GLY4822 Exam 1
Which of the following is generally necessary when installing a well in a competent rock aquifer?
a surface seal
Bank storage occurs when:
flooding temporarily raises surface water levels above the water table.
While studying a cross-bedded sandstone, you find that hydraulic conductivity is the same everywhere but varies with direction, due to the cross-bedding. The resulting aquifer would be considered:
homogeneous and anisotropic
Which of Florida's confining units would you expect to have the highest natural gamma ray reading?
intermediate (or upper)
Which of the following factors determines whether a weir can be used, rather than measuring velocity and depth in many subsections of a stream?
the size of the stream
For small streams, a _____________ provides an alternative means to determine discharge, rather than measuring depth and velocity.
weir
You're planning to investigate an alluvial aquifer using geophysics. Which of the following is true? Assume that all sediments are saturated and the fluid is fresh (non-saline) water
*Floodplain deposits will tend to have more clay and channel deposits more sand and gravel. It is uncertain which will have higher porosity or tend to form a larger borehole. Some additional information that is not vital to answering the question: Clay minerals tend to have lower resistivities than sand. Unconsolidated sand tends to form larger boreholes than clay due to clay's cohesion (and sand's lack of cohesion).*
A hydraulic conductivity of 18.3 ft/day would be _______ cm/s. Answer to 4 decimal places.
0.0065 Converting ft/day to cm/s For the example, we'll use 2 ft/day 2 ft/day x 1 m/3.2808ft x 100 cm/m x 1 day/86400 s =0.0007 cm/s
Imagine a system of 3 layers. The thicknesses and hydraulic conductivities are shown below. All hydraulic conductivities within layers are isotropic. Layer 1 thickness is 7 m and hydraulic conductivity is 2 m/day Layer 2 thickness is 6 m and hydraulic conductivity is 0.005 m/day Layer 3 thickness is 7 m and hydraulic conductivity is 10 m/day What is the equivalent vertical hydraulic conductivity? Answer to 4 decimal places.
0.0166
If the horizontal hydraulic conductivity is 0.25 m/day and the thickness is 153 ft, the transmissivity is__________ m2/day.
11.7 *T = K x thickness In this problem, the feet of thickness must be converted to m by dividing by 3.28 ft/m.*
An aquifer has a transmissivity of 17.5 m2/day which is _____ ft2/day. Answer to zero decimal places.
188.0 *There are 3.28 ft in every m, so to convert m2 /day to ft2/day, multiply by 3.28 ft/m x 3.28 ft/m*
To calculate the vertical hydraulic gradient across a confining unit, hydraulic head data from at least _________ wells are needed.
2 *vertical hydraulic gradient can be determined from two wells. They should be in the same location and screened at different depths. In this case, one should be above and one should be below the confining unit.*
If the horizontal hydraulic conductivity is 0.46 m/day and the thickness is 159 ft, the transmissivity is__________ m2/day. Answer to 1 decimal place.
22.3 *T = K x thickness In this problem, the feet of thickness must be converted to m by dividing by 3.28 ft/m.*
According to the refraction relationship, if \alpha α 1 is 5° from vertical, K1 is 4.5 ft/day, and K2 is 26.5 ft/day what will \alpha α 2 be (in degrees)? Answer to 1 decimal place.
27.258 *Eq 3.16 in the text: tan(\alpha α 1)/tan(\alpha α 2)=Kt1/Kt2 Rearranged: \alpha α 2 =atan [ tan(\alpha α 1) x Kt2/Kt1]*
Imagine a system of 3 layers. The thicknesses and hydraulic conductivities are shown below. All hydraulic conductivities within layers are isotropic. Layer 1 thickness is 1 m and hydraulic conductivity is 2 m/day Layer 2 thickness is 6 m and hydraulic conductivity is 0.004 m/day Layer 3 thickness is 5 m and hydraulic conductivity is 9 m/day What is the equivalent horizontal hydraulic conductivity? Answer to 2 decimal places.
3.92 *Eq Kh = (K1 x thickness1 + K2 x thickness2+K3 x thickness3)/total thickness*
An aquifer has a transmissivity of 3.5 m2/day or _____ ft2/day.
