Sedimentary GeologySedimentary GeologyEPSC-455EPSC-455Lab 9 PresentationLab 9 Presentation

Groundwater and Sedimentary Groundwater and Sedimentary Geology: Geology:

What makes good aquifers, and What makes good aquifers, and what are the roles of sedimentary what are the roles of sedimentary

aquifers in water quality?aquifers in water quality?

Eric Alarie, Witold Ciolkiewicz

Presentation summaryPresentation summary

The importance of aquifers – some The importance of aquifers – some factsfacts

Sedimentary aquifersSedimentary aquifers Key concepts in aquifer hydrogeology.Key concepts in aquifer hydrogeology. What makes a good aquifer What makes a good aquifer

Roles of sedimentary aquifers in Roles of sedimentary aquifers in water qualitywater quality Non-sedimentary aquifers.Non-sedimentary aquifers.

Quick facts about waterQuick facts about water ~ 1.2 billion humans have no access to

clean water (every fifth inhabitant of the world).

Every second person in the world has no sanitary facilities.

80 % of all illnesses in developing countries can be traced back to polluted water.

Just under 1 % of the world-wide quantities of water is available for direct use.

Source: Source: www.atv.de/english/download/Facts-Figures.pdfwww.atv.de/english/download/Facts-Figures.pdf

Freshwater consumption in Freshwater consumption in CanadaCanada

1999 domestic water consumption by ocean drainage basin (liters/day/person)

       0

       290

       327

       339

       541

Across Canada, nearly all of the water used by municipal water systems comes from lakes and rivers. The remainder (12% of the total) comes from groundwater.   Source:     http://atlas.gc.ca/site/english/maps/freshwater/consumption/domestic

AquiferAquifer

From Latin From Latin aquaaqua, meaning water and , meaning water and ferreferre: to bear.: to bear.

An aquifer is a geologic unit capable An aquifer is a geologic unit capable of storing and producing ground of storing and producing ground water of consumptive economic water of consumptive economic importance.importance.

Aquifer typesAquifer types

Unconfined aquiferBounded at its upper surface by the water table

Confined aquifersBounded above and below by low permeable unitsSource: Kasenow, 1997Source: Kasenow, 1997

Key properties of Key properties of aquifersaquifers

PorosityPorosity Hydraulic conductivityHydraulic conductivity TransmissivityTransmissivity Specific yieldSpecific yield

PorosityPorosity Effective porosityEffective porosity (n (nee) is the amount of pore space within ) is the amount of pore space within

a section of sediment or rock, available for water flowa section of sediment or rock, available for water flow

sample theof volumetotal

sample theof voidsctedinterconne theof volumen e

Source: Kasenow, 1997Source: Kasenow, 1997

Hydraulic conductivityHydraulic conductivity Hydraulic conductivityHydraulic conductivity (K) is the ability of (K) is the ability of

geologic material to transmit a liquid under a geologic material to transmit a liquid under a hydraulic gradienthydraulic gradient

Hydraulic gradientHydraulic gradient (i) if the change in ground (i) if the change in ground water elevation over distancewater elevation over distance

K = hydraulic conductivityK = hydraulic conductivity

Q = groundwater dischargeQ = groundwater discharge

A = cross-sectional area of A = cross-sectional area of flowflow

ΔΔh = head lossh = head loss

L = distance over which L = distance over which ΔΔh is h is measuredmeasured

i = i = ΔΔh/L = hydraulic gradienth/L = hydraulic gradient

Ai

Q

hA

QLK

TransmissivityTransmissivity

TransmissivityTransmissivity is the rate at which is the rate at which geologic material transmits ground water geologic material transmits ground water through a unit prism that extends through through a unit prism that extends through the aquifer’s entire thicknessthe aquifer’s entire thickness

K = hydraulic conductivityK = hydraulic conductivity

b = aquifer thicknessb = aquifer thicknessKbT

Specific yieldSpecific yield

Specific yieldSpecific yield (S (Syy) is the amount of ) is the amount of groundwater released from a section of groundwater released from a section of sediment or rock under the influence of gravity sediment or rock under the influence of gravity drainage.drainage.

