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Naturlig nedbrytning av klorerade lösningsmdel : en modellering i Biochlor baserat på en fallstudie

Olsson, Sofia LU (2015) In Examensarbeten i geologi vid Lunds universitet GEOL01 20151
Department of Geology
Abstract
Chlorinated hydrocarbons have been used in various Swedish industries, mainly during the 1900s. The main uses have been as solvents in the manufacturing industry and as washing liquid in dry cleaners. Some of the common chlorinated solvents are tetrachloroethene (PCE) and trichloroethene (TCE). Most of the chlorinated hydrocarbons are somewhat insoluble in water and the density is higher than water. Due to these properties they are referred to as Dense Non-Aquous Phase Liquids and may occur as a free phase. They will be transported vertically through soil layers and groundwater until the capillary force binds the fluids or until the fluid reaches an impermeable layer. The pollutions are then dissolved into the groundwater. Natural... (More)
Chlorinated hydrocarbons have been used in various Swedish industries, mainly during the 1900s. The main uses have been as solvents in the manufacturing industry and as washing liquid in dry cleaners. Some of the common chlorinated solvents are tetrachloroethene (PCE) and trichloroethene (TCE). Most of the chlorinated hydrocarbons are somewhat insoluble in water and the density is higher than water. Due to these properties they are referred to as Dense Non-Aquous Phase Liquids and may occur as a free phase. They will be transported vertically through soil layers and groundwater until the capillary force binds the fluids or until the fluid reaches an impermeable layer. The pollutions are then dissolved into the groundwater. Natural degradation can occur in the groundwater in the right circumstances. Tetrachloroethene degrades to trichloroethene that then degrades to cis-dichlorothene (c-DCE), which in turn degrades to vinyl chloride (VC). Complete degradation from vinyl chloride to ethane, a harmless degradation product, can then occur. Degradation does not need to be complete but can rather result in the accumulation of more toxic components in the aquifer. An area can be sanitised through monitored natural attenuation (MNA), which means that the natural attenuation reduces, among other things, the mass and toxicity of contaminants. Different models can be used to evaluate whether MNA is a viable sanitation/attenuation method. Biochlor is a model that simulates the dispersion and degradation of chlorinated solvents in the groundwater. A specific case study is taken as an example and modelled in Biochlor. The results show that MNA is not a viable sanitisation method for the case study based on both the model and the criteria for MNA. According to the model the contamination plume extends 250 m from the contamination source yet this is likely an underestimation due to Biochlor overestimating the rate of degradation in this case. A better calibration could have been performed had there been more measurement points downstream from the source thus allowing for a more reliable set of modelling results. The main purpose of Biochlor is, however, to provide a rough estimate of the dispersion and degradation of chlorinated solvents. (Less)
Abstract (Swedish)
Klorerade kolväten har använts inom diverse svenska industrier under framförallt 1900-talet. De främsta användningsområdena har varit som lösningsmedel inom verkstadsindustrin och som tvättvätska i kemtvättar. Några av de vanligaste lösningsmedlen är tetrakloreten (PCE) och trikloreten (TCE). De flesta klorerade kolväten är intermediärt vattenlösliga och har högre densitet än vatten vilket benämns Dense Non-Aquous Phase Liquids. De kemiska egenskaperna gör att ämnena kan förekomma i en separat fri fas och transporteras vertikalt genom jordlagren och grundvattnet. När de kapillära krafterna binder upp vätskan eller när den fria fasen möter ett impermeabelt lager bromsas spridningen upp. Föroreningar löses sedan ut från det förbipasserande... (More)
