Physics and Chemistry of the Earth 66 (2013) 27–32

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Physics and Chemistry of the Earth

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An analysis of the chemical and microbiological quality of ground waterfrom boreholes and shallow wells in Zimbabwe

1474-7065/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.pce.2013.06.003

⇑ Tel.: +277 221 812 667.E-mail address: Ngoni.Moyo@ul.ac.za

N.A.G. Moyo ⇑Aquaculture Research Unit, School of Agricultural and Environmental Sciences, Faculty of Science and Agriculture, University of Limpopo(Turfloop Campus), Private Bag X1106,Sovenga 0727, South Africa

a r t i c l e i n f o

Article history:Available online 5 July 2013

Keywords:WaterPrincipalMicrobialQualityPollution

a b s t r a c t

Groundwater from boreholes and shallow wells is a major source of drinking water in most rural areas ofZimbabwe. The quality of groundwater has been taken for granted and the status and the potentialthreats to groundwater quality have not been investigated on a large scale in Zimbabwe. A boreholeand shallow well water quality survey was undertaken between January, 2009 and February, 2010 todetermine the chemical and microbial aspects of drinking water in three catchment areas. Groundwaterquality physico-chemical indicators used in this study were nitrates, chloride, water hardness, conductiv-ity, alkalinity, total dissolved solids, iron, magnesium, manganese, potassium, calcium, fluoride, sul-phates, sodium and pH. The microbiological indicators were total coliforms, faecal coliforms andheterotrophs. Principal component analysis (PCA) showed that most of the variation in ground waterquality in all catchment areas is accounted for by Total Dissolved Solids (TDS), electrical conductivity(EC), sodium, bicarbonate and magnesium. The principal dissolved constituents in ground water are inthe form of electrically charged ions. Nitrate is a significant problem as the World Health Organizationrecommended levels were exceeded in 36%, 37% and 22% of the boreholes in the Manyame, Mazoweand Gwayi catchment areas respectively. The nitrate levels were particularly high in commercial farmingareas. Iron and manganese also exceeded the recommended levels. The probable source of high iron lev-els is the underlying geology of the area which is dominated by dolerites. Dolerites weather to give soilsrich in iron and other mafic minerals. The high level of manganese is probably due to the lithology of therock as well as mining activity in some areas. Water hardness is a problem in all catchment areas, par-ticularly in the Gwayi catchment area where a value of 2550 mg/l was recorded in one borehole. Theproblems with hard water use are discussed. Chloride levels exceeded the recommended levels in afew areas under irrigation. Most of the chloride is probably from agricultural activity particularly theapplication of potassium chloride. Fluoride levels were particularly elevated in the Gwayi catchment areaand this is because of the geology of the area. There was no evidence of microbial contamination in all theboreholes sampled as the total coliform, faecal coliforms, heterotrophs count was nil. However, severemicrobial contamination was found in the wells especially those in clay areas.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Groundwater resources in Zimbabwe underpin rural livelihoodsbecause the water is used for irrigation, livestock and consump-tion. Most people in the rural areas now solely depend on ground-water since rivers and dams are heavily silted (Moyo and Mtetwa,2002). The overall use of the groundwater resources in Zimbabweis estimated to be 4% of the abstracted water (Chenje and Johnson,1996). Groundwater accounts for less than 10.00% of the water usein Zimbabwe. However, Zimbabwe is a water scarce country and tosecure future development more groundwater exploration and

exploitation is required. A country wide survey of the groundwaterquantity and quality was carried out by Interconsult between 1983and 1985. The major findings of the study were that the groundwa-ter resources of Zimbabwe are suitable for the development of pri-mary water supplies by means of dug wells or boreholes(Interconsult-NORAD, 1985). However, this report did not focuson the microbiological and chemical factors affecting water qual-ity. In Zimbabwe, groundwater occurs within crystalline rocks thatcover most of the country (66%). The groundwater developmentpotential of these rocks is generally low, yet they form the mainsource of drinking water for the rural population. Despite itsimportance, little information is available on the extent of ground-water pollution in Zimbabwe. Moyce et al. (2006) showed thatlandfills and cemeteries significantly affected shallow ground

