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Numerisk grundvattenmodellering och föroreningsanalys av PFAS-ämnen i anslutning till nedlagd brandövningsverksamhet i Bodens kommun
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2019 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Numerical Groundwater Modelling and Contaminant Transport of PFASs from Former Firefighting Training Facilities in Boden Municipality (English)
Abstract [sv]

Poly- och perfluorerade alkylsubstanser (PFAS) är samlingsnamnet för en stor grupp kemikalier som det senaste årtiondet tilldelats världsomfattande uppmärksamhet med anledning av frekventa förekomster i vattenmiljö, djurliv och människor. Samtliga PFAS som uppträder i miljön är antropogena och har blivit industriellt framtagna och tillämpade i över 60 år. På grund av deras fysiska och kemiska stabilitet och ytaktiva egenskaper är PFAS eftertraktade inom en rad olika industriella och kommersiella produkter, från filmbildande brandskum till vatten-, smuts- och fettavvisande ytbeläggningar. De omfattande möjligheterna för användning har resulterat i utsläpp av PFAS i miljön, antingen av direkta källor (~80 %) som tillverkning och tillämpning av PFAS-innehållande produkter, eller indirekta källor (~20 %) som nedbrytning och transport av prekursorer. Åtgärder har därför tagits på nationell, regional och global nivå för att begränsa användningen och spridningen av selekterade PFAS-ämnen.

En av de mest uppmärksammade föroreningsproblemen med PFAS i Sverige är utsläppen av filmbildande brandsläckningsskum (AFFF) från brandövningsplatser. Som en konsekvens av flera decenniers användning och okontrollerat utsläpp till miljön har koncentrationerna av PFAS uppmätts att vara som högst i anslutning till övningsplatserna. Ämnenas mobilitet och höga vattenlöslighet gör att risken för transport till kringliggande områden är stor, vilket ökar risken att förorena närliggande grundvattentäkter. Flera exempel på PFAS-haltigt dricksvatten i svenska hushåll har bland annat upptäckts i kommuner såsom Uppsala, Ronneby, Halmstad, Botkyrka.

Två före detta brandövningsplatser i Bodens kommun har brukat AFFF i övningssyfte i samband med brandövningar då platserna var aktiva. NIRAS Sweden AB har på uppdrag av Försvarsmaktens miljöprövningsenhet utrett området med avseende på PFAS och konstaterade förhöjda nivåer av ämnena i grundvattenmiljö. Eftersom flera ytvattenförekomster gränsar till brandövningsområdet finns det en oro för ämnenas spridningsbenägenhet och potential att påverka närmsta dricksvattentäkt. Syftet med examensarbetet har av den anledningen varit att kartlägga spridningen av PFAS i grundvatten från de två före detta brandövningsstationerna i Boden. Tillvägagångssättet har gått ut på att upprätta en grundvattenmodell i modelleringsprogrammet Visual MODFLOW Classic. Den hydrogeologiska modellen har tillämpats för att utföra föroreningstransport med hjälp av insticksmodulerna MODPATH och MT3DMS. Transport av det mest framträdande PFAS-ämnet i området, PFOS, modellerades från båda brandövningsplatserna och föroreningsplymens utveckling har visualiserats i flera tidssteg.

Resultatet från grundvattenmodelleringen visade att grundvattnet från brandövningsområdena i det övre grundvattenmagasinet rör sig i nordvästlig till nordöstlig riktning, men även mot Luleälven. I det undre grundvattenmagasinet rör sig vattnet i nordvästlig, men har också tendens att röra sig mot Luleälven. Föroreningstransporten visade att PFOS har benägenhet att röra sig mot Luleälven i en sydvästlig riktning. Transporttiden av PFOS från brandövningsplatserna till Luleälven beräknades med MODPATH till sex respektive 7 år för den kalibrerade modellen och område 13/24. Visualisering av PFOS-plymen med MT3DMS visade att det tar cirka 100 år för ämnena att nå Luleälven.

Abstract [en]

Poly- and perfluoroalkyl substances (PFASs) is the collective name for a large group of organic chemicals which in the past decade have gained global attention due to their frequent occurence within the aquatic environment, wildlife and humans. All PFAS that occur in the environment are man-made and have been industrially created and used for over 60 years. Due to their physical and chemical stability and surface active attributes, PFAS are coveted within an array of industrial and commercial products, such as film-forming fire foam to water, dirt and grease-repellent coatings. The many possibilities to use PFAS have led to environmental emissions, either through direct sources (~80%) like manufacturing and application of PFAS-containing products, or indirect sources (~20%), through decomposition and transport of precursors. Within the PFAS-family, perfluoroctanesulfonat (PFOS) and perfluoroctaneacid (PFOA) are the most well-known and studied chemicals which have gained particular attention due to their persistence and high frequency in the environment, in turn leading them to be easily detected in humans and animals globally. PFOS and PFOA have further shown bioaccumulative and toxic traits and have thus increased the regulatory interest in the chemicals in questions of environmental and human health. Measures have therefore been taken on national, regional and global levels to restrict the use and dispersion of selected PFAS-substances affiliated with negative effects.

