Groundwater Resources for Lusaka and selected Catchment Areas
T E C H N I C A L R E P O R T N O . 3
HYDROGEOLOGY OF THE ITAWA SPRING IN NDOLA.
BASELINE STUDY ON HYDROGEOLOGY AND HYDROCHEMISTRY
by
Max Karen, Dr. Tobias El-Fahem and Mumba Kolala
Lusaka, December 2015
REPUBLIC OF ZAMBIA Ministry of Energy and Water Development
Groundwater Resources for Lusaka and selected Catchment Areas
Hydrogeology of the Itawa Spring in Ndola. Baseline Study on Hydrogeology and Hydrochemistry
Author: Max Karen (GReSP), Dr. Tobias El-Fahem (BGR), Mumba Kolala (District Water Officer, Department of Water Affairs, Ndola)
Commissioned by: Federal Ministry for Economic Cooperation and Development (Bundesministerium für wirtschaftliche Zusammenarbeit und Entwicklung, BMZ)
Project: Groundwater Resources for Lusaka and selected Catchment Areas
BMZ-No.: 2011.2010.2 BGR-No.: 05-2361-01 BGR-Archive No.:
Date: December 2015
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TABLE OF CONTENTS
TABLE OF CONTENTS ...... 3 ANNEX ...... 4 LIST OF FIGURES ...... 5 LIST OF TABLES ...... 5 Acronyms, abbreviations and units ...... 6 List of reports compiled by the project in Phase III ...... 7 Summary ...... 8 Executive Summary ...... 9 1. Introduction ...... 11 2. Project Objective ...... 12 3. Location of the Itawa Springs ...... 12 4. Background ...... 13 4.1 General ...... 13 4.2 Topography and Drainage ...... 14 4.3 Climate ...... 16 4.4 Vegetation ...... 16 5. Geology ...... 18 6. Hydrogeology ...... 20 6.1 Introduction ...... 20 6.2 Aquifer Characteristics ...... 21 Aquifer A – Basement Complex ...... 21 Aquifer B – Muva Group and Lower Roan Quartzites ...... 23 Aquifer C – Upper Roan Group ...... 23 Aquifer D – Kakontwe Limestone ...... 23 Aquiclude X - Lower Roan Argillites and Shales ...... 24 Aquiclude Y - Mwashia Formation ...... 24 Aquiclude Z - Border Group ...... 25 6.3 Groundwater Infiltration ...... 25 6.4 Groundwater Flow Directions ...... 26 6.5 Discharge Measurements from Artesian Boreholes and Springs ...... 31 7. Hydrochemistry ...... 32
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7.1 Sampling Methodology ...... 33 7.2 Hydrochemical Results ...... 36 8. Environmental Isotopes ...... 37 8.1 Occurrence of Deuterium and Oxygen-18 ...... 37 8.2 Stable Isotopes in Precipitation and Surface Water ...... 38 8.3 Stable Isotopes in Groundwater ...... 40 9. Identification of Threats to Groundwater ...... 42 9.1 Local Contamination from Leaking Sewers ...... 42 9.2 Sanitation ...... 44 9.3 Effluent Drains ...... 45 9.4 Heavy Metal and Industrial Contamination ...... 47 9.5 Reduction of Protective Soil Cover ...... 48 9.6 Hydrocarbons ...... 48 10. Conceptual Hydrogeological Model ...... 48 10.1 The Upper Spring Section ...... 49 10.2 The Lower Section ...... 52 10.3 Contamination and Protection ...... 52 11. Groundwater Protection Zones ...... 52 11.1 Inner Protection Zone - Zone 1 ...... 53 11.2 Outer Protection Zone - Zone 2 ...... 54 11.3 Total Catchment - Zone 3 ...... 54 12. Groundwater Monitoring ...... 55 13. Slope Stability and Backpressure ...... 56 14. Conclusions and Recommendations ...... 57 15. Recommendations ...... 58 References ...... 60
ANNEX Annex 1 2015 DGPS Water Level Data Annex 2 2015 DWA Water Level Measurement Annex 3 2015 Inorganic Hydrochemistry Annex 4: 2015 Microbiology Results
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LIST OF FIGURES Fig. 1: Location map...... 11 Fig. 2: Location of the Itawa Spring...... 13 Fig. 3: Topography and drainage system...... 14 Fig. 4: Spring eye...... 15 Fig. 5: Itawa spring area...... 15 Fig. 6: Sunrise view over the spring area...... 17 Fig. 7: Maize cultivation down slope...... 17 Fig. 8: Schematic cross section (modified, after HADWEN, 1972)...... 19 Fig. 9: Geological map...... 19 Fig. 10: Granite outcrop close to railway track...... 20 Fig. 11: Hydrogeological units...... 22 Fig. 12: Groundwater flow directions...... 27 Fig. 13: Measuring ground elevation using DGPS...... 28 Fig. 14: Groundwater flow contours ...... 29 Fig. 15: Pit latrine near pump house...... 30 Fig. 16: Measuring artesian head ...... 31 Fig. 17: Surface flow measurement...... 32 Fig. 18: Sampling sites...... 34 Fig. 19: Piper Diagram of hydrochemical and pollution indicators ...... 36 Fig. 20: Examples of the relationship between δ2H and δ18O in meteoric water, evaporating water and water in interactions with rock (taken from COOK AND HERCZEG 2000)...... 38 Fig. 21: Stable isotope composition of rainfalls in Ndola, Lusaka and Chongwe...... 40 Fig. 22: Stable isotope composition of groundwater equals the mean annual precipitation (from CLARK & FRITZ, 1997)...... 41 Fig. 23: Stable isotope composition of the 51 groundwater samples in Ndola in relation to the rainfall samples...... 41 Fig. 24: Itawa area contamination sources...... 42 Fig. 25: Main sewer leakage...... 43 Fig. 26: Image of pit latrine close to hand dug well...... 45 Fig. 27: Effluent channels...... 46 Fig. 28: Effluent drain...... 47 Fig. 29: Conceptual local groundwater flow...... 49 Fig. 30: Conceptual groundwater flow...... 50 Fig. 31: Schematic cross section from West to East...... 51 Fig. 32: Setting of the protection zones 1 and 2...... 53 Fig. 33: Estimated catchment - outer protection zone...... 54 Fig. 34: Monitoring network...... 56
LIST OF TABLES Tab. 1: Lithology and Hydrogeological Units ...... 21 Tab. 2: Monitoring well data...... 31 Tab. 3: Stable isotope composition of local rainfall...... 39 5 of 60
Acronyms, abbreviations and units
approx. approximately BGR Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute for Geosciences and Natural Resources) ca. circa DGPS Differential Global Positioning System DRC Democratic Republic of Congo DWA Department of Water Affairs GPS Global Positioning System GReSP Groundwater Resources Management Support Programme GIZ Gesellschaft für international Zusammenarbeit (German Corporation for International Cooperation) ITCZ Intertropical Convergence Zone IWaSP International Water Stewardship Program JICA Japanese International Cooperation Agency IWRM Integrated Water Resources Management KWSC Kafubu Water and Sewerage Company l/s litres per second m3/a cubic metres per annum m3/day cubic metres per day masl metres above sea level mbgl Metres below groundelvel MB Monitoring Borehole (drilled and named through ASTA 2013) MEWD Ministry of Energy and Water Development PPP Public Private Partnership SRTM Shuttle Radar Topography Mission WARMA Water Resources Management Authority WHO World Health Orgnaisation ZABS Zambian Bureau of Standards ZB Zambian Breweries ZEMA Zambian Environmental Management Authority
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List of reports compiled by the project in Phase III
Date Authors Title Type May 2015 Megan Jenkins, Impact of Small Scale Farmers on the Technical Report Andrea Nick, Chongwe River. Survey on Land Use No. 1 Dickson Mwelwa, and Water Abstraction from Chongwe Timothy Simwanza River
December Andrea Nick The Chongwe Catchment: A Technical Report 2015 hydrological, hydrogeological and No. 2 hydrochemical Characterization for the Establishment of a Catchment Management Plan
December Max Karen, Dr. Hydrogeology of the Itawa Spring in Technical Report 2015 Tobias El-Fahem, Ndola. Baseline Study on No. 3 Mumba Kolala Hydrogeology and Hydrochemistry
December Max Karen, Dr. Hydrogeology of the Town Area of Technical Report 2015 Tobias El-Fahem, Solwezi. Baseline Study on No. 4 Levy Museteka Hydrogeology and Hydrochemistry
November Tewodros Tena & Survey on the Technical Forum Advisory Report 2013 Dr. Tobias El- No. 01 Fahem
March Andrea Nick; Dr. Groundwater quality and vulnerability Advisory Report 2014 Tobias El-Fahem & in the area of Lusaka West No. 02 Dr. Roland Bäumle
May 2013 Martin Blümel IT-Infrastructure GReSP Technical Note 01
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Summary
Authors: Max Karen, Dr. Tobias El-Fahem, Mumba Kolala
Title: Hydrogeology of the Itawa Spring in Ndola. Baseline Study on Hydrogeology and Hydrochemistry.
Keywords: Itawa, groundwater, Ndola, Zambia, hydrochemistry
The Itawa Spring in Ndola is an important water resource for the industries and households in its vicinity. In order to improve the knowledge about the hydrogeology of the Itawa Spring and to support the delineation of protection zones around it an extensive field assessment was conducted during the year 2015. The assessment combined an intensive field reconnaissance for the mapping of the area; a groundwater table measurement campaign covering greater parts of Ndola; borehole data collection and also groundwater sampling campaign for hydrochemical analysis. Additionally rainwater samples have been taken to analyse the stable water isotopes. The collected data and the interpretation of the samples reveal a rather complex hydraulic environment around the Ndola dome due to faulting and changing geological facies. Different origins of the groundwater flowing from the spring were identified and also a conceptual model explaining the artesian pressure in some places was developed. A number of contamination sources and land use changes were identified during the study which pose a significant threat to the groundwater quality of the spring, the source and direct impact were quantified within the conceptual model of the groundwater flow system. Around the Itawa Spring a public private partnership group was established under the International Water Stewardship Program (IWaSP) which brings together the main users of the spring, Zambian Breweries, the local community and the governmental bodies in charge of environment, health and water such as ZEMA and WARMA. During the hydrogeological work on the spring staff of the Water Resources Management Authority (WARMA) staff has been trained in different aspects of groundwater data collection and with the resulting data the Groundwater Resources Management support Programme (GReSP) could provide important suggestions for the future development of protection zones around the spring.
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Executive Summary The Itawa Spring is an important water resource. In recent years the spring has come under threat due to land use changes and aging infrastructure. The objective of this study was to increase the knowledge base and to understand where the spring water was coming from and quantify the threats to the water quality of the spring.
The spring water has its origin from groundwater which rises at an impermeable barrier in the subsurface. Where the rising groundwater level meets the surface, it causes the surface flow – the spring. The spring however it not a single spring but a much larger system that includes multiple points where the water flows from the ground and an elongated zone on either side of the stream where water continuously seeps through the soil into the stream that flows east towards the Itawa Dambo.
The spring area also has two artesian boreholes that flow continuously. This can be explained by the impermeable barrier that causes the spring to flow in fact being a confining layer, which dips into the ground in an easterly direction. As the water flows from the higher ground towards the low point where the spring is found, it will be put under pressure at depth; the borehole intersects this confining layer and releases the pressure causing the water to flow at the surface.