28 N.A.G. Moyo / Physics and Chemistry of the Earth 66 (2013) 27–32

water in Harare. High levels of contamination of metals, phospho-rus, nitrates and coliform bacteria were also detected. The sourceof the microbial contamination was decomposing bodies and hea-vy metal contamination was probably due to natural hydrolysis ofthe aquifer rock unit. Love et al. (2004) reported high levelscalcium and magnesium above accepted limits at a farm in Hararewhere sewage effluent is discharged. In the rural areas the ground-water from shallow wells is not monitored and it is probably thesource many waterborne diseases plaguing Zimbabwe. Dwairoet al. (2006) assessed impacts of pit latrines on groundwater qual-ity and indicated that pit latrines were microbiologically impactinggroundwater quality up to a distance of 25 M.

The few studies done on ground water quality in Zimbabwe havebeen highly localised (Tevera, 1991; Madyiwa et al., 2002; Ravengaiet al., 2004; Zingoni et al., 2006; Hoko, 2005; Hoko, 2008) Ground-water quality on a national scale has not been investigated yet itis intrinsically linked to the chemical properties of the aquifer’sgeology through which it flows. Thus, there is spatial variability inthe quality of groundwater from one aquifer to another. Geologyis not the only factor determining groundwater quality; anthropo-genic factors also play an important role. Pitchard et al. (2007)and Pitchard et al. (2008) reported on the impact of people ongroundwater quality in Malawi. Uzoigwe and Agwa (2012) recordedhigh counts of faecal coliforms in boreholes and shallow wells neardumpsites. The main objective of this study was to determine thechemical and microbiological parameters of groundwater in threedifferent catchment areas in Zimbabwe. A groundwater quality sur-vey on a large scale is important as a first step in the development ofa groundwater management strategy for Zimbabwe.

2. Materials and methods

Zimbabwe has been divided into seven major catchment areas(Fig. 1). Seventy boreholes were randomly selected using stratified

Fig. 1. Catchment are

random sampling technique to capture the main dominant geologyof the aquifer between January, 2009 and February, 2010. Theboreholes were selected from a list 16000.00 boreholes registeredwith the Zimbabwe National Water Authority (ZINWA). Twenty-four boreholes were selected from Manyame, twenty-three fromMazowe and twenty-three from Gwayi. The depth of the boreholesranged between 44 M and 95 M.

The stratified random sampling technique was also employed toselect thirty shallow family wells. Water samples were analysedfor physico-chemical and microbiological parameters in duplicatebetween January, 2009 and February, 2010. The borehole watersamples were collected in glass sampling bottles sterilized byautoclaving. pH and conductivity were determined on site usinga Horiba U23 multiprobe meter. Fluoride was determined by ion-selective using a combination electrode. Sulphate was measuredusing the BaCl2 turbidimetric method. Chloride ion was measuredby argentometric titration method. Sodium was determined byflame atomic absorption spectrophotometry. The wells that weresampled were family wells lined with fired bricks and were cov-ered with concrete well covers. The well lead was raised thus,diverting storm water. The lifting device was the bucket and wind-lass system. None of the wells near pit latrines, cattle pens or graveyards.

Iron and manganese were determined using atomic absorptionspectrophotometry (APHA, 1985). Nitrate was determined by usingthe chromotropic acid method (Madera et al., 1982). Totaldissolved solids (TDS) were determined by filtering 100 ml ofwater and evaporating gradually in pre-weighed crucibles. Thechange in weight was used to determine the dissolved salts. Waterhardness was determined using an AR 25 pH meter. Alkalinity,calcium, bicarbonate, sulphate and magnesium were determinedusing standard methods (APHA, 1985). A random selection methodwas used to select ten wells in each of the three catchment areas.Nalgen glass sampling bottles (500 ml) were used to collect well

as of Zimbabwe.

Table 2Water quality eigenvectors of the correlation matrix in the Manyame catchment.

