UNEPUNESCOUNCHECA

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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
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ORDER OF PRESENTATION

• INTRODUCTION
• RESULTS
• HYDROGEOLOGICAL CONDITIONS
• ACTIVITIES
• CONCLUTIONS

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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

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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

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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.  
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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.
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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 . 

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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.
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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.
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  5.1 Variation in pH  
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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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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.  
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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.  
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VARIATION IN NITRATE CONCENTRATION IN STUDY
AREA  
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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 .
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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.  
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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.

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  Table 1. Variation in Piezometric Water Level
With Time   Station No. Static water level
(m) TG1 0.78 TG2 1.36 TG3 0.69 TG6 0.89 TG
7 0.84 TG8 0.70 TG10 0.70 TG11 0.48 TG12
0.52 TG13 2.38 TG16 0.88 TG17 0.73       Ta
ble 2. Variation in pH with Time and Location
at Dzelekorfe-Norlivime   Station pH   DN2 7
.21 DN4 6.91 DN6 7.64 DN9 7.42 DN10 7.
49 DN11 7.32 DN12 7.29 DN14 7.34 DN16
7.43          
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Table 3 Variation in Conductivity with Time and
Location at Tegbi   Location/Date 15-June
02 31Jul-02 15Aug 02 4-Sept-02 TG1 14160 15180
155501 17300 TG2 719 593 776 821 TG3 1093 10
79 1059 1008 TG6 3360 3550 3800 3720 TG7 80
8 783 786 861 TG8 1228 1236 1237 1234 TG10
3710 3460 3360 3440 TG11 744 654 741 759 T
G12 438 433 443 413 TG13 8960 7140 6630 67
20 TG16 1828 1739 1706 1596 TG17 602 659 59
1 452 TG18 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 14.02 TG7 17.78 0.22
0.98 0.0 TG8 0 0 0.68 1.82 TG10 0 0.2 0
0 TG11 20.08 0.14 0 0 TG12 9.94 0 1.06 0
TG13 13.56 0.18 11.08 2.02 TG16 19.02 0.16
18.44 0 TG17 18.12 0 1.22 0 TG18 0.36 1.1
4 0  
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  Table 5. Variation in Nitrate concentration at
Keta Area   Location/date 15-June
02 31Jul-02 15Aug 02 4-Sept-02   Ket1 19.14 53.3
2 43.62 38.24 Ket4 36.14 53.9 20.04 32.40 Ke
t5 251.1 24.34 37.9 46.34 Ket6 54.16 57.76
40.42 0 Ket8 79.72 79.56 51.28 79.78 Ket10
167.28 151.1 96.12 Ket12 14.78 2.52 9.28 0
Ket14 103.34 19.24 19.56 19.78 Ket16 22.16 1
53.04 143.92 139.78 Ket17 130.04 3.94 46.42
13.7 Ket18 16.42 37.16 53.6 53.0 Ket20 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 11.2 1 August 7.14 15August 19.82 4
September 23.38  
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Table 7 Distribution of Number of
Bacteriological Species by Sampling
Stations Station No. Number of Bacteriological
Counts KK37 550 KK39 130 TG3 50 DN9 1800 K
ET6 1600 TG17 1800 DN2 1600 KET16 1800 KK9
130 DN16 425 DN10 900 KET3 1800 KK33 18
00 KK17 1600 KK29 550 KET17 1600