The behaviour of the groundwater was investigated by the use of groundwater sampling that looked at the contents of the water to identify its origin; this was complimented by the use of stable isotopes. The water quality was also tested at multiple points to look at whether the water was contaminated with E.coli, a faecal coliform that is a health hazard. The hydrochemical data indicates that the water is of recent origin and has not flowed any great distance; the stable isotope data confirm the inorganic sample data. The sample analysis from around Ndola and the spring area from all the main aquifers indicate that no concentration in heavy metals was found above the Zambian and WHO standards.
The flow of the groundwater was investigated by looking at flow direction by taking water levels all over the larger Ndola area and with numerous points around the spring; the levels were compared accurately by using differential GPS to measure the land surface elevation. The combination of the water level data and the hydrochemistry indicate that the water is not flowing from any great distance with the origin of the water from the quartzite aquifer that occurs around the edge of the dome creating a conduit for groundwater, the quartzite aquifer is also linked to shallow groundwater flow off the basement aquifer of the Ndola dome. The geological and water level data also indicate that there is a third aquifer, the Upper Roan Dolomite, which occurs below the pump house and is the source of the seepage water around the stream.
For the purposes of conceptualising the aquifer the spring is described as having an upper section, with water from the quartzite and the granite and a lower section underlain by the dolomite aquifer where water continuously seeps from the ground into the stream. The groundwater level data indicates that water is flowing from the upper section close to the railway track to the east, this is important due to the fact that the large Mapalo community which has no sewer infrastructure and uses pit latrines, is located down gradient from main spring eye; this is with the exception of the
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houses that have been built to the north of the spring whose pit latrines represent a direct contamination threat.
The upper section is important as a water source for the local community and as the sole source for the major brewery operation that is located to the south of the spring. The water quality around the spring was tested for E.coli, the results revealed that at the point where the spring flows from the surface is it not contaminated, but within metres of surface flow it becomes contaminated. This could be caused by local contamination such as open defecation which occurs in the undergrowth around the spring but may also be caused by a leaking sewer line that occurs 200m southwest and uphill of the spring.
Land use practise around the spring is of major concern for the sustainability of the spring. The original vegetation has been removed and the slopes around the spring have been used for cultivation of crops such a maize. The cultivation has involved the use of steep slopes around the spring and poor farming practise such as aligning ridges down slope which increases erosion; this has led to erosion and migration of the spring towards the railway track. One of the main spring eyes is now less than five metres, in the horizontal plane from the railway track, this poses a major threat to the stability and structural integrity of the land beneath the railway track, especially during high intensity rainfall events which do occur in the region. If there were to be a collapse over the main spring eyes this could compromise the structural integrity of the railway foundation and the collapse which could cause the spring eye to migrate due to backpressure.
The changes in land use and the infrastructure, specifically the contamination threats in the area are an immediate and major threat to the spring. The current initiative by the International Water Stewardship programme (IWaSP) in collaboration with local community, Zambian Breweries, WARMA and other stakeholder needs to be implemented urgently to protect the spring. This programme must implement protection zones around the spring which include an inner protection zone with a physical barrier around the upper section of the spring which has a security presence; however this can only be done if the water source from the artesian borehole close to the pump house is replaced by a similar source outside the protection zone.
This report makes recommendations for the spring protection zones and also for the larger area where identification and mitigation of contamination and other threats need to be quantified. In order to quantify and improve knowledge of the spring system the protection zones should also be complemented by an ongoing monitoring system that looks at all the inputs and outputs to the system. This should include shallow and deep monitoring boreholes, surface flow measurement points and rainfall; the monitoring should also include water levels and hydrochemistry. The ongoing monitoring is not simply of scientific interest, it will have great commercial value for Zambian Breweries, who hold the sole water right to the spring, so that they can help to quantify and ensure the sustainability of this important water resource.
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1. Introduction The Itawa Spring has major economic, social and ecological importance as a water resource for domestic and industrial purposes to the city of Ndola (Fig. 1). The environment around the spring has been altered by industrial development and by people settling close to the spring; the development has created issues due to the changes in land use and related issues such as sanitation and related water quality.
Fig. 1: Location map.
The issues related to the settlements and changes in land use have increased to the point where the water supply and quality of the spring is under threat. The spring is the sole source of water for Zambian Breweries (ZB) which holds the only water right to the spring of 8,250 m3/day. The potential deterioration in water quality has a major economic cost which has led ZB to develop a spring protection concept that involves all the stakeholders to safeguard the water quality.
The development of a spring protection programme is being developed by ZB through a Public Private Partnership (PPP) approach which is part of the International Water Stewardship programme (IWaSP) supported by GIZ. GIZ and ZB requested BGR to review the existing proposal. The review by BGR, through the Zambian based Groundwater Resources Management Support Programme (GReSP), a cooperation between BGR and the Zambian Water Resources Management Authority (WARMA), revealed that the hydrogeological complexity of the spring was not sufficiently considered for the delineation of spring protection zones, especially due to the high risk of pollution.
In accordance with the technical cooperation partners, BGR through GReSP became a stakeholder in the IWaSP Ndola project.
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The economic importance of the spring cannot be viewed in isolation; the large community that has developed around the spring are key stakeholders that use the spring for clean water supply and for agriculture and leisure. The need to protect the spring must therefore balance the economic and social issues based on an improved understanding of how the spring works.
2. Project Objective The objective of this report is to provide an improved understanding of the spring from a groundwater perspective that can be used to assist in the protection of this resource. The key objective is the premise that in order to protect the spring it is essential the source, hydraulic characteristics of the aquifers and the factors that control vulnerability to contamination are understood.
The protection of all water resources is the responsibility of WARMA as described by the Water Resources Management Act 21 of 2011. WARMA has therefore to develop concepts for the establishment of protection zones and has to define those areas in Zambia.
In order to protect the spring it is first necessary to understand that the spring is coming from groundwater that has been forced to the surface based on the characteristics and structure of the rocks. This report aims to combine the existing knowledge on the spring with a hydrogeological investigation that involved field mapping of the spring in combination with measurements of water levels and hydrochemical sampling. The objective is therefore to create a hydrogeological baseline of the spring to assist in future investigation and assessment and to assist the existing initiatives to protect the spring.
In order for this report to be a useful tool in the protection of the spring the target audience for the report was considered. A hydrogeological baseline must of course consider the technical aspects however the key elements of the report are described using the objective that it should be understood by a non-technical audience.
3. Location of the Itawa Springs The Itawa springs are located on the eastern side of the city of Ndola between the hill that forms the residential area called Northrise and the wide flat bottomed valley known locally as the Itawa Dambo (Fig. 2). The springs are also surrounded by the Mapalo informal residential developments that is now established around the spring (Note - the area is officially known as the Chipulukusu, meaning “Cursed land”, which the community has now renamed Mapalo, meaning “Blessed land”. The name Mapalo has been adopted to describe the community around the spring).
The spring is also bounded by the railway line that runs along the hill contour line and passes within metres of some of the main spring outflows; in addition to the railway line a major sewer line managed by Kafubu Water and Sewerage Company (KWSC) also runs parallel to the railway line. Zambian Breweries have major facilities situated to the Southwest of the spring.
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Fig. 2: Location of the Itawa Spring.
The Itawa dambo area is bounded by the border with the Democratic Republic of Congo to the East and the North of the spring (Fig. 3). The international border runs along the catchment boundary between the Kafue and Tanganyika Basins but does not form the border of the different geological formation; many of the formations extend into the DRC which is important when considering recharge to the aquifer and for any future detailed groundwater resource calculations.
4. Background
4.1 General The City of Ndola is situated in the Copperbelt Province of Zambia and is the third largest city in Zambia. The city has grown considerably in the last 60 years, in 1969 the population was just 10,000 people; the population at the census of 2000 was close to 375,000, making it the third largest town in Zambia. The city is one of Zambia’s main industrial and commercial centres, though the mining sector has in general moved northwest towards Chingola and North Western Province.
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4.2 Topography and Drainage The city of Ndola is situated on the Central African Plateau at an elevation of 1300 m. Much of the area is gently undulating which can be generally interpreted as the low lying marshy plains being underlain by limestones while the steeper and more hilly areas being underlain by the harder rocks in the area, generally granite, schist and quartzite.
Fig. 3: Topography and drainage system.
The Itawa spring and the Ndola area are located within the Kafubu drainage basin which is a major tributary of the Upper Kafue River. The main drainage feature is the Itawa dambo (Fig. 3) which forms a wide flooded valley. The digital elevation model in Fig. 3 used the shuttle Radar Topography Mission (SRTM) to create an image of the topography; hill shading has been added along with 20 m topographic contours.
The rivers that flow from the Itawa dambo are perennial and fed in large part by outflow from groundwater. The outflow from the spring forms a tributary that flows into the Itawa dambo area; this area is the headwater of the Kafubu River which flows to the south, then southwest as is passes through Ndola. The topography in the area varies from 1,380 masl at the top of the Ndola dome to less than 1,240 masl in the Itawa dambo with some of the steepest hillslopes located close to the Itawa spring. Just above the spring on the slope of the hill (Fig. 4) the railway has been cut into the hillside along the topographic contour.
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Railway track located 4m above spring
Spring Eye
Maize cultivation on steep slopes around spring
Fig. 4: Spring eye.
The spring topography has two distinct zones, the Upper Zone where the main spring eyes are located; in this area there are defined spring eyes where water flows in channels which are however difficult to see due to dense vegetation (Fig. 4). This is the area where the water for the spring is channelled to the pump house (Fig. 5) which supplies Zambian Breweries with water.
Fig. 5: Itawa spring area.
In the Lower Zone, below the area of the pump house, the channels coalesce into a main channel that flows east towards the Itawa dambo, on either side of the channel the water seeps through the soil to
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the stream in an elongated seepage zone which is over 1000 m long on either side of the channel; to the south where the seepage zone is over 50 m wide is used extensively for agriculture.
4.3 Climate The climate of the area has three distinct seasons, with over 95% of the average annual rainfall of 1200 mm occurring from November to March during the hot wet season. The other seasons are mild to cool dry season from May to August, then a hot dry spell from September until the annual rain arrive in October/November.
The monthly maximum mean temperature is about 31.5oC and monthly minimum mean temperature is 7.7oC and the mean annual temperature is 21oC. The average pan evaporation is 1865 mm per year and the average potential Evapotranspiration is 1650 mm per year in the Ndola Rural region (JICA, 1995).
The rainfall in the area is linked to the southward shift of the Inter Tropical Convergence Zone (ITCZ). The southward shift of the ITCZ creates a convergence of the trade winds into a low pressure zone and pronounced convective activity which is associated with heavy tropical rainfall. The intensity of the rainfall is an important factor for the hydrogeology for two main reasons:
1. The recharge to the aquifers is from rainfall, extreme intensity rainfall events lead to increased surface runoff and less infiltration to groundwater (relative to total rainfall) in the recharge areas at higher altitude. 2. Where there is land use changes extreme intensity rainfall events can erode the surface if the protective vegetation cover is removed.
The response of the groundwater to rainfall provides important data on the aquifers; however, no long term water level measurements were available.
4.4 Vegetation The area lies within the Miombo ecological zone, this type of woodland is usually dominated by semi evergreen tress 15 – 21 m high with a well-developed grass layer. The vegetation in the Itawa springs has been radically altered from the natural woodland by human activity and many invasive species are now present in the area. The remaining large trees are not indigenous, however, there is evidence that the area was once a thick forest. Fig. 6 shows a view over the springs taken from the south looking northwards towards the Zambian Breweries’ pump house, the main spring area is shown to the West with the cultivated area and the few remaining large trees to the East.