Variable PC1 PC2 PC3

Hardness 0.225806 0.375052 0.019770TDS 0.391099 �0.116704 0.077032Alkalinity 0.354906 0.134710 0.055526Calcium 0.237386 0.338430 �0.029893Chloride 0.293129 �0.303039 �0.064551Conductivity 0.391094 �0.116722 0.077189Iron �0.124804 �0.120691 0.428684Bicarbonate 0.374380 0.153063 0.012473Magnesium 0.122557 0.370435 0.005704Sodium 0.303014 �0.263692 �0.190859Nitrate �0.019075 �0.121295 0.467391Sulphate 0.283518 �0.312625 �0.138276pH 0.116985 �0.215538 0.417741Manganese �0.004135 0.289033 0.098375

N.A.G. Moyo / Physics and Chemistry of the Earth 66 (2013) 27–32 29

water samples. The sampling bottles were sterilised in an auto-clave for field use. The water samples were transferred to thelaboratory on ice.

The standard membrane filtration technique (Ziel et al., 1998)was used to assess the microbiological water quality. A volumeof 100 ml of each water sample was passed through 0.45 lm poresize, 47 mm diameter sterile filter membranes and the membranesplaced on the relevant substrate medium before incubation. Theaverage number of colony forming units per 100 mm (cfu,100 ml�1) was determined.

For total coliform bacteria, M-ENDO (DIFCO) agar plates wereincubated at 37 �C for 24 h. Colonies with a golden metallic sheerwere counted as total coliforms. For the detection of faecal coli-forms and heterotrophs the M-FC (DIFCO) agar plates were incu-bated at 37 �C for 48 h; and for enterococci bacteria theM-Enterococcus (DIFCO) agar plates were incubated at 44.5 �C for24 h. All dark blue colonies were counted as faecal coliforms andall reddish-pink colonies were counted as faecal enterococci. TheWHO (2004) were used to categorize each well as follows:

Indicators organisms Water quality assessment criteria

Good Marginal Poor

Total coliform 10 cfu 100 ml�1 11–150 cfu 100 ml�1 >100 cfu 100 ml�1

Faecal coliform 0 cfu 100 ml�1 1–10 cfu 100 ml�1 >10 cfu 100 ml�1

Faecal enterococci 0 cfu 100 ml�1 1 cfu 100 ml�1 >1 cfu 100 ml�1

� Good indicates negligible risk of microbial infections and fit forhuman consumption.� Marginal indicates slight risk of microbial infection; must be

treated before. consumption.� Poor indicates high risk of infectious disease transmission; not

fit for human consumption.

The physico-chemical parameters determined in all the catch-ment areas were analysed using Principal Component Analysis(PCA). PCA was used to determine the factors that account for mostof the variation in ground water quality.

3. Results

In the Manyame catchment area, the first three components ac-counted for 73% of the variability in water quality parameters (Ta-ble 1). PC1 accounted for 35% of the variability and it had amoderate positive correlation for TDS, alkalinity, conductivity,bicarbonate and sodium (Table 2, Fig. 2). PC1 represents the prin-cipal dissolved constituents in groundwater, and they occur inthe form of electrical charged ions. PC2 accounted for 24% and

Table 1Physico-chemical variables eigenvalues of the correlation matrix at Manyame,Mazowe and Gwayi catchment areas.

Component Eigenvalues Difference Proportion Cumulative

Manyame1 5.92924581 1.93092072 0.3488 0.34882 3.99832509 1.54088650 0.2352 0.58403 2.45743859 0.83859422 0.1446 0.7285

Mazowe1 8.29075444 6.17536838 0.5182 0.51822 2.11538606 0.68522897 0.1322 0.65043 1.43015709 0.40317808 0.0894 0.7398

Gwayi1 5.98606014 3.11818434 0.3991 0.39912 2.86787581 0.79967046 0.1912 0.59033 2.06820535 0.58892783 0.1379 0.7281

had a moderate positive correlation for hardness, calcium andmagnesium. Calcium and magnesium determine water hardness.

PC2 represents water hardness. PC3 was associated with iron,nitrate and pH and accounted for 15% of the variance. PC3 repre-sents the agricultural activity in the area. Iron was associated withgranite/gneiss rock formation (Fig. 2). Water hardness was stronglyassociated with siltstone/sandstone (Fig. 2).

In the Mazowe catchment area, the first three components ac-counted for 74% of the variability in the water quality parameters

Fig. 2. Manyame catchment area: PCA of physico-chemical variables and the rockformations.

Table 3Water quality eigenvectors of the correlation matrix in the Mazowe catchment.

