UNEP/UNESCO/UNCH/ECA
URBAN POLLUTION OF SURFICIAL AND GROUNDWATER AQUIFERS VULNERABILITY IN
AFRICA
EARLY WARNING REPORT FOR KETA SHALLOW AQUIFER
Dr. Bruce Banoeng-YakuboNational CoordinatorGeology Department. University of Ghana
ORDER OF PRESENTATION
INTRODUCTION RESULTS HYDROGEOLOGICAL CONDITIONS ACTIVITIES CONCLUTIONS
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DENU
NSAWAM
BEGORO
AKATSI
DODOWA
SOMANYAADIDOME
ATIMPOKU
SOGAKOPE
AMASAMAN
ADA FOAH
KOFORIDUA
TEMA MUNICIPAL AREA
ACCRA
Keta
50 0 50 100 Kilometers
Map of souteastern Ghana showing insert of the geology of the Keta basin
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Annual_rain.shpBound.shpClipbound.shpContour.shpContoursp.shpElevation.shpMarshp.shpRiversp.shpContour1.shpVolta_lk.shpWaterb_body.shp
Map of southeastern Ghana showing an insert of part of the Keta basinAcid & Basic Gneiss & SchistsMarine Series Of Sh.,Ss.& LmstRed Cont. Dep. Of Limonitic Sand Sandy CUnconso. Sand, Clay & Gravel
Water bodies# Towns
Roads.shp
LEGEND
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
Geological map of the Keta Basin showing the Project area
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'WOE (k48)
HAVE (tk20)
VODZA (k26)
ACHAUE (k40)
TSIAME (k34)
KEDZI (k17)
ANYAKO (k18)
ANLOGA (k39)
)SASIAME(k38)
AGAVEDZI (k23)
ATITO(prop/bh.)
ATIAVE (k32,32a)
KETA (k21,26,50)
BLEKUSU (k24,A,28)
ALAKPLE (prop/bh.)
kk3
kk21
kk30kk39
DN 3
TG 1 TG 2
TG 4
TG 10
ket 18
# Ketapoint.shp# Gh_dist_cap.shp
Geologyp.shpAcid & Basic Gneiss & SchistsMarine Series Of Sh.,Ss.& LmstRed Cont. Dep. Of Limonitic Sand Sandy CUnconso. Sand, Clay & Gravel
# Ketaboys34.dbf# Sampling points
Keta LagoonArea of current sampling
' TownsMarsh land
10 0 10 20 Kilometers
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6 6
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6
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1
1
6 6
The project for Ghana started late so the first sampling was done in June 2002. 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 2002. 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 .
Figure 1. Distribution of Mean Monthly Rainfall and Pan Evaporation in the Keta Area
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Time (Months)
Mea
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on
thly
Rai
nfa
ll &
P
an E
vap
ora
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mm
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Monthly Rainfall (mm) Monthly P an Evaporation (mm)
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.
Figure 2. Variation in Piezometric Level at Tegbi in the Study Area
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1.5
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2.5
3-Ju
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13-J
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3-Ju
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13-J
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23-J
ul-0
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ug-0
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12-A
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ep-0
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Date
Wat
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evel
(m
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TG1
TG2
TG3
TG6
TG7
TG8
TG10
TG11
TG12
TG13
TG16
TG17
TG18
Figure 3. Variation in Piezometric Level at Tegbi in the Study Area
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Wat
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evel
(m) TG1
TG2
TG3
TG6
TG7
TG8
TG10
TG11
TG12
TG13
TG16
TG17
TG18
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.
5.1 Variation in pH
Figure 3. Variation in pH with Time at Selected Sites in Study Area
66.26.46.66.8
77.27.47.67.8
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03-Jun-02
13-Jun-02
23-Jun-02
03-Jul-02
13-Jul-02
23-Jul-02
02-Aug-02
12-Aug-02
22-Aug-02
01-Sep-02
11-Sep-02
Time
pH
DN2
DN4
DN6
DN9
Dn10
DN11
DN16
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.
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kk3
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DN 3
TG 1 TG 2
TG 4
TG 10
ket 18
VUIDUDU
HEKPA
TEGBI
DEREKE
KPOKPE
WOGONA
AFEDOME
DZIAKPOR
KLAMATSI
KEDZEKOPE
DZELUKOPE
AGBADATOR
TETEVIKOPE
ABUTSIAKOPE
AELEGLOKOPE
#S Keta
# Ketaboys34.dbf
Ketangeology.shpRed Cont. Dep. Of Limonitic Sand Sandy CUnconso. Sand, Clay & Gravel
Keta Lagoon# Ketantowns.shp
Map of conductivity distribution in the Keta Basin< 500500 - 10001000 - 15001500 - 20002000 - 2500> 2500
# Sampling pointsMarsh land
% TownsRoadsp.shp
3 0 3 Kilometers
Conductivity variations in Parts of the Keta area
LEGEND
Figure 4. Temporal and Spatial Variation in Conductivity
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Location
Con
duct
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(uS/
cm)
Date: 14 &15 J ul 2002 Date: 31st J uly 2002 Date:14 &15 J ul 2002 Date: 31st J uly 2002
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.