In the area around the main spring eyes above the pump house the vegetation is very dense. Many invasive species are present at the spring including Tithonia diversifola or the Wild Sunflower and Lantena camara; it is the Lantana or tick berry which is a major problem in the spring area where it forms dense thickets which deter natural vegetation growth. Lantana has been the focus of biological control attempts for a century but remains a problem in many regions of Zambia (ASTA 2013).
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Remaining Trees
Pump House Cultivated Area
Spring Area
Fig. 6: Sunrise view over the spring area.
The area has also been altered by cultivation; many crops are now grown in the area. The area close to the main spring eyes (Fig. 7) is cultivated; this cultivation includes the use of steep slopes where maize is grown on ridges which should be aligned across the slope. Fig. 7 shows an area just south of the main spring eyes where maize is grown with the ridges aligned down the slope instead of across the slope. In the Ndola area there are numerous high intensity rainfall events and cultivation down slope encourages erosion.
Remaining Trees
Pump House Spring Area
Maize Growing Ridges Aligned Down Slope
Fig. 7: Maize cultivation down slope.
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5. Geology Ndola is located within the Zambian Copperbelt; the geology of the area has been and remains a key element of the Zambian economy due to the presence of the Mine series and associated mining exploitation of metals such as copper, cobalt and lead. The economic importance of the area has led to the geology and structures in the area being extensively explored and mapped, mainly for mineral exploration. The knowledge of the geology and structures is used in understanding the groundwater flow and the vulnerability in the area.
The surface topography is controlled by the geology. In the Ndola area the low ground is formed by the limestone and fine grained rocks (phyllites) with the hills and ridges being formed from the harder rocks such as the granite and schist. The topography of the area is dominated by the Granite dome which forms the high ground where much of Ndola City has been developed.
In terms of the spring formation the syncline (Fig. 8) to the East of Ndola is the most significant since the spring and the aquifer are located on the edge of the Ndola dome. Other structures are noted such as the syncline that runs parallel with the Kafubu River and the anticline to the North of the Itawa springs, both these structures will also affect the aquifer properties. The structural geology is vital in order to understand the spring.
The structures of the area form part of a much larger regional geological structure known as the Lufilian Arc which extends across Zambia and into the DRC for 800 kilometres in a series of synclines and anticlines. The greater Ndola area includes part of the Kafue anticline and Mufulira syncline; between these two structures the Ndola dome was emplaced. The geological structures are important to hydrogeology due to the fact that the permeability of the rocks is affected by the structural history and the bedding angles and fractures that the structural movements have imposed on the rocks.
The succession of rocks in the greater Ndola area is presented as Table 1. The geology of the area can be divided into three broad classifications consisting of the Basement Complex, the Muva Supergroup and the Katanga Supergroup, of these is it the Mine series of the Katanga group that is economically most important since is hosts the copper and other commercial mineralisation. The Muva Supergroup or System is defined for the purposes of this report as all post basement and pre Katanga Rocks.
The geological map, (Fig. 9), has been digitised from section of the larger geological map (Degree Sheet 1228, SE Quarter, Department of Water Affairs 1968 – digitised by GReSP) produced for the area, that depicts the geology of the larger Ndola area. The objective of the map was large scale mapping with an emphasis on major structures, lithological types and mineralisation, in the Itawa area detailed geological mapping was not carried out. During the field mapping minimal outcrops were located of all the lithologies with the exception of the granite; outcrop of granite (Fig. 10) was found along the railway track and in close proximity to the spring area.
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Anticline Axis Syncline Axis Ndola Dome Zambia DRC A Border Formation A’ Itawa Dambo Itawa Spring Lower Roan Kakontwe Limestone Phyliites Aquiclude X Upper Roan Dolomites Muva/Lower Mwashia Roan Quartzites Formation Granite Basement
Fig. 8: Schematic cross section (modified, after HADWEN, 1972).
Fig. 9: Geological map.
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Fig. 10: Granite outcrop close to railway track.
The location of the granite outcrop indicates the presence of the granite close to the spring. In other areas around Ndola there is a distinct break in slope below the granite that is coincident with two other spring locations at the edge of the granite (Monkey Fountain and Ngwazi Spring). The topography is linked to the change in lithology from the granite dome to the quartzite of the Muva/Lower Roan which forms the quartzite aquifer known in the area as the Bwana Mkubwa aquifer. Below the Itawa spring the topography then flattens out (Fig. 5) into the area where there is a long seepage zone, this is interpreted as a further change in geology to the Upper Roan Dolomites; this interpretation is consistent with the main work (HADWEN 1972) on the groundwater resources around Ndola.
6. Hydrogeology 6.1 Introduction The Itawa springs is a groundwater discharge zone which is the result of a number of processes; in order to understand the spring it is necessary to look at not just the area around the springs but the larger area. Identification of the recharge area or areas is fundamental to protecting the spring since the flow direction will determine the source of the groundwater and where it is vulnerable along the flow path.
The hydrogeology of the area (Fig. 11) is best understood by simplifying the rocks of the area into seven units that are essentially aquifers and aquicludes. Aquicludes are geological units that either allow very little water to flow or form a complete hydraulic barrier. They are very important in relation to the Itawa spring project in that they restrict and channel the flow of groundwater within the aquifers which is one of the principle reasons for the spring occurrence. A hydrogeological summary is presented in Table 1 which also includes the lithological units.
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In the area the limestone and dolomitic aquifers have the greatest groundwater potential and have been exploited over much of the Ndola area, they are also the aquifers that form important and prolific aquifer in the Lusaka, Kabwe and Mazabuka areas. The third aquifer unit, Aquifer B, which is in fact a combination of formations, is the quartzite aquifer known locally as the Bwana Mkubwa aquifer, this aquifer is not considered to be as productive as the carbonate rocks however this aquifer unit is vital in order to understand the spring formation in the area. In the Ndola area there are a number of springs (Fig. 11) which are coincident with the Bwana Mkubwa aquifer.
Tab. 1: Lithology and Hydrogeological Units
Supergroup Major Sub Group Formation Rock Types Hydrogeological Group Unit Border Mudstone and Aquiclude Z Formation Shale Lower Kakontwe Dolomitic Aquifer D Kundelungu Kundelungu Formation Limestones Mwashia Carbonaceous Aquiclude Y Formation Shale and Lava Aquifer C Dolomite and Katanga Upper Roan Upper Roan Skyways Quartzite Industrial Aquifer Hanging Wall Upper Section Argillite and Shale Mine Series Formation Aquiclude X Ore Quartzite, Arenite Lower Roan Formation and Arkose Aquifer B Footwall Quartzite and Bwana Mkubwa Formation Shale Aquifer Muva All Post Basement Pre Kalonga Quartzite, Mica System Katanga Rocks Formation Schist Aquifer A Basement Granite and Basement Complex Gneiss Aquifer
The three aquicludes in the area are also fundamental to understanding the hydrogeology, though not in terms of groundwater supply; they are essential for controlling groundwater flow since their low permeability forces groundwater to flow in distinct directions and also act as flow barriers that prevent mixing of groundwater.
6.2 Aquifer Characteristics
Aquifer A – Basement Complex The basement complex aquifer is made up of crystalline rocks, the rocks underlie a large part of the area and are directly relevant to the hydraulic system related to Itawa Spring because these rocks form the dome that is directly west of the spring area. The aquifer is made up of igneous rocks and metamorphosed sediments which have little primary porosity and permeability, the main water bearing features are related to weathering and secondary fracturing.
The yield of this aquifer typically around 1 l/s (HADWEN 1972) however does not compare to the quartzite and carbonate aquifer. The importance of this aquifer is due to the secondary permeability 21 of 60
combined with the location of the aquifer above the quartzite; the proximity indicate that the there is a hydraulic connection in terms of recharge and groundwater flow.
Fig. 11: Hydrogeological units.
The groundwater potential of the basement rocks is not comparable to the other three main aquifer units however in terms of the number of private boreholes and hand dug wells that supply groundwater for domestic water supply the aquifer is a very important water source.
It is important to note that the granitic aquifer on the hillside above the spring is considered highly vulnerable due to the thin weathered profile above the fresh basement rock and the high degree of fracturing.
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Aquifer B – Muva Group and Lower Roan Quartzites The rocks of the Muva system and the Lower Roan are combined (Table 1) into one hydrogeological unit, Aquifer B, known locally in Ndola as the Bwana Mkubwa aquifer. The aquifer extends around the edge of the Ndola dome and north through the forest reserve (Fig. 11) into the DRC. Aquifer B also forms the high ground in the hills to the south in the Bwana Mkubwa area. The formations in this aquifer have very different ages but the similarities in terms of structure and permeability combined with good hydraulic connection mean that they effectively can be conceptualised as one aquifer (HADWEN 1972).
The aquifer is thought to be the main source of groundwater for the Itawa Spring and to other springs in the Ndola area (Fig. 11), in particular the springs located at the Monkey Fountain and Nkwazi areas. The reason the springs are associated with this formation is due to the lithological composition of the two formations. The main permeable zones in both the Muva and Lower Roan formations are the quartzites which are highly faulted and steeply dipping. The fault and bedding structures significantly increase the permeability and recharge potential of the quartzite.
The width of the formation decreases from the north towards the Itawa area; this indicates a change in structure with the formations becoming more steeply angled near the Itawa Spring.
The quartzite is the formation which creates the aquifer from which the spring water flows but the formation of the spring is linked to fine grained shales and argillite layers which occur in two defined beds (HADWEN 1972) at the top of the Lower Roan Formation (Aquiclude X see below).
Aquifer C – Upper Roan Group Above the confining units of the Lower Roan is a thick sequence of dolomite, quartzite and argillite that forms the excellent and highly productive Aquifer C. The aquifer is found around the edge of the Ndola dome and over much of the industrial area of Ndola. The relationship between the Aquifer C and B based on the lithology is that they are separated by an impermeable unit (Aquiclude X – see below), but the separation is not continuous.
In terms of the spring formation the aquifer is present in the Itawa area but down gradient from the main spring eyes. The aquifer is believed to be source of much of the water that emerges from the ground in the long seepage zone on either side of the Itawa stream which occurs past the pump house on either side of the stream towards the bridge in Itawa.
Aquifer D – Kakontwe Limestone The Kakontwe Limestone is the major aquifer in the Ndola area and underlies the entire Dambo area (Fig. 11) between Ndola and the Congo border; the aquifer also extends into the Congo. The aquifer and limestone is of great economic importance for cement manufacturing and water supply for Kafubu Water and Sewerage Company (KWSC) but for the purposes of understanding the Itawa Spring it is not directly relevant as the unit is located down the hydraulic gradient from the springs and is separated from the Aquifer C Dolomites by the Mwashia Aquifer, Aquiclude Y (see below).
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Aquiclude X - Lower Roan Argillites and Shales Aquiclude X is not a separate defined formation such as the Mwashia and Border formations (see below) but is very significant in relation to the spring formation at Itawa and other locations around Ndola. The aquitard layers are two defined beds near the top of the Lower Roan Formation that are composed of phyllites and shales (rocks with major component being formed by clays sized particles, <2µm, with subsequent very low permeability) which form compact, non-leaky barriers (HADWEN, 1972).
These low permeability units have been documented during drilling (HADWEN, 1972) where artesian groundwater has been intersected, in the Itawa areas there are two artesian boreholes that have been flowing continuously since they were drilled (no drilling information was available). The artesian flow indicates the presence of a confining unit. This is of great relevance to understanding the flow at the spring since the two artesian boreholes close to the Itawa spring are believed to intersect Aquiclude X and then penetrate the quartzite aquifer below where it is confined and under pressure.