Variable PC1 PC2 PC3

Depth 0.083068 0.337438 0.013391Hardness 0.321520 �0.052522 0.195263TDS 0.334696 �0.088109 0.069728Alkalinity 0.285697 0.330139 0.004775Calcium 0.330327 �0.009042 0.153057Chloride 0.295151 �0.322063 0.064649Conductivity 0.343681 �0.060952 0.048778Iron 0.136939 �0.235178 �0.620827Bicarbonate 0.170049 0.532848 0.005527Magnesium 0.176170 �0.085300 0.335315Sodium 0.333203 �0.026106 �0.046097Nitrate �0.072808 �0.228143 0.327719Sulphate 0.314424 �0.249133 �0.012705pH 0.067267 0.409549 0.002666Manganese 0.203037 0.038578 �0.563822

Table 4Water quality eigenvectors of the correlation matrix in the Gwayi catchment.

Variable PC1 PC2 PC3

TDS 0.368790 0.186199 0.099610Alkalinity 0.153124 0.222005 �0.562680Calcium 0.396575 �0.058199 �0.014643Chloride 0.072788 0.441746 0.376607Conductivity 0.375788 �0.157517 0.023208Fluoride 0.330638 �0.069857 0.044427Iron 0.110004 �0.416657 0.106238Bicarbonate �0.089976 0.369732 �0.358303Magnesium 0.356338 �0.113075 �0.182484Manganese 0.056223 �0.110554 0.292032Sodium 0.022324 0.435512 0.432703Sulphate 0.376067 �0.029495 0.1666419pH �0.137405 0.152644 �0.012133Nitrate �0.169644 �0.288974 �0.026447

Fig. 4. Gwayi catchment area: PCA of the physico-chemical variables and the rock

30 N.A.G. Moyo / Physics and Chemistry of the Earth 66 (2013) 27–32

(Table 1). PC1 accounted for 52% of the variability and it was asso-ciated with hardness, TDS, calcium and sodium (Table 3, Fig. 3). Asin the Manyame catchment area PC1 represents the ionic constitu-tion of the groundwater which is associated with the schist rockformation. PC2 accounted for 13% of the variation and was associ-ated with alkalinity, bicarbonate, pH and depth. PC3 accounted for9% of the variation and was associated with magnesium and ni-trate. Nitrate was associated with all the rock formations (granite,schist and dolerite). This indicates widespread use of fertilizer in allthe areas.

In the Gwayi catchment area, three components PC1, PC2 andPC3 were selected with them accounting for 40%, 19% and 14% var-iation in water quality respectively. PC1 was associated with TDS,calcium, conductivity, fluoride and magnesium (Table 4, Fig. 4).As in the previous catchments PC1 reflects the main ionic constit-uents of the groundwater. PC2 was mainly associated with sodium,chloride and bicarbonate. PC3 was associated with sodium, chlo-ride and manganese. PC3 represents irrigated land.

Iron, manganese, nitrate and water hardness exceeded the stip-ulated limits by at least 20% in all the catchment areas (Table 5).

Fig. 3. Mazowe catchment area: PCA of the physico-chemical variables and the rockformations.

formation.

In the Manyame catchment area only two wells had water fit forhuman consumption without needing treatment (Table 6). In theMazowe catchment only one well had water fit for human con-sumption prior to treatment compared to two in the Gwayi catch-ment area. In all the instances where the water could be consumedwithout treatment, the background substrate was sand (Table 6).

4. Discussion

The PCA suggests that in all the catchment areas, groundwaterquality is mainly controlled by TDS, conductivity, sodium andbicarbonate. Water hardness was high in the three catchmentareas reflecting the high concentrations of the calcium, magnesiumand bicarbonate. Wanda et al. (2011) used PCA in a hydro-geo-chemical appraisal of groundwater quality from weathered base-ment aquifers in northern Malawi and concluded that calciumand bicarbonate accounted for most of the variation in groundwa-ter quality. The southern portion of the Gwayi catchment is under-lain by karoo system rocks which contain basalt which onweathering may release calcium and magnesium thus contributingto the hardness of the water (Love et al., 2004). Hard water whichis high in calcium and magnesium is typical of dolomitic aquifers.It causes ‘‘fur’’ in kettles and soap does not easily make lather inhard water. Hard water thus wastes soap and synthetic detergents.

