Land That Contains Substances Environmental Sciences

Metals have played an important role in the development of man, gold and copper, both native metals have been worked into desirable objects since 15000BC. 'Advanced' smelting techniques were developed by 4000BC, used to extract copper from ores and within a further 1,000 years, other metals were being extracted, including silver, lead, tin and zinc. The development of the blast furnace centuries later led to the large scale production of iron and steel (sgm.ac.uk 2002). The last 100 years has seen Great Britain shaped by the 'great' industrial revolution and witnessed the development of a plethora of industries, notably, the steel, coal and chemical industries. Industrial 'visionaries', focused on the development of industry had not planned a sustainable future and the consequences to the environment were overridden by expansion. It is this lack of planning that has led to historical industrial processes allowing waste to be disposed of by simply tipping it onto the land, chemicals and raw materials were often spilt in situ resulting in land contamination (sepa.org.uk 2012).

Contaminated land

Land that contains substances in or under the land that are considered to be a potential hazard to human health or the Environment is considered to be 'Contaminated' (environmental-protection .org.uk 2012). Contamination can be categorised into various forms and can impact in different ways, depending upon numerous factors including; type, concentration and the nature of the substance resulting in a vast array of impacts to both human health and the environment (sepa.org.uk 2012).

A report undertaken by the British Geological Survey (BGS) in 2009, estimates that in England alone, there are around 15,470 hectares of land that is classed as contaminated (nerc.ac.uk 2009).

Contamination is assessed on a site - site basis, in a bid to facilitate the deployment of the most efficient and practicable technique. In order to determine the best technique, details of the contaminant(s) contained within the soil first need to be assessed along with the type of ground materials present at the surface and in the subsurface (defra.gov.uk 2010).

Following initial investigations, contaminants can be determined and classified into groups depending on their properties (organic or inorganic) (Brown 2009).

Table 1: Contaminant classes used to determine remediation technique applied. Adapted from (defra.gov 2010).

OrganicTypical examplesHalogenated volatile organic compounds (VOCs)

1-chlrobutane, methoxyflurane, pentafluoropropan-1ol

Halogenated semivolatile organic compounds (SVOCs)

Chlorophenol, Tetrachlorophenol, Chlordane

Non-halongenated volatile organic compounds (VOCs)

Benzene, Xylene, acetone, Carbon disulphide

Non-halongenated semivolatile organic compounds (SVOCs)

Polycyclic aromatic hydrocarbons (PAH), phenol

Organic Corrosives

Acetic acid, aniline

Organic cyanides

Organonitriles

Polychlorinated biphenyls (PCBs)

PCB (Arochlor)-1016

Pesticides / herbicides

4, 4-DDT, Heptachlor

Dioxins / Furans

2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran

InorganicMetals

Lead, Mercury, Chromium, Zinc

Radionuclides

Radioactive isotopes of uranium, radon

Corrosives

Hydrochloric acid, sulphuric acid

Cyanides

Metallic cyanides

Asbestos

Blue, brown, white

MiscExplosives

2,4,6-trinitrotoluene (TNT), hydrazine

Table 1 is intended to provide a rudimentary view of the classification of contaminants, assessing the appropriateness of remediation techniques is a complicated process in reality, in reality, several component contaminants will be contained within the target site, each category of contaminant would be assessed individually to assess the applicability of a remediation technique (epa.gov 2012).

Remediation of contaminated land

Environmental risks associated with contaminated land are typically remediated - a technique that seeks to remove contaminants contained within the soil (ny.gov 2012). Remediation techniques are typically subject to an array of regulatory requirements - Part 2A of the Environmental Protection Act 1990 that is based on the likelihood of significant harm to human health and significant pollution of the water environment (northdevon.gov.uk 2012).

Appropriate remediation

The appropriate remediation solution should be implemented to result in the land being 'suitable for use'. Remediation should render the land no longer contaminated and the effects of any significant harm, or pollution of controlled waters that has occurred has been remedied , the appropriately selected remediation technique can in many situations see the level of contamination reduced to such a level that any considered significant risk is minimal, this does not however imply that all contaminants are removed completely, in some situations the contaminants are at such low levels that they pose no risk or that they are permanently contained in-situ (environment-agency.gov.uk 2004).