The existence of the artesian boreholes indicates that there is a vertical flow component; this component is due to a combination of two mechanisms:
1. Aquiclude X acts as a confining bed which causes the water to be pressurised due to the weight of the water and rock above; which is then released by the boreholes being drilled through the confining bed, thus releasing the pressure.
2. The area is a discharge zone and there is a significant horizontal and vertical flow component due to the water flowing from higher ground to the lower elevation of the discharge area.
The aquiclude X layers forms the barrier between Aquifer B, the Lower Roan Quartzite aquifer, and Aquifer C, the dolomite aquifer; this defines the upper zone of the spring. The aquiclude X forms a variable and non-continuous layers around the Ndola dome (HADWEN 1972). This is of significance in relation to flow between the quartzite aquifer and the dolomitic Upper Roan aquifer (Aquifer C). In the context of the Itawa spring this lack of continuity of the flow barrier could allow waters from the dolomitic Aquifer C to mix with the quartzite Aquifer B. The degree of mixing between the aquifer units is fundamental to the recharge and groundwater flow in the Ndola area.
Aquiclude Y - Mwashia Formation The Mwashia Formation overlies the Upper Roan Dolomites to form the lowest unit of the Kundelungu Series (See Table 1), the Mwashia Formation which for classification is termed Aquiclude Y, is composed of a tillite (glacial clay) unit and carbonaceous shale. These rocks form the eastern and southern flanks of the Ndola dome.
The low permeability and the location of the bed between aquifer C and D is also a factor in the spring formation, especially in the lower section east of the main spring eyes. Evidence for the presence is inferred based on geological maps and due to the penetration of boreholes drilled for water supply that intersected Iron rich groundwater in the area of the bridge at Itawa; which is associated with shales and tillites.
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The unit does vary significantly across the Ndola area with the unit being composed of carbonaceous shale in the area of the spring and changes to include a lava unit to the North of the Ndola Dome (MOORE, 1967). The Mwashia formation is also important as this mostly impermeable units lies at the base of the Kakontwe Limestone, the formation thus could form an impermeable barrier for the Kakontwe Limestone reservoir.
Aquiclude Z - Border Group The border units forms the local catchment divide between Kafue and Congo and is located along the border between Zambia and DRC to the East of Ndola. The unit is not thought to have any relevance to the hydrogeology of the Itawa Springs.
6.3 Groundwater Infiltration The rate to which groundwater infiltrates is important to the formation of the spring for two reasons:
1. The degree that the upper soil layers provide a protective cover is an important element in understanding and protecting the spring. 2. The recharge mechanisms to the aquifer are directly related to physical/hydraulic properties and the presence or absence of the upper soil layers.
Another part of the equation where soil relates to groundwater is that the Ndola area has very high evaporation rates (JICA 1995), in order for rainwater to infiltrate it is necessary for the water to travel quickly through the upper layer or be lost to evaporation and therefore groundwater recharge.
The permeability of the soils of the main units was analysed using sand analysis curves (MENDELSOHN, 1961). This allows the relative proportion of clay, silt and sand to be calculated and the permeability of various parts of the soil and weathered zone to be inferred.
In general the soils of the granite and quartzite have better permeability than the carbonate aquifer which has very high clay content in the soil. Unsurprisingly the aquicludes have the poorest infiltration rates, which are in fact not that dissimilar to the limestone soils in terms of clay and silt content.
The infiltration capacity reveals that the soils make good protective cover but when removed the pathways created can and do provide fast recharge infiltration pathways. In the case of the main aquifer for the springs the removal of the soil cover and/or the exposure of the aquifer will lead to rapid infiltration and high vulnerability.
In the Itawa area the soil generally correlate to the geological units in combination with the topography. To the West of the spring the soils are formed over the basement rock, these are general beige coloured clay and sands. On the slope of the hill the soils change to light textured loam in the area underlain by the quartzite in the upper section of the spring and then change again in the spring seepage area where the soils are red/brown silt and clay which are developed over the limestones and mudstones.
The soil is also part of the weathering process which forms as rocks are altered due to chemical and physical weathering. The depth of the weathering profile plays a key role in recharge and vulnerability of groundwater. In the case of the area on the hillside above the spring the construction of the railway
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involved cutting into the slope which is underlain by granite. This has reduced the natural soil and weathered zone and in places exposed fresh fractured granite (Fig. 10). This changes fundamentally the vulnerability of the groundwater especially as an unlined drain runs along the track below ground level and adjacent to fractured granite outcrop in places.
In the spring area other activities also cause the soil and weathered zone to be reduced, these were identified as:
Cultivation on steep slopes Aligning crop ridges downslope Brick making Digging to expose fresh rock that is broken for sale as building aggregate
These activities increase erosion and create holes, some of which are then used for rubbish disposal; all these activities increase the vulnerability of the groundwater to contamination
6.4 Groundwater Flow Directions The direction of groundwater flow is a function of both the topography and the aquifer characteristics. The flow directions are vital to understanding the spring since they determine where the recharge areas are and in which direction the groundwater is flowing. The flow system involves flow from the recharge area along a pathway to a discharge area. In general flow off the dome forms a subdued reflection of the topography.
Fig. 12 shows the topography and highlights the areas that are above 1,300 masl; the flow directions are seen to be perpendicular to the topography in the granite basement area. Within the shallow basement aquifer the groundwater flow will follow the topography to a greater extent than within the structurally controlled Katanga aquifers. In the area above the spring the groundwater will form a subdued reflection of topography, the topographic divide will therefore also act as a groundwater divide that will form part of the recharge area for the spring. Based on the available geological and other reports the flow directions for the water that flows at the Itawa Springs is due to flow along quartzite Aquifer B. The quartzite aquifer is located to the north and south of the spring (fig. 12) around the edge of the dome and outcrops again in the hill to the south. The groundwater flow was thought to be from the high ground to the south in the Bwana Mkubwa area (ASTA, 2013) north towards the Kafubu River, then towards the Itawa spring, a distance of about 20 kilometres.
Flow from the north along Aquifer B has not been cited as an important consideration however based on the geological and topographic maps flow is possible. The aquifer extends to the North of Itawa to higher elevations where there exists a forest reserve and into the DRC, these areas are potential recharge areas that are close to the Itawa spring where the aquifer B is at a higher elevation and does not have to flow under the Kafubu River.
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Fig. 12: Groundwater flow directions.
The boundary between Aquifer A, the Basement aquifer of the Ndola dome with the quartzite Aquifer B is extensive along the edge of the dome. In the vicinity of the spring the boundary is metres from the spring and coincident with steep topographic slope directly to the west of the spring towards the residential area of Northrise. The effect of this extensive contact is that the basement aquifer must contribute some groundwater flow to the quartzite.
Based on the field mapping and literature review the springs are controlled by flow within aquifer B meeting a subsurface impermeable barrier that forces the groundwater to the surface. In order to confirm the reported and observed groundwater flow direction, water levels throughout the Ndola area were measured in both boreholes and hand dug wells. In the case of the boreholes a key element 27 of 60
was to understand whether the borehole had been pumped recently in order to identify if the water level was a dynamic (effected by pumping) or a static water level that would correctly indicate the rest water level and therefore be of use to measure the relative heights of water levels and hence groundwater flow directions. The water level data is presented as Appendix I.
In order to understand the groundwater flow directions in a complex hydrogeological setting the ground level at each point had to be used as a reference in order to compare water levels where there is significant topography. For a selection of boreholes (Fig. 13) and wells in the Itawa area and in selected boreholes across Ndola the surface elevation was measured using the more accurate Differential GPS (DGPS). Using the DGPS the ground level can be used as reference for water levels in boreholes which can then be measured as metres above sea level (masl) with a deviation of less than 10 cm in comparison to handheld GPS with an elevation accuracy of plus or minus 4 m.
Fig. 13: Measuring ground elevation using DGPS.
The groundwater flow directions and the permeability of the hydraulic units can be inferred from the groundwater contours. The contour lines (Fig. 14) represent point of equal height of the water table with the groundwater flow being in general at right angles to the contour. The spacing of the contour lines is largely controlled by the permeability of the aquifers and aquitards. The contour lines and water levels in the Itawa area indicate that there is widely spaced contour to the East of the main spring and closely spaced contours on the edge of the granite dome.
The contour spacing around the spring confirms the geological interpretation that the quartzite aquifer unit borders a low permeability layer that forces the groundwater to be impounded and thus forced to the surface. The low permeability boundary is coincident with the phyllite and shale beds between the Lower and Upper Roan – Aquiclude X. The geological map also shows a change in structure of the upper member of Aquifer B, the hanging wall formation, to the immediate north of the formation; the formation, based on the geological map, is seen to narrow (Fig. 14) as it approaches the spring. The change is due to a steepening of the angle and a constriction of the formation which is a structural control for the spring formation.
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Fig. 14: Groundwater flow contours
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The low permeability units also provide the hydraulic explanation for the presence of the artesian boreholes that are present close to the spring. The upward flow component necessary for artesian conditions was in the case of the Itawa spring interpreted as the release of pressure due to intersection of the quartzite aquifer where it is confined at depth by a hydraulic barrier formed by aquiclude X. The necessary head for the artesian flow can be attributed to the higher groundwater levels in aquifer B to the north of the spring.
Artesian Borehole Zambia near to pump house Breweries and spring
Pump house
Pit Latrine
House built metres from artesian borehole
Fig. 15: Pit latrine near pump house.
The water levels indicate steep groundwater flow gradients to the West and North of the spring and much shallower gradients past the pump house and on both sides of the stream which are interpreted as a groundwater seepage zone; this indicates that there are two possible sources for the spring:
1. The quartzite aquifer where the upper part of the spring flows shows groundwater flow direction from the north. 2. The water level flow direction measured indicate a water flow to the south in the area in the area to the south of the spring in close to the Kafubu River and across the Kafubu the water level height was measured as lower than the spring level, this confirms that groundwater flow is not from the south towards the spring. 3. The steep water level gradients and from the dome indicate flow from the off the basement aquifer to the west of the spring, this is significant locally in terms of the hydraulic connection and flow to the spring and also on a larger scale indicates a recharge source to the quartzite through the large contact area.
The groundwater flow gradient and contour lines in the vicinity of the spring and especially beyond the pump house indicate that the groundwater is flowing below the upper zone from west to East in the Itawa spring area. This is significant since most of the pit latrines that are densely concentrated around the Itawa area are down gradient from the main spring area where water is abstracted for Zambian Breweries. This does not mean that the pit latrines are not contaminating the local water supply wells and the stream that runs through Mapalo; measurement of contamination in shallow 30 of 60
wells and the stream by this project and others (ASTA 2013, LIDDLE 2014), have measured high levels of faecal coliform contamination.
There is one area (Fig. 15) where houses have been constructed just 60 m north of the pump house. The artesian boreholes and the spring are situated below the houses; in this area pit latrines do pose a contamination threat to the spring which has been confirmed by the flow direction measurement which indicate water levels above the spring level, this indications that there is flow from the North. During the ASTA project in 2013 monitoring borehole were drilled around the spring (Tab. 1), two monitoring borehole were drilled close to the effluent channel. The water levels were measured at the end of the dry season in October and November in 2013.
Tab. 2: Monitoring well data.
