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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Small Island Developing States>


PART B - ALTERNATIVE TECHNOLOGIES

3. TECHNOLOGIES APPLICABLE TO SMALL HIGH, VOLCANIC ISLANDS

3.1 Freshwater Augmentation Technologies

3.1.1 Boreholes

Groundwater is the most common source of freshwater on small islands. It is used extensively on small, low-lying islands for most uses, including potable uses. It is also used on small, high islands, particularly those where surface water catchments do not exist or are too small or too difficult to develop. Dug wells and infiltration galleries, which are the preferred technologies on small, low-lying islands were described in Section 2 of Part B. This section covers technologies like boreholes and other types of deeper-water wells.

Technical Description

The same basic considerations that apply to dug wells also apply to boreholes. Boreholes are generally appropriate for use when the distance from the land surface to the water table is too great or geological conditions too difficult for alternatives such as dug wells or infiltration galleries to be satisfactorily used. As previously noted, a thorough hydrogeological investigation should be conducted prior to locating and selecting a groundwater abstraction system. A list of the different groundwater assessment technologies can be found in Section 1 of Part B.

There are a number of well construction techniques including driving, jetting or drilling (boring). Drilling is the most common. No single water well construction technique is applicable for all conditions. The most appropriate technique will depend on hydrogeological, environmental, social, cultural, and economic conditions at the site of the proposed well. Detailed information on these techniques, particularly different methods of drilling, well construction, and development can be found in other specialised literature.

In general, every well consists of two main elements, the casing and the intake (Figure 28). The casing serves as a housing for the pumping equipment, and as a vertical conduit for the water flowing upward from the aquifer to the pump intake. The part of the borehole length serving as a conduit may be left uncased when the well is constructed in consolidated rock. This intake portion of the well, when constructed in unconsolidated and semi-consolidated aquifers, is generally screened to prevent sediment from entering the borehole with the water and to serve as a structural retainer supporting the loose material on the sides of the hole. After the completion of each well, its performance must be assessed normally by conducting a pumping test which provides information about yield and drawdown of the well. Pump selection has been described previously in Section 2 of Part B. Detailed information and specifications of the different types of pumps are obtainable from pump manufacturers and suppliers.

Extent of Use

This technology is extensively used on the high islands of Fiji, French Polynesia, American and Western Samoa, Vanuatu, Solomon Islands, Hawaii, Seychelles, Mauritius, Jamaica, Montserrat, Aruba, and Barbados.

Operation and Maintenance

The operation and maintenance of water wells or boreholes mainly concerns the pump unit and associated equipment. Relevant information relating to the operation and necessary maintenance of specific pumps is provided by pump manufacturers and suppliers. In addition, the well, itself, should be checked periodically to ensure that the flow of water into the well through its screens is not impeded.

Figure 28

Figure 28. Schematic diagram of a typical well (Davis and Lambert, 1995)

Level of Involvement

Professional engineers or hydrogeologists are required for investigations, initial well design, drilling supervision, well development and testing, and pump selection. Experienced drilling teams are also required. Some small islands have their own drilling teams, while most have contract drilling teams that can be used as necessary.

Costs

Construction costs include the costs of drilling and pump installation. Operational costs include the costs of energy required for pumping and the cost of maintaining the equipment. In Western Samoa, typical groundwater development costs in 1995 were as follows:

* Construction of 50 m depth borehole for submersible pump unit (drilling and case only) $430/m3

* Construction of 25 m depth borehole for handpump (drilling and case only) $340/m3

* Operation cost to supply pumped groundwater (diesel driven) $0.19/m3

Effectiveness of the Technology

Assuming the wells have been correctly sited, this is a very efficient technology. Wells are a very reliable sources of freshwater, even during extended dry periods. Furthermore, in the case of deep wells, the risk of contamination of the water is lower than in shallow wells.

Suitability

This technology is suitable for use on islands where there are adequate volumes of groundwater available. Groundwater abstraction should be considered as an appropriate water supply option whenever possible.

