Lecture 13 Soil Pollution Control PDF

COE113 – Environmental Science and Engineering Soil Pollution Control Lecture 13 / Week 07 / 1st SEM AY2022-2023 Objectives At the end of this lecture the class should be able to understand the following concepts: 1. Soil Erosion 2. Methods of Controlling Soil Erosion 3. Methods of...

COE113 – Environmental Science and Engineering Soil Pollution Control Lecture 13 / Week 07 / 1st SEM AY2022-2023 Objectives At the end of this lecture the class should be able to understand the following concepts: 1. Soil Erosion 2. Methods of Controlling Soil Erosion 3. Methods of Soil Treatment Soil Erosion Soil erosion is the process by which the top layer of soil is removed by natural forces such as wind and water, or through human activities. This process leads to the loss of fertile soil, negatively impacting agricultural productivity and the environment. Erosion reduces the soil’s ability to retain water and nutrients, leading to decreased agricultural yields, loss of soil biodiversity, and the siltation of water bodies. It can also contribute to desertification and habitat loss. Root Causes of Soil Erosion Natural Causes: Water Erosion: Rainfall and Surface Runoff: Heavy rainfall can dislodge soil particles, which are then carried away by surface runoff. This is especially severe on sloped land where water flows more rapidly. River and Stream Flow: Moving water in rivers and streams can erode banks and carry soil downstream, leading to the formation of gullies and loss of land. Wind Erosion: Strong Winds: In dry and arid regions, strong winds can lift loose, dry soil particles and transport them over long distances, a process known as deflation. This can lead to the formation of dust storms. Gravity: Landslides and Mudslides: On steep slopes, gravity can cause large amounts of soil to move downhill rapidly, often triggered by heavy rain, earthquakes, or volcanic activity. Root Causes of Soil Erosion Human-Induced Causes: Deforestation: Removal of Vegetation: Trees and plants anchor the soil with their roots. When forests are cleared for agriculture, logging, or development, the soil becomes loose and more susceptible to erosion by wind and water. Agricultural Practices: Overgrazing: Livestock can overgraze vegetation, leaving the soil bare and more prone to erosion. Monoculture Farming: Continuous planting of a single crop can deplete soil nutrients and degrade soil structure, making it more vulnerable to erosion. Improper Plowing Techniques: Plowing along the slope rather than across it can accelerate water runoff and increase soil erosion. Urbanization: Construction Activities: The removal of topsoil during construction exposes subsoil, which is more susceptible to erosion. Urban runoff from paved surfaces can also increase erosion in surrounding areas. Methods of Controlling Soil Erosion Vegetative Methods: Afforestation and Reforestation: Planting trees and vegetation in deforested or barren areas helps to stabilize the soil through root systems, reduce wind speed, and decrease the impact of raindrops on the soil surface. Cover Crops: Growing cover crops, such as clover or rye, during off-seasons protects the soil from erosion by providing ground cover, enhancing soil structure, and improving organic content. Contour Plowing: Plowing along the contours of a slope, rather than up and down, reduces the speed of water runoff and helps to prevent soil from being washed away. Terracing: Building terraces on steep slopes transforms the land into a series of steps, reducing runoff velocity and allowing water to infiltrate the soil, thus preventing erosion. Methods of Controlling Soil Erosion Structural Methods: Check Dams and Silt Fences: Small dams or barriers constructed across gullies or streams reduce water flow speed, trap sediment, and prevent further erosion downstream. Retaining Walls: In areas prone to landslides or heavy runoff, retaining walls can be constructed to hold back soil and prevent erosion. Riprap: Placing large stones or concrete blocks on slopes or along shorelines helps to protect against water erosion by absorbing and deflecting the energy of waves or flowing water. Methods of Controlling Soil Erosion Soil Management Techniques: No-Till Farming: Avoiding tilling the soil preserves soil structure, reduces disruption to soil microorganisms, and minimizes erosion. Mulching: Applying a layer of organic or inorganic material (e.g., straw, wood chips, or plastic) on the soil surface protects it from erosion by reducing the impact of raindrops, retaining moisture, and stabilizing the soil temperature. Contour Bunding: Constructing small embankments along the contours of the land helps to slow down water flow and allows more time for water to infiltrate, reducing the risk of erosion. Methods of Controlling Soil Erosion Water Management: Drainage Control: Properly