Monitoring Well ID Groundwater level (in mbgl) 15th October 22nd October 15th November MB1 3.33 3.40 3.39 MB2 5.30 5.32 5.34 MB3 5.32 5.34 5.48 MB4 1.40 1.38 1.42 MB5* 3.15 3.25 3.12 MB6 4.79 4.62 4.52 MB7* 6.33 6.25 5.89 MB8 6.58 6.62 6.73 * Visible on Fig. 23.
Most of the monitoring boreholes show the expected seasonal water drop, however the monitoring boreholes 5, 6 and 7 show water level rises. Water level contours east from the effluent channel also show a higher relative water level (Fig. 14); the explanation for the both water level observations is that there must be a recharge source; the proximity of the effluent channel makes this the most probable source. This also is an indication that there is shallow groundwater flow from north to south towards the lower zones of the spring which is highly significant as the main contaminant threat from the effluent drain will not affect the upper zone.
6.5 Discharge Measurements from Artesian Boreholes and Springs Flow measurements were carried out at three locations, the two artesian boreholes and the point upstream of the bathing pool where a number of spring outflow coalesce to form a defined channel. The flow measurements at the artesian boreholes were carried out by fabrication of temporary caps over the artesian flow that forced all the flow into a pipe where the outflow was measured using a container of known volume. The temporary caps were also designed so that manometers could be installed that would channel all the flow into a clear plastic tube so the water level above the surface, the piezometric surface, could be measured (Fig. 16).
Fehler! Verweisquelle konnte nicht gefunden werden.: Measuring artesian head
The design of the caps was emphasised to be temporary to the local community who use both boreholes as important water resources from drinking, washing, brick making and irrigation.
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Permission from community representatives and the local councillor were obtained before the measurements were made; the caps were then removed and normal flow resumed.
V Notch Weir
Fig. 16: Surface flow measurement.
The flow measurement at the artesian borehole 1 located close to the pump house were measure at 5.5 l/s with an artesian head of 1.45 m above ground level, the flow measurement made by ASTA (2013) measured as 7.9 l/s. The second artesian borehole had a slightly lower flow rate of 4.5 l/s but the head was seen to be significantly different at 5.5 m above ground level; however when the DGPS survey was carried out it was calculated that the difference in elevation was 4 m, this indicates a similar origin for the water. The flow measurement made by ASTA (2013) was virtually identical at 4.44 l/s.
Measurements of surface flow were carried out in the upper section near the main spring eyes, the measure was made at a single point where several channels coalesce. This point was located 40 m from the main spring eye. The surface flow from the springs was constrained into a defined channel with solid sides; the point chosen was the point close to the men’s bathing pool where one of the main inlets for the pipe that flows to the ZB pumping house was located, at this point a V-notch weir was installed (Fig. 16) The flow at this point was measured at 17 l/s on August 7th 2015.
It must be underlined that the measurement made by this project and the measurements carried out by ASTA in 2013 were flow measurement taken at a single point in time and during the same season; in this case both sets of measurements were carried out during the dry season. In order to create a complete picture of flow at the spring it is necessary to monitor the flow at key points (See Chapter 12) throughout the year in combination with rainfall measurements of both quantity and intensity, in order to build a detailed picture of the water balance from at least one complete cycle of dry to wet to dry season. It must be noted that one cycle may not be representative if it includes above or below annual rainfall and an ideal situation should include at least measurement during a low rainfall season, but ideally a minimum of two or three cycles that should include wet and dry rainy seasons.
7. Hydrochemistry Water samples were taken in order to provide information on the origin of the water for the Itawa Spring and to assess the general water quality from boreholes, shallow wells, springs and surface
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water in Ndola. The sampling was carried out during two field campaigns. The initial reconnaissance campaign was carried out in November 2013 when 15 samples were taken from the Itawa spring area and all the major aquifers. A second field sampling campaign was carried out in May/June 2015 where 51 water samples were taken.
The sample locations were chosen in order to identify the source of the water for the spring, the flow directions and the general water quality both in terms or inorganic and microbiological water quality. The emphasis for the hydrochemical sampling (Fig. 17) was to understand groundwater flow to the spring. Particular emphasis was put on the quartzite aquifer identified as the main source for the spring, the quartzite aquifer B; two other springs were sampled that were located and reported to have their origin in the quartzite aquifer.
The second field campaign also sampled water from all the possible flow directions towards the Itawa Spring/Kafubu River system, thus samples and water levels were taken from the far south in the Bwana Mkubwa area where the eventual origin of the water was noted (ASTA, 2013) and other possible flow lines which were based on analysis of the geological structures.
7.1 Sampling Methodology The inorganic sampling was carried out in order to look at the relationship between the aquifer lithological types and the groundwater composition. At each site water was sampled in separate bottles for the analyses of major anions, cations and heavy metals. Alkalinity was analysed on-site by potentiometric titration with 0.01 N HCl (TITRISOL). Water samples for cations and heavy metals analysis were microfiltered (0.45 μm) and acidified with HNO3. Stable isotopes were also sampled during the second sampling campaign. All the inorganic water samples were analysed by the Water Laboratory of the Federal institute of Geosciences and Natural Resources (BGR) in Hanover.
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Fig. 17: Sampling sites.
Organic water quality was determined by collecting water samples for analysis at a laboratory for microbiological water quality. The laboratories used were the Seeds of Hope (a local NGO) and the ZB laboratory. The Seeds of hope laboratory sampled for E. coli and general coliforms; the Zambian Breweries analysed only for total coliforms (sum or E.coli and general coliforms). The samples were collected and stored in a cool box then delivered to the laboratories within 6 hours of collection.
The objective of the E.coli analyses was to look at thermophilic bacteria which represent bacteria that could have their origin in mammalian digestive systems and thus act as indicators of faecal contamination. The tests done at ZB for total coliforms were carried out for comparison. It should be noted that positive reading for coliforms are not a definite indication of faecal contamination since coliforms can have their origin from natural processes.
Stable isotopes were also sampled at the 51 locations, this technique has been extensively used to examine the hydrological cycle and act as ideal tracers of analysing the movement of water; in particular for this project isotopes studies were intended to look at the potential recharge, flow
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direction and length and the discharge areas. The isotope samples were tested for the naturally occurring isotopes of Deuterium (2H) and Oxygen-18 (18O) in water. Stable isotopes compositions were determined by Cavity Ring-Down Spectrometry (CRDS). In situ measurements were taken and recorded during the sampling along with supporting information about the site. The in situ measurement included EC, pH, Eh and water temperature. The parameters were taken on site as changes in temperature and pH can occur within minutes (e.g. BARTRAM ET AL. 1996); the pH is key to understanding the occurrence of certain elements in particular metals which become mobile under certain pH. In the Copperbelt metal mobility in groundwater (CZECH GEOLOGICAL SURVEY 2003, KAMBOLE 2003) is a major concern due to the legacy of and ongoing mining activities though it should be pointed out that mineralised areas can and do have a naturally occurring concentration of metals which should be identified as a baseline and that certain elements such as arsenic can occur naturally.
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7.2 Hydrochemical Results As chemical analyses were taken from all the main units with the exception of the border formation, it would be expected that there would be significant variations in groundwater chemistry based on the groundwater being a reflection of the aquifer mineralogy. The results however indicate (Fig. 19) that there is not clear indication in the samples that could be attributed to the mineralogy of the different geological units with the exception of an expected increase in calcium in the carbonate aquifers.
Fig. 18: Piper Diagram of hydrochemical and pollution indicators
The lack of a clear relation between the chemical signature and the lithology indicate that the water is young in that it has not been in contact with the host rock of the aquifer for long. This is confirmed when the stable isotope data is interpreted as the water from the 51 samples plot along the meteoric line with only a slight deviation which is probably due to evaporation. Trace elements were analysed and the samples did not show elevated levels of heavy metals that are associated with the Mine Series. This may be due to the buffering capacity of the carbonates in the
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aquifers C and D. Aquifer C underlies much of the industrial area, the lack of heavy metal contamination in may be due to pH buffering but will also be due in large part to the fact that Ndola, with the exception of the Bwana Mkubwa Mine was never a mining centre. This does however not preclude the possibility that there are other contaminants in the water. As groundwater flows other processes also take place such as ion exchange. These changes would be expected to be seen if water had flowed from the Bwana Mkubwa area over 20km towards the spring, there is no indication of ion exchange along a flow line north towards the spring from the Bwana Mkubwa high ground were found. The water chemistry indicates that the recharge area for the Itawa spring water and the water from the other springs is nearer to the spring and due to recent recharge. Indications of faecal contamination were found at 15 of the 51 sites sampled. The springs at Ngwazi and Monkey fountains both tested positive for E.coli. The surrounding area is different in both cases, the Ngwazi area having obvious contamination sources due to being surrounded by a high density informal settlement but the Monkey Fountain Spring has no obvious contamination sources nearby. This is an indication that the contamination is possible through subsurface flow within the quartzite aquifer. Four of samples also indicate elevated levels of nitrate, sulphate and chloride (Fig. 19), these levels are pollution indicators and there location close to pit latrines in further confirmation of contamination due sanitation. At the Itawa spring the artesian boreholes and the spring at its highest point were found to be free of E.coli, however the surface flow at the V notch site was highly contaminated with 92 colonies per 100 ml, this is especially of concern as this is the point where the flow was measured at 17 l/s. The level of contamination means that there could be a link between the leaking sewer and the spring system through shallow surface pathways.
8. Environmental Isotopes
8.1 Occurrence of Deuterium and Oxygen-18 The concentration of the natural occurring stable isotopes deuterium (2H) and oxygen-18 (18O) in water has been used as a tool to examine the hydrological cycle. MAZOR (1997) considers them as ideal tracers for analysing the movement of water. Recharge and discharge processes of aquifers or between surface water and groundwater can be identified through the analysis of stable isotopes. The isotope relationship of a water sample is notated as deviation in ‰ from the international reference concentration, the Vienna Standard Mean Ocean Water (VSMOW). The deviation of deuterium and oxygen-18 is calculated by.
22 ( H/H)Sample -( H/H) VSMOW 2 H[‰]= ×1000 (2 H/H) VSMOW
18 16 18 16 ( O/ O)Sample -( O/ O) VSMOW 18O[‰]= ×1000 18 16 ( O/ O)VSMOW δ = relative deviation in ‰
RatioSample = isotope content of the sample 37 of 60
RatioVSMOW= isotope content of the Standard Mean Ocean Water
The relationship between 2H and 18O in global precipitation can be expressed by the formula:
2 18 H 8 O d d = deuterium excess The comparison of worldwide precipitation data through Craig (1961) determined the global meteoric water line (GMWL) with a d-excess of 10:
2 18 H 8 O 10 The meteoric line is normally plotted in a δ2H -δ18O diagram where it is used as a reference line. Fehler! Verweisquelle konnte nicht gefunden werden. shows also a selection of fractionation processes which may influence the isotope values in rain water and consequently the composition of groundwater. The isotope values of rainwater may be influenced by the temperature of rainwater, evaporation, the altitude or its intensity. Groundwater may also interact with its geological environment.