Advantages

Groundwater abstraction using this technology provides a reliable quantity of freshwater at a reliable quality when abstracted at a rate equal to or less than the sustainable yield of the aquifer.

Disadvantages

Development of borehole wells requires skilled drillers and trained operators, and sometimes incurs high construction costs. Deep wells have high operating and maintenance costs compared with shallow wells. Because of the specialised nature of the submersible pumps used with this technology, spare parts may not always be accessible. Overpumping of wells can lead to seawater intrusion into the aquifer, particularly in unconsolidated substrates.

Cultural Acceptability

Land ownership issues may preclude the drilling of wells in otherwise favourable areas.

Further Development of the Technology

The technology is already well developed. However, minor improvements in drilling technologies, and in the materials and equipment, used in constructing deep wells and for pumping are continually being made.

Information Sources

Anon. 1979. Proceedings of the Seminar on Selected Water Problems in Islands and Coastal Areas with Special Regard to Desalination and Groundwater. Pergamon Press, New York.

Basak, P. 1982. Groundwater Buildup and Depletion in Islands During Monsoon and Summer. Journal of Hydrology, 66:265-275.

Bear, J. 1979. Hydraulics of Groundwater. McGraw Hill, New York.

Bouwer, J. 1989. Estimating and Enhancing Groundwater Recharge. In: M.L. Sharma (Ed.), Groundwater Recharge, Balkema, Rotterdam. pp. 1-10.

Brodie, J.E., G.W. Lee, and R.A. Prasad 1983. Well-water Quality in South Pacific Island States. South Pacific Journal of Natural Sciences, 4:14-32.

Clark, L. 1988. The Field Guide to Water Wells and Boreholes. Geological Society of London Professional Handbook Series, Geological Society of London, London.

CSC [Commonwealth Science Council] 1984. Workshop on Water Resources of Small Islands. Commonwealth Science Council Technical Publications Series No. 143, Part 1; Commonwealth Science Council Technical Publications Series No. 154, Part 2; Commonwealth Science Council Technical Publications Series No. 182, Part 3.

Custodio, E. and G. Bruggeman 1987. Groundwater Problems in Coastal Areas. UNESCO Studies and Reports in Hydrology No. 45, UNESCO, Paris.

Davis, J. and R. Lambart 1995. Engineering in Emergencies. Intermediate Technology Publications, London.

Detay, M., E. Alessandrello, P. Come, and I. Groom 1989. Groundwater Contamination and Pollution in Micronesia. Journal of Hydrology, 112:149-170.

ESCAP [Economic and Social Commission for Asia and the Pacific] 1987. Water Resources Development in Asia and the Pacific: Some Issues and Concerns. United Nations Water Resources Series No. 62.

ESCAP [Economic and Social Commission for Asia and the Pacific] 1989. Development and Conservation of Ground-water Resources and Water-related Natural Disasters and Their Mitigation in Selected Least Developed Countries and Developing Island Countries in the ESCAP Region. United Nations Water Resources Series No. 66.

Everett, L.G. 1984. Groundwater Monitoring. Genium Publishing Co., Schenectady, NY

Foster, S.D. 1985. Potable Groundwater Supplies and Low-cost Sanitary Engineering - How Compatible?, Natural Resources Forum, 9(2):125-132.

Freeze, R.A. and J.C. Cherry 1979. Groundwater. Prentice Hall, New York.

Hofkes, E.H. (Ed.) 1983. Small Community Water Supplies, Technology of Small Community Water Supply Systems in Developing Countries. International Reference Centre for Community Water Supply and Sanitation Technical Paper Series No. 18, John Wiley and Sons, London.

Huisman, L. and T.N. Olsthoorn 1981. Artificial Groundwater Recharge. Division of Sanitary Engineering, Delft University of Technology, Delft.

