Chapter 14 Flashcards
What is the difference between porosity and permeability?
Porosity is the proportion of open space (space that can be filled with water), within a rock or unconsolidated sediment. Permeability is an expression of the ease with which water will flow through that material.
Both sand and clay deposits can have high porosity, but while most sand also has high permeability, clay does not. Why not?
Clay deposits have low permeability because of the small size of the clay fragments. Water is tightly held to the grains by surface tension, and in the very small spaces between grains in clay there is virtually no water that is not able to flow.
Arrange the following types of rock in order of their likely permeability, as measured by the hydraulic conductivity (K): mudstone, fractured granite, limestone in a karst region, sandstone, and unfractured gneiss.
From least to most permeable: unfractured gneiss, mudstone, sandstone, fractured granite, limestone in a karst region.
Two wells 70 metres apart have water levels of 77 metres and 83 metres above sea level respectively. The aquifer has a hydraulic conductivity of 0.0003 metres per second and a porosity of 20%. What is the likely velocity of groundwater flow in the region between these two wells?
V = (Ki)/n i = the gradient which is the elevation difference (83 − 77 = 6 metres) over the distance (70 metres) = 0.09, n is the porosity, therefore V = (0.003 * 0.09)/0.2 = 0.00135 metres per second.
Explain why it is important for provincial governments to operate observation well networks.
Governments have the responsibility to protect our resources and to do their best to make sure that individuals and industry can access the groundwater that they need. Without observation well networks governments will have no independent information on how water levels are changing, and will be unable to make decisions on what might need to be done to ensure an adequate water supply for all.
What is the main difference between natural and anthropogenic contamination of groundwater?
Natural groundwater contamination originates from the natural reactions between the groundwater and the aquifer minerals. Anthropogenic groundwater contamination typically comes from human-sourced chemicals at or near to surface that are allowed to leak into the aquifer.
Why is a highly permeable aquifer more vulnerable to anthropogenic contamination than a less permeable aquifer?
Water travels faster through a highly permeable aquifer and thus can spread the contamination further than in a less permeable one.
How can a livestock operation lead to contamination of groundwater? What is the most likely contaminant?
Livestock wastes are rich in nitrogen compounds, and these most commonly lead to nitrate contamination within the groundwater. Livestock wastes may also contain pharmaceuticals, which could contaminate groundwater.
Which mineral in the rock of a mining operation is typically responsible for acid rock drainage?
The mineral pyrite is most likely to be responsible for acid rock drainage.
Why is it necessary to test the permeability of the soil before constructing a septic field?
The waste water in a septic field needs to percolate slowly through the ground in order for natural processes to break down the contaminants. If the permeability is too low the waste water could come to surface. If the permeability is too high it could contaminate groundwater.
