Soil Permeability's Impact
On The
Movement Of Pollution To Ground Water
Thanks to : Brady L.
On The
Movement Of Pollution To Ground Water
Thanks to : Brady L.
The purpose of this experiment is to see how different soil permeability’s prevent the movement of pollutants through them. My hypothesis is that the outcome of my experiment will show that soils with greater pore space will let more water pass through them.
My manipulated variables were four soil types with different particle sizes (gravel, sand, dirt, and clay). The responding variable is the permeability coefficient(k). The control groups were the constant head permeability test on each soil. The controlled variables are the time period for the water to flow through the constant head permeameter(t), the change in head(h), horizontal cross-sectional area of the soil sample(A), and the length of the soil sample(L).
My measurements were: k=coefficient of permeability(cm/sec), Q=volume(ml) of water flowing through the soil in a time t, t=time period(sec) for the volume(Q) to flow, h=change of head in water surfaces(cm), A=horizontal cross sectional area(cm2) of soil sample, and L=length(cm) of the soil sample. I chose to do a physical science project to determine water permeability on different soils.
To increase validity I used a constant water flow, filters between soil particles, and the same constant head permeameter and water source. One main limitation was the time to have gotten a reading on the permeability of clay. It would have been months before I would have been able to measure a flow.
My results conclude that soils with greater pore space are more permeable and soils which have smaller pore space are less permeable or more impermeable.
PURPOSE
The purpose of this experiment is to see how different soil permeability’s prevent the movement of pollutants through them. I became interested in this topic because of the recent issues in Yakima regarding new dairies in the valley and the impact they can have on surface and ground water. My project will benefit society because it will show why we need to protect this precious resource. The project will show which soils are able to better prevent pollutants from moving through them and impacting ground water .
HYPOTHESIS
I believe that soils with a greater pore space will be more permeable allowing greater volumes of water through them faster than fine grained soils. So soils with denser particles will limit the movement of liquid through them acting as an impermeable liner between the pollutants and other soils and ground water. I arrived at this hypothesis after researching several documents relating to soil mechanics and ground water pollution (refer to graph 1).
EXPERIEMENT DESIGN
Manipulated variable- Four soil types with different particle sizes (gravel, sand, dirt, clay).
Responding variable - Permeability coefficient. Using Darcy’s equation Flow is expressed as cm/sec.
Control groups - A constant head permeability test on each of the for soils.
Controlled variables - Time period for the water to flow through the constant head permeameter (t), the change in head (h), horizontal cross-sectional area of the soil sample (A), and length of the soil sample (L).
Measurements - Using Darcy’s Law for Flow the experiment will measure the quantity of water flowing through the soil in a given period.k=(Q/t)(L/Ah)
k=coefficeint of permeability (cm/sec)
Q=volume (ml) of water flowing through the soil in a time t
t=time period (sec) for the volume (Q) to flow
h=change of head in water surfaces (cm)
A=horizontal cross sectional area (cm2) of soil sample
L=length (cm) of the soil sample
Responding variable - Permeability coefficient. Using Darcy’s equation Flow is expressed as cm/sec.
Control groups - A constant head permeability test on each of the for soils.
Controlled variables - Time period for the water to flow through the constant head permeameter (t), the change in head (h), horizontal cross-sectional area of the soil sample (A), and length of the soil sample (L).
Measurements - Using Darcy’s Law for Flow the experiment will measure the quantity of water flowing through the soil in a given period.k=(Q/t)(L/Ah)
k=coefficeint of permeability (cm/sec)
Q=volume (ml) of water flowing through the soil in a time t
t=time period (sec) for the volume (Q) to flow
h=change of head in water surfaces (cm)
A=horizontal cross sectional area (cm2) of soil sample
L=length (cm) of the soil sample
MATERIALS
Quantity Item
4 plastic cubes (6x6x8cm)
1 plastic tubing (0.7cm dia.x 22cm)
1 15x7cm wood base
2 plastic containers (14x22cm)
1 metric ruler (cm)
1 pitcher (ml)
1 timer (sec)
1 340g pea gravel
1 460g sand
1 340g soil (from yard)
1 140g clay
8 gauze pads for filters
1 tube of plastic cement
1 role of electrical tape
1 gram scale
4 plastic cubes (6x6x8cm)
1 plastic tubing (0.7cm dia.x 22cm)
1 15x7cm wood base
2 plastic containers (14x22cm)
1 metric ruler (cm)
1 pitcher (ml)
1 timer (sec)
1 340g pea gravel
1 460g sand
1 340g soil (from yard)
1 140g clay
8 gauze pads for filters
1 tube of plastic cement
1 role of electrical tape
1 gram scale
PROCEDURES
Construction of Constant-head permeameter-(see diagram and follow instructions)
1. Assemble 3 cubes together with top two having the ends removed.
2. Connect bottom cube to wood base.
3. In the bottom cube drill a hole for 0.7cm tubing.
4. Connect last cube (out fall basin) to base and drill hole to connect to the other bottom cube.
5. Drill three holes in outfall basin for 0.7cm tubing and cement three pieces in.
6. Drill one hole in top cube for 0.7cm tubing and cement in.
1. Assemble 3 cubes together with top two having the ends removed.
2. Connect bottom cube to wood base.
3. In the bottom cube drill a hole for 0.7cm tubing.
4. Connect last cube (out fall basin) to base and drill hole to connect to the other bottom cube.
5. Drill three holes in outfall basin for 0.7cm tubing and cement three pieces in.
6. Drill one hole in top cube for 0.7cm tubing and cement in.
Permeability test for pea gravel
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 340g of pea gravel.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 60 seconds timer when out fall basin begins to discharge.
8. After 60 seconds measure the amount that flowed into that container.
9. Repeat steps for the pea gravel two more times.
10. Use average volume of the three tests for calculations of permeability.
11. Record results.
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 340g of pea gravel.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 60 seconds timer when out fall basin begins to discharge.
8. After 60 seconds measure the amount that flowed into that container.
9. Repeat steps for the pea gravel two more times.
10. Use average volume of the three tests for calculations of permeability.
11. Record results.
Permeability test for sand
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 460g of sand.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 120 seconds timer when out fall basin begins to discharge.
8. After 120 seconds measure the amount that flowed into that container.
9. Repeat steps for the pea gravel two more times.
10. Use average volume of the three tests for calculations of permeability.
11. Record results.
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 460g of sand.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 120 seconds timer when out fall basin begins to discharge.
8. After 120 seconds measure the amount that flowed into that container.
9. Repeat steps for the pea gravel two more times.
10. Use average volume of the three tests for calculations of permeability.
11. Record results.
Permeability test for yard soil
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 340g of yard soil.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 1800 seconds timer when out fall basin begins to discharge.
8. After 1800 seconds measure the amount that flowed into that container.
9. Record results.
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 340g of yard soil.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Continue constant pour until it flows out bottom out fall basin.
7. Start 1800 seconds timer when out fall basin begins to discharge.
8. After 1800 seconds measure the amount that flowed into that container.
9. Record results.
Permeability test for clay
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 140g of clay.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Stop pour let water stand for several days.
7. Measure out fall.
8. Record results
1. Insert filters in permeameter.
2. Fill middle cube of the constant-head permeameter with 140g of clay.
3. Seal connected cubes with electrical tape.
4. Set up plastic containers at each out fall.
5. Pour water in top cube until you have a constant flow coming out top tubing.
6. Stop pour let water stand for several days.
7. Measure out fall.
8. Record results
BACKGROUND REPORT
INTRODUCTION: This project was done to inform people about the permeability of soils and pollution of ground water. It will help people who are involved with ground water projects. Knowing which soils are the most permeable is a great asset to people who are designing lagoons, landfills, and who are applying chemicals to the soil for fertilization, pest, and disease control.
