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GROUNDWATER: a hidden resource to protect�

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Emma PETRELLA

Associate Professor of Hydrogeology �@Department of Chemistry, Life Sciences and Environmental Sustainability�University of Parma

TEACHING

Since 2013 two courses:

- APPLIED HYDROGEOLOGY�- HYDROGEOLOGICAL SURVEY

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RESEARCH INTEREST

- Landslide Hydrology�- Microbial contamination of groundwater in carbonate aquifers;�- Groundwater protection.

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If I say: FRESHWATER what do you image?

Kivu Lake, Rwanda

Nyabarongo River

Wetland in Kigali, Rwanda

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Only 0,3% of available freshwater can be seen on the surface

Instead 30% of freshwater on Earth is stored underground and out of sight. ��OR IN OTHER WORDS:�Two thirds of the Earth’s freshwater is frozen in glaciers and ice caps, and nearly one third is groundwater

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Why groundwater �is so important?

It is the source of about 40% of the water used for all purposes (agriculture, tap water, industries, bottling, etc)�

Almost 50% of the world population depends of groundwater every day

Groundwater is also very important as it supplies springs, ponds, swamps, rivers ecc.

It is cleaner than the water rivers due to its self-purifying power

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So what is the problem?

Groundwater is the most abundant resource of freshwater on Earth

It remains an hidden resources. �(“out of sight, out of mind”)�

Most of the time the knowledge of groundwater processes are not known and so it is also difficult to manage it.

Groundwater faces several challenges�1. OVER-ABSTRACTION�2. CLIMATE CHANGE

3. POLLUTION

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Over-abstraction

Over the past 50 years, global demand for groundwater has dramatically increased�

- Increasing in the world population �- Inhabitants of the industrialized countries use ten time around ten times as much water per day as the inhabitants of the emerging countries�- Emerging countries are also changing in life style in favor of water-intensive behavior�- Increase in water-consuming type of cultivation

Although groundwater is an enormous resource, in some places it has been abstracted at a faster rate than it has been recharged. ��More than 30% of the world’s largest groundwater systems are experiencing a long-term decline in groundwater

Global Water Report, 2022

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Climate change

Earth’s average temperature is increasing.�Some areas are becoming drier and other places are becoming wetter. �

Human behavior will also change in response to climate change. �🡪 If an area becomes drier and hotter, there will be less recharge to groundwater, leading to lower water tables and less spring flow. �🡪 Less recharge may also mean farmers have to pump more groundwater to water crops, leading to even lower water tables and less spring flow.

Sea levels are expected to rise in some areas.

🡪 As sea levels rise, saltwater from the sea can mix with the freshwater in the aquifers, causing the groundwater polluted.

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Pollution

Common contaminants: nitrate, hydrocarbons, metals, and pathogens. �At high concentrations, contaminants can make groundwater unsuitable for drinking, they can harm groundwater-dependent ecosystems-

Confined aquifers are better protected, but unconfined aquifers are especially sensitive to pollution because the water is not protected by an impermeable layer.

Although humans are responsible for a lot of contamination, some contaminants can occur naturally.�One famous example is in parts of Bangladesh, where millions of people drink groundwater that is contaminated with toxic arsenic that is released naturally from rocks and minerals in the aquifers.

Polluting man’s activities: Waste disposal, industrial activities, farming, ect.

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What is groundwater?

Groundwater is stored under the surface in soils and rocks that are able to hold water in their opening and cracks, like a sponge.

Data on ground water and aquifers in Rwanda is incomplete. However information available estimates that the discharge for the available resource is 66m³/s (Kabalisa, 2006)

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UNDERSTAND GROUNDWATER

Some precipitation infiltrated the ground and percolates down until they reaches a depth where all the voids are saturated with water. �The space under the ground could be divide into two zones:

UNSATURATED ZONE: �where voids contains both air and water

Soil zone: supports plant growth. Evapotranspiration processes take place in this zone� Intermediate zone: its thickness is variable� Capillary fringe: water is affected by capillary forces

SATURATED ZONE: �where voids contains water��WATER TABLE: surface that dived the unsaturated zone from the saturated zone. Is the expression of first occurrence of groundwater and represent its level.

All water beneath the land surface is referred to as GROUNDWATER. �The equivalent term for water in the land is SURFACE WATER.

The space under the ground could be divide into two zones:

One zone, which occurs immediately below the land surface, in which voids in rocks contains both air and water and is called UNSATURATED ZONE.�The unsaturated zone always lies on the saturated zone, where all interconnected openings are full of water.��The unsaturated zone could be divided also into three zones: �A soil zone that extend from land surface to a maximum depth of few meters, which supports the plant growth. Some voids are filled with roots and also by some worm. THE POROSITY and the PERMEABILITY of this zone tend to be higher than the underlining zones. �Down to the soil zone there is a intermediate zone which differs in thickness from place to place, and at the bottom of the unsaturated zone there is a capillary fringe, where water is affected by capillary force that is the results of the attraction between water and rocks. ��The surface that dived the unsaturated zone from the saturated zone is called WATER TABLE and represent the water level in unused well. In other words the water talbe is the first occurrence of groundwater.

Some precipitation infiltrated the ground and percolates down until they reaches a depth where all the voids (pore and/or fractures) are saturated with water.

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Influence of the topsoil of pyroclastic origin on the migration of microbial cells from ground towards the groundwater

Influence of rainfall regime on the breack-throught at the springs

The reliability of fecal coliforms and fecal enterococci as bacterial indicator of microbial contamination

Effectiveness of microorganisms as natural tracers for some hydrogeological purposes

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SOIL: �Pyroclastic origin

AQUIFER: �Carbonate rocks �

TYPE OF CONTAMINATION: �Microbial pollution (E. Coli, E. Faecalis)�

ORIGIN OF CONTAMINATION: �Grazing and manure spreading.

ACQUA DEI FAGGI

Carbonate aquifer

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Aquifer characterization

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1

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Aquifer characterization

Activities carried out at the field:

Monitoring of meteorological parameters
Monitoring of springs’ discharge
Sampling springs water for microbiological analysis

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Case (a): Karst system entirely located into the unsatured media

Aquifer characterization

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*in red the value od Entecococci faecalis expressed in CFU/100ml

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Case (b): Karst system partially located into the aquifer

Aquifer characterization

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*in red the value od Entecococci faecalis expressed in CFU/100ml

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Re-interpretation and modification of some parameters of vulnerability assessment

taking into account the two different hydrogeological setting

Parameter	(a) Karst system entirely located into vadose zone	(b) Karst system partially located in the aquifer	Point
Depth to water	10	10	5
Recharge	4	4	4
Acquifer media	10	8	3
Soil media	10	10	2
Topography	10	10	1
Impact of vadose zone	10	10	5
Hydralic conductivity	10	4	3
Sum	206	182

Vulnerability assessment

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MAP OF DINAMIC LAND USE LIMITATIONS

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TAKE HOME MESSAGE

Even if we don’t see it, groundwater is one of the most valuable natural resources

Improve the knowledge on groundwater processes

Appropriately management policy and protection action are necessary to ensure its sustainability (quantity and quality)

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THANK YOU FOR YOUR ATTENTION

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