Matematyica

ARTICLE IN PRESS
Journal of African Earth Sciences xxx (2010) xxx–xxx

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Journal of African Earth Sciences
journal homepage: www.elsevier.com/locate/jafrearsci

Analysis of groundwater quality using multivariate and spatial analyses in the Keta basin, Ghana
Sandow Mark Yidana *, Bruce Banoeng-Yakubo, Thomas M. Akabzaa
Department of Earth Science,Box LG 58, University of Ghana, Legon, Accra, Ghana

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A holistic assessment of the quality of groundwater from the shallow unconfined aquifers of the Keta strip of the Keta basin has been conducted using multivariate statistical and spatial analyses. A groundwater classification scheme has been developed for groundwater in the area using a robust waterquality index (WQI) modified for the case of the Keta basin. On the basis of the WQI so computed, groundwater in the area has been spatially classified into ‘good’, ‘fair’, and ‘marginal’ water types using ordinary kriging developed from a well fitted linear semivariogram function. This study finds that the salinity of groundwater in the basin is largely attributed to mineral weathering and seawaterintrusion. Groundwater is stable within kaolinite and Na-smectite field, suggesting the predominance of Na-rich silicate minerals over the high temperature Ca-rich minerals. There are localized influences of domestic waste discharge and agricultural activities on the hydrochemistry of groundwater in the area. Where these effects are high, high nitrate and fluoride concentrations have been noted. Fourgroundwater clusters have also been distinguished: clusters 1 and 4 are low salinity Ca–HCO3 waters distinguished by differences in pH, whereas clusters 2 and 3 represent high and intermediate salinity Na–Cl waters respectively. This study further finds that clusters 1 and 4 present the best water types for irrigation purposes in the Keta basin. On account of high salinity, cluster 2 members arenot suitable for irrigation of any crop in the basin. Sodium adsorption ratio (SAR) appears to display weak seasonal variations due to the influence of seawater intrusion, whose effects vary with the level of the water table relative to sea level. During dry seasons when the water table is low, saline water intrusion elevates the content of sodium in groundwater. This is reflected in the SAR values insome of the wells sampled. Ó 2010 Elsevier Ltd. All rights reserved.

Article history: Received 5 December 2009 Received in revised form 4 March 2010 Accepted 8 March 2010 Available online xxxx Keywords: Keta basin Groundwater Multivariate Water quality index Kriging

1. Introduction In the Keta basin attention on groundwater abstraction from the aquifers has increased during the last decade(Bannerman, 1994; Jorgensen and Banoeng-Yakubo, 2001; Helstrup et al., 2007). This is due to rising water demands from a growing population and an increased electrical conductivity (EC) of especially near coastal shallow groundwater in the Keta basin (Helstrup et al., 2007). A major problem in drinking water quality and management of domestic water supply in the Keta basin is salinization ofgroundwater in dug wells and in deep boreholes (Gill, 1969; Bannerman, 1994; Helstrup et al., 2007). A lot of prospective sites for wells and boreholes were not completed due to salinity problems in the aquifers, and some existing deep wells and dug wells have been abandoned due to increasing salinity over time. Almost all communities in the basin have relied on groundwater from the perched shallowaquifers to meet both domestic and irrigation needs over the past several years. However, sanitary conditions around the wellhead in most cases are very poor leading to contamination from surface sources.
* Corresponding author. Tel.: +233 203143351. E-mail addresses: yidanas117@gmail.com, smyidana@ug.edu.gh (S.M. Yidana). 1464-343X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved....