Skip to main content

LUP Student Papers

LUND UNIVERSITY LIBRARIES

Grundvattenmodellering av Nässjö bangård - Avsänkning, föroreningstransport och jämförelse av två modelleringsprogram

Gjörup, Anna LU and Olsson, Per-Ivar LU (2013) VTG820 20131
Engineering Geology
Environmental Engineering (M.Sc.Eng.)
Abstract
A facility for preservation of wooden rail road sleepers has been operating at the railway yard in Nässjö between 1918 and 2005. The main preservative used at the site was creosote which contains polycyclic aromatic hydrocarbons (PAH) that can be harmful to humans and the environment. The soil at the railway yard is due to these activities heavily polluted and the Swedish Transport Administration (Trafikverket) has decided that an environmental remediation is to be conducted. Tyréns AB has investigated the site and compiled background material for the remediation.
The remediation of the site will be carried out by excavation which will require a lowering of the groundwater table. The aim of this thesis is to create groundwater models in... (More)
A facility for preservation of wooden rail road sleepers has been operating at the railway yard in Nässjö between 1918 and 2005. The main preservative used at the site was creosote which contains polycyclic aromatic hydrocarbons (PAH) that can be harmful to humans and the environment. The soil at the railway yard is due to these activities heavily polluted and the Swedish Transport Administration (Trafikverket) has decided that an environmental remediation is to be conducted. Tyréns AB has investigated the site and compiled background material for the remediation.
The remediation of the site will be carried out by excavation which will require a lowering of the groundwater table. The aim of this thesis is to create groundwater models in two different software, Feflow and Microfem, which describe the hydrogeological situation at the site. These models are used to simulate the area of influence of the lowering of the groundwater and the Feflow model is besides this used to study the contaminant transport. The purpose was also to compare the results of the two models and earlier performed assessments and to evaluate the usability of the modeling programs. Within the railway yard the average absolute difference between modeled and observed values is about 0.2 meters. The resulting simulated groundwater levels are similar in the two models even though their construction differs in some aspects. In most parts of the model the difference between the Microfem and Feflow result is less than half of a meter. The sensitivity analysis also indicates that the models are alike and that they in general are sensitive to the same parameters.
The simulations of the lowering of the groundwater table gave similar results in both models but the affected area was a bit larger in Microfem. Since earlier assessments do not include all excavations it is difficult to compare them with the results of the simulations. However the extensions of the effects coincide quite well in general but the area where the depression of groundwater is greater than one meter was smaller in the simulations. The spreading of naphthalene, one of the components of creosote, was simulated to give an example of the contaminant transport at the site. Since the degradation rate of naphthalene is relatively high the simulated spreading was limited even though the extension of and the
concentration at the source was modeled as a worst case scenario. The modeling of contaminant transport contains several uncertainties and the model is neither calibrated nor verified.
The model could have been improved by more field investigations focused on the parameters shown to be most important by the sensitivity analysis: recharge, water level at Höregölen and properties of the zone of fractured rock between soil and relatively solid bedrock. Both programs have their advantages and disadvantages concerning usability. In general the
experience in this project was that Microfem was more stable and the construction of the finite element grid was easier. It was easier to share information with other programs in Feflow which made it easier to set up the model. Another difference between the software is that Feflow has
additional and more flexible possibilities for visualization. (Less)
Abstract (Swedish)
På bangården i Nässjö har det mellan 1918 och 2005 legat en impregneringsanläggning för järnvägsslipers. Som impregneringsmedel användes främst kreosotolja vilket innehåller polycykliska aromatiska kolväten (PAH) som kan vara skadliga för människa och natur. Marken
på bangården är nu kraftigt förorenad och ska därför saneras. Tyréns AB har på uppdrag av Trafikverket tagit fram ett förfrågningsunderlag för saneringen som ska ske genom schaktning vilket kommer att kräva en sänkning av grundvattenytan. Det här examensarbetet har gått ut på att göra en grundvattenmodellering av bangården i två olika programvaror, Feflow och
Microfem, med målet att få ökad kunskap om avsänkningens utbredning och dessutom i Feflow studera... (More)
På bangården i Nässjö har det mellan 1918 och 2005 legat en impregneringsanläggning för järnvägsslipers. Som impregneringsmedel användes främst kreosotolja vilket innehåller polycykliska aromatiska kolväten (PAH) som kan vara skadliga för människa och natur. Marken
på bangården är nu kraftigt förorenad och ska därför saneras. Tyréns AB har på uppdrag av Trafikverket tagit fram ett förfrågningsunderlag för saneringen som ska ske genom schaktning vilket kommer att kräva en sänkning av grundvattenytan. Det här examensarbetet har gått ut på att göra en grundvattenmodellering av bangården i två olika programvaror, Feflow och
