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Contamination and protection of the Cape Flats Aquifer, South Africa
Abstract and Figures
In the last decade the water supply needs for drinking and industrial purposes have increased remarkably in the Cape Municipality, requiring the exploitation of groundwater as a consequence of the reduced quantity of surface water resources. Monitoring has detected elevated levels of chlorides, nitrates, fluorides, and metals. This paper focuses on conceptualising the dominant spatial trends of essentially non-point pollution and identifying the main controlling factors within the Cape Flats. The groundwater pollution trends and source identification are all emphasised. In considering the Cape Flats aquifer as a water resource, these factors are important. Subsequent to point source identification and the various non-point or diffuse sources of pollution , the need for protection zoning in the wellfields of the Cape Flats aquifer has also been highlighted.
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... Data from 20 boreholes located in the area show elevated Cl, Na, and total dissolved solids (TDS) 246 Applied groundwater studies in Africa associated with saline intrusion. Chloride concentrations between 1500 and 2000 mg/l are recorded in some boreholes (Adelana & Xu, 2006). Within the Cape Municipality, the size, density and location of settlements have been found to determine the degree or intensity of pollution (DWAF, 1999). ...
... Within the Cape Municipality, the size, density and location of settlements have been found to determine the degree or intensity of pollution (DWAF, 1999). The various sources of pollution have been classed according to the varying human activities (Adelana & Xu, 2006). Significant sources of contaminants in and around the city of Cape Town is from leakage of underground storage tanks for petrol and diesel, nutrients and pathogens in human wastes (e.g. ...
Groundwater is the preferred source for piped water supplies in many urban areas across sub-Saharan Africa and its development is forecast to increase dramatically in an attempt to improve urban water supply coverage. The provision of clean drinking water while providing adequate sanitation and storm-water disposal has become a major challenge for many cities. The hydrogeology and groundwater situation of Addis Ababa, Abidjan, Cape Town, Dakar, Lagos, and Lusaka are highlighted as examples that illustrate the status of urban groundwater in sub-Saharan Africa. The history of urban development and the current groundwater management practices under each case example is also discussed. The main man-made impacts on groundwater in the various cities under consideration are rapid urbanisation and changes in land use surrounding cities. The impact of urbanisation is not only viewed in terms of groundwater quality but as it affects recharge.
... In addition to the point sources, various non-point or diffuse sources of pollution exists and have also been linked to land use. The major non-point pollution source identified is stormwater as described in the previous studies (Adelana & Xu 2006). Figure 4 shows the recent urban development and the location of solid waste disposal sites. ...
... Land use and water quality within the vicinity of the Cape Flats(Adelana & Xu 2006) Land Use: Mostly dense residential and small commercial/industrial areas Land Use: Mixed land use includes less densely populated areas such as Welgemoed and Newlands as well as highly urbanised areas such as Athlone, Botheheuwel and Joe Slovo. Industrial areas include Epping, Ndabeni and Paarden Eiland. ...
Proceedings of 36th IAH Congress, October, 2008 Toyama, Japan
Integrating Groundwater Science and Human Well-being
Impacts of land-use changes on a shallow coastal aquifer, South-Western Cape, South Africa
[1] Segun ADELANA, [2]Yongxin XU
[1]IAH Vice-President, Sub-Saharan Africa
c/o University of Ilorin, Geology Department, Ilorin, Nigeria, email: sadelana@gmail.com
[2]Earth Sciences Department, Univesity of the Western Cape, Bellville, South Africa
Abstract: Studies on groundwater contamination in shallow coastal aquifers were carried out on selected
sites in the Western Cape within the Cape Metropolitan area, to determine the impact of urbanization on
groundwater quality in relation to land-use changes. Investigation on the usability of the Cape Flats aquifer
for water supply augmentation in the City of Cape Town has shown strong influence by estuarine processes,
seasonal fluctuations in rainfall and groundwater levels, topography and land-use changes. Groundwater
levels are generally shallow in the wells tapping from an unconfined sand aquifer. Historical chemical data
from the last four decades were analyzed with modern-day sampling for chemistry, and the results
presented in various graphical forms that allow interpretations and inferences on groundwater quality in
order to aid resource management planning. Over the years, various land-use changes have taken place as
lots of the natural bushland in the area was developed to its present mainly urban situation. As there is
limited exploitation of this shallow groundwater, the processes of seawater intrusion determined in this
study are relatively natural. The study further attempts to integrate GIS technology, geological and
hydrochemical characteristics and its relation to land-use changes.