38.0 *There are 3.28 ft in every m, so to convert m2 /day to ft2/day, multiply by 3.28 ft/m x 3.28 ft/m.*
A 100-m thick aquifer system is 10% silt layers and the remainder is sand layers. All hydraulic conductivities within layers are isotropic. The silt's hydraulic conductivity is 0.5 m/day The sand's hydraulic conductivity is 29 m/day What is the equivalent vertical hydraulic conductivity (in m/day)? Answer to 2 decimal places.
4.33
A 100-m thick aquifer system is 40% silt layers and the remainder is sand layers. All hydraulic conductivities within layers are isotropic. The silt's hydraulic conductivity is 0.9 m/day The sand's hydraulic conductivity is 10 m/day What is the equivalent horizontal hydraulic conductivity (in m/day)? Answer to 2 decimal places.
6.36 *Eq Kh = (K1 x thickness1 + K2 x thickness2)/total thickness*
An aquifer has an area of 6.4 km2, which is ____________ m2.
6400000.0 *There are 1000 m in every km, so to convert km2 to m2, multiply by 1000 m/km x 1000 m/km or 1,000,000 m2/km2.*
According to the refraction relationship, if \alpha α 1 is 2° from vertical, K1 is 2 ft/day, and K2 is 165.5 ft/day what will \alpha α 2 be (in degrees)? Answer to 1 decimal place.
70.9 *Eq 3.16 in the text: tan(\alpha α 1)/tan(\alpha α 2)=Kt1/Kt2 Rearranged: \alpha α 2 =atan [ tan(\alpha α 1) x Kt2/Kt1]*
If the transmissivity is 1798 ft2/day and the thickness is 67 m, the horizontal hydraulic conductivity is __________ ft/day. Answer to 1 decimal place.
8.2 *T=hydraulic conductivity x thickness so K=T/thickness The thickness must be converted from m to ft by multiplying by 3.28 ft/m*
An aquifer has an area of 98.3 km2, which is ____________ m2. Answer to zero decimal places.
98300000.0 *There are 1000 m in every km, so to convert km2 to m2, multiply by 1000 m/km x 1000 m/km or 1,000,000 m2/km2.*
0.073 *The mass of the water is the wet total mass minus the dry mass The volume of the water is the mass/density (or the same as the mass because the density is 1 g/cm3) Porosity is water volume/total volume*
A 5.5 cm3 sample of saturated sandstone sample weighs 10.4 grams. After oven-drying, you find the sample weighs 10 grams. The water has a density of 1.0 g/cm3. What is the porosity of the sample? Your answer should be fractional porosity (not percentage) with three decimal places (for example: 0.520 or 0.052)
1.7 *bulk density = mass/volume*
A 7.6 cm3 saturated sandstone sample weighs 12.9 grams. What is the bulk density? Answer in g/cm3 to two decimal places. (Example: 2.23)
1.95 *bulk density = mass/volume*
A 9.8 cm3 saturated sandstone sample weighs 19.1 grams. What is the bulk density? Answer in g/cm3 to two decimal places (example: 2.21)
3E-7
A gravel has a hydraulic conductivity of 3 m/s. The K was measured using water with a density of 1000.0 kg/m3 and a viscosity of 1.0 x 10-3 kg/(m·s). What is the gravel's permeability (in m2)? Note: 3 E-9 is the same as 3 x 10-9
0.004 *Converting ft/day to cm/s For the example, we'll use 2 ft/day 2 ft/day x 1 m/3.2808ft x 100 cm/m x 1 day/86400 s =0.0007 cm/s*
A hydraulic conductivity of 11.2 ft/day would be _______ cm/s. Answer to 4 decimal places.
7.3 x 10-10 m2 *k= K x viscosity /(density x g)*
A sand has a hydraulic conductivity of 0.008 m/s. The hydraulic conductivity was measured using water with a density of 1001.0 kg/m3 and a viscosity of 0.9 x 10-3 kg/(m·s). What is the sand's permeability (in m2)? Choose the closest answer below
Which of the following would have the highest primary porosity?
A sand in an alluvial aquifer *Primary porosity is the remaining porosity from when a rock formed or a sediment was deposited. So ignore any secondary porosity. Primary porosity is decreased by compaction and cementation.*
Which of the following Florida aquifers is primarily carbonate?
All of the above -- and the Biscayne -- are primarily carbonate, although there might also be other sediments such as sand.
8600000.0 *There are 1000 m in every km, so to convert km2 to m2, multiply by 1000 m/km x 1000 m/km or 1,000,000 m2/km2*
An aquifer has an area of 8.6 km2, which is ____________ m2. Answer to zero decimal places.