SOIL PORE SPACE: The space between soil particles is the pore space which consists of different amounts of water and air. Soil porosity depends on the soils texture and structure. Silty and clayey soils contain smaller pores but also have more pores than sandy soils. Water is held tighter in small pores rather than in large pores. So for example lets say you have silt and gravel. Which of these has a greater pore space? The gravel has the greater pore space and the silt has smaller but has many more pore spaces than the gravel. Pore space effects the movement of water through soil by its size, shape, and the number of pore openings it has.
DARCY’S LAW FOR FLOW: H. Darcy performed experiments in the mid-eighteenth century on the study of the flow of water through sands. He mathematically concluded that:
k=(Q/t)(L/A h)
where Q= volume of water flowing through the soil in a time t.
t= time period for the volume Q to flow.
h= is the change in head.
A= Cross-sectional area of the soil sample.
L= length of soil through which flow occurs.
k= coefficient of permeability(constant of proportionality).
k=(Q/t)(L/A h)
where Q= volume of water flowing through the soil in a time t.
t= time period for the volume Q to flow.
h= is the change in head.
A= Cross-sectional area of the soil sample.
L= length of soil through which flow occurs.
k= coefficient of permeability(constant of proportionality).
Through this equation Darcy found that if the flow was to be great or small, it depended on how easy or difficult the water moved through the soil. Darcy’s Law for Flow found that the quantity of water flowing through a soil in a given period was proportional to the soil area normal to the direction of the flow and the difference of the levels in which the piezometers (open standpipes), and inversely proportional to the length of the area between the open standpipes through which the flow took place.
PERMEABILITY: Soil particles come in many shapes and sizes which make up many different pore sizes. In a mass of particles that are rounded and roughly the shame dimensions in shape as gravels, sands, and silts, or are platey or flake-like, such as clays, the pore spaces are interconnected. Fluids then can travel through the pore spaces in the soil. From this conclusion the deposits are porous and the material is then a permeable material. The permeability of a soil is effected greatly by its in-place structure. A loose soil would permit greater flow than a dense soil would. The constant-head permeability instrument is used for coarse-grained soils where the volume of water that will pass through the soil is quite large.
WATER POLLUTION AND GROUND WATER: Water pollution is one of the most serious environmental problems in our nation. It occurs when water is contaminated by industrial wastes, sewage, and agricultural chemicals. When a substance is released to the ground and water is introduced it moves toward the water table due to the force of gravity. Because ground water moves in a linear fashion contaminants that dissolve will move with the ground water flow lines which cause plumes. Plumes are basically contaminated flow lines for the contaminated ground water. The mobility of the plumes is determined by many things including the velocity of the certain types of soil. If the soil at which it is released is a clayey soil it will not go very far or fast into the water table. But if a contaminant was to be released into a porous soil it would move quite quickly to the water table.
SUMMARY: After reading this report I hope people will understand how ground water can become contaminated easily. This information can be used in the field when dealing with chemicals, lagoons, and landfills and many more activities that deal with ground water.
RESULTS
What I wanted to show in this experiment is how different soil permeability’s do or do not prevent the movement of pollutants through them. More water went through the larger pore spaces which is the pea gravel than the yard or clay soil which have the smaller pore spaces. As you notice in the graph the gravel is represented by the red bar and the clay by the yellow. It is not hard to see which has the greater pore space (refer to graph 1).