Table 5Percentage of boreholes above accepted limits.

Catchment NO3 Cl F Fe Mn Hardness TDS SO4 Na K

Manyame 36 11 0.3 50 29 61 30 22 4 0Mazowe 37 10 0 46 27 74 30 23 7 0Gwayi 22 12 14 24 23 42 42 20 1 0

N.A.G. Moyo / Physics and Chemistry of the Earth 66 (2013) 27–32 31

It also leaves unsightly soap scum rings in the bath tub. Further-more, hard water builds up scale and thus clogs hot water pipes.In rock formations that did not contain carbonates such as sand-stone, the pH was low. This is because the carbon dioxide in solu-tion formed carbonic acid. Water hardness is not a health hazard.Drinking hard water may contribute a small amount towards totalcalcium and magnesium in human dietary needs. However, hardwater can cause problems for irrigated crops as it can cause whitescale like deposits to develop on plant leaves. Continued use ofhard water in irrigation may increase soil pH and thus affect plantsthat thrive under acid conditions such as petunias.

Iron and manganese exceeded recommended limits in a signif-icant number of boreholes in all the three catchment areas. TheWHO recommended levels for iron and manganese in potablewater are 0.30 mg/l and 0.05 mg/l respectively. One borehole inthe Gwayi catchment area recorded an iron concentration of15.5 mg/l. The iron levels were very high where the underlyinggeology was dominated by dolerites which weather to give soilsrich in iron and other mafic minerals. Water with high concentra-tions of iron or manganese may cause the straining in plumbingfixtures or laundry. Elevated levels of iron and manganese haveno health implications.

Chloride levels in all the irrigated areas were above the back-ground level of 100 mg/l and the main source is probably irrigatedagriculture. The use of potassium chloride as a fertilizer has prob-ably contributed to high chloride levels in low-lying and poorly

Table 6Microbial quality of water in wells in three catchment areas.

Catchment area Sample Depth (M) Soil type Land use

Manyame W1 5.0 Sand CW2 5.5 Sand CW3 6.0 Clay CW4 5.0 Clay CW5 5.2 Clay CW6 6.3 Sand CW7 6.8 Clay CW8 5.1 Sand CW9 5.2 Clay CW10 6.1 Sand NC

Mazoe W11 5.0 Sand CW12 4.2 Sand CW13 5.6 Clay CW14 6.8 Clay CW15 7.1 Clay CW16 6.8 Sand CW17 4.4 Sand CW18 5.8 Sand CW19 5.7 Clay CW20 6.4 Sand NC

Gwai W21 6.8 Clay CW22 6.2 Sand NCW23 6.3 Sand CW24 5.3 Sand CW25 5.5 Clay CW26 6.2 Clay CW27 6.8 Sand CW28 6.1 Clay CW29 6.9 Clay CW30 5.4 Sand C

C = Cultivated; NC = Not cultivated.

drained soils. Fluoride levels were high in the Gwayi catchmentarea which is underlain by the Permian–Triassic Karoo sandstone.Nitrate levels ten times higher than the WHO recommended levelsof 10 mg/l in some areas. High nitrate levels may cause methaemo-globinaemia in young children (Johns and Lawrence, 1973; Lewiset al., 1980). The possible source of nitrates is agriculture. The soilsof Zimbabwe are inherently deficient in nitrogen and the use ofmineral fertilizers or manure is necessary for substantial agricul-ture and natural occurring nitrate levels do not exceed 4–8 mg/lin Zimbabwe (Ellwell and Stocking, 1988). Nitrate levels as highas 35 mg/l were recorded in some agricultural areas. In Indianitrate levels of up to 1500 mg/l were found in groundwater inan agricultural area (Jacks and Sharma, 1983). Sunguro et al.(2000) suggested that groundwater resources in Zimbabwe be clo-sely monitored within a framework of integrated water resourcesmanagement.