VVgg = volume of water = volume of water drained by gravitydrained by gravity

VVTT = total volume of = total volume of waterwaterT

gy V

VS

Specific yield - factorsSpecific yield - factors

Sedimentary aquifers can vary in their Sedimentary aquifers can vary in their specific yield:specific yield: Maximum in sediments ranging from Maximum in sediments ranging from

medium to coarse-grain sand.medium to coarse-grain sand. Angular, well-rounded grains will give Angular, well-rounded grains will give

higher yield.higher yield. They are our best aquifers, however, They are our best aquifers, however,

because of the high water quality, because of the high water quality, compared to aquifers in other rock compared to aquifers in other rock types.types.

Sedimentary AquifersSedimentary Aquifers

Sedimentary aquifers are somewhat Sedimentary aquifers are somewhat better for water quality compare to better for water quality compare to other rock type because: other rock type because:

High porosityHigh porosity The overall transmissivity of The overall transmissivity of

sedimentary aquifers is lower than sedimentary aquifers is lower than in other rock typesin other rock types

Porosity comparisonPorosity comparison

Porosity vary enormously depending Porosity vary enormously depending on the sorting and the grain size. on the sorting and the grain size.

The highest porosity are normally The highest porosity are normally reached in fine grain sediments reached in fine grain sediments leading to high specific yield. leading to high specific yield.

Metamorphic and igneous rocks Metamorphic and igneous rocks have low porosity in general and is have low porosity in general and is mainly due to fractures. mainly due to fractures.

J. Russell Boulding, Jon S. Ginn, 2004, Practical handbook of soil, vadose zone, and ground-water contamination : assessment, prevention, and remediation, 2nd ed. Lewis Publishers

Quality of WaterQuality of Water

The quality of water depends on :The quality of water depends on : Country rock dissolutionCountry rock dissolution Degradation of organismsDegradation of organisms Salinity of waterSalinity of water Other contaminantsOther contaminants

Country Rock DissolutionCountry Rock Dissolution

If the water moves a lot, there is less If the water moves a lot, there is less chance for the country rock to be chance for the country rock to be dissolved. dissolved.

Carbon dioxide can be dissolved from Carbon dioxide can be dissolved from soil and create a weak acid that can soil and create a weak acid that can dissolved or precipitate minerals dissolved or precipitate minerals depending on temperature and pressure. depending on temperature and pressure.

Natural contamination can occur. For Natural contamination can occur. For example, we can find As into the water. example, we can find As into the water.

Salinity of WaterSalinity of Water

The salinity of water depends :The salinity of water depends : on the country rock composition on the country rock composition geographic situation on the continent. If geographic situation on the continent. If

the aquifer is closer to sea, fresh and the aquifer is closer to sea, fresh and salty water could mixed. Rain tends to salty water could mixed. Rain tends to be more rich in Na.be more rich in Na.

PercolationPercolation

Because of low transmissivity, water Because of low transmissivity, water undergoes slower percolation which undergoes slower percolation which limits:limits: Suspended material Suspended material Undissolved solids. Undissolved solids. The presence of disease-causing The presence of disease-causing

microorganisms, due to a long microorganisms, due to a long residence time.residence time.

ContaminantsContaminants

Water into the aquifer can be contaminated Water into the aquifer can be contaminated by the exterior if it is not confined or if faults by the exterior if it is not confined or if faults open the system. Source of contaminants can open the system. Source of contaminants can be various including:be various including:

Fertilizers on agricultural land, Fertilizers on agricultural land, Pesticides on agricultural land and forests, Pesticides on agricultural land and forests, Contaminants in rain, snow, and dry Contaminants in rain, snow, and dry

atmospheric fallout, atmospheric fallout, On-site septic systems, On-site septic systems, Municipal landfills, Municipal landfills, etc.etc.

http://www.ec.gc.ca/water/en/nature/grdwtr/e_gdwtr.htm

http://www.ec.gc.ca/water/en/nature/grdwtr/e_gdwtr.htm

http://www.ec.gc.ca/water/en/nature/grdwtr/e_gdwtr.htm

WATER! You have neither taste, nor colour nor aroma. No one can describe you.

We taste you without knowing what you are.

It is not that we need you to live - you Are life!

Antoine de Saint-Exupéry (1900-1944)