REPUBLIC OF ZAMBIA. Roland Bäumle & Levy Museteka Fringilla Lodge, Feb 8 th, 2011

Transcription

1 Groundwater in Lusaka a - A Resource in Need of Protection - Roland Bäumle & Levy Museteka Fringilla Lodge, Feb 8 th, 2011

2 Presentation Outline 1. Groundwater Pollution 2. Groundwater Protection 3. Vulnerability 4. Lusaka Groundwater Systems 5. Groundwater Chemistry and Quality in Lusaka 6. Conclusions

3 World wide fresh water resources = 35 Mio. km3 Fresh groundwater Lakes 0,26% Rivers 0,0057% Wetlands 0,033% Unsaturated soil 0,05% 30,1% Atmosphere 0,04% Source: Water for People, Water for Life UN World Water Development Report (WWDR); UNESCO Ice and snow ( + glaciers and permafrost) 68,8%

4 Groundwater: Relevance of groundwater worldwide most important resource for drinking water supply (nearly 60% of all drinking water worldwide is abstracted from groundwater, in arid and semi-arid zones up to 100%! ) in many countries used for agricultural irrigation (over 50% in Bangladesh, India and Iran; ca. 30% in Argentina, Mexico, and Pakistan; nearly 20% in China karst aquifers) secure water supply (natural protection against pollution, important storage function during dry season) relatively cheap to develop for rural water supply (local resource, low development costs, no sophisticated pipeline system needed, in most cases no or only minor treatment costs)

5 Groundwater Pollution in Urban Areas Land-use activities commonly responsible for groundwater pollution in the urban area How do aquifers become polluted? When contaminants (effluents, discharge or leachate) are inadequately controlled and disposed of or exceed natural attenuation capacity of underlying soils and strata

6 Common g/water contaminants & associated pollution sources Pollution source Type of contaminant Agricultural Activity nitrates; ammonium; pesticides; faecal organisms In-situ Sanitation Gasoline Filling Stations & Garages Solid Waste Disposal Dry Cleaning Sewage Sludge Disposal Leather Tanneries nitrates; faecal organisms; trace synthetic hydrocarbons benzene; other aromatic hydrocarbons; phenols ammonium; salinity; some halogenated hydro- carbons; heavy metals trichloroethylene; tetrachloroethylene nitrates; various halogenated hydrocarbons; lead; zinc chromium; various halogenated hydrocarbons; phenols

7 Peri-urban settlements Present situation in many peri-urban settlements : Uncontrolled settlement Predominant use of on site-sanitation Uncontrolled waste dumping Water supply predominantly from shallow wells or open water ponds Extensive contamination by nitrate, nitrite, ammonia, and faecal bacteria Frequent outbreak of water-borne diseases (diarrhea, cholera).

8 Contamination Sources Source: Nkhuwa 2006

9 Contamination Pathway Soil: Retention of solids Infiltration i of liquids id High water level: l Short cut Nitrates Pathogens Polluted groundwater Viruses Source: GTZ (Werner) 2005

10 Pathogenic germs Unaffected groundwater is free of pathogenic germs and is in good bacteriological conditions 50 days of underground passage is sufficient to virtually kill all harmful bacteria Time in days Empirical correlation of the so-called 50-day line Mortality Rate in %

11 Groundwater Protection Protection of water resources by employing G/w Protection Zones Zone 1 Immediate Protection Zone Protects well/spring from direct contamination Well I II III Groundwater Flow Direction Zone II Inner Protection Zone Protects drinking water source against pathogenic constituents bacteria, viruses, parasites. Zone III Outer Protection Zone Protects against contamination affecting drinking water source over long distances (for chemical substances, which are non- or hardly degradable)

12 Protection Zones Groundwater Protection Zones around well fields (public sector) Graded protection and controlled use To protect drinking water resources supplied from groundwater upstream of the well/spring from pollution. Protection zone I has the highest priority (area directly surrounding the production well) Protection zone II: no groundwater pollutants and no industry, no untreated wastewater Protection zone III limited use, construction/ housing limited Catchment area Integrated Water Resources Management (IWRM) Catchment Boundary Zone III Zone II Zone I Well Catchment Boundary

