TC Zambia: Groundwater Information System and Management Programme for Lusaka

Report of the project:

Fig. 1: Location of project area

Background
The project “Groundwater Resources for Southern Province” (GReSP) was launched in May 2005 with the objectives to facilitate an effective groundwater resource planning and management in the Southern Province and to strengthen the capacities in the Zambian water sector. After the conclusion of the first phase in 2009, the project has been extended from Southern to the Lusaka Province. The City of Lusaka is facing various social and economic challenges. Unplanned urban sprawling along the city margins and poor sanitary conditions pose high risks to the Lusaka aquifer system, which represents the main drinking water resource of the city (60% of the total water supply originates from groundwater).

The population of the City has grown according to unofficial sources to over two million people living in formal and informal urban areas where the majority is using on-site sanitation facilities. One of the major factors influencing water quality is the provision of safe sanitation. A lack of city planning and its implementation, especially in terms of new industrial and commercial areas, puts the resource further at risk. Poor drainage and uncontrolled dumping of industrial and domestic waste together with unplanned developments have significantly contributed to the problem of groundwater contamination. These and many other concerns have created a huge challenge for effective groundwater resource management in Lusaka.

Fig. 2: Vulnerable groundwater

The project area within Lusaka Province covers an area of approximately 5,000 square kilometres and extends over the City of Lusaka and adjacent areas including Lower Kafue and Chongwe Catchments (Figure 1). The tropical continental highland climate is characterised by a cool and hot dry season lasting from May to October and a wet season between November and April. Due to the combined effect of low latitude (16 - 18°S), continental position and high elevation above sea level, the climate shows the combination of a clear division into a dry and a rainy season, the predominance of the diurnal cycle over the seasonal, and large daily ranges of temperature. Annual rainfall for the thirty-year period from 1963 to 1993 averages at 857 mm. Rainfall amounts usually peak during January with monthly totals ranging from 206 to 237 mm. 82% of the total annual rainfall occurs during the four-month period from December to March. Little is known on the influence of urban development, deforestation and overall change in land use on evaporation. An expansion of build-up areas and deforestation are thought to increase urban surface runoff and reduce infiltration and evaporation from land surfaces.

Despite of its importance, the use of groundwater has not been regulated until the enactment of the Water Resources Management Act in 2011 which incorporates groundwater management regulations. It is however obvious, that the implementation of the Act including the formulation of bylaws will take considerable time.

Fig. 3: Groundwater management plan

Activities
A core activity during this phase was the extension of the existing groundwater information system developed for Southern Province to the Lower Kafue and Chongwe Catchments, which comprise the Lusaka groundwater systems. This included the collecting, collating and digitising of all relevant hydrogeological data and information on the project areas; additionally the database includes information of all major hydrogeological investigations carried out since the mid- 1970s. Other completed activities towards the development of a groundwater management strategy are:

The interpretation of satellite images,
The establishment and operation of a hydrometric monitoring network,
The conduction of a comprehensive hydrogeological investigation program including groundwater modelling in order to determine groundwater recharge, flow and aquifer potential,
The assessment of groundwater quality,
The detection of potential groundwater pollution sources and the determination and mapping of the susceptibility of groundwater to pollution,
The development and distribution of thematic maps showing hydrogeology, groundwater chemistry and vulnerability using ArcGIS,
Training courses for scientists, engineers and technicians in hydrological/hydrogeological field investigations and resource management,
Regular dissemination of project results and achievements as well as consultations with regulation and planning authorities and other stakeholders over the developed strategies,
The development of guidelines for effective use, protection and management of groundwater.

The German Federal Institute for Geosciences and Natural Resources (BGR) offered support to the Zambian Authorities in developing and implementing a groundwater management plan (Figure 3), to protect the vulnerable groundwater resources and to secure a sustainable drinking water supply of the city. Advisory was also given to the Lusaka City Council, which is the local authority, and to the commercial utility of Lusaka, the Lusaka Water and Sewerage Company. Furthermore, advocacy work for groundwater in other planning institutions and awareness raising on the governmental and non-governmental level was continously provided by the project.

Hydrogeological maps at scales 1:100,000 and 1:250,000 have been developed that include water usage as well as lithological characteristics and potential of aquifers. A third map was produced at scale 1:75,000 showing the vulnerability of aquifers to pollution. The design and legend of the maps follow international guidelines and can be adopted as a national standard for groundwater maps of other regions. The developed groundwater information system and the thematic maps support efforts on exploring, managing and protecting the groundwater resources.