+20
0 ‰ Meteoric Water ‰ Lines -20 δ2H = 8δ18O + d Israel, d = +24 ‰ -40
, VSMOW)
‰ Evaporation -60 Arizona, d = 0 Global (Craig, 1961), d = +10
H (
2
δ Mean -80 Geothermal Exchange Low Temperature Water-Rock Exchange -100 -12 -10 -8 -6 -4 -2 0 +2 +4 δ18O (‰, VSMOW)
Fig. 19: Examples of the relationship between δ2H and δ18O in meteoric water, evaporating water and water in interactions with rock (taken from COOK AND HERCZEG 2000). 8.2 Stable Isotopes in Precipitation and Surface Water During the rainy season 2014/2015 rainwater has been collected in Ndola at the site of the Zambian Breweries through a standard rain collector. Data, amount and duration of rainfall events were noted. If quantities of rainwater allowed for, it has also been collected in 50 ml plastic bottles. In total 10 rainwater samples were taken in Ndola. Additionally rainwater isotope data from collectors in Lusaka (6 samples) and Chongwe (5 samples) was analysed and used for comparison (Tab. 3). Since Chongwe is very close to Lusaka rainfall measurements are considered together with those from Lusaka. The Meteoric Water Lines of Ndola and also of Lusaka are described by a very similar linear fit (see Fig. 20). Since the data for interpretation is limited it can be assumed that the isotopic composition of 38 of 60
precipitation at both locations is comparable. In addition the Meteoric Water Lines are also very close to the standard Global Meteoric Water Line (GMWL) which is by definition a global mean trend of the stable isotope composition of precipitation.
Tab. 3: Stable isotope composition of local rainfall.
No. Code Location d18O [‰] d2H [‰] DE* Symbol 1 P-CHO-D-06 Chongwe -7.81 -50.1 12 □ 2 P-CHO-D-07 Chongwe -2.32 -3.7 15 □ 3 P-CHO-D-08 Chongwe -4.54 -22.9 13 □ 4 P-CHO-D-09 Chongwe -3.27 -14.2 12 □ 5 P-CHO-D-01 Chongwe -4.15 -26.5 7 □ 6 P-LUS-E-061 Lusaka -3.83 -17.0 14 ∆ 7 P-LUS-E-062 Lusaka -2.90 -9.8 13 ∆ 8 P-LUS-E-063 Lusaka -5.58 -33.5 11 ∆ 9 P-LUS-E-064 Lusaka -5.17 -33.7 8 ∆ 10 P-LUS-E-065 Lusaka -2.72 -10.6 11 ∆ 11 P-LUS-E-066 Lusaka -10.44 -69.9 14 ∆ 12 P-NDO-R-036 Ndola -0.02 11.3 11 ○ 13 P-NDO-R-037 Ndola -2.10 -8.2 9 ○ 14 P-NDO-R-038 Ndola -4.31 -26.2 8 ○ 15 P-NDO-R-039 Ndola -3.42 -22.6 5 ○ 16 P-NDO-R-040 Ndola -4.15 -21.2 12 ○ 17 P-NDO-R-041 Ndola -2.81 -11.4 11 ○ 18 P-NDO-R-042 Ndola -2.03 -8.2 8 ○ 19 P-NDO-R-043 Ndola -7.51 -46.6 13 ○ 20 P-NDO-R-044 Ndola -6.42 -42.8 9 ○ 21 P-NDO-R-045 Ndola -7.04 -45.4 11 ○ *DE = Deuterium Excess
It also observed that samples from different rainfall events are scattered along the MWL representing temperature differences.
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Fig. 20: Stable isotope composition of rainfalls in Ndola, Lusaka and Chongwe.
8.3 Stable Isotopes in Groundwater The stable isotope composition of groundwater in the Ndola area generally represents the mean annual precipitation (Fig. 21). The 51 groundwater samples from Ndola (Fig. 22) are grouped close along the MWL. This would point at the infiltration of rainfall being the origin of shallow and also deep groundwater. However, a slight scatter of samples along the GMWL can be observed which may point at local or seasonal differences in the isotope composition of the precipitation. This observation can be eventually interpreted as an indication of a yet not fully accomplished mixing with groundwater. This may be due to local differences or eventually also because of a rather recent recharge of groundwater. Other tests, e.g. tritium analyses, may reveal more information regarding the recharge age of groundwater in the Ndola area which cannot be derived from stable isotope results. Radioisotope studies for the aquifers of Kabwe and Lusaka by TEMBO & NKHUWA (1997) calculated a mean age of 5 to 14 years derived from tritium measurements. Water in comparable systems could therefore be equally recent. The groundwater samples are also plotting very close to the MWL. Although a mathematical fit of the groundwater sample points shows a linear fit with a lower slope than the MWL it seems that evaporation plays a minor role for the recharge of the groundwater resources. Therefore infiltration of rainwater is likely to occur very close to where the rainfall occurred and also happened quite quickly. The infiltration from surface water bodies seems to be of lesser importance.
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It could be recommendable to run a local tracer test in the Itawa area in order to determine the eventual flow paths towards the spring and the flow velocity. Also the comparison of isotope data from the different groundwater boreholes in regard to their respective tapped geology is not very distinct from another. That may also show that groundwater in Ndola is formed by recent recharge and that at least the major part of recharge to the Itawa Spring Catchment takes place locally or nearby. Infiltration may occur rapidly since also an effect of evaporation is not clearly observed by the isotope distribution.
Fig. 21: Stable isotope composition of groundwater equals the mean annual precipitation (from CLARK & FRITZ, 1997).
Fig. 22: Stable isotope composition of the 51 groundwater samples in Ndola in relation to the rainfall samples.
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9. Identification of Threats to Groundwater The main objective of the project is to assist other organisations in the protection of the spring. Understanding of the hydrogeology of the aquifer is a key component but other factors must be included; the identification of the potential contamination threats within their hydrogeological context is essential. The main threats were identified as:
Local contamination due leaking sewers Sanitation Effluent discharge Heavy metal and industrial contamination Reduction of protective soil cover Hydrocarbons
9.1 Local Contamination from Leaking Sewers The field mapping in the area around the spring identified two locations where the main sewer line was leaking; the location of the leaks was in the vicinity of the north eastern section of the Zambian Breweries plant (Fig. 23) and the railway line.
Fig. 23: Itawa area contamination sources. 42 of 60
The presence of a main sewer line was confirmed with KWSC who were unaware of the leak; plans of the sewer network were also located which show a main sewer line running parallel to the railway track.
The source of the main leak was initially thought to be very close to the railway track however the main leak was covered by a dense thicket of Lantana and other vegetation; the location was traced by following and cutting back the foliage along the flow of effluent (Fig. 24). The density of the thicket is thought to be due to the presence of the leak being present from many months or possibly years; the liquid thus supplies water and a high nutrient load due to the untreated sewage. The main break was located next to the wall with the flats adjacent to the ZB plant.
Fig. 24: Main sewer leakage.
A second smaller leak was located next to the wall with ZB which was interpreted to be a continuation of the main sewer line, this is indication that the sewer line then passes under the Zambian Breweries
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plant and would then continue south to the treatment plant situated by the dambo although the route was not confirmed.
The location of the leaks is within 250 m of the main spring eye and uphill from main spring eyes. The effluent from the leaks flows downhill to close to the railway track then ponds; at this point there is no further surface flow and infiltration is taking place in an area where the granite has only a minimal weathered horizon due to the slope and alteration of the topography as a result of the railway track construction. These leaks represent major point source groundwater contaminant threats.
9.2 Sanitation The sanitation in the area of the spring is by pit latrines which are dug by the residents in close proximity to their houses. In general there is a pit latrine for each house due to the fact that shared facilities are not preferred because of conflict over cleaning and security. In much of the area the water table is very shallow; the result of the shallow water table is that the water supply wells are highly vulnerable to pollution from pit latrines. This is exacerbated by a lack of planning whereby in a number of locations pit latrines were found metres (Fig. 25) away from shallow unlined water wells which increases the contamination threat.
In the main spring area the groundwater quality was found to be poor due to the presence of E.coli bacteria in the water. Reported levels of E.coli (ASTA 2013) in shallow wells in the Itawa area exceeded 1,000 E.coli colonies. In the Itawa area the density of the housing causes major health issues due to the proximity of water supply wells and pit latrines. Fig. 25 shows a water supply well with a pit latrine 5 metres away.
Both the artesian boreholes and the spring were sampled along with a further sample 30 metres from one of the main spring eyes; of the four samples the artesian boreholes and the main spring eye were not found to contain E.coli but the sample from the V-Notch measurement site (Fig. 23) contained E.coli; this indicates a local contaminant source.
In general the groundwater flow direction in the Mapalo area indicate that contamination from pit latrines will not affect the main spring eye, the exception is the houses built close (Fig. 23) to the artesian borehole which are situated over the groundwater flow lines. The pit latrines in this area coupled with the shallow weathering create a possible contamination pathway.
The secluded area around the main spring eye is used by local men for use for bathing and recreation, this bathing pool (Fig. 24) is very close to the main inlet for the buried pipe that supplies water to the pump house. The contamination in the water and evidence of open defecation in the area is an imminent contamination source.
Uphill from the spring in the Northrise area there exists a sewer network but the extent to which the houses are linked to the main sewer system was not quantified; what was observed was that the sewer system in the flats adjacent to Zambian Breweries (Fig. 24) were leaking, though this could be due to the blockage that is causing the main leak identified near the boundary. In other residential areas of Northrise the possibility of leaking sewers and private septic tanks is a contamination threat in an area where direct groundwater flow towards the spring is possible.
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Pit Latrine 5m from Well
Hand Dug Shallow Well
Fig. 25: Image of pit latrine close to hand dug well. 9.3 Effluent Drains Within the Itawa spring area one of the components of flow is a natural drainage channel that rises to the west of the spring which then runs south of ZB (Fig. 26), when the channel reaches the southern entrance to the brewery it becomes a lined concrete channel, which is covered, that runs through the adjacent property then north towards the spring; the channel then turns East and runs in an unlined channel past Kola Compound to meet the Itawa stream near the bridge.
The water quality of the channel changes as it runs to the south of the brewery in the covered channel. Where the water quality change occurs coincides with the route of the main sewer line which is the same main sewer line which is leaking to the north of the spring. The occurrence of sewer can be easily detected by its smell. It is highly probable that the water quality change from water with no smell to water with a definite smell of sewerage is due to this channel and the main or a local sewer line being connected.
As the drain runs along the Zambian Breweries plant it is lined with concrete, however when it crosses the railway track and flows north towards the Itawa Bridge the drain is unlined. The monitoring borehole MB7 and MB5 recorded water level rises (Table 2) in October to November 2013 (ASTA, 2013); a possible source for this recharge is infiltration through the base of the channel to shallow groundwater in the area.
A second effluent source was located near to Artesian Borehole 2; the location was initially noted due to the density of cultivation and vegetation. It was then observed on two occasions that effluent flows from a pipe directly onto the fields. The source was not confirmed but is thought to come from the treatment works at the Zambian Breweries plant.
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Fig. 26: Effluent channels.
The unlined channel and the pipeline are contaminant sources which based on the monitoring borehole data are leaking into the groundwater. The second artesian borehole is in close proximity to both these contaminant sources but the water quality test revealed low nitrates and no E.coli. This demonstrates that the confining layer which causes the artesian pressure also acts as a protective layer from local contamination.
In the close vicinity to the drain is a bottling plant for Aquapura mineral water, this is located within 100 m of the drain near the Zambian Breweries plant. Water was sampled for both inorganic and microbiological contamination and no contamination was found at this site. The lack of contamination at the Aquapura borehole can be attributed to two causes:
1. The groundwater flow direction is away from the borehole and to the north towards the spring. 2. The borehole abstracts water from a deeper part of the aquifer and the abstraction rate does not cause vertical flow. 3. The borehole intersects a confined aquifer similar to the artesian boreholes.
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Fig. 27: Effluent drain.