The microbiological quality of the water from all the boreholesin the different catchments was acceptable for human consump-tion. None of the boreholes was contaminated with indicator bac-teria. This is probably due to the depth at which water fromboreholes was sampled. The minimum borehole depth sampledwas 44 m. Borehole water is generally of excellent quality becauserocks act as filters. Microbial contamination from surface sources isremoved within the first 30 m as groundwater passes through sat-urated sand or unfissured rock. In the unsaturated zone no morethan 3 m may be necessary to purify ground water. However, ina fractured aquifer microbial contaminants can rapidly passthrough the unsaturated zone to the water table. The efficiencyof the purifying process is reduced under these circumstances. Afew studies have been done in Zimbabwe which indicated thatsome boreholes water was contaminated (Love et al., 2004; Zvidzaiet al., 2007; Dwairo et al., 2006). Unfortunately none of these stud-ies give the depth of boreholes where water samples were taken. Itis however, most likely these boreholes were not deep. The results

Heterotrophs TC FC Enterococci

62 5 0 0340 8 0 04.9 � 104 2.84 � 105 9 � 103 01.17 � 103 2.76 � 103 1.12 � 103 96.92 � 104 2.40 � 105 4.0 � 103 5156 10 0 05.6 � 103 3.84 � 104 1 � 102 0146 284 114 04.2 � 103 5 � 103 1.3 � 103 539 300 30 0

205 50 22 0400 139 92 24.6 � 105 2.0 � 103 5 � 102 02.5 � 103 505 31 06.8 � 104 4.4 � 104 4.0 � 103 51102 54 2 047 4 0 0272 206 0 06.9 � 104 5.5 � 104 3.2 � 103 106156 25 13 0

2.2 � 103 1.17 � 103 1.1 � 103 15305 218 110 12.2 � 105 1.5 � 103 3 � 102 05 1 0 0706 415 0 07.2 � 104 5.7 � 104 5.0 � 103 73203 215 0 03.2 � 103 1.3 � 103 1.5 � 103 46.0 � 103 4.2 � 103 1.8 � 103 549 10 0 0

32 N.A.G. Moyo / Physics and Chemistry of the Earth 66 (2013) 27–32

from this study indicated that boreholes are a safe source of pota-ble water as they did not yield any coliforms of E. coli. Similar find-ing were also reported by Zvidzai et al. (2007) in a small area ofnorth eastern Zimbabwe.

High levels (above the WHO recommended guidelines) of faecalcoliforms and faecal enterococci were detected in some shallowwells. The average depth of the wells was 5.5 m. The present studyshowed that the most of the water from wells is not fit for humanconsumption prior to treatment. It was observed that the wellwater quality was particularly bad during the rainy season and inwell dug out in clay areas. The sources of the pollutants of wellwater were not conclusively identified in this study. In the early1990’s the Ministry of Health, through the Blair Research Institute,initiated a family based upgraded wells programme. During thisstudy, the family wells using windlass and bucket system weresampled. Between 1984 and 1995 the microbiological quality ofwater from traditional wells, buckets pumps and hand pumpswas examined. The results showed that the nature of the well itselfand the protection from the surface (Lead works) were criticalfactors in determining the quality of the water from shallow wells(Mtakwa and Chimbunde, 1997). Water from the traditional wellshad higher E. coli count than the upgraded family wells. In thecurrent study some of the upgraded family wells recorded highE. coli counts. The source of the microbiological contamination isprobably the defective fissures that were observed in some wellsparticularly in clay soils. Conboy and Goss (2000) also indicatedthat wells in clay soils were more susceptible to microbial contam-ination than sandy soils. The major factor affecting the water qual-ity from well is well construction. High hygienic standards wereexercised by the communities with family wells and thus poorhygiene could not have been the source of contamination.

5. Conclusion and recommendation

The physico-chemical parameters of the borehole water werelargely a function of the geology of the area. However, agriculturalactivities have resulted in high nitrate and chloride levels in someareas. Some of the wells in this study contained high microbiolog-ical indicator bacteria which were in excess of WHO recommendedguidelines for drinking water. Poor maintenance of the wells is thelikely reason for the contamination. The economic downturn Zim-babwe experienced in the last decade contributed to the poormaintenance of these wells and it is suggested that the govern-ment and aid agencies assist the villagers with resources to reha-bilitate these family wells.

Acknowledgements

I am grateful to my graduate assistant, Mmaditshaba Rapatsawho helped with many aspects of this study. Mr. E. Zingoni helpedwith initial data compilation and his efforts are acknowledged. Mr.Dhau and Mr. Ramudzuli helped with the map and their efforts areappreciated.

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