designed drainage systems can direct water away from vulnerable areas, reducing the potential for soil erosion. Rainwater Harvesting: Capturing and storing rainwater reduces surface runoff and provides water for agricultural use, decreasing the pressure on soil and reducing erosion. Methods of Soil Treatment Soil can be contaminated by many different human activities when hazardous substances are not used, stored or disposed of safely. Instances of soil contamination are highest in urban areas and former industrial sites, where manufacturing, industrial dumping, land development, waste disposal, and excessive pesticide or fertilizer use could potentially occur. Some contaminants, such as agricultural chemicals, are applied to the soil surface. Others are released below the surface, due to leaks from buried tanks, sewage pipes, or landfills. Atmospheric contaminants containing hazardous substances can also cause problems. Contamination is not always limited to a specific site and can seep through the soil into groundwater or be carried to nearby land and waterways in rainwater, or as dust. Methods of Soil Treatment After testing to determine the type and level of contaminants present, soil can be subjected to remediation techniques for the purposes of site decontamination. This can be carried out in-situ, or soil may excavated and removed for treatment ex-situ. Options for treating contaminated soil include: 1. Biological treatment/bioremediation uses bacteria to break down substances in the soil 2. Chemical oxidation converts contaminated soils into non-hazardous soils 3. Soil stabilisation involves the addition of immobilizing agents to reduce a contaminants’ leachability 4. Physical methods, like soil washing, use water to separate or remove contaminants Methods of Soil Treatment: Bioremediation Bioremediation is the use of biological processes to degrade, transform, or essentially remove contaminants from soil and water. This process relies on micro-organisms including bacteria and/or fungi, which use the contaminant as a food source. For this reason, bioremediation is widely used to remediate organic contaminants and can be an effective means of mitigating: hydrocarbons halogenated organic solvents halogenated organic compounds non-chlorinated pesticides and herbicides nitrogen compounds metals (lead, mercury, chromium) radionuclides Often, bioremediation presents a more economic option to disposal, however it can take anything from one to several months to carry out. Methods of Soil Treatment: Chemical oxidation Chemical decontamination methods generally focus on chemical oxidation, whereby reactive chemical oxidants are injected into the soil and groundwater for the purpose of rapid and complete contaminant destruction. In situchemical oxidation (ISCO) is a versatile solution, particularly when remediating contaminants located in difficult to access areas such as soils at depth or soils beneath buildings. Chemical oxidation has wide ranging applications and can be used to treat various organic contaminants including TPH, BTEX and PCBs. TPH – triphenylhexane BTEX (usually BTX) - benzene-toluene-xylene PCB - polychlorinated biphenyls Methods of Soil Treatment: Soil stabilisation Stabilisation reduces the risks from contamination by effectively locking contaminants in the soil. It can be achieved in two ways: firstly, by modifying the contaminant in the ground to a less dangerous form; secondly, through solidification, by reducing the mobility of the contaminant and binding it in place so it can’t reach any receptors. Soil stabilisation relies on the addition of immobilizing agents which reduce a contaminants’ leachability and bioavailability. This technique can also be used to improve the geotechnical competency of the ground, making it more suitable for construction work due to higher resistance and lower permeability. Methods of Soil Treatment: Soil washing Soil washing eliminates hazardous contaminants by washing the soil with a liquid wash solution. During this process, fine grained soils, such as silts and clays, are washed away along with contaminants, which are more prone to bind to fine soils. Thus, contaminated fines are separated from cleaned coarse grained soils, such as sands and gravels, which can be safely re-used. Soil washing does not destroy or remove the contaminants and therefore the contaminated soil must be disposed of in a licensed facility. Due to the health risks that soil contamination poses to humans, animals and plants, soil remediation is essential in many cases. As an expert in soil remediation, Enva offers a range of services from soil investigation and testing, through to site decontamination and soil treatment. It also operates the only licensed contaminated soil treatment facility in Ireland, which can help reduce costs by removing the need for expensive soil export.