One of the contamination issues to have gained most attention in Sweden is the emission of film-forming fire foam from fire drill locations. The PFAS-containing foam has been used throughout the country for practicing extinguishing fires related to class B: liquid fires, and has been predominantly used by military, airports and industries. As a consequence from the multi decennial use and uncontrolled emissions, the PFAS concentration, mainly PFOS and PFOA, has been measured to be highest in connection with the exercise sites. The substances mobility and high water solubility has increased the risk for their transportation to nearby areas and they may through rainfall infiltrate the ground to potentially reach the groundwater where they risk contaminating nearby groundwater sources. In Sweden, contaminated PFAS-areas are a particularly debatable issue, as about 50% of Swedish drinking water comes from groundwater-related water sources and for that reason, they have increased the general concern for human exposure. Several examples of PFAS-rich drinking water in Swedish households have been found in municipalities as Botkyrka, Halmstad, Ronneby and Uppsala and have in some cases been so high that related water resources have been withdrawn. Even if the intake of drinking water containing large quantities of PFAS substances is not considered to give rise to acute health effects, awareness of the long-term effects of exposure to PFAS is still very limited. A number of experimental and epidemiological studies focusing on PFOS and PFOA, on the other hand, have documented that both high and low doses of the substances can cause a number of adverse health effects.

More recently, regulations on legislation for PFAS have reduced the scope of application, preferably for PFOS, but in accordance with this, products such as PFOS-containing fire foams have been substituted with other PFAS which have continued to be used at fire drill locations in Sweden. Continuous emissions of PFAS at these sites are thus still an up-to-date and forthcoming issue, as the substances - together with already existing pollutants - will remain for a long time to come. There are therefore reasons to limit the use further, but due to the lack of data for most PFAS pollutants, there is currently no benchmark value issued by the EU for PFAS other than PFOS. However, the National Food Agency has issued limit values based on the presence of 11 PFAS substances (PFBS, PFHxS, 6:2 FTSA, PFBA, PFPeA, PFHxA, PFHpA, PFNA, PFDA, PFOA och PFOS) with an action threshold of 90 ng·L-1and a health-based limit value for 900 ng·L-1. The values ​​should give an indication that levels of PFAS which are larger in scope than the recommendation are too high and that measures should be taken to minimize the risk of spreading and unhealthy exposure to humans. For this reason, fire drill locations using fire-containing foam containing PFAS in Sweden are a high priority for mapping PFAS distribution in the country and identifying potential areas that are at risk of being affected by the spread of the pollutants in soil and water.

As a result, two closed fire drill locations in Boden municipality - as part of a nationwide survey - have been investigated with regard to the fire extinguishing foam that has historically been used and caused pollution in the area. The PFAS-based fire foam is assumed to have had historical application to two exercise sites that operated between 1940 – 1985 and 1987 – 2005, respectively. In 2016, an environmental technical soil survey was carried out with regard to the presumed PFAS occurrence for the area. The investigation was based on sampling of soil and groundwater at four and eight different points respectively, centered around the two fire drill locations, and the results showed that the current contamination in the area was clearly noticeable and that the levels were higher than the Swedish Food Agency's recommended action threshold. Findings of PFOS that exceeded SGI's preliminary target value in groundwater (45 ng·L-1) and in soil (10 µg/kgTS) were also measured in connection with the two fire drill sites, which increased the interest in broadening the mapping of the current pollution situation with the aim of creating a better understanding of the extent of the pollution and potential spreading potential. Because the knowledge of the groundwater flow direction is limited, a hydrogeological model over the fire drill location can lead to a better understanding of the groundwater flow direction and thus the possible spreading direction of the present PFAS substances. The model can also be used as a tool for calculating the time required for the potential of the pollutants to affect the nearest protection object and thereby estimate and prevent the risks for human exposure in the area at the conceivable start of construction work in the now discontinued area.

The results from the groundwater modelling showed that the groundwater from the fire drill areas in the upper groundwater reservoir moves in a northwesterly to northeasterly direction, but also towards the Lule River. In the lower groundwater reservoir, the water moves to the northwest and towards the Lule River. The contamination transport showed that PFOS tends to move toward the Lule River in a southwesterly direction. The transport time of PFOS from the fire training sites to the Lule River was estimated with MODPATH to 6 and 7 years respectively for the calibrated model and area 13/24. Visualization of the PFOS plume with MT3DMS showed that it takes about 100 years for the substances to reach the Lule River.

Place, publisher, year, edition, pages
2019. , p. 82
Series
Examensarbete vid Institutionen för geovetenskaper, ISSN 1650-6553 ; 475
Keywords [en]
poly- and perfluoralkyl substances (PFASs), groundwater modelling, firefighting foam, MODFLOW, contaminant transport, Boden Municipality
Keywords [sv]
poly- och perfluorerade alkylsubstanser (PFAS), grundvattenmodellering, brandsläckningsskum, MODFLOW, föroreningstransport, Bodens kommun
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-399028OAI: oai:DiVA.org:uu-399028DiVA, id: diva2:1377410
External cooperation
NIRAS Sweden AB
Subject / course
Earth science
Educational program
Master Programme in Earth Science
Presentation
2019-11-12, Geocentrum, Villavägen 16, 752 36, Uppsala, 15:00 (Swedish)
Supervisors
Examiners
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved

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