Fig. 4: Lusaka aquifer system

Results
Geology: Regionally, the Lusaka rocks are part of the Zambezi Belt that, by definition, is separated by the Mwembeshi Shear Zone, from the Lufilian Belt to the north. The Lusaka area is covered by strongly folded overthrusted metasedimentary rocks of Katanga (Neoproterozoic) age which have been intruded by granitic and basic bodies. Owing to the intense tectonical deformation of the Katanga sequence, the stratigraphic succession and its regional correlation are still not fully clarified. Based on the stratigraphical succession proposed by Simpson et al. (1963) the metasedimentary cover can be divided into three formations: the Chunga Formation comprising schist and quartzites, the Cheta Formation including schist and carbonates and the Lusaka Dolomite Formation.

Hydrogeology: The Lusaka aquifer system (Figure 4) covers an area of nearly 2,800 km² and comprises:

Main aquifer hosted by the Lusaka Dolomite Formation extending from Mwembeshi in the WNW to the Shantumbu area in the ESE over a distance of about 65 kilometres,
Subordinate aquifers in the crystalline limestone and dolomite of the Cheta Formation located to the north, west and south of the Lusaka Dolomite aquifer,
Minor aquifers developed in the schists, psammites and quartzites of the Cheta and Chunga Formations,
Local aquifers within alluvial deposits, e.g. near the International Airport.

Water quality reconnaissance study: A groundwater reconnaissance sampling campaign in the Lusaka aquifer systems was designed and conducted between January and October 2008. Sampling points included perennial and seasonal springs as well as water supply wells operated by Commercial Utility, the Lusaka Water and Sewerage Company (LWSC). The water quality sampling included analyses of major and minor constituents of groundwater, heavy metals and trace elements as well as micro-organisms. The water from springs and water supply wells in the limestones and dolomites corresponds to the Ca-Mg-HCO₃ type as was expected. In terms of water hardness, the water is generally hard (>250 mg/l CaCO₃) to very hard (>375 mg/l CaCO₃). Groundwater hosted by schist can be distinguished from the carbonate springs by overall lower TDS, slightly lower pH, lower HCO₃:SiO₂ ratios as well as much lower hardness and alkalinity (i.e. buffering capacity).

Groundwater pollution from human activities was apparent in higher levels of EC reaching 1450 μS/cm, sodium contents of up to 138 mg/l, chloride levels of up to 123 mg/l, and sulphate concentrations of up to 172 mg/l. Whilst these values still comply with the Zambian Drinking Water Standard (ZDWS), nitrate levels frequently exceeded the recommended standard of 10 mg/l NO₃-N equalling 44.3 mg/l NO₃. The high nitrate loads can be linked to the overall poor sanitary situation in these areas. It was found that microbiological contamination is widespread confirming descriptions of numerous previous publications. Concentrations of heavy metals and iron were low throughout the campaign. This could be due to the low solubility of iron and the heavy metals such as cadmium, lead and zinc at the prevailing high pH and the abundance of bicarbonate ions.

Fig. 5: Groundwater sampling

A more comprehensive water quality survey was conducted in April and May 2010, covering approximately 100 boreholes in Lusaka and neighbouring areas. The parameters analysed comprise in-situ measurements of physical parameters, inorganic compounds and microbiological indicators. The sampling and analysis of chlorinated volatile organic carbon (CVOC) and monoaromatic compounds (BTEX) was included in the campaign as an experiment (Figure 5). Both groups of organic chemical compounds are well known groundwater contaminants of anthropogenic origin. Measurable concentrations of these organic pollutants were found in 10 samples, while BTEX contamination was only detected at one well that is no longer used for groundwater abstraction. The results from the microbiological analyses show that elevated concentrations of E. coli occur much less frequent than of Total Coliforms. Only one third of samples stay below the Total Coliform limit given in the Zambian Drinking Water Standard. Nitrate levels were found to be very high in many boreholes and often exceeded the ZDWS limit of 44 mg/l NO₃. The median for nitrate in the study area is 16.9 mg/l NO₃, with two samples showing values below detection limit and a maximum value of 260 mg/l NO₃. While the large production boreholes of the commercial utility exhibit nitrate concentrations below the ZDWS, boreholes for the local supply of peri-urban (high-density settlement) areas show considerably higher values of more than 44 mg/l NO₃ (some even of more than 100 mg/l). Based on the results from the 2010 sampling campaign nine production boreholes and one spring were chosen for monthly water quality monitoring (starting from November 2010).

In addition to the Lusaka region, also the hydrogeological settings of selected adjacent catchments were investigated. In the Chongwe catchment, which covers an area of 5,150 km², groundwater use is currently marginal but its relevance is expected to rise in the future given that population and economic growth continues. Still, the investigation of the catchment shows that the potential for groundwater abstraction is limited to one moderately yielding carbonate aquifer. Two sampling campaigns to determine the water quality in the catchment were conducted in December 2014 and March/April 2015. The quality of the carbonate aquifer water is good, but can be easily put at risk due to a high level of direct recharge, which results from the thin protective cover.

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