Soil Contamination And Shear Strength Lab
There are various types of pollution like water pollution, air pollution, land pollution. Land pollution is basically pollution of soil with materials like chemicals etc. because of the globalization. The contamination of soil with higher concentration of chemicals shows various adverse effects on humans as well as other organisms. Soil pollution is a diverse topic as it involves contamination of soil by pesticides if we focus on agricultural fields and if we go for industrial fields pesticides concentration is negligible and chemical concentration superimpose over it. So we can conclude that soil contamination varied with nearby chemical, atmospheric, biological, radioactive or nuclear and lethospheric changes.
2. CAUSES & EFFECTS
Soil pollution is a consequence of many activities and experiments done by humans and some of the leading soil pollution reasons are discussed below.
1) Industrial wastes, such as harmful gases, agricultural pesticides and chemicals, fertilizers and insecticides are the most important causes of soil contamination.
2) Ignorance towards managing soil and related systems.
3) Unfavorable and harmful irrigation practices.
4) Improper septic system and management and sustainment of the same.
5) Leakages from sanitary sewage.
6) Acid rains, fumes get blended with rains after releasing from industries.
7) Fuel leakages from automobiles, that get rinsed away due to rain and deep into the closeby soil.
8) Unhealthy waste management techniques, that are release of sewage's characterized into the big dumping grounds & nearby streams or rivers.
The effects of contamination on soil are quite alerting and can drive huge disturbances in the ecological balance and welfare of creatures living on earth. Some of the dangerous soil pollution effects are mentioned below:-
1) Decrement in soil fertility and therefore decrement in the soil yield.
2) Deprivation of soil and nutrients which are natural present in it. Event Plants would not flourish in such a soil, which would further encourage soil erosion.
3) Disturbance in the equilibrium of fauna and flora residing in the soil.
4) Increment in soil's salinity, which makes it bad for vegetation, thus making it useless and infertile.
5) Generally crops cannot grow and thrive in a contaminated soil. Still some crops contend to grow, then those would be sufficiently poisonous to cause many serious problems in health in people consuming them.
6) Another potential effect of soil contamination is existence of toxic dust.
7) Foul smell due to industrial chemicals and gasolenes might result in headaches, fatigue, nausea, in a lot of people.
8) Soil pollutants would bring in modification in the soil structure, which would guide to many essential organisms's death. This would also impact the larger predators and obligate them to move to other places, once they miss their food supply.
2.3 HEALTH RISKS
In many areas there is tender land usage where people are in direct involvement with soils such as their houses, offices, roadside and parks. Soil contaminants are also inhaled in vapourized state. A large number of health consequences can result from exposure to soil contamination depending on type of pollutant, path of attack and vulnerability of the people. Chromium and and lot of the pesticide and herbicide formulations are carcinogenic to every human
2.4 ECOSYSTEM EFFECTS
Presence of hazardous chemicals in the soil has severe effects on its physical structure and chemical composition. The altered chemistry due to high concentrations of alien chemicals affects biological cycles going on in the soil and the metabolic activity of microorganisms. If the microorganisms digest the hazardous substances it results in altered food chains. This may cause extinction of some species which are placed higher in the food chain. Contaminants also affect the metabolism in the vegetation growing over contaminated soil. It is found responsible for poor growth and decreased lifespan of plants and crops. This, in turn, leads to reduced crop yield.
Soil contamination has serious effects which threat healthy life and even challenge the existence of some species of birds/animals. There is an immediate need to take proper steps intended to decontamination of sites and the control further spread of soil pollution. Treatment of industrial waste before disposal, purification of waste water and similar preventive steps should be taken to address the problem.
3. REMEDIAL SOLUTIONS
3.1 Remediation technologies
3.1.1 List of in situ techniques
1) Soil air infiltration
- using activated carbon
-washing of waste air
-combustion of waste air
2) Cleaning ground water
-using activated carbon
-stripping+cleaning of waste air
-removal of heavy metals
3) Biological procedures
-using heavy metal tolerant plants
4) Special procedures
3.1.2 List of on-site/off-site techniques
1) Thermal treatment
2) Washing the soil
-with auxiliary substances
3) Biological procedures
4) Special procedures
-using a desorption reactor
3.2 Check list of the required information
1. Physical/chemical properties of the contaminant
2. Information concerning the distribution and the migration behavior of the contaminant
3. Information concerning the (hydro) geological conditions
4. Assessment of the resulting environmental risk
5. Selection of the remedial procedures
3.3 Summary of Remediation Technologies
Bioremediation is a process of treatment of contaminated soil by biological means. The treatment of soil contaminated by hydrocarbons is biggest in use. However, some of the successful projects have involved the treatment of soil by heavy metals and soil contaminted by PCB.
Bioremediation is a biological process is bascically a function where the microbes either aerobic or anarobic cultered on contaminated soil. The main advantage of this method is that the microbes starts vanishing once the contamination is ingested . The biggest disadvantage of this process is the time factor. Time and temperature are inversely related to each other . The colder the ambient climate, the longer is the time it takes to clean-up. Even if the conditon are favorable having temperature approximately 70F, the time for clean-up calculated in weeks and months. The time factor in more colder climates can be calculated in years. This reveals that the soil affected is lost to productivity use during remediation.
Bioventing is a growing technique associated with bioremediation that deserves mentioning. This technique is being used on hydrocarbon spills where it is impossible to disturb the contamination site. In this technique biotreatment is done by air injection or soil vapour extraction.With the presence of oxygen in the soil strata the micro-organisms grow up and they finally get water and carbon dioxide by breaking down hydrocarbons. This process is inferior in comparison to air spraging as it takes much more time.