Which of the following is in correct order from top to bottom? Note: These are not complete lists. Some aquifers/confining units are missing from each
Biscayne aquifer, intermediate confining unit, upper Floridan aquifer, Cedar Keys anhydrite *Top to bottom: Surficial aquifer system, which includes the Biscayne and Sand and Gravel aquifers Intermediate confining unit/ Intermediate aquifer upper Floridan aquifer middle confining unit(s) lower Floridan aquifer, which includes the Boulder zone Cedar Keys anhydrites*
Which of the following would be expected when transitioning from young reef-deposited limestone to a layer of evaporites in a borehole? Assume fluid properties remain constant.
Both the fact that the limestone was formed in a reef environment and its "youth" would contribute to high porosity. In contrast, evaporites precipitate from solutions and generally have low porosity. Decreased porosity means higher density, resistivity, and sonic velocity. There is no reason to expect NGR values to decrease.
Which of the following sedimentary rocks is MOST likely to form an aquifer?
Carbonate rocks that were formed in a high-energy reef environment and never deeply buried. *An aquifer requires high permeability, so needs large pores or well-connected pores. Deposits from low-energy environments are unlikely to be aquifers unless fractured. Evaporites are generally low permeability. Deeply buried sediments are less likely to become aquifers than sediments that have not been deeply buried.*
Which of the following is true concerning mapping of hydraulic head?
Confined aquifers can have a potentiometric surface above the land surface.
Which of the following locations or aquifer name is correctly listed with its aquifer type?
Dakota aquifer; sandstone
turbulent
Darcy's law is not applicable if groundwater flow is:
Which of the following is true of groundwater flow in intrusive igneous and metamorphic rocks?
Hydraulic conductivity is often anisotropic. *Most metamorphic rocks (with the exception of marble, which can dissolve) and intrusive igneous rocks depend on fractures to form aquifers. Even with fractures, porosity remains below 10%. Fractures are generally most common near the land surface and decrease with depth. This is due to the greater stresses (weight above and lateral pressure) that squeezes fractures shut. Of course, this can depend on lithology, because some rock types are easier to fracture (more brittle) than others.*
0.42 *For one dimensional flow: Hydraulic gradient= (h1-h2)/distance*
In a Darcy experiment, h1=14.9 cm, h2=11.1 cm and the distance between the two piezometers is 9 cm. What is the magnitude of the hydraulic gradient? Answer to 2 decimal places (example: 0.32)
0.002 *Darcy's Law q=Ki*
In a Darcy experiment, hydraulic gradient is 0.1 and the hydraulic conductivity is 0.02 cm/s. What is the specific discharge (in cm/s)? Answer to three decimal places (Example: 0.042 or 0.421)
0.0098 *discharge (Q)= volume/time specific discharge = discharge/cross sectional area*
In a Darcy experiment, the cylinder has a cross-sectional area of 12 cm2. You measure a flow rate of 2.7 ml of water in 23 seconds. Calculate the discharge (Q) and then specific discharge (q). For your answer enter only the specific discharge in cm/s. Provide your answer to 4 decimal places. (Example: 0.0052)
Which of the following lists confining units in Florida from younger to older?
Intermediate (or upper), Middle, lower
The _____________________ aquifer (or aquifer system) is used in ____________________________ Florida.
Intermediate; southwest Sand and Gravel; northwest Biscayne; southeast
Which of the following best describes permafrost regions?
Intervals with frozen sediments act as confining layers.
Which of the following is true concerning spatial and directional variation in hydraulic conductivity? Choose all correct answers.
It is possible for a material to be homogeneous and anisotropic. It is possible for a material to be heterogeneous and isotropic. *Homogeneous/heterogeneous refer to whether K differs with location. Isotropic/anisotropic refer to whether K differs with direction.*
Which of the following would be useful to determine whether groundwater is flowing out of a stream?
Measure hydraulic heads in and near the stream to determine flow directions. *Losing water won't affect the chemistry and temperature of the stream. *
Which of Florida's aquifers (or aquifer systems) consists mostly of siliciclastic sediments?
Sand and Gravel
Which of the following best describes glacial sediments?
Sediments deposited by glacial ice (such as till) are lower hydraulic conductivity than sediments deposited by meltwater streams (glaciofluvial deposits).