13 Groundwater Protection Zones Need regulatory embedding Need public awareness Need monitoring Usually imply land use restrictions to balance competing user interests. t

14 Definition of Vulnerability Term Aquifer Vulnerability Definition Sensitivity to contamination, ti determined d by the natural intrinsic characteristics of geological strata forming the overlying confining beds or vadose zone of the aquifer concerned Threats to groundwater pollution are a function of: Thickness & properties of overlying soil Depth to the water table Infiltration rates, and others A variety of vulnerability assessment tools may be used, e.g.: DRASTIC, PI methods

15 How can groundwater pollution hazard be assessed? Vulnerability Assessment DRASTIC D - Depth to water R - Nt Net Recharge A - Aquifer media S - Soil media T - Topography I - Impact of vadose zone C - hydraulic Conductivity

16 Vulnerability Map The ultimate goal of a vulnerability map is the subdivision of an area into several units showing the different degree of vulnerability.

17 Lusaka Groundwater system in perspective Lusaka is capital of Zambia with population of [at least] 1.3 million people with population growth rate of 3.7% per annum. Water supply coverage by municipal Service Provider (LWSC) is at 68%. LWSC pumps 52% of water supply from groundwater. 48% comes from Kafue River 45km from Lusaka.

18 Challenges Karstic aquifer system characterized by shallow water tables and epikarstic zone extending between 5 and 25m Unregulated groundwater abstraction Increase in unsafe disposal of solid and liquid waste in highly karstified aquifer Small-scale l quarrying Low sanitation coverage of 17%

19 Program to Develop Aquifer Management Strategy Hydrogeological Investigations Groundwater G balance Resource assessment Groundwater Modelling Groundwater Information System Water point database Hydrometric & water quality monitoring GIS/Thematic Mapping Water Quality Assessment Pollution source/ risk detection Vulnerability assessment Remote Sensing Land use Karst features & geological structures Development of a groundwater management strategy Review Consultative ti Protection ti Zoning Process Management guidelines

20 Lusaka Groundwater Systems Plateau of 3,000 sq.km covering Lusaka City and adjacent parts of Mwembeshi and Chongwe catchments Quartzite & Schist 1. Main aquifer hosted by marbles of the Lusaka Dolomite fast flowing GW 2. Subordinate aquifers within marbles of the Cheta formation located to the north and south fast flowing GW 3. Minor Aquifers developed in schists and quartzites of the Cheta and Chunga formations and within alluvial deposits slower GW flow and more filtrationti

21 Lusaka Groundwater Systems groundwater flows (like surface water) from the higher (potential / water table) to the lower (potential / water table) Regional flow (shown here) but locally it can differ due to pumping of boreholes

22 Some Past Water Quality studies conducted on the Lusaka Aquifers ECZ, Lusaka Groundwater Contamination Assessment Project Concentrated on a) Libala Tipping site. b) Leopard s Hill c) Lusaka industrial area UNEP, Assessment of pollution Status and Vulnerability of Water Supply Aquifers of African cities, 2005 The most important t water quality problem in the project areas of John Laing and Misisi is faecal pollution together with the associated disease-causing organisms Water from boreholes is less affected by bacteriological problems than that from shallow wells Conductivity and nitrate generally show elevated levels during the dry season and lower concentrations during the wet season, probably resulting from dilution due to increased saturation in the aquifer

23 GReSP Water quality sampling 2010

24 Chemical Results GW Quality in Lusaka- Apr/May 2010 Piper Diagram Results grouped according to lithology and nitrate content

25 Nitrate Spatial Presentation of Results

26 Conclusions Untreated wastewater from households and industry infiltrate into the soil and endanger aquifers and thus the drinking water supply The Lusaka Aquifer management strategy will depend on thorough assessment of: Groundwater potential Current pollution status Potential risks and vulnerability of the Lusaka groundwater system Development of suitable management concepts that take specific situation in and around Lusaka into account Thus decentralized sanitation and wastewater treatment concepts are some alternatives that could be used The concept of protection zones, the separation of abstraction, renewal and catchment area is essential for sustainable drinking water supply Integrated concepts can help in the long run to save considerable investments in water treatment and supply schemes as well as for health services Successful implementation will rely on institutional framework and capacities

27 Thank you