Keywords: Urban Groundwater, contamination, aquifer management, Cape Flats
... A large proportion of urban development in the Cape Flats is informal. Waste water disposal from informal settlements covering the flat sandy plains might contribute to high nitrogen concentrations and other organic and microbial contaminants reaching the groundwater [39]. Gaining information on waste water disposal from informal settlements is a major challenge, particularly due to a variety of political and social aspects [40]. ...
Since the 1990’s, the groundwater quality along the southern coast of the Western Cape Province of South Africa has been affected by increasing land use activities. Groundwater resources have become increasingly important in terms of providing good quality water. Polluted coastal groundwater as a source of submarine groundwater discharge also affects the quality of coastal water. For this study, land use activities causing groundwater pollution and areas at particular risk were identified. An assessment approach linking land use/land cover, groundwater and submarine groundwater discharge on a meso-scale was developed and the methods applied to two study regions along the southern coastal area. Dryland and irrigated crop cultivation, and urbanized areas are subject to a “high” and “very high” risk of groundwater nitrogen pollution. Application of fertilizer must be revised to ensure minimal effects on groundwater. Practice of agricultural activities at locations which are not suited to the environment’s physical conditions must be reconsidered. Informal urban development may contribute to groundwater nitrogen pollution due to poor waste water disposal. Groundwater monitoring in areas at risk of nitrogen pollution is recommended. Land use activities in the submarine groundwater discharge contribution areas was not found to have major effects on coastal water.
The need to ensure groundwater security is vital, particularly in urban areas. Assessing the impact of land use and climate variables on groundwater quality can help improve sustainable management. The vulnerability mapping of groundwater contamination identifies high-risk areas. Using models and technologies that forecast the distribution of contamination risk over time and place can help prioritize groundwater monitoring. Based on such needs, the Cape Flats aquifer in Cape Town, South Africa, was chosen as the case study for assessing the potential for groundwater contamination risk in urban and coastal hydrogeological settings. The Cape Flats aquifer has been highlighted as an alternate water supply source to augment current supply sources in Cape Town. However, the shallow aquifer is under pressure from agricultural and industrial activities and long-term climate variables, among other factors. The study assessed and validated the vulnerability of the South African coastal aquifer to contamination using an integrated method that included geospatial spatial modeling, a WorldWater model, a down-scaled GCM to the local scale, and a DRASTIC model based on the Geographic Information System (GIS). In this thesis, three approaches are taken: evaluating the effects of changes in key climate variables such as temperature, precipitation, and sea-level rise on groundwater quality in Cape Flats aquifer systems; using the DRASTIC index and selected water quality parameters to assess the vulnerability of the Cape Flats aquifer to groundwater contamination; using a GIS-based model to assess the risk of groundwater contamination in the Cape Flats aquifer under changing climate and land use. Groundwater vulnerability maps were created using ArcGIS software. The WaterWorld model calculates hydrological scenarios for 1950–2000 (baseline) and 2041–2060 using global data at a resolution of 1 km (impact period). Precipitation will increase until 2041 and then fall until 2060, according to the simulation. Temperatures were expected to increase by 1.9-2.3 ° C. In the future, a dry climate, will increase evapotranspiration by 45 mm/year (10%) and decrease water balance by 6.8%. The A1B-AIM scenarios were used to simulate precipitation, temperature, and sea-level rise for two time periods, the 2040s and 2060s, using 20 GCMs integrated into the Greenhouse Gas-Induced Climatic Variables Model/Regional Climate Scenario Generator (MAGICC/SCHENGEN). The region's climate change projections say that there will be less precipitation in the summer and more in the winter, with temperature rises of 1.9 to 2.1 degrees Celsius. The probability that coastal areas are affected by an increase in sea level rise (17–19 cm) and increases in temperature by mid-2060 ranges from 12% to 58%. The DRASTIC model uses seven layers of hydrogeological data: depth to the water table, net recharge, aquifer media, soil media, topography, the impact of the vadose zone, and hydraulic conductivity of the aquifer. The vulnerability index ranges from 109 to 222, with 9% very high, 28% high risk, 46% moderate risk, and 17% low risk. The study area shows that increasing the DRASTIC model by LU increases the very high-risk zone by 26% while decreasing the low-risk zone by 52%. In