0.034 *q=vne so ne=q/v*
Specific discharge has been found to be 8.6 x 10-4 ft/day in an aquifer. The groundwater velocity is 0.025 ft/day. What is the effective porosity? Your answer should be fractional porosity to 3 decimal places (for example: 0.281).
Which of the following lists aquifers (or aquifer systems) in Florida from top to bottom?
Surficial, Intermediate, Upper Floridan, Lower Floridan
Drilling down from the surface, you observe (from top to bottom) saturated clay, saturated limestone with some dissolution, saturated shale, saturated sandstone, and unfractured granite. Assuming these reflect continuous layers, the best description is:
The saturated limestone with some dissolution is a confined aquifer, and the sandstone is a confined aquifer. The aquifers are separated by a shale confining unit.
Drilling down from the surface, you observe (from top to bottom) unsaturated sand, saturated sand, clay, unsaturated sand, saturated sand, and clay. Assuming these reflect continuous layers, the best description is:
The saturated sand over the clay and unsaturated sand is a perched aquifer. There is also an unconfined sand aquifer.
What is the main difference between a perched aquifer and an unconfined aquifer?
There is unsaturated material beneath a perched aquifer but not beneath an unconfined aquifer.
Which of the following could be used to determine whether groundwater is flowing into a stream? Choose ALL correct answers.
Use temperature measurements in the stream and shallow groundwater (assuming groundwater temperatures differ from surface water) Compare the chemistry of the stream, precipitation, and groundwater. Measure hydraulic heads in and near the stream to determine flow directions. compare the stream's discharge at two locations and see if it is gaining water during a period without precipitation/runoff.
Which of the following is true of jetted wells?
Water pressure is used to create a borehole.
Equivalent hydraulic conductivity parallel to layers is generally lower than equivalent hydraulic conductivity perpendicular to layers. *Layering due to bedding is characteristic of sedimentary rocks and will lead to anisotropy. It will be easier for flow to follow the layers than cross the layers*
Which of the following is NOT true of a layered heterogeneous system?
Sandstones generally have lower hydraulic conductivity than sand. A fractured granite can have low porosity and relatively high hydraulic conductivity.
Which of the following is true about porosity and hydraulic conductivity? Note: "High porosity" and "high hydraulic conductivity" are relative terms. For this question, you can consider high porosity >0.25 and high hydraulic conductivity >10-5 cm/s. Choose ALL correct answers.
If a sediment grain has a diameter of 1 x 10-4 mm, it would be classified as a clay.
Which of the following is true concerning grain size?
The term clay can refer either to a type of mineral or a grain size.
Which of the following is true concerning grain size?
For groundwater flow, effective porosity is more important than total porosity. A cave in limestone is an example of secondary porosity.
Which of the following is true concerning porosity?
A cave in limestone is an example of secondary porosity. Sandstone will have a lower porosity than the sand that it formed from. Due to compaction, primary porosity will tend to decrease with depth beneath the surface. Poorly sorted sediment generally has lower porosity than similar well-sorted sediments because smaller grains fill the spaces between larger grains.
Which of the following is true concerning porosity? Choose ALL correct answers.
If hydraulic conductivity varies with direction, the material is anisotropic. It is possible for a material to be heterogeneous and isotropic. If hydraulic conductivity varies with location, the material is heterogeneous. It is possible for a material to be homogeneous and anisotropic. *Homogeneous/heterogeneous refer to whether K differs with location. Isotropic/anisotropic refer to whether K differs with direction*
Which of the following is true concerning spatial and directional variation in hydraulic conductivity?
Groundwater flows from higher to lower hydraulic head.
Which of the following is true of hydraulic head?
All of these: Turbulent flow rarely occurs in flow through clay confining units. When flow is turbulent, the relationship between specific discharge and hydraulic gradient is not linear. Turbulent flow does not obey Darcy's law.
Which of the following is true of turbulent flow?
