GLY 3882: Exam 1 Study Guide
If a 100 milliliter (ml) sediment sample contains 80 ml of solids, its porosity is 0.8. - correct answer
✔✔The answer is false. The sample would have 20 ml of voids so the porosity would be 20 ml/100 ml or
0.2.
In general, pore spaces are filled with water below the water table. - correct answer ✔✔This is generally
true. Exceptions will occur where gases (for example methane) or other liquids (for example oil) exist.
If the fluid flowing through a rock is changed from water to oil, the hydraulic conductivity will change but
the permeability will remain the same. - correct answer ✔✔True. Hydraulic conductivity is a function of
the rock and the fluid, whereas permeability depends only on the rock properties.
Secondary porosity from dissolution commonly occurs in limestone, dolostone, and evaporites. - correct
answer ✔✔This is true. All of these rocks have minerals that dissolve easily in water.
The centers of basalt flows tend to have the highest hydraulic conductivity. - correct answer ✔✔False.
The tops of basalt flows have the highest hydraulic conductivity because the flow surface is generally
very irregular and rough. When a later flow covers the top of these irregularities a higher porosity is
produced when compared to the rest of the flow. The centers of basalt flows have the lowest
conductivity because they cool slower and are much more compact.
Unless fractured or dissolved, evaporites generally act as confining units. - correct answer ✔✔True.
Evaporites generally have low hydraulic conductivity (see the table in the reading), so would act a
confining units.
According to the table in the reading, clay can have higher porosity than gravel. Therefore, it is
reasonable to assume that it generally has higher hydraulic conductivity. - correct answer ✔✔False.
, The size of the pore spaces is very important. Clay generally has very small pore spaces that result in low
permeability and hydraulic conductivity. Even if the porosity is higher than gravel, the hydraulic
conductivity is generally lower (see the table).
While studying a sandstone, you find that hydraulic conductivity is the same everywhere and is the same
in all directions. The resulting aquifer would be considered homogeneous and anisotropic. - correct
answer ✔✔False. It would be homogenous, because it is the same in all locations, and isotropic, because
it is the same in all directions.
Because the upper boundary of an unconfined aquifer is the water table, the saturated thickness of an
unconfined aquifer can vary through time. - correct answer ✔✔This is true.
If the water table rises, the thickness of saturated material in the unconfined aquifer will increase. If the
water table falls, the thickness of saturated material will decrease.
Digging down from the surface, you find (from top to bottom) unsaturated sand, saturated sand,
saturated clay, and saturated gravel. Based on the hydraulic conductivities, it is reasonable to assume
that these form an unconfined aquifer, a confining layer, and a confined aquifer. - correct answer
✔✔True.
The sand will form an aquifer. Since it does not have any low hydraulic conductivity material above it, it
will be unconfined. Clay generally has low hydraulic conductivity and forms confining layers. Gravel has
high hydraulic conductivity and will form an aquifer. Because the clay is above it, the gravel will probably
be confined (if the clay is continuous).
Which of the following can have a high porosity and a very low hydraulic conductivity? - correct answer
✔✔Clay is made up of very small particles which means the pore spaces are small. Water flowing
through these small spaces are slowed by friction on the grains. Therefore, even though clay can have a
high volume of pores, the fact that they are small leads to low hydraulic conductivity.
Based on the cross section, the Dakota aquifer _____________________ in western Kansas. - correct
answer ✔✔is confined
The Upper Cretaceous aquitard (green) lies above the Dakota aquifer (blue) and is continuous in Western
Kansas which means the Dakota aquifer would be confined in that area. Flow lines on the cross-section
If a 100 milliliter (ml) sediment sample contains 80 ml of solids, its porosity is 0.8. - correct answer
✔✔The answer is false. The sample would have 20 ml of voids so the porosity would be 20 ml/100 ml or
0.2.
In general, pore spaces are filled with water below the water table. - correct answer ✔✔This is generally
true. Exceptions will occur where gases (for example methane) or other liquids (for example oil) exist.
If the fluid flowing through a rock is changed from water to oil, the hydraulic conductivity will change but
the permeability will remain the same. - correct answer ✔✔True. Hydraulic conductivity is a function of
the rock and the fluid, whereas permeability depends only on the rock properties.
Secondary porosity from dissolution commonly occurs in limestone, dolostone, and evaporites. - correct
answer ✔✔This is true. All of these rocks have minerals that dissolve easily in water.
The centers of basalt flows tend to have the highest hydraulic conductivity. - correct answer ✔✔False.
The tops of basalt flows have the highest hydraulic conductivity because the flow surface is generally
very irregular and rough. When a later flow covers the top of these irregularities a higher porosity is
produced when compared to the rest of the flow. The centers of basalt flows have the lowest
conductivity because they cool slower and are much more compact.
Unless fractured or dissolved, evaporites generally act as confining units. - correct answer ✔✔True.
Evaporites generally have low hydraulic conductivity (see the table in the reading), so would act a
confining units.
According to the table in the reading, clay can have higher porosity than gravel. Therefore, it is
reasonable to assume that it generally has higher hydraulic conductivity. - correct answer ✔✔False.
, The size of the pore spaces is very important. Clay generally has very small pore spaces that result in low
permeability and hydraulic conductivity. Even if the porosity is higher than gravel, the hydraulic
conductivity is generally lower (see the table).
While studying a sandstone, you find that hydraulic conductivity is the same everywhere and is the same
in all directions. The resulting aquifer would be considered homogeneous and anisotropic. - correct
answer ✔✔False. It would be homogenous, because it is the same in all locations, and isotropic, because
it is the same in all directions.
Because the upper boundary of an unconfined aquifer is the water table, the saturated thickness of an
unconfined aquifer can vary through time. - correct answer ✔✔This is true.
If the water table rises, the thickness of saturated material in the unconfined aquifer will increase. If the
water table falls, the thickness of saturated material will decrease.
Digging down from the surface, you find (from top to bottom) unsaturated sand, saturated sand,
saturated clay, and saturated gravel. Based on the hydraulic conductivities, it is reasonable to assume
that these form an unconfined aquifer, a confining layer, and a confined aquifer. - correct answer
✔✔True.
The sand will form an aquifer. Since it does not have any low hydraulic conductivity material above it, it
will be unconfined. Clay generally has low hydraulic conductivity and forms confining layers. Gravel has
high hydraulic conductivity and will form an aquifer. Because the clay is above it, the gravel will probably
be confined (if the clay is continuous).
Which of the following can have a high porosity and a very low hydraulic conductivity? - correct answer
✔✔Clay is made up of very small particles which means the pore spaces are small. Water flowing
through these small spaces are slowed by friction on the grains. Therefore, even though clay can have a
high volume of pores, the fact that they are small leads to low hydraulic conductivity.
Based on the cross section, the Dakota aquifer _____________________ in western Kansas. - correct
answer ✔✔is confined
The Upper Cretaceous aquitard (green) lies above the Dakota aquifer (blue) and is continuous in Western
Kansas which means the Dakota aquifer would be confined in that area. Flow lines on the cross-section