addition to mapping groundwater vulnerability, the modified DRASTIC method can explain how urban hydrogeology affects coastal aquifers. The study uses an AHP to determine the weighting value for each hydrogeological parameter. GIS tools were used to create the GWQI map. The GIS-based model divides areas at risk of contamination into four categories: very high, high, moderate, and low. The study area has a moderate risk of groundwater contamination (42%). The southern and central suburbs of the study area are the most at risk. Based on data on the levels of water quality parameters in groundwater, the modified DRASTIC vulnerability map is consistent with land use data. In a correlation of these parameters, climate variability and land-based activities had significant effects on groundwater quality. A water quality index was calculated using selected parameters for general quantification and validation. Using chemical water quality parameters, this thesis created a groundwater quality index that ranged from 56 to 142. The contamination risk index and the measured groundwater quality values showed a significant and strong positive correlation (R2 = 0.96). The findings of the study are relevant to the management of water resources in the Cape Flats catchment and elsewhere in the world, particularly in Africa. DRASTIC uses GIS to assess groundwater contamination and provide data for better water resource management. As a result, computer models of contaminant transport can be used to test the DRASTIC parameters.
South Africa has been facing significant challenges in meeting demands in its water and energy sectors in recent years and planning for both sectors has mostly been done separately. The City of Cape Town has started to supplement its dwindling conventional freshwater supplies with groundwater, wastewater and seawater, in light of the drought that commenced in 2015. The Cape Flats Aquifer in Cape Town represents an important resource whose yield could be increased to 85 000 m³/day through artificial stormwater recharge in the Zeekoe Catchment alone. The abstraction and treatment of this water would require significant amounts of energy and thus this paper explores the links between energy usage in the water sector and its carbon footprint. The three alternatives investigated were 'centralised', 'desalination' and 'decentralised' approaches. The former two are centralised treatment mechanisms to produce potable water utilising existing and new treatment infrastructure, respectively, and the latter proposed minimal treatment for non-potable end-users. The energy intensities of the alternatives were evaluated by identifying energy-intensive components and carrying out a preliminary design of the networks and the required treatment mechanisms. South Africa's future potential electricity mixes were used to conceptualise the significance of the associated energy demand. The centralised approach's energy intensity was found to be the lowest of the three, ranging from 1.16 to 1.57 MJ/m³, while those of the decentralised and desalination approaches ranged from 3.57 to 7.31 MJ/m³ and 7.41 to 9.62 MJ/m³, respectively. The Western Cape Water Supply System has an installed capacity of 47.6 MW which could potentially increase by at least 2.7%, 5.7% and 12.3% through the centralised, decentralised and desalination options, respectively. This paper contributes to a growing knowledge on the water-energy nexus in South Africa.
The study utilized the point count index method (using well log data and field measurements) developed following the DRASTIC and SINTACS procedures to assess the vulnerability of part of a coastal plain sand aquifer to contamination in the Western Cape area (South Africa). The following parameters with the acronym CALOD were used for the vulnerability assessment: Clay layer thickness, Aquifer media character, caLcareous layer thickness, Overlying layer character and the Depth to groundwater level. Therefore the CALOD vulnerability potential index (CALOD index) is computed as the sum of the products of weights and ratings assigned to each of the input parameters in a manner similar to DRASTIC and SINTACS methods. The CALOD approach is modified to the local hydrogeological setting of the Cape Flats and data availability. The result shows groundwater in the Cape Flats is sensitive to contamination on the basis of hydrogeologic conditions.
The computed CALOD index values (I-CALOD) for each borehole data point was used to produce a vulnerability potential map. The resulting map indicates that the study area generally have high pollution potential. The highest potential area for contamination is a stretch from southeast to the northwest through the centre of the study area, with I-CALOD values >60. However, in the south-western and north-eastern corners of the study area, the I-CALOD values varied between 40 and 60, indicating a medium to high potential for contamination. The result of this local, smaller-scale, site-specific mapping agrees with the earlier vulnerability index on a national level (scale 1:1,000,000) that the Cape Flats aquifer is vulnerable to pollution.
