UNEP/UNESCO/UNCH/ECA URBAN POLLUTION OF SURFICIAL AND GROUNDWATER AQUIFERS VULNERABILITY IN AFRICA EARLY WARNING REPORT FOR KETA SHALLOW AQUIFER Dr. Bruce Banoeng-Yakubo National Coordinator Geology Department. University of Ghana

ORDER OF PRESENTATION INTRODUCTION RESULTS HYDROGEOLOGICAL CONDITIONS ACTIVITIES CONCLUTIONS

OBJECTIVES OF STUDY assess the groundwater vulnerability in a selected urban community identify hot spots and major threats on these aquifers in the selected area develop policy options for better safeguarding surficial and groundwater aquifers in the area, including pollution and health mitigation. establish an early warning network for possible water supply contamination

HYDROGEOLOGICAL CONDITIONS The Keta-Anloga area is underlain by recent unconsolidated beach sands and lagoon clays, which deepen westwards towards the Volta river estuary. The recent deposits rest on a series of continental beds of Middle Tertiary age. The rocks are unconsolidated limonitic argillaceous sands and gritty sands with persistent gravelly beds at their base. The gravelly beds are persistent from the Ghana- Togo border and they are about 2 m thick. The Middle Tertiary rocks have very permeable soils and subsoils resulting in low run-off as a greater part of the rainfall infiltrate into them and percolate into the groundwater

The project for Ghana started late so the first sampling was done in June This covered as many sampling points as 106 in order to enable us identify the wells to monitor. Subsequently, these were reduced to 52. Four measurement campaigns were undertaken within the period from mid-June to September The monitoring was concentrated on the shallow aquifer. This report is based on the results of these four measurement campaigns.

Selection of Survey Four main zones were established in the study area and sampling was done at these four zone. These zones are: Keta, Kedzikorfe, Dzelekorfe-Norlivime and Tegbi. For simplicity, the following abbreviations have been made: KET denotes the Keta area; KK denotes Kedzikorfe, DN denotes Dzelekope-Norlivemi and TG stands for Tegbi.

CLIMATE  The study area lies within the Dry Equatorial Climatic region of Ghana. This region is the driest in the country.  It has two clearly defined seasons; a rainy season and a dry season. The rainy season exhibits double maxima, the main occurring between April and June and the minor one between September and October. June is normally the wettest month.  In general, the relative humidity is high in the mornings and at night but is at a minimum in the afternoon. Instantaneous values as high as 96% and as low as 63% have been recorded the morning and afternoon respectively.  The mean annual rainfall for Keta based on data spanning the period from 1913 to 1992 was 800.8mm. The highest mean monthly value of 187.5mm occurs in June while the minimum mean monthly value of 10.6mm occurs in January.  Annual potential evaporation of rate of 1785 mm/annum. This figure is high compared to the annual precipitation figure. On a monthly basis, it is only in June that rainfall exceeds potential evaporation.

WATER LEVEL VARIATIONS The water level variation is presented for Tegbi area. From the graph shown in Figure, the following was observed:  there was a general rise in water level from June through August to September. However, in a few cases, water level fell within the period in question.  Because most of the wells are in use, some of the observations are a function of water use just before sampling. It is believed that the monitoring period (June to September) was too short to observe any trends in the piezometric level.

VARIATION OF pH AND CONDUCTIVITY  At the peak of the rainy season, the pH was high at all sampling points except one. During the second campaign, the pH value had dropped in almost all the sampling stations under consideration.  This second campaign was towards the end of the major rainy season. There was a general rise in the pH again during the third campaign, but this was more noticeable for three stations namely DN2, D10 and DN11  Between the third and fourth campaigns, the variation in pH was less noticeable except for one station (DN10) that exhibited a clear reduction. The changes in pH values over the measurement period ranged from a low of 6.6 to a high of 7.6.