Remediation technologies available

Historically, the remediation of contaminated land can be expensive and relies heavily upon processes that are fundamentally very technical (defra.gov.uk 2010). Many of these processes have involved heavy engineering solutions, although considered to be very effective, and in many cases, the only viable option, they have high environmental, social and economic impacts (clu-in.org 2012).

Classification of soil remediation technologies

Soil remediation technologies can be categorised into four distinct broad classes (Table 1) according to the fundamental principles involved in the removal / containment of contaminant(s) which can be further sub-divided into in-situ and ex-situ techniques (ehu.es 2012).

In situ clean-ups require no excavation of contaminated material, in situ techniques are often preferred because of their lower application cost; however, the general consensus is that these techniques take longer to reach the preferred status and are more difficult to monitor because of non-uniformity in treatment because of variances in soil materials (DETR 1998). Ex situ approaches (excavation of a contaminated area) and treating it on site (ex situ, on-site) or transporting it to a remote site for 'cleaning' (ex situ, off-site) is generally considered to be the more expensive option given the logistics of the operation, however, ex-situ techniques present the advantage of removing the majority of contamination preventing further spread (iastate.edu 2012).

Table 1: Overview of both in situ and ex situ remediation technologies available, adapted from: (defra.gov. 2010).

In-situTechnologyBiologicalPhysicalChemicalThermal

Chemical oxidation and reduction



Electro - remediation



Enhanced bioremediation using redox amendments



Flushing



Phytoremediation



Air Sparging



Biosparging



Stabilisation and solidification



Thermal Treatment



Venting



Vitrification

Ex situ

Biopiles



Slurry phase bioreactors



Chemical oxidation and reduction



Soil washing and separation processes



Stabilisation and solidification



Thermal desorption



Incineration



Ex situ soil vapour extraction



Vitrification



Water and gas / vapour treatment

Biological remediation technologies

Bioremediation uses microorganisms (yeast, fungi or bacteria) to degrade organic contaminants; bioremediation can be carried out both in-situ and ex-situ. The contaminants act as a food source for the microorganisms that break them down. Aerobic processes require a source of oxygen, dispelling carbon dioxide COâ‚‚ and water H2O (clu-in.org 2012) (Figure 1)

Figure 1: Schematic diagram of aerobic biodegradation in soil (tamu.edu 2008).

Ex situ techniques include slurry-phase bioremediation, a process of maintaining contact between microorganisms and contaminants by adding water to contaminated soils to form 'slurry' (iastate.edu 2012). Other bioremediation techniques include;

Bioventing

Injection of hydrogen peroxide (H202)

Solid phase bioremediation

Landfarming

Soil biopiles

Composting (clu-in.org 2012).

Bioremediation is an economical process for a broad range of applications of organic wastes. Many of the processes can be handled in situ avoiding the need to transport hazardous materials from site (sa.gov.au 2005).

Physico - Chemical treatments

Physical methods of soil reclamation are those that do not change the physic-chemical properties of the pollutants accumulated in the soil to be cleaned (cieh.org 2007). Physical remediation techniques include simplified processes such as soil extraction and storage of polluted soils along with more complicated and technological techniques (defra.gov.uk 2010). In the physical processes, the phase transfer of pollutants is induced. In the chemical processes, the chemical structure of the pollutants is changed by means of chemical reactions to produce less toxic or better separable compounds from the solid matrix (unido.org 2012).

Physical remediation techniques offer a cost effective solution that can be concluded relatively quickly, and consume very little engineering or energy resources (eugris.info 2012). Physical applications can be engaged both in-situ and ex-situ, and have the advantage that a broad spectrum of pollutants can be removed from the contaminated site and that they can be widely administered (small, local sites) (unido.org 2012).

Physical-chemical treatments include;

Soil Flushing

Soil washing (Figure 2).

Fracturing

http://renewcanada.net/wp-content/uploads/2010/03/swallowtail2.png

Figure 2: Soil washing technique (renewcanada.net 2010)

Thermal treatments

It is generally considered that thermal processes are the most costly, however, a quick remediation time is offered as compensation (unido.org 2012). Thermal remediation involves the introduction of hydrocarbon contaminated soils into a heated vessel and retaining those soils until they reach a uniform temperature. Contaminants are heated by the thermal process, heat is applied to increase the volatility, to burn, decompose, destroy or melt the contaminant. The risk of releasing dioxins into the atmosphere is an important consideration and therefore, operating temperatures are limited to 800°F (purdue.edu 2006).