What can however be interpreted from the data is that the effluent channels , especially the main unlined channel that flows past Kola Compound (Fig. 27), is that the shallow groundwater is being contaminated as samples from ND50B, a borehole in Kola Compound tested positive for faecal coliforms. However this could also be attributed to contamination from pit latrines.
The locations of the monitoring wells in proximity to the effluent channel and pipe, coupled with a shallow groundwater table and the lack of an impermeable liner are all condition that makes direct infiltration of the contaminated water to groundwater possible.
9.4 Heavy Metal and Industrial Contamination The Industrial area of Ndola is located south of the springs; the area extends from the ZB plant south and across the Kafubu River. Much of the area is also underlain by the Bwana Mkubwa Quartzite aquifer and the Upper Roan Dolomite. The risk of contamination from industrial areas is a known and documented problem around the world (e.g. BEDIENT ET AL. 1994).
The presence of most of the towns in the Copperbelt is related to the economic concentration of mineral such as copper, cobalt and lead. In many mineralised areas it is essential to create a baseline for the water quality in the groundwater in order to assess if contamination is present and also for a comparison for future monitoring and attenuation attempts.
The possible contamination from industry and past mining activities was assessed by the water sampling where major, minor and trace elements were analysed (Annex 3 and Annex 4), the results indicate that there is no build-up of heavy metals in the groundwater. This result is surprising given
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the history of the area and could be due to a combination of factors such as retardation with the soil and weathered zone, buffering due the carbonate lithology and dilution due to high permeability of the aquifer that underlie the industrial area. The lack of heavy metal contamination in the analysed samples however acts as a baseline and should form a basis for continued monitoring, especially during or after the rains.
9.5 Reduction of Protective Soil Cover The soil and weathered zone form a protective cover over the aquifer in the Itawa area; in the area of the spring the depth of the soil and weathered zone was observed to be shallow. The shallow depth to bedrock makes the protective soil and weathered zone cover of even greater importance and a barrier to contamination. The soil and weathered zone was however found to be reduced due to the following reasons:
1. Brickmaking - close to the pump house and spring bricks are made using the water from Artesian Borehole 1, the removal of the soil layer reduces the protective layer thus increasing the vulnerability of the aquifer and is also often used afterwards for rubbish disposal. 2. Poor cultivation techniques - cultivation on steep slopes and aligning the ridges down slope increase erosion which removes the soil layer. One of the main spring eyes is situated almost directly underneath the railway track, the location of the main spring eyes in the mapping done by HADWEN in 1972 records the main spring eyes tens of metres from the railway track, the migration of the spring eye can be attributed to headward erosion. The location of the spring eye closest to the railway track is the result of erosion that has now developed to such an extent that it threatens the stability of the slope which forms the foundation for the railway track. 3. Aggregate Production – in the spring area outcrop of granite was exposed the local population have been using this area to produce building aggregate which involves excavating the fresh rock for breaking to aggregate; this activity increases the vulnerability of the aquifer by removing the protective cover. The excavations were also found to be filled with rubbish.
9.6 Hydrocarbons The presence of a petrol station (Fig. 27) adjacent to the Zambian Breweries plant is a possible contamination threat. Evidence from Europe and America indicate that many underground fuel storage tanks leak, the location of the petrol station on the steep slope coincides with the location of the quartzite aquifer. The lack of a deep weathered layer on the slopes and the structure of the aquifer create conditions where leakage of fuel could infiltrate into the aquifer. Hydrocarbons pose a health risk when present in even very small quantities, one part per million, and are very difficult and expensive to clean from an aquifer.
10. Conceptual Hydrogeological Model The conceptual hydrogeological model is a description of how the system works that is accessible to a wide range of audiences. In order to create the model it is necessary to make certain assumption and simplifications, this is especially true in the case of the Itawa spring where there is a complex
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system of aquifers and a spring system that is not a single isolated outflow but is a combination of defined spring eyes and a wide extended seepage zone.
The geology and structure of the units present in the Itawa area consist of multiple changes in lithology but what is important is how and where the water is flowing from and where are the discharge points. The hydrogeological domain for the Itawa Spring is made more complex by the interpretation that there is an upper and lower section of the spring that is fed by two different aquifer systems.
10.1 The Upper Spring Section The upper section of the spring is defined as the area to the west of the pump house where there is more defined flow from distinct spring eyes. This section of the spring lies on the slope of the Ndola dome where outcrop of granite was located along the railway track. The main spring eyes in the conceptual model (Fig. 29) correspond with one of the impermeable aquiclude X layers; flow at the surface at this point is at the topographic low point.
0 50 100 200 Legend Stream Metres Aquiclude X Railway Track Aquifer C Aquifer B Aquifer A Groundwater Flow Direction
Spring Flow From Topographic Low Main Spring Point Intersecting Eyes Pump House ! Impermable Layer !
! of Aquiclude X !
Upper Section Lower Section of Spring of Spring
Fig. 28: Conceptual local groundwater flow.
Flow in Aquifer B has three flow directions where adjacent impermeable layers form no-flow boundary conditions. The main flow component is conceptualised as being from the North due to the hydraulic head distribution and high permeability of the quartzite aquifer; other flow components could be from the south and off the dome due to the hydraulic connection with the basement rocks.
Below the quartzite aquifer the basement rocks are seen to outcrop at multiple locations along the drain of the railway track within 100 m of the main spring eyes. The basement aquifer is in contact with the quartzite aquifer all around the edge of the dome but for the purposes of defining a hydrogeological domain the area that contributes to flow to the spring should be identified. Groundwater flow in basement aquifers is usually a subdued reflection of the topography and the water level contours confirm this, the effect on the model is that a groundwater divide (Fig. 30) will follow the topographic divide above the spring and define an area which is part of the model domain. 49 of 60
Fig. 29: Conceptual groundwater flow.
The quartzite Aquifer B occurs around the edge of the dome and to the south in the Bwana Mkubwa area from which it gets its local name. The flow in the upper section of the spring has been attributed to flow from the hills to the South, which are over 20 km away, however the water level and hydrochemical data indicate a more local source.
The water level data indicates that there is flow occurring between the basement aquifer (Aquifer A) and the quartzite aquifer (Aquifer B). The basement aquifer, however, is not as prolific as the other aquifers in the area, but it is permeable and has flow paths in the weathered upper section and in fractures. Along the railway line just above the spring shallow weathering and fractures were
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observed. The combination of observed data and the known hydrogeological properties of basement crystalline aquifer make flow from the dome highly probable.
The shallow groundwater flow from the hill intersects the highly permeable quartzite aquifer, for the purposes of the model it is assumed that that there are numerous hydraulic connections and a significant flow component comes from the granite. The groundwater will then flow through the quartzite and down the hydraulic gradient, to the north of the spring in the forest reserve area the geological maps indicate that the quartzite occurs at elevation over 60 m above the spring outflow level, this provides the explanation for another of the components of flow in the upper section of the Itawa Spring.
The discharge of the spring occurs in a defined area, this is explained by the aquifer meeting a flow or multiple flow boundaries. In the case of the Itawa Spring the geological record indicate that there are two impermeable layer at the top of the Mine Series, for the purposes of creating a conceptual model these units provide the explanation for the hydraulic boundary that must be present and the two layers provide an explanation for the artesian flow found at two boreholes near the spring.
The two artesian boreholes are located near to the spring and a second is located approximately 200 m to the southeast. The artesian flow can be best explained by the concept that the boreholes intersect the impermeable layers which are confining groundwater flow, by intersecting a confined aquifer this releases the pressure that is created by flow from a higher points and causes flow at the surface.
Railway Main Spring Elevation 1256masl 1252.5masl Piezometric Head
Artesian BH1 Seepage Collar 1251masl WL = 1252.5masl Aq Aq uic uiclu Artesian Bh2 lud de Upper Roan e X X La Collar 1247masl Laye yer 2 Dolomite Aquifer r 1 WL = 1252.5masl Basement Aquifer Qu artzi te Aq uifer
Fig. 30: Schematic cross section from West to East.
Both boreholes were measured during the project and it was found that both had similar yields (Fig. 31) and also the water levels above the ground (piezometric head) were very close. The other similarity between the artesian boreholes and the spring is that the hydrochemistry of the water was similar and when the water was tested previously (ASTA, 2013) and during this project there were no faecal coliforms found in the water. This differs from the water measured within 20 m of the main spring eye at the V notch site where contamination was found.
In the upper section of the spring the issue of understanding why contamination is occurring is one of the main reasons for the project. Multiple contamination sources have been identified around the spring and quantifying the threat they pose can only be done once the hydrogeology is understood.
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10.2 The Lower Section The demarcation of the upper and lower section of the spring corresponds with the second impermeable layer of Aquiclude X which is also the boundary between Aquifer B and C; near the spring this corresponds to an arc near the pump house (Fig. 28). The area to the east of the pump house is characterised by an elongated seepage zone and no defined spring eyes. The dolomite aquifer in Ndola is a highly permeable carbonate aquifer; the presence of the aquifer provides an explanation for the seepage zone below the upper section of the spring.
Further to the east the geological map indicates the second aquiclude layer, the Mwashia Formation, followed by the main aquifer in the area, the Kakontwe aquifer (Aquifer D). The presence of an aquiclude which is believed to be located above the bridge and to form an impermeable boundary layer, and the lack of defined spring eyes can be explained by the permeability of the aquifers and the flat topography beyond the pump house. The extended seepage zone in the lower section is thus fed by these two carbonate aquifers.
10.3 Contamination and Protection Water from shallow wells and samples from the stream in the lower zone of the spring indicate that this area is highly contaminated. The contamination, however, will not affect the upper section of the spring as it is down gradient but it is of great concern as the levels of contamination even from swimming are well beyond acceptable limits. The levels of E.coli found in shallow wells and the stream is due to the density of pit latrines and due to the effluent drain, the leakage from the main sewer lines and the effluent pipe (Fig. 24 & Fig. 26) may also be a component to this contamination.
The conceptual model has an additional purpose in that defining the source of the groundwater and the way the groundwater flows to the discharge points assist in the definition of groundwater protection zones. These zones are based on the conceptualised model but must also be based on reality on the ground. Since large scale relocation of people is politically difficult and thus unlikely to happen. Other methods to reduce the contamination risk and to ensure the sustainability of the spring should be assessed.
A conceptual model is an attempt to describe the system based on the available information. In addition to protection zones the conceptual model can also be used to identify the main areas where there are data gaps and those areas where more information is needed. In order to protect the spring more comprehensively the groundwater and the surface water should be better understood by the installation of a monitoring network.
11. Groundwater Protection Zones
Groundwater protection zones are based on understanding the pattern of groundwater flow and the contamination threat; however they must be based on technical and practical aspects of implementation and must prioritise the main threats to groundwater. The protection must also take into account the three main flow components:
The deeper flow in the upper section of the spring that is the source of water to the artesian boreholes and the main spring eyes
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Possible shallow groundwater flow around the main spring eyes Shallow groundwater flow in the lower section; the seepage zone on either side of the channel
The main groundwater flow to the upper section of the spring is from the north and the west with a possible smaller flow component from the south. The main contamination threats to the upper part of the spring are due to surface activity around the main spring eyes and contamination threats due to the main sewer line and the effluent channels.
The contamination threat from pit latrines mostly affects the lower section of the spring, with the exception of the houses to the north (Fig. 28). The lower section of the spring will be much harder to protect due to the shallow water table and the lack of sanitation infrastructure.
