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

#

#

#

##

#

#

#

##

#

#

#

#

#

#

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

N

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

N

#######################################################

#

##

#########

####

######

####

####

# #### ###

##

########################################################

#

##

#########

####

######

####

####

# #### ###

##

#######################################################

#

##

#########

####

######

####

####

# #### ###

##

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'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

1

1

6 6

1

1

6

6

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

0

20

40

60

80

100

120

140

160

180

200

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Time (Months)

Mea

n M

on

thly

Rai

nfa

ll &

P

an E

vap

ora

tio

n (

mm

)

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

0

0.5

1

1.5

2

2.5

3-Ju

n-02

13-J

un-0

2

23-J

un-0

2

3-Ju

l-02

13-J

ul-0

2

23-J

ul-0

2

2-A

ug-0

2

12-A

ug-0

2

22-A

ug-0

2

1-S

ep-0

2

11-S

ep-0

2

Date

Wat

er L

evel

(m

)

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

0

0.5

1

1.5

2

2.5

Date

Wat

er L

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

8

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.

##########

##

#####

####

##

##

#### ##

###

#####

##

###

# ########

##

#

#

#

# ##

#

##

##

#

#

#

##

##

##

##

#

#

##

## #

#

#

##

#

##

#

#

#

#

###########

##

#####

####

##

##

#### ##

###

#####

##

###

# ########

##

#

#

#

# ##

#

##

##

#

#

#

##

##

##

##

#

#

##

## #

#

#

##

#

##

#

#

#

#

%

%

%

%%

%

%%

%

%

%

% %

%

%

%

kk3

kk21kk30kk39

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

0

2000

4000

6000

8000

10000

12000

14000

16000

Location

Con

duct

ivity

(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)

0

5

10

15

20

25

Location

Flu

ori

de

(mg

/l)

0

2000

4000

6000

8000

10000

12000

14000

Ch

lori

de

(mg

/l)

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

0

50

100

150

200

250

300

Date

Nitr

ate

Con

cent

ratio

n (m

g/l)

KET1

KET4

KET5

KET8

KET10

KET12

KET14

KET16

KET17

KET18

KET20

##########

##

#####

####

##

##

#### ##

###

#

#####

####

# ######

####

#

#

#

# ##

#

##

##

#

#

#

##

##

##

##

#

#

##

## #

#

#

##

#

##

#

#

#

#

#

#

#

#

#

##

##

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

N

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

0

200

400

600

800

1000

1200

1400

1600

1800

2000

KK37KK39

TG3

DN9KET6

TG17

DN2KET16

KK9DN16

DN10

KET3KK33

KK17KK29

KET17

Station

Ba

cte

ria

l Co

un

t

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