Page 289 - Hydrogeology Principles and Practice

HYDC07 12/5/05 5:33 PM Page 272

272 Chapter Seven

Table 7.4 Percentage distributions of
Jaffna municipal area Valigamam region Valigamam region
distances between pit latrines and dug
wells and length of lining in dug wells in
Distance (m) % dug wells Distance (m) % dug wells Lining (m) % dug wells
the Jaffna Peninsula, Sri Lanka. After
Rajasooriyar et al. (2002).
<1.5 5.7 <10 13.6 <1.0 7.4
1.6–3.0 8.0 10.1–20.0 48.2 1.1–3.0 41.5
3.1–4.5 5.7 >20.1 38.2 >3.1 38.5
4.6–6.0 6.8 Damaged 12.6
>6.1 73.8

secure self sufficiency in food production. Also, the microbes, and also in the adsorption, breakdown and
use of irrigation to provide crop moisture require- removal of many chemicals. Given the potential for
ments poses the risk of leaching of nutrients, espe- groundwater pollution in developing countries, pro-
cially from thin, coarse-textured soils. Increases in tection of water supplies requires a broad-based
chloride, nitrate and trace elements will result from approach that should include a strategy of minimum
excessive land application of waste water, sewage separations, depending on the hydro-geological situa-
effluent and sludge, and animal slurry. tion, between a groundwater supply source and pit
Other pollution sources occur in urban areas latrines for microbiological protection. The water
where increasing numbers of small-scale industries, laws and codes of practice of many countries require
such as textiles, metal processing, vehicle mainten- a minimum spacing between groundwater supply
ance and paper manufacture, are located. The quant- source and waste disposal unit of 15 m. There is,
ities of liquid effluent generated by these industries however, considerable pressure to reduce this per-
will generally be discharged to the soil, especially in mitted spacing to as little as 5 m in some developing
the absence of specific control measures and the pro- countries such as Bangladesh and parts of India and
hibitive cost of waste treatment. Larger industrial Sri Lanka (Table 7.4), often resulting from the lack
plants generating large volumes of process water will of space in very densely populated settlements. This
commonly have unlined surface impoundments for example of law governing the location of waste dis-
the handling of liquid effluents. posal units demonstrates that criteria for ground-
Unless shallow dug wells have adequate protec- water pollution protection is rather arbitrary, based
tion from surface water runoff and are sufficiently dis- on limited or no technical data.
tant from pit latrines, this type of groundwater source Other practical recommendations include the
is vulnerable to both water table decline in drought delineation of dilution zones of modified land use to
periods, and to contamination. Although simple alleviate the impact of polluting activities (Foster 1985)
measures such as boiling can help combat water- and the replacement of unsanitary municipal dump-
borne diseases, it is understandable that the large aid sites, or tips, by controlled landfills using simple tech-
programmes in the last few decades have focused nology at a sustainable and realistic cost appropriate
on drilling deeper boreholes and installing simple to gross domestic product (GDP). For example, in
pumping apparatus. As a result, hand-pumped tube Tanzania and the Gambia, controlled but unlined
wells are very common across much of Africa and landfills at existing quarry sites have been proposed
Asia, but even these sources are now associated with that will operate on a dilute and disperse basis. Risk
problems, as illustrated graphically by the natural assessments demonstrate that local aquifers are not at
occurrence of arsenic in groundwater in Bangladesh risk, such that some local groundwater contamina-
and West Bengal in India (Box 7.6). tion is acceptable in return for major improvements
The natural soil profile can be effective in purifying in health and hygiene resulting from the removal of
human wastes, including the elimination of faecal the current dumpsites (Griffin & Mather 1998).