The protection zones are grouped into three sections:
11.1 Inner Protection Zone - Zone 1 This section should be protected by a physical barrier that prevents access to the area. Zone 1 (Fig. 32) should cover the areas around the main spring eyes and prevent cultivation of the slopes around the spring and open defecation. The slopes in the area should also be stabilised by the introduction of indigenous vegetation and the removal of invasive species. The installation of the physical barrier should occur concurrently with replacing the current water supply from the artesian flow from the borehole located close to the pump house.
Fig. 31: Setting of the protection zones 1 and 2.
Zone I should reach at least 50 m and 25 m upstream of the spring or the well, respectively. The extension of the zone on both sides of the extraction point (spring/well) is around 50 m and 25 m. Only official staff shall be granted access to protection zone 1 should for operation and maintenance services.
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11.2 Outer Protection Zone - Zone 2 The outer protection zone (Fig. 32) should cover the area where the main contamination threats are located based on the groundwater flow directions to the upper part of the spring. This area should include the main sewer lines, the effluent channels south of the Zambian Breweries facility and the pit latrines located just to the North of the spring. The houses on the slope above the spring in Northrise should also be part of the spring and assessment and monitoring should be part of the protection plan. Activities in Zone 2 shall be limited to residential activities and organic agriculture. Priority is to be given to the establishment of an appropriate sewerage network or a safe sub-surface disposal system. Zone 2 is usually based on a 50 day travel time; this cannot be quantified without tracer and/or numerical modelling. The Zone 2 protection zone is based on the assumption that the primary objective is to protect the upper part of the spring in the initial phase.
11.3 Total Catchment - Zone 3
Legend Inner Zone 1 Inner Zone 2 Total Catchment Zone 3 0 0.3 0.6 1.2 1.8
Kilometres
Fig. 32: Estimated catchment - outer protection zone.
The total catchment area (Fig. 33) for the spring covers a large area that is not defined; the main flow directions are understood. The total catchment area has been estimated but the area has many residential and industrial properties which have boreholes which can be monitored. To the south the proposed protection zone extends into the watershed covered by the basement aquifer; this is done to introduce a factor of safety as there are numerous industries with potential contamination sources
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in the area. Implementing changes to sanitation and waste disposal should be made through information exchange and guidelines; the main objective will be to identify contamination threats in order to find solutions rather than imposing rules that cannot be enforced. All development, agricultural, industrial and social activities are allowed in this zone (unless they fall into Zone 1 or Zone 2), under the condition that they comply with the laws and legal instruments applied by the Government of the Republic of Zambia and environmentally sound practices issued by ZEMA and WARMA.
This area should be monitored by identification of boreholes that can be monitored, in particular unused historical boreholes. Locating borehole around the spring should be a key objective of the ongoing project and the monitoring of water levels and quality should be seen as an essential element in the ongoing sustainable use of the spring.
12. Groundwater Monitoring Monitoring data is essential for building up a picture of the groundwater flow, which can be used to understand not only the flow patterns but also to assess the groundwater resource, both in terms of quantity and quality. Eight groundwater monitoring boreholes (Fig. 33) were installed in 2013 (ASTA, 2013) and water levels at each of them was measured three times. Since November 2013 monitoring was terminated due to lack of funding. Several boreholes have now been vandalised and can no longer be used.
It is essential that a monitoring network is set up and expanded to cover the area which is above the spring so that groundwater flow can be monitored and better understood. The monitoring network below the spring should also be established and expanded. The network should include at least one borehole that samples water from below the confining layer i.e. where the artesian water is flowing from; this is essential as both artesian boreholes are blocked. The monitoring borehole in the deeper confined aquifer must be grouted to prevent mixing of the unconfined and confined groundwater.
The monitoring network should include water level measurements which should be done on a weekly basis. The network should also include measurement of surface flow at key location in order to quantify the water balance of different seasons. The existing monitoring boreholes should be better protected and included in the network and the monitoring boreholes south of the stream (MB 5 – 7) should be either cleaned out or redrilled. It would also be advisable to increase the diameter of these boreholes to at 6” or 8” allowing the lowering water pumps in order to obtain groundwater samples. The last component of a complete monitoring network should be rainfall measurement this should be done at ZB. The quantity and the intensity of rainfall should be measured so that water levels and quality can be monitored after high intensity rainfall events where increased surface flow could increase contamination threats.
The water quality should be measured at the monitoring points with an initial round of sampling followed by sampling for inorganic contamination at a fairly low frequency, say once per year. Testing for faecal contamination should be carried out with higher frequency (monthly, or at least quarterly) so that water quality can be analysed in relation to intensity and volume of rainfall and the related effect on groundwater levels.
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Fig. 33: Monitoring network.
Since November 2013 during the ASTA project water levels have not been measured. This is in spite of the fact that continued monitoring was one of the recommendations from the report. Several of the monitoring boreholes have since been vandalised. It is clear that in order to implement a monitoring programme it needs a single party to coordinate the monitoring.
Monitoring of all water resource is the responsibility of WARMA, however for the protection of the spring local partnership with all stakeholder is necessary with the possibility of involving parties with logistic capacity such as ZB to assist in the implementation of implementing the monitoring network and assisting with long term monitoring.
Due to the fact that ZB have a major economic interest in ensuring and protecting the groundwater resource the practical implementation of the monitoring network is recommended to be carried out by ZB in coordination with WARMA. It is essential that the measuring points are secure.
13. Slope Stability and Backpressure The erosion around the main spring eyes has led to the migration of the main spring inflows towards the railway track. This is thought to be in part due to the use of the steep banks for maize cultivation
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in combination with other poor agricultural techniques such as alignment of the maize ridges down the slope which increases erosion.
The migration of the spring eyes back from the position marked by HADWEN in 1972 indicates that the main spring eyes have migrated over 20 m towards the railway track. One of the spring eyes is less than four metres from the railway track in the horizontal direction and four metres below the track in the vertical orientation, this creates possible ground instability which could lead to the collapse of the bank over the spring eye. A collapse of the bank would be very expensive for both Zambia Railways and Zambian Breweries for the following reasons:
A major collapse over a spring eye causes backpressure on the spring, springs are dynamic and if a flowpath is blocked it could migrate to a different location A collapse would create major turbidity in the water in the area where the main water intake is situated for the pump house The railway track could become unusable if it is undermined and consequently collapses which would be very expensive to repair
For this reason alone the fencing of the area around the main spring eyes should be implemented as soon as possible, the contamination issues add further urgency to the need to protect this area.
14. Conclusions and Recommendations
The Itawa spring is in fact not a single spring but a spring system fed by groundwater flow from different aquifers. The upper part of the spring is linked to the quartzite aquifer which occurs around the edge of the Ndola dome and the hill to the south in the Bwana Mkubwa area. The Ndola dome is made up of crystalline basement rocks which occur adjacent to the quartzite aquifer; the results of the field work indicate that the shallow aquifer is linked to the quartzite aquifer where recharge and potential contamination could flow from the hill above the spring to the quartzite aquifer.
The upper part of the spring in the area west of the pump house is the area that supplies water to ZB and is used as a drinking water source by the local community. There have been major changes to the local environment that are potential threats to the water quality and integrity of the slopes around the spring.
The lower part of the spring past the pump house is fed by the Upper Roan dolomite aquifer; this area is mostly fed by an elongated seepage zone along the edge of the stream that flows from the upper section. There are major sanitation issues that affect the water quality of the stream beyond the pump house due to on site sanitation in the Mapalo area where most facilities are pit latrines which in combination with a very shallow water table creates potential pathways for contamination.
Below the pump house the stream increases in flow which is due to seepage of groundwater through the soil; this seepage also transports contaminants from the pit latrines to the stream. Water quality in the stream was found to deteriorate (ASTA 2013) below the pump house and become highly contaminated once the effluent channel flowed into the stream near the bridge. The increase in stream flow below the pump house and deterioration in water quality (ASTA, 2013) must be due to
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shallow groundwater seeping into the stream. The stream is also contaminated by an effluent drain that runs from the dome past the ZB and is believed to intersect a sewer line.
The spring needs to be protected urgently; based on the revised hydrogeological conceptual model protection zones have been recommended based on the groundwater flow and the land use around the spring. The recommended protection measures comprise of an inner protection zone (Zone 1) that should have a physical barrier, surrounded by Zone 2, which is the area that should be protected by identification and mitigation of any contamination issues. The final zone, Zone 3 is the area interpreted to be the total catchment for the spring. Delineation of Zone 3 is based on flow lines and water levels and should be verified and amended by other techniques such as tracer tests and/numerical modelling to better define the catchment.
A monitoring network is essential to the sustainable management of the Itawa spring; this project has condensed information on the spring but there are data gaps which can only be filled by monitoring of the spring system. The monitoring measurements must be carried out over at least one dry to wet season provided that this must include a low rainfall event. The ideal should be long term monitoring that will create valuable data on the groundwater system.
The major contamination issues were investigated and several sources were located. These issues need to be addressed as significant contamination was found in a water sample 20 m from one of the main spring eyes in the upper part of the spring. The water from the artesian boreholes and the spring eye were not found to contain organic contamination, however the samples were taken from the dry season and vulnerability could increase during and after heavy rain due to runoff and infiltration.
15. Recommendations The main recommendations are as follows:
Sewer line repair
The first priority must be the repair the main sewer line which runs above the spring, this represents a major contamination source and threat to water quality and health. The sewer line is believed to flow under the ZB plant and the need to identify the route of the sewer line within the sewer network is essential.
Pit latrines
The pit latrines close to the spring are a contamination threat which is further increased considering the revised flow direction from the north. Plans to relocate the people and demolish the houses should take place in conjunction with the area being restricted for residential structures.
Open defecation
The area where the main spring eyes is located is very close to the men’s bathing pool, this area is used for open defecation and rubbish disposal, it is essential that this area is protected as contamination of the spring water takes place. It is essential that there is a physical barrier that has a security guard; this also applies to the other activities (see below) that taken place close to the spring.
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Monitoring network essential
One of the major data gaps is that there is no ongoing monitoring, it is essential that a monitoring network is set up. This should include the rehabilitation of the monitoring network set up in 2013 and the extension of the network to include flow from the north and of the Ndola dome and also the flow at the spring itself.
Flow measurement of the surface flow should also be included in the network at specific points that are based on the different flow components. The flow measurements should also be combined with rainfall measurements that include quantity and intensity of rainfall. It is anticipated that ZB will play a key role in implementation of the monitoring network due to the vested interest in the spring.
Cultivation close to the spring
The area around the main spring eyes should not be used for agriculture. In the past decades cultivation of the spring area has led to erosion to the point that the railway line is almost undermined by the main spring eyes which have migrated backwards due to erosion, this could lead to a collapse of the embankment over some of the main spring eyes.
Cooperation with Zambian Breweries
ZB has a major economic vested interests in the spring, both in terms of water quality and quantity. The practical aspects of installing protected areas around the spring and enforcing the exclusion zones must be done based on cooperation between the commercial interests of the ZB with the local community who should also benefit.
The major contamination threats should be dealt with in close cooperation with the water utility KWSC, ZEMA, WARMA and all other stakeholders.
Protection zones
To define areas for protection zones what is needed is a balance between what is needed and what is possible, within the socio economic situation. The protection of a spring catchment has to consider the given hydrogeological and environmental limits. However, human activities inside the protection zones can be guided through environmental friendly practices and technologies.
One of the main observations in this report is that a greater emphasis must be placed on flow from the dome to the west of the spring and flow from the north. This report confirms the need to relocate people living close to the spring and create a physical barrier around the main spring eye.
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