0.011 *n= Volume of voids/total volume. In this case, the water is assumed to fill all the voids so n=volume of water added/total volume*
You have a 100 mL beaker with well-sorted sand. You then fill the same beaker with water. It takes 1.1 mL of water to fill the pores to the top of the sand. Calculate the porosity, assuming that the water has completely filled the pore spaces. Your answer should be fractional porosity (not percentage) with three decimal places (for example: 0.520 or 0.052)
Borehole logging identifies a thin layer of high resistivity, high velocity, low natural gamma ray, and high density. Which of the following is LEAST likely?
a clay layer
Which of the following geophysical logs should be MOST useful for identifying the boundary between the lowermost clay of the Hawthorn Group and the limestone at the top of the Floridan aquifer system?
a decrease in NGR *The biggest difference is lithology and the top of the Floridan aquifer often appears as a drop in NGR values. generally, the limestone would be expected to have higher velocity, higher density, and higher resistivity. (But --there often isn't much of a velocity, density, or resistivity change from the Hawthorn clay to the limestone. The top of the limestone is often very affected by dissolution).*
Permafrost is a layer of frozen soil. Which of the following would you LEAST expect at the boundary between unfrozen to frozen soil?
a decrease in seismic velocity as you move from the unfrozen to the frozen soil.
If a confining unit within the Floridan aquifer system is primarily due to a finer grain size and lower porosity within the carbonate rocks (but not a change in composition) it should be observable with which of the following?
a large vertical hydraulic head gradient when comparing wells above and below. *Smaller and less pore space in a saturated material means: - lower neutron porosity - higher density - higher resistivity -higher seismic velocity - There might be a difference in appearance on the visual logs, but that depends on the logs and the pore sizes. -natural gamma ray (NGR) will not be very sensitive to the change because it doesn't affect radioactive minerals. - A low-permeability confining unit can allow for a large head difference between overlying and underlying material. *
Which of the following settings is least likely to create a homogeneous sedimentary deposit?
a large volcanic eruption *Volcanic eruptions will form igneous rather than sedimentary rocks. The other choices (deep ocean, beach, or lake) are sedimentary.*
When sampling a well, you observe that the water has a lot of suspended fine sediments. This suggests that the well needs:
additional development
Which of the following would be expected when transitioning from glacial outwash to glacial till in a borehole? Assume fluid properties remain constant.
an increase in natural gamma ray values *Glacial outwash is generally sand and gravel. Clay-sized material generally won't be deposited until the meltwater reaches lakes or the ocean. Glacial till contains a wide range of material, including clay. Clay minerals are more likely to attract radioactive minerals and increase the NGR value. Glacial till is also compacted by the ice, so higher density (lower porosity), which will make velocity higher also. Another reason that porosity is low in till is due to the poor sorting.*
Which of the following would be expected when transitioning from poorly-cemented sandstone to well-cemented sandstone. The "cement" is formed of calcite. Assume fluid properties remain constant.
an increase in resistivity *Cement fills up pore spaces and decreases porosity. That means that density will increase, velocity will increase, and resistivity will increase. ** The cement will also increase rigidity which would further increase velocity. The cement is calcite, so wouldn't affect the NGR values.*
Which of the following would be expected when transitioning from pure sandstone with 15% porosity to argillaceous (clayey) sandstone with 5% porosity? Assume fluid properties remain constant.
an increase in sonic velocity an increase in NGR values an increase in resistivity *Lower porosity leads to higher density (and velocity and resistivity). Increase in clay content leads to higher NGR values.*
What is the difference between quickflow and baseflow?
baseflow reaches the stream though the saturated zone, and quickflow moves on the surface or in the unsaturated zone
Consider a coastal plain system where the sediment source was from erosion of mountains. Where would you expect to find sediments with the highest permeability?
closer to the mountains. *The question asks about permeability, so ignore any effects of fluids. Highest permeability will tend to be in sediments closest to the source, in this case the mountains. Lowest permeability will tend to be in low-energy environments such as the deep ocean, lakes or swamps. Evaporite minerals can tend to have low permeability because they are formed (precipitated) from a solution. Evaporite minerals can also cause low permeability in other sediments by filling pore spaces. After burial, consolidation will lower permeability.*
An important difference between mapping hydraulic head in confined and unconfined aquifers is:
confined aquifers are not commonly connected to surface water.
A split-spoon sampler is used to collect:
cores
When crossing from freshwater to saltwater in pore spaces, resistivity would:
decrease
Packers and liners are used to:
isolate sections of the borehole
Which of the following methods is commonly used in unconsolidated sediments and not used in rock?
jetted wells hollow-stem auger
After a precipitation event recharges an aquifer, baseflow tends to exponentially decay through time. This is called the baseflow _________________.
recession