Inouchi, K. and T. Kakinuma 1988. Groundwater Pollution in an Island - Seawater Intrusion and Fertilizer Dissolution. In: Proceedings of the Sixth World Congress on Water Resources, International Water Resources Association, Ottawa. pp. 420-429.

Kerr, C. 1988. Community Water Development. Intermediate Technology Publications, London.

Kinzelbach, W. and W. Schaefer 1989. Coupling of chemistry and transport. Groundwater Quality Management: Quantity and Quality, 188:237-260.

Kruseman, G.P. and N.A. de Ridder 1970. Analysis and Evaluation of Pumping Test Data. TNO Bulletin No. 11, International Institute for Land Reclamation and Improvement, Waegeningen.

Lau, L.S. and J.F. Mink 1987. Organic Contamination of Groundwater: a Learning Experience. Journal of the American Water Works Association, 79(8):37-42.

Libbrecht, D. 1988. Gizo (Western Province): Groundwater Development. Internal Report SOL/29. United Nations Department of Technical Cooperation for Development, Project RAS/97/009: Solomon Islands, United Nations Development Programme, New York.

McGowan, R. and J. Hodgkin 1989. Pump Selection: A Field Guide for Developing Countries. Water and Sanitation for Health Project Technical Report No. 61, United Nations Development Programme, New York.

Mink, J.F. 1986. Groundwater Resources and Development, Trust Territory of the Pacific Islands. United States Environment Protection Agency Report, Region 9, Washington. 27 pp.

Nielsen, G.L. and J.M. Widjaya 1989. Modelling of Ground-water Recharge in Southern Bali, Indonesia. Groundwater, 27(4):473-480.

Peterson, F.L. 1981. Geological and Hydrological Framework: A History of Development. In: F.N. Fujimura and W.B. Chang (Eds), Groundwater in Hawaii. A Century of Progress, Water Resources Research Center, University of Hawaii. pp. 1-14.

Peterson, F.L. 1984. Hydrogeology of High Oceanic Islands. In: Proceedings of the Regional Workshop on Water Resources of Small Islands, Commonwealth Science Council Technical Publication Series No. 154, Part 2, 431-435.

Preble, R.E. and R. Roark 1988. The Selection of Drilling Rigs for Rural Water Supply. Water and Sanitation for Health Project Technical Report No. 42, United Nations Development Programme, New York.

UNESCO [United Nations Education Scientific and Cultural Organization] 1991. Hydrology and Water Resources of Small Islands, A Practical Guide. Studies and Reports on Hydrology No. 49, UNESCO, Paris. 435 pp.

United Nations Department of Technical Cooperation for Development 1983. Ground Water in the Pacific Region. Natural Resources/Water Series No. 12, Report No. ST/ESA/121, United Nations, New York.

United States Geological Survey 1984. National Water Summary 1984: Hydrologic Events, Selected Water-quality Trends, and Ground-water Resources, United States Geological Survey Water-Supply Paper No. 2275, Reston.

Urish, D.W. 1981. Discussion of 'A groundwater resources study of a Pacific ocean atoll, Tarawa, Gilbert Islands' by Lloyd, J.W., Miles, J.C., Chessman, G.R. and Bugg, S.F. Water Resources Bulletin, 17(5):899-900.

Vacher, H.L. 1988b. Ground Water in Barrier Islands: Theoretical Analysis and Evaluation of the Unequal-sea Level Problem. Journal of Coastal Research, 4(1):139-148.

Wiseman, R. 1985. Hand Rig for Well Boost. World Water, August, 19.

Yee, J.J.S. 1986a. Trust Territory of the Pacific Islands, Saipan, Guam and American Samoa: Ground-water Quality, National Water Summary 1986. US Geological Survey Water-Supply Paper No. 2325, 483-488.

Yee, J.J.S. 1986b. Hawaii Ground-water Quality, National Water Summary 1986. US Geological Survey Water-Supply Paper No. 2325, 223-228.

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