Figure 5. Fluoride and Choride Variation in Space at Keta (Date: 13/06/02)
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Location
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(mg
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4000
6000
8000
10000
12000
14000
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lori
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(mg
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Cl-
F-
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
Figure 6. Variation in Nitrate Concentration in Study Area
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Nitr
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g/l)
KET1
KET4
KET5
KET8
KET10
KET12
KET14
KET16
KET17
KET18
KET20
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VUI
VODZA
HEKPADEREKE
ADZIDZE
KEDZEKOPE
DZELUKOPE
AGBADATOR
TETEVIKOPE
ABUTSIAKOPE
#
Keta
# Unesco-keta corrected.txtBound_line.shp
Geologyp.shpAcid & Basic Gneiss & SchistsMarine Series Of Sh.,Ss.& LmstRed Cont. Dep. Of Limonitic Sand Sandy CUnconso. Sand, Clay & Gravel
Nitrate concentration distribution in the Keta area0 - 1010 - 2020 - 3030 - 4040 - 5050 - 6060 - 7070 - 8080 - 9090 - 100100 - 110110 - 120120 - 130130 - 140140 - 150150 - 160160 - 170170 - 180180 - 190190 - 200
Road# Setllement.shp
Keta Lagoon
3 0 3 6 Kilometers
Nitrate concentration distribution in the keta area
LEGEND
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8.0 BACTERIOLOGICAL ANALYSIS The bacteriological analysis was carried out for 16 shallow wells in the study area. The samples were taken on 28th September 2002. 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 .
Figure 8. Bacteriological Quality of Selected Wells in Study Area
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KK37KK39
TG3
DN9KET6
TG17
DN2KET16
KK9DN16
DN10
KET3KK33
KK17KK29
KET17
Station
Ba
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un
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9 CONCLUSIONS. 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)TG1 0.78TG2 1.36TG3 0.69TG6 0.89TG7 0.84TG8 0.70TG10 0.70TG11 0.48TG12 0.52TG13 2.38TG16 0.88TG17 0.73 Table 2. Variation in pH with Time and Location at Dzelekorfe-Norlivime Station pH DN2 7.21DN4 6.91DN6 7.64DN9 7.42DN10 7.49DN11 7.32DN12 7.29DN14 7.34DN16 7.43
Table 3 Variation in Conductivity with Time and Location at Tegbi Location/Date 15-June 02 31Jul-02 15Aug 02 4-Sept-02TG1 14160 15180 155501 17300TG2 719 593 776 821TG3 1093 1079 1059 1008TG6 3360 3550 3800 3720TG7 808 783 786 861TG8 1228 1236 1237 1234TG10 3710 3460 3360 3440TG11 744 654 741 759TG12 438 433 443 413TG13 8960 7140 6630 6720TG16 1828 1739 1706 1596TG17 602 659 591 452TG18 383 361 270 Table 4. Fluoride and Chloride Concentrations in Shallow Aquifers in mg/l Location/Date 15-June 02 31Jul-02 15Aug 02 4-Sept-02 TG1 0.66 0.88 0.42 1.6
TG2 8.78 0 0 0
TG3 21.28 0 1.36 0
TG6 20.58 0 14.02TG7 17.78 0.22 0.98 0.0TG8 0 0 0.68 1.82TG10 0 0.2 0 0TG11 20.08 0.14 0 0TG12 9.94 0 1.06 0TG13 13.56 0.18 11.08 2.02TG16 19.02 0.16 18.44 0TG17 18.12 0 1.22 0TG18 0.36 1.14 0
Table 5. Variation in Nitrate concentration at Keta Area Location/date 15-June 02 31Jul-02 15Aug 02 4-Sept-02 Ket1 19.14 53.32 43.62
38.24Ket4 36.14 53.9 20.04
32.40Ket5 251.1 24.34 37.9
46.34Ket6 54.16 57.76 40.42
0Ket8 79.72 79.56 51.28
79.78Ket10 167.28 151.1
96.12Ket12 14.78 2.52 9.28
0Ket14 103.34 19.24 19.56
19.78Ket16 22.16 153.04 143.92
139.78Ket17 130.04 3.94 46.42
13.7Ket18 16.42 37.16 53.6
53.0Ket20 62.84 1.66 1.0
5.3 Table 6 Variation in Nitrate Concentration with time at DN 16 in Dzelekorfe –Norlivime Date Concentration (mg/l)14 June 11.21 August 7.1415August 19.824 September 23.38
Table 7 Distribution of Number of Bacteriological Species by Sampling StationsStation No. Number of Bacteriological CountsKK37 550KK39 130TG3 50DN9 1800KET6 1600TG17 1800DN2 1600KET16 1800KK9 130DN16 425DN10 900KET3 1800KK33 1800KK17 1600KK29 550KET17 1600