Microfem, med målet att få ökad kunskap om avsänkningens utbredning och dessutom i Feflow studera föroreningstransporten. Syftet är också att jämföra resultaten mellan de båda programmen och med tidigare gjorda bedömningar samt utvärdera programvarornas användbarhet. Trots att modelluppbyggnaden är något olika i de två använda programvarorna skiljer sig de resulterande grundvattennivåerna relativt lite åt. I merparten av modellområdet är skillnaden mindre än en halv meter. Inom bangården är avvikelsen i modellerna från observerade värden i genomsnitt ungefär 0,2 meter. Känslighetsanalysen som genomförts för båda modellerna visar också på stora likheter i resultaten och att modellerna är ungefär lika känsliga för förändring av samma parameter. Simuleringen av grundvattenavsänkningen gav också liknande resultat i de båda modellerna även om påverkansområdet generellt blev större i Microfem. Då de tidigare bedömningarna inte tar hänsyn till alla schakt på en gång är det svårt att jämföra dem rakt av med simuleringarna men överlag överensstämmer avsänkningens påverkansområde ganska väl. Området där påverkan är större än en meter blev dock mindre vid simuleringen. Föroreningsmodelleringen i det här projektet innehåller en rad osäkerheter och modellen är varken kalibrerad eller verifierad. Den förorening som användes för modelleringen är naftalen, ett av de många ämnen som ingår i kreosotolja. Eftersom naftalen har en relativt hög nedbrytningshastighet blev den modellerade spridningen mycket begränsad även om antaganden angående föroreningens utbredning och koncentration vid källan valdes som ett värsta tänktbart scenario. Modellen hade kunnat göras mer tillförlitlig med hjälp av fler fältundersökningar med fokus på de parametrar som känslighetsanalysen pekar ut som viktigast, det vill säga nybildning, Höregölens nivå och krosszonens mäktighet och hydrauliska konduktivitet.
Utvärderingen av de båda programvarornas användbarhet visade att båda programmen har sina för- och nackdelar. Generellt kan man säga att Microfem upplevdes som mer driftsäkerhet än Feflow och att uppbyggnaden av finita elementnät kändes enklare. I Feflow var det lättare att dela och ta emot information från andra program vilket underlättade modelluppbyggandet. En annan stor skillnad som upplevdes mellan programmen är att visualiseringsmöjligheterna skiljer sig åt där Feflow har många fler och flexiblare möjligheter än Microfem. (Less)
Please use this url to cite or link to this publication:
author
Gjörup, Anna LU and Olsson, Per-Ivar LU
supervisor
organization
alternative title
Groundwater modeling of Nässjö railway yard - Changes in groundwater level, contaminant transport and comparison of two modeling software
course
VTG820 20131
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
lowering of groundwater, modeling, groundwater, Nässjö, Microfem, Feflow, kreosot, föroreningstransport, avsänkning, modellering, grundvatten, contaminant transport, creosote
report number
TVTG-5129
language
Swedish
id
3912751
date added to LUP
2013-08-16 08:32:50
date last changed
2014-09-04 08:30:25
@misc{3912751,
  abstract     = {A facility for preservation of wooden rail road sleepers has been operating at the railway yard in Nässjö between 1918 and 2005. The main preservative used at the site was creosote which contains polycyclic aromatic hydrocarbons (PAH) that can be harmful to humans and the environment. The soil at the railway yard is due to these activities heavily polluted and the Swedish Transport Administration (Trafikverket) has decided that an environmental remediation is to be conducted. Tyréns AB has investigated the site and compiled background material for the remediation.
The remediation of the site will be carried out by excavation which will require a lowering of the groundwater table. The aim of this thesis is to create groundwater models in two different software, Feflow and Microfem, which describe the hydrogeological situation at the site. These models are used to simulate the area of influence of the lowering of the groundwater and the Feflow model is besides this used to study the contaminant transport. The purpose was also to compare the results of the two models and earlier performed assessments and to evaluate the usability of the modeling programs. Within the railway yard the average absolute difference between modeled and observed values is about 0.2 meters. The resulting simulated groundwater levels are similar in the two models even though their construction differs in some aspects. In most parts of the model the difference between the Microfem and Feflow result is less than half of a meter. The sensitivity analysis also indicates that the models are alike and that they in general are sensitive to the same parameters.
The simulations of the lowering of the groundwater table gave similar results in both models but the affected area was a bit larger in Microfem. Since earlier assessments do not include all excavations it is difficult to compare them with the results of the simulations. However the extensions of the effects coincide quite well in general but the area where the depression of groundwater is greater than one meter was smaller in the simulations. The spreading of naphthalene, one of the components of creosote, was simulated to give an example of the contaminant transport at the site. Since the degradation rate of naphthalene is relatively high the simulated spreading was limited even though the extension of and the 
concentration at the source was modeled as a worst case scenario. The modeling of contaminant transport contains several uncertainties and the model is neither calibrated nor verified.
The model could have been improved by more field investigations focused on the parameters shown to be most important by the sensitivity analysis: recharge, water level at Höregölen and properties of the zone of fractured rock between soil and relatively solid bedrock. Both programs have their advantages and disadvantages concerning usability. In general the 
experience in this project was that Microfem was more stable and the construction of the finite element grid was easier. It was easier to share information with other programs in Feflow which made it easier to set up the model. Another difference between the software is that Feflow has 
additional and more flexible possibilities for visualization.},
  author       = {Gjörup, Anna and Olsson, Per-Ivar},
  keyword      = {lowering of groundwater,modeling,groundwater,Nässjö,Microfem,Feflow,kreosot,föroreningstransport,avsänkning,modellering,grundvatten,contaminant transport,creosote},
  language     = {swe},
  note         = {Student Paper},
  title        = {Grundvattenmodellering av Nässjö bangård - Avsänkning, föroreningstransport och jämförelse av två modelleringsprogram},
  year         = {2013},
}