Klorerade kolväten har använts inom diverse svenska industrier under framförallt 1900-talet. De främsta användningsområdena har varit som lösningsmedel inom verkstadsindustrin och som tvättvätska i kemtvättar. Några av de vanligaste lösningsmedlen är tetrakloreten (PCE) och trikloreten (TCE). De flesta klorerade kolväten är intermediärt vattenlösliga och har högre densitet än vatten vilket benämns Dense Non-Aquous Phase Liquids. De kemiska egenskaperna gör att ämnena kan förekomma i en separat fri fas och transporteras vertikalt genom jordlagren och grundvattnet. När de kapillära krafterna binder upp vätskan eller när den fria fasen möter ett impermeabelt lager bromsas spridningen upp. Föroreningar löses sedan ut från det förbipasserande grundvattnet. Naturlig nedbrytning kan ske i grundvattnet om rätta förhållanden finns. Tetrakloreten (PCE) bryts ner till trikloreten (TCE) som sedan bryts ner till cis-dikloreten (c-DCE) som i sin tur bryts ner till vinylklorid (VC). Fullständig nedbrytning kan sedan ske från vinylklorid till etan som är en ofarlig nedbrytningsprodukt. Nedbrytningen behöver inte vara fullständig utan kan resultera i ackumulation av mer toxiska nedbrytningsprodukter i akviferen. Ett område kan saneras genom övervakad naturlig självrening (ÖNS) vilket innebär att de naturliga självreningsprocesserna minskar bland annat massa och toxiciteten hos föroreningarna. För att utvärdera om ÖNS är en alternativ saneringsmetod kan olika modelleringsverktyg användas. Biochlor är en modell som simulerar spridning och nedbrytning av klorerade lösningsmedel i grundvattnet. En utvald fallstudie i form av en nedlagd kemtvätt används som exempel och modellerades i Biochlor. Resultatet visar att ÖNS inte är en lämplig saneringsmetod för fallstudien baserat på både modelleringen och på de kriterier som finns för ÖNS. Enligt modellen sträcker sig föroreningsplymen 250 meter från föroreningskällan men detta är troligtvis en underskattning eftersom Biochlor sannolikt överskattar nedbrytningshastigheten i detta fall. Modelleringsresultatet hade blivit mer säkert om det hade funnits fler mätpunkter nedströms källområdet så att en bättre kalibrering hade kunnat utföras. Det huvudsakliga syftet med Biochlor är dock att göra en grov uppskattning av spridning och nedbrytning av klorerade lösningsmedel. (Less)
Please use this url to cite or link to this publication:
author
Olsson, Sofia LU
supervisor
organization
alternative title
Natural attenuation of chlorinated solvents : a case study modelled in Biochlor
course
GEOL01 20151
year
type
M2 - Bachelor Degree
subject
keywords
klorerade lösningsmedel, Biochlor, naturlig nedbrytning, modellering, DNAPL
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
435
language
Swedish
id
5465462
date added to LUP
2015-06-22 09:14:11
date last changed
2015-06-22 09:14:11
@misc{5465462,
  abstract     = {Chlorinated hydrocarbons have been used in various Swedish industries, mainly during the 1900s. The main uses have been as solvents in the manufacturing industry and as washing liquid in dry cleaners. Some of the common chlorinated solvents are tetrachloroethene (PCE) and trichloroethene (TCE). Most of the chlorinated hydrocarbons are somewhat insoluble in water and the density is higher than water. Due to these properties they are referred to as Dense Non-Aquous Phase Liquids and may occur as a free phase. They will be transported vertically through soil layers and groundwater until the capillary force binds the fluids or until the fluid reaches an impermeable layer. The pollutions are then dissolved into the groundwater. Natural degradation can occur in the groundwater in the right circumstances. Tetrachloroethene degrades to trichloroethene that then degrades to cis-dichlorothene (c-DCE), which in turn degrades to vinyl chloride (VC). Complete degradation from vinyl chloride to ethane, a harmless degradation product, can then occur. Degradation does not need to be complete but can rather result in the accumulation of more toxic components in the aquifer. An area can be sanitised through monitored natural attenuation (MNA), which means that the natural attenuation reduces, among other things, the mass and toxicity of contaminants. Different models can be used to evaluate whether MNA is a viable sanitation/attenuation method. Biochlor is a model that simulates the dispersion and degradation of chlorinated solvents in the groundwater. A specific case study is taken as an example and modelled in Biochlor. The results show that MNA is not a viable sanitisation method for the case study based on both the model and the criteria for MNA. According to the model the contamination plume extends 250 m from the contamination source yet this is likely an underestimation due to Biochlor overestimating the rate of degradation in this case. A better calibration could have been performed had there been more measurement points downstream from the source thus allowing for a more reliable set of modelling results. The main purpose of Biochlor is, however, to provide a rough estimate of the dispersion and degradation of chlorinated solvents.},
  author       = {Olsson, Sofia},
  keyword      = {klorerade lösningsmedel,Biochlor,naturlig nedbrytning,modellering,DNAPL},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Naturlig nedbrytning av klorerade lösningsmdel : en modellering i Biochlor baserat på en fallstudie},
  year         = {2015},
}