groundwater quality protection · soil in the vadose zone actively attenuates many pollutants esp....

Groundwater Quality Assessment and Protection

MODULE 5

Groundwater provides a potable water supply for vast population

Often unprotected

Pollution threats are increasing

Contaminants persistent

Why do groundwater merit protection?

Do you have contaminated groundwater supplies? What has been the impact?

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

Sources

Natural: derived from rocks: Fluoride, arsenic, uranium

Man-made: Accidental Spills, Illegal Dumping, industries, agriculture, domestic waste

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?

IGRAC

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.

How do aquifers become polluted?

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

Chronic problems in Africa

Chemical Spills and Groundwater Pollution

Groundwater Contamination

Point Sources

Single sources on a site like

leakage from fuel tanks

waste water channels,

accidents with chemicals

Diffuse Sources

Diffuse sources, enter the groundwater over a large area

Often originate from a combination of sources.

Eg mining wastes, urban runoff, agriculturalrunoff, or any combination of these.

These sources are difficult to quantify, isolate and control

Open landfill

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

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

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

Source: Nkhuwa 2006

Contamination sources not separate from water supply

Lusaka

How to supply potable water

here?

Prevention is better thanCure!

Suggest ways to reduce

waste disposal to the streets and drains

What are the impacts of

this waste on water?

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

Emalahleni Water Reclamation Plant

Produces: clean water 25 Ml/day

Cost= R300 million ≈ $20M

Good for Water Security

Public-private participation

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

Non-aqueous phase liquid contamination

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.

fresh groundwater

ground surface

saline groundwater

sea

phreatic water table

zone of diffusion

impervious layer

Actions to reduce the

incidence of saline water

intrusion?

Pollution pathways by sanitation

Identify management

actions that can be taken here to

reduce contamination

www.wateraid.org/images/cm_images/pump-web.jpgwww.ualberta.ca/~xcle/img/pump.jpg

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.

How can groundwater pollution hazard be assessed?

DRASTIC map: pollution hazardmapping

DepthRechargeAquiferSoilTopographyImpact vadose zoneConductivity

Intrinsic Vulnerability map, Addis Ababa

1-100 low

100-140 medium

140-200 High

>200 Very high

DI=

South Africa

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

GW quality protection

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 non-or hardly degradable)

Establishing protection zones will imply landuse restrictions!!!

Protection Zones

GROUNDWATER PROTECTION AREAS (GPA)

GPAs also need:- regulatory embedding

- public awareness- monitoring

designed to provide special vigilance for groundwater destined for public supply

simple powerful concept readily understood by planners:

Sign posts: Ethiopia

Marion County Wellfield: Indianapolis, USA

Georgia, USA

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.

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

What this implies

• Monitoring has taken place, water chemistry wasknown while fit for use but has changed and is nowunfit for the intended use.

•There is a source of contamination. This could be anatural degradation process, but is more commonlyfrom toxic substances, related to human activities, thatcontaminate groundwater.

There is a pathway or connection from the source tothe water body.

The water can be affected by the source ofcontamination.

Prevention of Groundwater Pollution

➢legislating adequate controls at wastedisposal sites

➢installing appropriate monitoring andleachate collection structures at suchsites.

➢Education must form part of theprevention campaign

➢Policing of waste sites and illegaldumping manpower is a problem

South Africa

Prevention of Groundwater Pollution

Prevention is better

and cheaper than remediation

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

Group discussion on water quality

pH= 8.5

Ca= 25o mg/L

Mg= 18 mg/L

Na= 15 mg/L

K= 6 mg/L

HCO3= 45 mg/L

SO4= 125 mg/L

Cl=450 mg/L

NO3= 102 mg/L

pH= 7.7

Ca= 25 mg/L

Mg= 8 mg/L

Na= 50 mg/L

K= 4 mg/L

HCO3= 45 mg/L

SO4= 55 mg/L

Cl=35 mg/L

F=5mg/L

Aquifer 1 TDS=570mg/l Aquifer 3 TDS=227 mg/lAquifer 2 TDS=1011mg/l

Discuss the causes for variation in groundwater quality

THANK YOU