Sedimentary Geology EPSC-455 Lab 9 Presentation Groundwater and Sedimentary Geology: What makes good aquifers, and what are the roles of sedimentary aquifers in water quality? Eric Alarie, Witold Ciolkiewicz

Presentation summary The importance of aquifers – some facts The importance of aquifers – some facts Sedimentary aquifers Sedimentary 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 water quality Roles of sedimentary aquifers in water quality Non-sedimentary aquifers. Non-sedimentary aquifers.

Quick 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:

Freshwater consumption in Canada 1999 domestic water consumption by ocean drainage basin (liters/day/person) 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: shwater/consumption/domestic

Aquifer From Latin aqua, meaning water and ferre: to bear. From Latin aqua, meaning water and ferre: to bear. An aquifer is a geologic unit capable of storing and producing ground water of consumptive economic importance. An aquifer is a geologic unit capable of storing and producing ground water of consumptive economic importance.

Aquifer types Unconfined aquifer Bounded at its upper surface by the water table Confined aquifers Bounded above and below by low permeable units Source: Kasenow, 1997

Key properties of aquifers Porosity Porosity Hydraulic conductivity Hydraulic conductivity Transmissivity Transmissivity Specific yield Specific yield

Porosity Effective porosity (n e ) is the amount of pore space within a section of sediment or rock, available for water flow Source: Kasenow, 1997

Hydraulic conductivity Hydraulic conductivity (K) is the ability of geologic material to transmit a liquid under a hydraulic gradient Hydraulic conductivity (K) is the ability of geologic material to transmit a liquid under a hydraulic gradient Hydraulic gradient (i) if the change in ground water elevation over distance Hydraulic gradient (i) if the change in ground water elevation over distance K = hydraulic conductivity Q = groundwater discharge A = cross-sectional area of flow Δh = head loss L = distance over which Δh is measured i = Δh/L = hydraulic gradient

Transmissivity Transmissivity is the rate at which geologic material transmits ground water through a unit prism that extends through the aquifer’s entire thickness Transmissivity is the rate at which geologic material transmits ground water through a unit prism that extends through the aquifer’s entire thickness K = hydraulic conductivity b = aquifer thickness

Specific yield Specific yield (S y ) is the amount of groundwater released from a section of sediment or rock under the influence of gravity drainage. Specific yield (S y ) is the amount of groundwater released from a section of sediment or rock under the influence of gravity drainage. V g = volume of water drained by gravity V T = total volume of water

Specific yield - factors Sedimentary aquifers can vary in their specific yield: Sedimentary aquifers can vary in their specific yield: Maximum in sediments ranging from medium to coarse-grain sand. Maximum in sediments ranging from medium to coarse-grain sand. Angular, well-rounded grains will give higher yield. Angular, well-rounded grains will give higher yield. They are our best aquifers, however, because of the high water quality, compared to aquifers in other rock types. They are our best aquifers, however, because of the high water quality, compared to aquifers in other rock types.

Sedimentary Aquifers Sedimentary aquifers are somewhat better for water quality compare to other rock type because: Sedimentary aquifers are somewhat better for water quality compare to other rock type because:  High porosity  The overall transmissivity of sedimentary aquifers is lower than in other rock types

Porosity comparison Porosity vary enormously depending on the sorting and the grain size. Porosity vary enormously depending on the sorting and the grain size. The highest porosity are normally reached in fine grain sediments leading to high specific yield. The highest porosity are normally reached in fine grain sediments leading to high specific yield. Metamorphic and igneous rocks have low porosity in general and is mainly due to fractures. Metamorphic and igneous rocks have low porosity in general and is 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 Water The quality of water depends on : Country rock dissolution Country rock dissolution Degradation of organisms Degradation of organisms Salinity of water Salinity of water Other contaminants Other contaminants

Country Rock Dissolution If the water moves a lot, there is less chance for the country rock to be dissolved. If the water moves a lot, there is less chance for the country rock to be dissolved. Carbon dioxide can be dissolved from soil and create a weak acid that can dissolved or precipitate minerals depending on temperature and pressure. Carbon dioxide can be dissolved from soil and create a weak acid that can dissolved or precipitate minerals depending on temperature and pressure. Natural contamination can occur. For example, we can find As into the water. Natural contamination can occur. For example, we can find As into the water.

Salinity 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 the aquifer is closer to sea, fresh and salty water could mixed. Rain tends to be more rich in Na. geographic situation on the continent. If the aquifer is closer to sea, fresh and salty water could mixed. Rain tends to be more rich in Na.

Percolation Because of low transmissivity, water undergoes slower percolation which limits: Because of low transmissivity, water undergoes slower percolation which limits: Suspended material Suspended material Undissolved solids. Undissolved solids. The presence of disease-causing microorganisms, due to a long residence time. The presence of disease-causing microorganisms, due to a long residence time.

Contaminants Water into the aquifer can be contaminated by the exterior if it is not confined or if faults open the system. Source of contaminants can be various including: Water into the aquifer can be contaminated by the exterior if it is not confined or if faults open the system. Source of contaminants can be various including:  Fertilizers on agricultural land,  Pesticides on agricultural land and forests,  Contaminants in rain, snow, and dry atmospheric fallout,  On-site septic systems,  Municipal landfills,  etc.

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 ( )