer, associated with the use of underground water since 2006.

Eleven of them died last year and a similar number in 2006. In 2007 the number was 12. This year, four people had died by June 30, while two others were bedridden. Twice, hundreds of livestock have died after taking ground water. In Nairobi prolonged drought, partly blamed on the destruction of catchment areas, has depleted water volumes at the city’s three main reservoirs, forcing the City Council to sink 50 boreholes in a bid to alleviate rationing.

According to Warma, the current water shortage has resulted in accelerated drilling of boreholes all over the country. Currently there were 18,300 boreholes in different parts of the country, said Warma CEO Philip Olum. According to the World Bank report, the high number of boreholes coming up in the city could result into cave-ins as the underneath structure gets weakened.

“The presence of clay and silt layers in the shallow sub-soil and of unconsolidated fractures and cooling joints may be potential sources of subsidence,” says the World Bank report. Figures from the report show that the number of boreholes in the city has been growing rapidly, from less than 10 in precolonial times to 2,250 in 2001, excluding shallow wells sunk using household implements in homesteads.

It says the average depth and static ground water, which is permanent regardless of fluctuations in the water table, have been going down. In 1958, the ground water level was 80 metres deep but by 1996 it was edging to 140.

The report comes at a time when Kenya is seeking a private sector solution to its water woes in a deal that could see a steep rise in costs and deny access to water to millions of urban residents in the low income brackets.

The deal will see the opening of harvesting and purification of underground water, which would then be pumped to homes and offices through existing supply networks.

The deal was disclosed through invitation of tenders from qualified bidders who are expected to tap underground water and add 300,000 cubic metres to the supply in Nairobi, and the surrounding districts, before a national roll-out.

Five independent water producers will sink large boreholes around the capital to boost supply, said Water ministry officials.

Tender notices published a week ago in local dailies indicate that the investors will be required to drill boreholes at depths of between 600 and 1,000 metres and show evidence of having carried out similar assignments in the past decade. Experts, however, are worried about the long term effects of drilling more boreholes.

Water depletion

According to Mr Mike Lane, a Nairobi-based hydrologist, the increased number of boreholes, especially in Nairobi, would also see the underground water decline at a faster rate. For instance, Mr Lane says water level decline in Lang’ata has been recorded at 1.2 metres a month.

“The decline means that abstraction will be reduced ... in those few boreholes that are deep enough, pumping cost will increase while older boreholes will dry up.” While he says there is no possibility that sinking of more boreholes could cause an earthquake, Mr Lane warns that there is a possibility that major ground water depletion may reduce the capacity of the geological material underneath.