MODULE 5. Groundwater Quality Assessment and Protection

Transcription

1 MODULE 5 Groundwater Quality Assessment and Protection

2 Why do groundwater merit protection? Groundwater provides a potable water supply for vast population Often unprotected Pollution threats are increasing Contaminants persistent Do you have contaminated groundwater supplies? What has been the impact?

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4 What causes degradation in groundwater quality? Mineralized rocks disease-causing agents: Pathogens Nutrients: Nitrate, phosphate, sulphate organic compounds: hydrocarbons inorganic chemicals: toxic chemicals radioactive substances: Uranium

5 Sources Natural: derived from rocks: Fluoride, arsenic, uranium Man-made: Accidental Spills, Illegal Dumping, industries, agriculture, domestic waste

6 Why should we worry? About 54 countries in the world have safe drinking water standards At least 700 potential pollutants have been found in municipal drinking water supplies. Of the pollutants tested, 97 cause cancers There is a limited effort in Africa to comply with water quality standard. Most African countries failed to meet MDGs. SDG (target 6) by 2030?

7 IGRAC

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9 How do aquifers become polluted? Contaminant load is uncontrolled and exceeds attenuation capacity of the ground. Soil in the vadose zone actively attenuates many pollutants esp. domestic wastewater, and increases the time available for contaminant elimination processes. Groundwater pollution affects primarily to shallow aquifers Sharply-focused pollution control measures can produce major benefits for relatively modest cost.

10 Chronic problems in Africa Rapid urban expansion Dependence of rural water supply from shallow aquifers Widespread pollution problems Poor sanitary infrastructure Rapid expansion of industry: African industrial revolution Poor water governance appetite

11 Chemical Spills and Groundwater Pollution

12 Groundwater Contamination

13 Point Sources Single sources on a site like leakage from fuel tanks waste water channels, accidents with chemicals

14 Diffuse Sources Diffuse sources, enter the groundwater over a large area Often originate from a combination of sources. Eg mining wastes, urban runoff, agricultural runoff, or any combination of these. These sources are difficult to quantify, isolate and control

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16 Open landfill

17 What are the important sources of groundwater pollution in your country?

18 Note the path of the chemical spill in the next few slides

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22 Aquifer Risk is a combination of aquifer vulnerability and pollution hazard.

23 Contamination sources not separate from water supply Lusaka How to supply potable water here? Source: Nkhuwa 2006

24 Prevention is better than Cure! Suggest ways to reduce waste disposal to the streets and drains What are the impacts of this waste on water?

25 Mining pollution reduces the availability of freshwater: still it is groundwater Acidic ph, toxic water loaded with metals & high in radioactivity Acid Mine Drainage Gold Tailings Dump FeS + H2O + O2 = H2SO4 + Fe2O3 PH = 2.1 => dissolved metals

26 Emalahleni Water Reclamation Plant Cost= R300 million $20M Public-private participation Good for Water Security Produces: clean water 25 Ml/day

27 Non-Aqueous Phase Liquid (N A P L) LNAPL: Light Non-Aqueous Phase Liquid: density < than water DNAPL: Dense Non-Aqueous Phase Liquid: density > than water

28 Non-aqueous phase liquid contamination

29 In coastal areas a natural balance exists between salt and freshwater; if over-pumped, salt water up-coning occurs, with mixing fresh and sea water. This is irreversible. ground surface phreatic water table sea Actions to reduce the incidence of saline water intrusion? fresh groundwater zone of diffusion saline groundwater impervious layer

30 Pollution pathways by sanitation Identify management actions that can be taken here to reduce contamination

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33 How can groundwater pollution hazard be assessed? Groundwater pollution hazard assessment is needed to protect groundwater quality; it should be an essential component of environmental best-practice Groundwater pollution hazard is the interaction between the aquifer pollution vulnerability and the contaminant load Aquifer vulnerability is essentially fixed by the natural hydrogeological setting but contaminant load varies Aquifer pollution vulnerability can be assessed from the hydrogeological characteristics of the overlying material => vulnerability index, which can be mapped Potential contaminant load can also be mapped and overlaid on the aquifer vulnerability map => groundwater pollution hazard.

34 DRASTIC map: pollution hazard mapping Depth Recharge Aquifer Soil Topography Impact vadose zone Conductivity

35 Intrinsic Vulnerability map, Addis Ababa DI= low medium High >200 Very high

36 South Africa

37 GW quality protection Well/well field protection Well spacing, pumping restriction GW zoning, land use planning/regulation Agrochemical (fertilizer/pesticide) use regulations Proper solid waste disposal facilities Proper sanitation and waste water treatment facilities Polluter-pay-principle or economic incentives Monitoring, early warning, trend analysis Public awareness raising

38 Protection Zones Zoning schemes: Zone I - Immediate Protection Zone Protects a well or spring from direct contamination Zone II - Inner Protection Zone Protects the drinking water source against pathogenic microbiological constituents such as bacteria, viruses, parasites and worm eggs Zone III - Outer Protection Zone Protects against contamination affecting the drinking water source over long distances (chemical substances which are nonor hardly degradable) Establishing protection zones will imply landuse restrictions!!!

39 simple powerful concept readily understood by planners: GROUNDWATER PROTECTION AREAS (GPA) designed to provide special vigilance for groundwater destined for public supply GPAs also need: - regulatory embedding - public awareness - monitoring

40 Sign posts: Ethiopia

41 Marion County Wellfield: Indianapolis, USA

42 Georgia, USA

43 Groundwater Protection from pollution GW protected from the surface by the unsaturated zone Acts as a filter removing solid particles Sediment is not a problem in groundwater Bacterial contamination is not as common in groundwater.

44 Groundwater Protection from pollution In the unsaturated zone chemical changes take place, some of these may degrade pollutants This is common e.g. biochemical degradation of organic contaminants Others retard movement of polluting substances by chemical reactions adsorption or ion exchange

45 What this implies Monitoring has taken place, water chemistry was known while fit for use but has changed and is now unfit for the intended use. There is a source of contamination. This could be a natural degradation process, but is more commonly from toxic substances, related to human activities, that contaminate groundwater. There is a pathway or connection from the source to the water body. The water can be affected by the source of contamination.

46 Prevention of Groundwater Pollution legislating adequate controls at waste disposal sites installing appropriate monitoring and leachate collection structures at such sites. Education must form part of the prevention campaign Policing of waste sites and illegal dumping manpower is a problem

47 South Africa

48 Prevention of Groundwater Pollution Prevention is better and cheaper than remediation

49 Group discussion on water quality Discuss the causes for variation in groundwater quality Aquifer 1 TDS=570mg/l ph= 3.9 Ca= 25 mg/l Mg= 8 mg/l Na= 150 mg/l K= 3 mg/l HCO3= 45 mg/l SO4= 250 mg/l Cl=89 mg/l Cd=2 m/l U=3.5 mg/l Aquifer 2 TDS=1011mg/l Aquifer 3 TDS=227 mg/l ph= 8.5 ph= 7.7 Ca= 25o mg/l Ca= 25 mg/l Mg= 18 mg/l Mg= 8 mg/l Na= 15 mg/l Na= 50 mg/l K= 6 mg/l K= 4 mg/l HCO3= 45 mg/l HCO3= 45 mg/l SO4= 125 mg/l SO4= 55 mg/l Cl=450 mg/l Cl=35 mg/l NO3= 102 mg/l F=5mg/L

50 THANK YOU