Factors that influence the timescale of effectiveness are the type and amounts of contaminants present that range from site to site, the physical size of the site and soil material present (clu-in-org 2012).

Thermal techniques can be applied both in-situ and ex-situ, the principle advantage of in-situ techniques is that soil can be treated without the need to remove and transport reducing operating costs, however, in-situ techniques generally take longer to de-contaminate a site and cost savings are negligible. Ex-situ techniques involve the excavation and removal of contaminated soils where they are exposed to high temperatures in treatment cells; the cells contain contaminated media during the application. Although ex-situ techniques offer a reduced treatment time, increased logistical implications offset treatment costs (clu-in-org 2012).

Thermal techniques typically include;

Hot gas contamination

Vitrification

Injection of hot air

Thermal Conduction

Additional techniques are shown in table ?

http://www.emis.vito.be/sites/default/files/data_sheets/migrated/schema%20thermische%20reiniging.PNG

Figure 3: Diagram of thermal cleansing (vito.be 2012).

2.0 A critical assessment of the effectiveness of soil remediation techniques and the protection of groundwater2.1 The Groundwater system

"The largest available reservoir of fresh water"

(Environment-agency.gov.uk 2012)

Water that is continually moving through the environment is known as the water cycle, however, most of the rain that falls will be soaked up by soil, through the process of infiltration, water will soak further down into the ground and eventually into underlying rocks, this is known as groundwater (groundwateruk.org 2012).

2.2 The importance of groundwater

70% of the global capacity of freshwater is groundwater, 30% of this amount is found within rivers, lakes and streams, many of these rivers and lakes etc. are fed directly by groundwater, it cannot be underestimated how much groundwater plays an important role within the human civilisation, groundwater is the lifeline afforded to global wetland sites and a major benefactor to industry in a global context (environment-agency.gov.uk 1999).

Whilst groundwater is generally of good biological quality, it is constantly threated by contaminants, pollutants that seep through the surface and into the groundwater system, pollution occurs from diffuse sources when a pollutant is spread onto the land in the form of an applied agricultural pesticide for example and also from point source pollution, where a chemical spillage has occurred for example. Some pollutants inputs will naturally degrade or will be filtered out as the water flows through permeable rocks, but on many occasions, the pollutants are persistent types and have to be subjected to typically costly remediation processes (groundwateruk.org 2012).

Figure 4: ????????????????(mfe.gov.nz 2007).

3.0 Are soil remediation technologies effective at protecting groundwater?

The mobility and fate of contaminants that enter soil are determined by a number of factors (table ?), in order for a comprehensive and realistic site risk assessment to be carried out, consideration should be given to the nature and prevailing conditions in the soils, including; geology, hydrogeology, hydrology, contaminant geochemistry, geotechnics, ecotoxicology and microbiology, once these have been properly addressed, a predicted behaviour model of the contaminant can be produced to aid in the selection of the most efficient and cost effective remediation technique (eugris.info 2012).

Relevant soil and groundwater properties may include:Relevant contaminant Physico-chemical properties may include:

Soil profile

Contaminant concentration

Soil texture (relative proportions of sand, loam and clay)

Chemical speciation e.g. the valency or oxidation state of a metal

Presence of mineral constituents such as clays, carbonates, phosphates, oxides and organic matter (expressed as the fraction of organic carbon foc)

Solubility in water (or other solvent if a non-aqueous free phase liquid is present)

Moisture content

Sorption (soil-water partition coefficient Kd and organic carbon-water partition coefficient Koc)

Particle size distribution

Octanol-water partition coefficient (kow)

Bulk dry density

Vapour pressure

Porosity (air-filled and water-filled)

Henry's Law constant

Sorption capacity of the soil

Biodegradation

pH and redox potential

Nature of metabolites

Microbial populations

Vegetable uptake (soil to plant concentration)

Elevation of water table

Weathering potential

Groundwater flow direction

Diffusion coefficient in air

Hydraulic gradient

Diffusion coefficient in water

Hydraulic conductivity

Viscosity (gases and vapours)

Hydraulic dispersivity

Viscosity (non-aqueous phase liquids)

Table ?: Factors influencing the fate and mobility rate of contaminants in soil, adapted from (eugris.info 2012).

Article name: Land That Contains Substances Environmental Sciences essay, research paper, dissertation