[Key words: Vulnerability mapping, pollution potential, Cape Flats aquifer]
This paper provides an integrated approach to the analysis of the geological, hydrological and hydrogeological characteris-tics of the Cape Flats: a coastal plain sand formed within the mountains of the Cape Town metropolitan area. The study is mainly based on evaluation of available data, on surface water and groundwater, rainfall and selected springs, to describe the Cape Flats aquifer. Qualitative analysis has shown that both surface water and groundwater of the investigated area are of good quality; whereas sources of contamination indicated are restricted to certain parts of the area. Interpretation of hydrogeological data and aquifer parameters revealed that the Cape Flats aquifer has good storage characteristics to support its development for water supply, although the generally unconfined conditions render it highly susceptible to pollution from the surface. From the analysis of long-term climate data in Cape Town, it is evident that fluctuation exists in the pattern of rainfall; this rainfall pattern has implications for recharge and water management issues in the city. Therefore, a conceptual hydrogeological model was developed to elucidate groundwater flow and recharge mechanisms in the Cape Flats.
The catchment area of the Great and Little Lotus Rivers presents a microcosm of South Africa's urban development, within a population of some 380 000 people. Communities in the catchment range from the fast- growing but desperately poor informal settlements, through low and middle-income communities with high levels of crime and gangsterism, and the economically important horticultural area of Philippi. to a high-income community' around the shores of the lake itself. The legacy of apartheid is strongly apparent in the make-up of these communities and to some extent in the political and social structures representing them.
The overarching vision of the Lotus River project was to create a vehicle whereby people from these very diverse communities could come together with a common desire to improve the environment and quality of life within the catchment in which they live. The end result would be to restore the downstream water body, Zcckoevlei, as a recreational amenity for people from all communities in Cape Town to enjoy, as well as to enhance quality of life within the catchment as a whole. Furthermore, the Lotus River project proposed to develop a "blueprint" for managing urban catchments at a local level, based upon sound multi-disciplinary research, which could then dovetail with the work of the much larger Catchment Management Agencies as set out in the National Water Act of 1998.
The aims and objectives of the Lotus River project were set out as follows:
•
• • • •
•
To establish a blueprint for urban catchment management in South Africa, focusing upon water quality and ecological stability and improvement, as well as upon hydraulics and flood control
To identify major sources of pollution in the catchment, both point and non-point sources
To earn' out a detailed flow gauging study and a water quality sampling programme
7
To study the ecology of the river systems, including riverine and benthic invertebrates, and macrophytes
To develop rehabilitation strategies aimed at improving water quality by instrcam measures, decanalisation. and the creation of wetlands
To identify' all major stake holders in the catchment and to develop a working model for community management of the catchment.
In the original project proposal, a major objective of much of the research would have been to build a GIS-bascd urban run-off model. Urban catchment management of the future will be based upon such models. Due to the limitations of time and funding, however, this was removed from the original list of aims and objectives. Indeed, it was found that much of the information necessary to carry out this task would not have been available. However, the work of the project continued to be underpinned by its Geographical Information System and the development of methodologies for the use of GIS in urban catchment management. Secondly, a major modification to the aims of the research, which was introduced during the course of the project, was in terms of the ecology of the river systems. The macro-invertebrate communities were found to be so impoverished, and the biodiversity of the river channels in general so low due to extensive canalisation, that having collected the base SASS data the focus of the project then shifted to looking at the ecological management of the catchment as a whole.
The Lotus River project focused from its inception upon creating a positive working relationship with the local authority structures. At all stages, "buy-in"' to the project on the part of the local authority was considered to be essential. This was necessary in order to ensure the sustainability of the project objectives in the long term. Sustainability in this context would be demonstrated after completion of the project, by the major stake holders continuing to further the aims of the project and to manage the catchment effectively, with a focus upon water quality and ecological stability and improvement, as well as upon hydraulics and flood control. Furthermore, this management would be carried out in a manner that is inclusive and participatory, working with the full range of stake holders and communities in the catchment.
