Groundwater Lab
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School
Durham Technical Community College *
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Course
230
Subject
Geography
Date
Dec 6, 2023
Type
Pages
8
Uploaded by AmbassadorComputerHorse22
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Groundwater Resources and Contamination Recharge area. Perched water table Water table Zone of aeration Aquitard Aquitard unconfined aquitard Confined Zone of saturation Aquifer Figure 2. Summary diagram indicating the different features associated with groundwater. QUESTIONS
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1. How does the zone of aeration differ from the zone of saturation? Zones of aeration have air and water while zones of saturation are filled with water. 2. In your own words define the water table. The upper layer of the zone of saturation where groundwater takes up all the spaces between the sediment and the cracks in rocks. 3. What is the difference between porosity and permeability. Porosity is the amount of water that can be held while permeability is the amount of water that can flow through. 4. Describe the following two situations: (1) sediment with high porosity and permeability; (2) rock with high porosity and low permeability. Which situation is an aquifer and which one is an aquitard. Defend your answer. Rock with high poroisty and low permiability is an aquitard. Water here is stored but is not mobile. Clay or non porous rock 5. Does the level of the water in a well always correspond with the elevation of the water table? Hint: Think about the level of water in a well drilled into a confined aquifer. What is the significance of the piesometric surface? No the level of well does not always corresponds to water tabel. It can vary with type of aquifer. Confined aquifer will lead to rising if water in well due to pressure. Piezometric surface helps identify confined and unconfined aquifers. It helps study the pore pressure. FOR QUESTIONS 6 AND 7 TAP INTO YOUR KNOWLEDGE OF Sandstone and Shale from previous labs. 6.
Which earth materials do you think would make a good aquifer? Fractured Sandstone
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7. Which earth materials do you think would make a good aquitard? Shale 8. Is it possible to have an aquitard with high permeability but low porosity? Explain in detail. It should be possible because high permeability means the water flows easily through the rock which would make the porosity low.
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9.
Is it possible to have an aquifer with low permeability but high porosity? Explain in detail. It should be possible because if there is low permeability that means there's nowhere for the water to flow out making it stay in the rock giving it a high porosity. 10. Drilling a well into a fractured bedrock aquifer can be problematic when compared with drilling into an aquifer consisting of loose sediment. Can you think of some of the problems associated with developing a fractured bedrock fracture as a source for extractable groundwater. By drilling a well are you guaranteed to hit a fractur filled with water. Explain! The fractures in the fractured bedrock can be clogged with clay minerals which could prevent groundwater from being released while drilling. 11.
Examine Figure 2 and correctly label the following features associated with groundwater. Examine the groundwater model in the rear of LVB 108. Labeled on figure 2 Determining Groundwater Flow and Areas of Groundwater Contamination Potential sources of groundwater contamination are divided into two categories: point sources and non-point sources. Point sources of contamination include domestic and hazardous waste landfills, leaky underground petroleum storage tanks, chemical spills at industrial sites, mine waste dumps, petroleum brine pits, and radioactive waste pits. Although contamination can sometimes be severe around such facilities (and they are often the focus of media attention), the impact of such contamination tends to be relatively local. Non-point sources of contamination such as overuse of pesticides, herbicides, fertilizers (including manure), septic tank fields, urban runoff and use of road salt in northern areas, may actually have a greater impact on groundwater
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585
591
Lake
589
590
C
592
589
592
595 596
590
585 585
595
591
589 588 588
594
596
592
595
596
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9
597
resources, because they are so widespread. Underlying a military base in northeastern Michigan is a shallow, sand and gravel unconfined aquifer. This subsurface layer is porous and permeable enough to conduct groundwater and to yield water readily to wells and springs. The water table lies between 10 and 25 feet below the ground surface. A leak in a storage drum has allowed a toxic organic liquid to enter the aquifer. This contamination is a potential threat to drinking water supplies on the base. The wells were drilled for various purposes, and their locations are shown on the map (Figure 3). Drinking water well - B 588 593 59
N 598 Drinking water well - 606 Storage Drum 604 604 604 600 601 599 601 601 600 600 594 598 Drinking water well - A 603 601 600 59 603 599 599 0 1000 2000 feet 36
Scale Figure 3. Well map 603
592 592
591
589
603
Base boundary
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QUESTIONS 12. The pollution on this military base is leaking from the storage drum illustrated on Figure 3. This represents what type of pollution. Point Source or Non-Point Source Storage Drum is a point source of pollution since, it is a stationary source of pollution which can be identified and its source can be traced. 13. Using a standard pencil, contour the water table elevation on the map for the following elevations. 600 ft - Just Below the Storage Drum 590 ft - Just Below Endangered Well C Draw each line so that they separate all elevations that are greater on one side from those that are less on the other side. Follow the rules of contour lines you learned in the topographic mapping lab
. 14. The direction of groundwater flow is generally perpendicular to the equipotential or contour lines, moving from higher to lower elevations. Using a red colored pencil, draw an arrow (or flow line) from the storage drum to well C indicating the direction of ground water movement. Hint: groundwater tend to move toward a surface water feature like a river or lake. Some Math – Darcy’s Law The rate of groundwater flow in the saturated zone can be calculated with Darcy’s Law: V = K Δ
H
(1) Δ
L
This equation shows that the velocity (V) of ground water movement is the product of the hydraulic conductivity (K) and the hydraulic gradient (
Δ
H /
Δ
L). The hydraulic gradient is the ratio of the vertical drop of the water table in feet (
Δ
H) to the horizontal distance of the groundwater flow in feet (
Δ
L). The hydraulic conductivity describes the rate at which groundwater can move through an aquifer. It is determined by experiment and depends on aquifer permeability and the properties of the transported fluid. QUESTIONS 15.
Determine the following elevations Storage Drum ft Endangered Well C ft
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16. Calculate the Δ
H between the storage drum and Endangered Well C. 14 ft 17. Determine horizontal distance of the groundwater flow in feet (
Δ
L) between the storage drum and Endangered Well C by using a ruler and the scale on the map. Leave this distance in ft. the distance between storage drum and G 10 is 2300 feet 18.
Determine the hydraulic gradient between the storage drum and the threatened well. Show your work. Round your answer to three digits pass the decimal place. This problem basically is a calculation of rise / run. Rise is the difference in elevation of the water table between the storage drum and the threatened well and the run is the horizontal distance between the storage drum and the threatened well.
1 mile = 5280 feet , 2300 feet = 0.4356 miles . Hydraulic gradient = 14 feet /0.4356 miles. = 32.139 feet / one mile . 19. Calculate the Darcy’s velocity of the ground water flow from the storage drum to the well (in feet per day). For the aquifer in this study, the hydraulic conductivity is 100 feet per day. Show your work. Round your answer to two digits pass the decimal place. darcy velocitu = v K = hydraulic conductivity . V = K ×
∆
H / ∆
L = 100
×
14 /2300 = 0.6086 m/day . 20.
Using the formula, time = distance / velocity, determine how long it will take the contaminates to reach the well (in days).
L = 2300 , V = 0.6086 Time taken = 2300/0.6086 = 3779.17 days 21.
Convert your answer to question 20 into years by dividing by 365 days per year. 10.3 years
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22. In Figure 3, groundwater ultimately flows into the lake on the northeastern corner of the map? True or False