5.1Variation in pH

VARIATION OF CONDUCTIVITY  There is high variation of conductivity spatially. The water conductivities of the aquifer towards Keta and close to the lagoon and sea are very high and relates to the high salinity recorded in these areas. Most of these areas are less than 2m above sea level.  However, intensive agricultural practices especially pumping of water to irrigate vegetables and other food crops have rendered the aquifer system vulnerable to saltwater intrusion.

FFLUORIDE AND CHLORIDE CONCENTRATION  In general, the level of Fluoride in the water samples are higher than the recommended 1.0 mg/l for drinking water. The mean value was 1mg/l for the zone under consideration.  Chloride levels in the water varied from below 2000mg/l to over 12,000 mg/l. Clearly the range for drinking water is far below the values obtained in this study. These values and their spatial distribution compare favourably with the conductivity measurements discussed in Figure.

VARIATION IN NITRATE CONCENTRATION IN STUDY AREA  Nitrate concentration in the study area is discussed using results from the Keta zone. In this zone, the concentration of nitrate varied between 0 and 251 mg/l.  In general the nitrate concentration decreased between June and August. This may be attributed to the fact that in June, runoff carried a lot of nitrate from farms and other areas in to the shallow aquifer.

VARIATION IN NITRATE CONCENTRATION IN STUDY AREA

8.0BACTERIOLOGICAL ANALYSIS The bacteriological analysis was carried out for 16 shallow wells in the study area. The samples were taken on 28 th September All necessary precautions were taken to preserve sample quality until the analysis were carried out within 24 hours of sampling. The results are presented in table below and illustrated in the following figure.

9CONCLUSIONS.  Nitrate (NO3), Ammonium and Phosphate concentrations were all high, exceeding the WHO guide line values for drinking water.  The same observation was made for Fluoride and Chloride concentrations. In general, conductivity was also above the WHO guideline values for drinking water for most of the locations. Fluoride and Chloride concentrations in the Keta area show that both are above the WHO recommended limits for drinking water with mean values of 1mg/l and 999mg/lrespectively.  The bacteriological quality of the water was bad, presenting both total and feacal coliforms in very high numbers. This is not surprising because of the nature of the soil (sandy) and the poor sanitation in some of the area.

PERSPECTIVES It is clear that the Keta-Anloga area is very polluted. The main thrust of subsequent sampling will be to identify the actual pollution areas apart from salinity from both the sea and the lagoon To delineate the freshwater-saline interfaces in order to establish monitoring points along them. To consolidate the monitoring process in order to determine long term trends and to also establish a network of monitoring wells in the Anloga area where irrigation and the use of manure and fertilizer is intensive. To disseminate our findings through the District Assembly and Community Water and Sanitation Agency and EPA that will provide a platform for public discussion.

Table 1. Variation in Piezometric Water Level With Time Station No.Static water level (m) TG10.78 TG21.36 TG30.69 TG60.89 TG70.84 TG80.70 TG TG TG TG TG TG Table 2. Variation in pH with Time and Location at Dzelekorfe-Norlivime StationpH DN27.21 DN46.91 DN67.64 DN97.42 DN DN DN DN DN167.43

Table 3 Variation in Conductivity with Time and Location at Tegbi Location/Date15-June 0231Jul-0215Aug 024-Sept-02 TG TG TG TG TG TG TG TG TG TG TG TG TG Table 4. Fluoride and Chloride Concentrations in Shallow Aquifers in mg/l Location/Date15-June 0231Jul-0215Aug 024-Sept-02 TG TG TG TG TG TG TG TG TG TG TG TG TG

Table 5. Variation in Nitrate concentration at Keta Area Location/date 15-June 0231Jul-0215Aug 024-Sept-02 Ket Ket Ket Ket Ket Ket Ket Ket Ket Ket Ket Ket Table 6 Variation in Nitrate Concentration with time at DN 16 in Dzelekorfe –Norlivime DateConcentration (mg/l) 14 June August August September23.38

Table 7 Distribution of Number of Bacteriological Species by Sampling Stations Station No.Number of Bacteriological Counts KK37550 KK39130 TG350 DN91800 KET61600 TG DN21600 KET KK9130 DN16425 DN10900 KET31800 KK KK KK29550 KET171600