3.3.3 Air Sparging
In the process of air sparging organic vapours are impelled to the surface by pumping large bulk of air. They are then treated by methods like carbon filtering. So, if a projects needs 3 years of air-sparging, it will need 15 years of bioventing.The depth of hydrocontamination, acidity level, basic level, penetration level, permeability tells us about the time factor.The promulgation of the bacteria(needed for breakdown of hydrocarbons) is controlled as the process is inhibited due to high moisture content and it prevents oxygen from reaching the bacteria.
Encapsulation involves the blending of the contaminated soils with other products such as lime, concrete, or asphalt. The contaminated soil becomes part of the product mix and the contamination is thus controlled from spreading to surrounding strata. Another type of encapsulation is vitrification which includes the glassification of the soil through heat generated by electrical current passed through electrodes set into the ground. Another proposition involves freezing of the soil and it has been tested upon in the northeastern U.S. on a limited scale.
The types of contamination treated changes with the desired end product mix. Encapsulations by lime and concrete have been used concurrently in the effective treatment of heavy metals and waste oil contaminated soil. Asphalt encapsulation has been used positively on hydrocarbon contaminated soils. The major disadvantage to these methods is that there has to be an immediate market need for the end product, or else the end result is arbitrary patches of concrete and asphalt. Glassification has been tested on heavy metals with special emphasis on radionuclide contamination. This method is expensive, dangerous, and highly debatable as to the efficiency in producting other than radioactive glass. Freezing the soil has been projected as a method of temporary containment of the perimeter of a contamination site, and not as a long term solution.
3.3.5 Solidification and Stabilization
This remediation technology mainly relies on the reaction between a binder and soil to stop or reduce the mobility of contaminants.
Stabilization process is basically addition of reagents to a contaminated soil to produce chemically more stable material, while Solidification process is the addition of reagents to contaminate soil to impart dimensional stability in order to contain contaminants in a solid product and reduce access by external agents.
Stabilization and solidification is an established and well known technology for contaminated soil remediation in many countries in the world.
3.3.6 Pump and treat
As the name itself suggests, this process involves pumping out contaminated groundwater by using a vaccum pump and then this groundwater is purified gradually through a series of vessels that contain materials designed to absorb the contaminants from the groundwater. Contaminants for petroleum-contaminated sites may be in the form of activated carbon in granular form. In order to reduce the contamination of groundwater, chemical reagents followed by sand filters can also be used.
Bioreactors can also be used to clean the water contaminated due to biodegradable materials.
3.3.7 Soil Vapor Extraction
Soil vapour extraction is a well known and effective technology in case of permeable soils. This technology makes use of granular activated carbon, thermal oxidation and vapor condensation.
Granular activates carbon is used as a filter for water. This activated carbon is positively charged and thus removes the negative ions such as ozone, chlorine, fluorides. This carbon must be replaced periodically. It is not that much effective in removing heavy metals (Mechx, 2002).
4. Direct Shear Test
The maximum shear stress which, a material can hold without a rupture is called its Shear Strength. It is a measure of the resistance that a material offers to deformation caused by continuous displacement of its individual particles. When stress is such that the particles slide or roll past each other, failure occurs.
Shear Strength of soils
It describes the maximum strength of the soil at which point a significant amount of plastic deformation or yeilding will occur due to an applied shear stress.
To determine the shearing strength of the soil using the direct shear apparatus.
A normal stress is applied to the sample in vertical direction. The shearing force is applied horizontally to the upper half of the soil. It is done by moving the two halves of the shear box relative to each other. As the two halver slide over each other and move in opposite directions with respect to each other, the shear stress increases with time. It eventually leads to the failure in the soil sample.
The vertical and shear stresses are observed through the two gauges. The procedure is repeated for variation of normal stress. The angle of friction (f) can be calculated by plotting shear stress with normal stress.
The procedure which is followed in performing direct shear test is as follows:
1. Measure inner side or diameter of shear box and find the area.
2. Make sure top and bottom halves of shear box are in contact and fixed together.
3. Weigh out 150 g of sand.
4. Place the soil in three layers in the mold using the funnel. Compact the soil with 20 blows per layer.
5. Place cover on top of sand.
6. Place shear box in machine.
7. Apply normal force.
Two soil specimens were chosen for the test.
Sample one: Clean and not contaminated with weight of 16 kg
Sample two: Contaminated with fuel ash with weight of 8 kg
As explained in the procedure above, two soil samples were tested. After the test, following results were obtained:
1. Load at failure for sample one = 87.5 N
2. Load at failure for sample two = 29.1 N
The contaminated sample will be used for the design project to asses it is commercial viability.
The selection of technology for remediation for contamination depends on various factors like physical properties and exact chemical composition of the soil, the intensity of contamination, distribution and migration behavior of the contaminants and geological conditions at the site of contamination. The information about the state of aggregation, stability and water solubility of the contaminant fuel ash is also needed for devising a solution. The remediation will also depend on the nature and extent of risks posed by contamination. For this reason, a hydro-chemical characterization of the soil water is also needed to be done for a fair assessment of the resulting health and environmental risks. If there is a case of high health and ecological risks, soil must be excavated to be treated at a different place. That is ex-situ method will be followed for high risk contamination. In this case, time consuming in-situ procedures should be avoided. The selection is to be made among the available ex-situ technologies. Issues related to cost, social and legal issues will also be taken into account before finalizing the selection of remediation.
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