The Cape Flats aquifer is unconfined, therefore it is vulnerable to pollution. In many places the groundwater level is close to the surface, which adds to the aquifer's susceptibility to pollution. Pollution of the aquifer by leachates from landfills and sewage effluents has been proved by water quality monitoring. Waste disposal and sanitary landfilling should always be carried out with full precautions, even if pollution is not expected. The thickness of the unsaturated zone below a sanitary landfill is possibly the most important factor determining the groundwater pollution potential of the fill. Serious interaction takes place when the groundwater is in contact with the waste. The disposal of treated sewage effluent from an activated-sludge plant into the aquifer is not necesarily deleterious. Leachate from sludge drying beds should not be allowed to reach the aquifer.
The Zandvliet Wastewater Treatment Works (WWTW) was established in 1989 on the eastern edge of the Cape Flats Aquifer (Figure 1). At present the WWTW handles some 55 ML/d of sewage. Failure of the original sludge drying beds because of a shallow water table resulted in development of temporary sludge lagoons south of the site. Following spills from the temporary sludge lagoons between April and June 1998, the Cape Metropolitan Council commissioned a detailed investigation into the impact of the spills on groundwater quality.
The study utilized the point count index method (using well log data and field measurements) developed following the DRASTIC and SINTACS procedures to assess the vulnerability of part of a coastal plain sand aquifer to contamination in the Western Cape area (South Africa). The following parameters with the acronym CALOD were used for the vulnerability assessment: Clay layer thickness, Aquifer media character, caLcareous layer thickness, Overlying layer character and the Depth to groundwater level. Therefore the CALOD vulnerability potential index (CALOD index) is computed as the sum of the products of weights and ratings assigned to each of the input parameters in a manner similar to DRASTIC and SINTACS methods. The CALOD approach is modified to the local hydrogeological setting of the Cape Flats and data availability. The result shows groundwater in the Cape Flats is sensitive to contamination on the basis of hydrogeologic conditions.
The computed CALOD index values (I-CALOD) for each borehole data point was used to produce a vulnerability potential map. The resulting map indicates that the study area generally have high pollution potential. The highest potential area for contamination is a stretch from southeast to the northwest through the centre of the study area, with I-CALOD values >60. However, in the south-western and north-eastern corners of the study area, the I-CALOD values varied between 40 and 60, indicating a medium to high potential for contamination. The result of this local, smaller-scale, site-specific mapping agrees with the earlier vulnerability index on a national level (scale 1:1,000,000) that the Cape Flats aquifer is vulnerable to pollution.
[Key words: Vulnerability mapping, pollution potential, Cape Flats aquifer]
Identification and prioritisation of groundwater contaminants and sources in South Africa's urban catchments
- B H Usher
- J A Pretorius
- I Dennis
- N Jovanovic
- S Clarke
- R Titus
- Y Xu
Usher, B.H., Pretorius, J.A., Dennis, I., Jovanovic, N., Clarke, S., Titus, R. & Xu, Y. 2004. Identification and
prioritisation of groundwater contaminants and sources in South Africa's urban catchments. WRC Report
No. 1326/1/04.
The Cape Flats Aquifer: Current status
- W Wright
- J Conrad
Wright, W. & Conrad, J. 1995. The Cape Flats Aquifer: Current status. CSIR report 11/95, Stellenbosch.
Examples of O-and H-isotopes to identify surface water pollution in groundwater
- I C Saayman
- S Adams
- C Harris
Saayman, I.C., Adams, S. & Harris, C. 2000. Examples of O-and H-isotopes to identify surface water pollution in groundwater. In Sililo et al. (eds), Groundwater: Past Achievements and Future Challenges:
599-603. Rotterdam: Balkema.
Department of Water Affairs and Forestry (DWAF). 1994. Minimum Requirements for the Establishment of a Waste Disposal Site
- Stormwater Catchment
- River Management
Catchment, Stormwater and River Management (CSRM) 2004. Annual Report for 2003/2004.
Department of Water Affairs and Forestry (DWAF). 1994. Minimum Requirements for the Establishment of a
Waste Disposal Site, DWAF, Pretoria.
The scenery and geology of the Cape Peninsula. Guidebook Geocongress '90
- C J H Hartnady
- J Rogers
Hartnady, C.J.H. & Rogers, J. 1990. The scenery and geology of the Cape Peninsula. Guidebook Geocongress
'90, Geological Society, South Africa.