Pea Gravel:
Q = Test1= 800ml Test2= 850ml Test3= 850ml Average=833ml
t = 1 minute(60 sec)
L = 7cm
A = (5.5X5.5= 30.25cm )
h= 15cm
k = (Q/t)(L/A h)= 833ml/1X7/30.25X15= 833 7/453.75
12.85 cm/min= .21 cm/sec
t = 1 minute(60 sec)
L = 7cm
A = (5.5X5.5= 30.25cm )
h= 15cm
k = (Q/t)(L/A h)= 833ml/1X7/30.25X15= 833 7/453.75
12.85 cm/min= .21 cm/sec
Sand:
Q = Test1= 155ml Test2= 150ml Test3= 165ml Average=157ml
t = 2 minutes(120 sec)
L = 5.5cm
A = 30.25cm
h= 15cm
k = (Q/t)(L/A h)= 157/2X5.5/453.775= 78.5X5.5/453.75=.95
.95cm/min= .01cm/sec
t = 2 minutes(120 sec)
L = 5.5cm
A = 30.25cm
h= 15cm
k = (Q/t)(L/A h)= 157/2X5.5/453.775= 78.5X5.5/453.75=.95
.95cm/min= .01cm/sec
Yard Soil(dirt):
Q = 34ml
t = 30 min(1800 sec)
L = 6cm
A = 30.25cm
h= 15
k= (Q/t)(L/A h)= 34/30X6/453.75
.015/1800= .0000083 cm/sec
t = 30 min(1800 sec)
L = 6cm
A = 30.25cm
h= 15
k= (Q/t)(L/A h)= 34/30X6/453.75
.015/1800= .0000083 cm/sec
Clay:
Q = Small amount(not measurable)
t = 4:45 p.m. -After 7 days first “drop” of water
L = 3.5cm
A= 30.25cm
h= 15
I decided to wait until at least a week for a drop of water to prove my hypothesis correct.
t = 4:45 p.m. -After 7 days first “drop” of water
L = 3.5cm
A= 30.25cm
h= 15
I decided to wait until at least a week for a drop of water to prove my hypothesis correct.
CONCLUSIONS
From my results I have learned that soils with greater pore space are more permeable. And soils which have smaller pore space are more or less impermeable. My graph shows that pea gravel has very large pore space allowing more water to go through than that of yard soil. Knowing which soils are permeable such as gravel is important to people who spray chemicals or make a lagoon. In my hypothesis I said that soils with greater pore space would allow water to come through at a more rapid rate than that of smaller pore space soils. My results therefore have made me except my hypothesis because they proved that gravel is more permeable because it has larger spore space than yard soil or clay. After seeing the results of the experiment I wonder if a falling-head permeameter would prove to work on the permeability of clay. The falling-head permeameter was made to test clays but it takes and incredible amount of time and effort to make sure no evaporation occurs and leaking. Some errors that could have occurred in my experiment are as follows: Evaporation, a flow rate that was not constant, starting time periods, incremental measurements, and compaction of soils could cause possible errors in this experiment.
BIBLIOGRAPHY
-Soil Types, Young People’s Science Encyclopedia, 1962, pg. 1573.
-Norman L. Klocke, How soil holds water, http://www.ianr.unl.edu/pubs/fieldcrops/g964.htm, 1996.
-Encarta Encyclopedia, Soil, http://encarta.msn.com/find/concise.asp?ti=761576446&sid=16#s16, 1993-2001 Microsoft Corporation, All rights reserved.
- McCarthy, David, Essentials of Soil Mechanics And Foundations, Virginia, Reston Publishing Company inc., 1982.
- Fair, Gordon, Geyer, John, Okun, Daniel, Elements of water supply and waste water disposal, Canada, John & Wiley Sons, 1958-1971.
- Environmental Protection Agency /625/6-87/016,Ground-water sampling, Ada Ok 74820, 1987.
- King County Resource Planning, Ground Water Resource Protection, King County, 1986.
-Norman L. Klocke, How soil holds water, http://www.ianr.unl.edu/pubs/fieldcrops/g964.htm, 1996.
-Encarta Encyclopedia, Soil, http://encarta.msn.com/find/concise.asp?ti=761576446&sid=16#s16, 1993-2001 Microsoft Corporation, All rights reserved.
- McCarthy, David, Essentials of Soil Mechanics And Foundations, Virginia, Reston Publishing Company inc., 1982.
- Fair, Gordon, Geyer, John, Okun, Daniel, Elements of water supply and waste water disposal, Canada, John & Wiley Sons, 1958-1971.
- Environmental Protection Agency /625/6-87/016,Ground-water sampling, Ada Ok 74820, 1987.
- King County Resource Planning, Ground Water Resource Protection, King County, 1986.
For more details :
http://share3.esd105.wednet.edu/mcmillend/02SciProj/BradyL/BradyL.html
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