Helen French

Seniorforsker

(+47) 928 23 962
helen.french@nibio.no

Sted
Ås - Bygg F20

Besøksadresse
Fredrik A. Dahls vei 20, 1430 Ås

Til dokument

Sammendrag

Degradation of organic chemicals in natural soils depends on oxidation-reduction conditions. To protect our groundwater resources we need to understand the degradation processes under anaerobic conditions. Available iron and manganese oxides are used as electron acceptors for anaerobic degradation and are reduced to the dissolved form of metallic cations in pore water. To monitor this process is a challenge, because anaerobic conditions are difficult to sample directly without introducing oxygen. A few studies have shown an impact of iron reduction on spectral induced polarisation (SIP) signature, often associated with bacterial growth. Our objective is to study the impact of iron and manganese oxide dissolution, caused by degradation of an organic compound, with spectral induced polarisation signatures. Twenty-six vertical columns (30 cm high, inner diameter 4.6 cm) were filled with a sand rich in oxides (manganese and iron) with a static water table in the middle. In half of the columns, a 2 cm high contaminated layer was installed just above the water table. As the contaminant degrades, the initial oxygen is consumed and anaerobic conditions form Every three days over a period of one month, spectral induced polarisation (twenty frequencies between 5mHz and 10 kHz) data were collected on six columns: three contaminated replicates and three control replicates. Chemical analysis was done on twenty columns assigned for destructive water sampling, ten contaminated columns and ten control. The results show an increase of the real conductivity associated with the degradation processes, independent of frequency. Compared with the pore water electrical conductivity in the saturated zone, the real conductivity measurement revealed the formation of surface conductivity before iron was released in the pore water. In parallel, we also observed an evolution of the imaginary conductivity in both saturated and unsaturated zones at frequencies below 1 Hz. Overall, the anaerobic reduction of iron and manganese oxide during the organic degradation increased both the conductive and polarisation component of the complex conductivity.

Til dokument

Sammendrag

Hvert år brukes det omtrent 7000 tonn vegsalt (MgCl2 og NaCl) på kommunale veger i Oslo. På grunn av de negative effektene som vegsalt kan ha, og med bakgrunn i bystyrevedtak fra 2012 om at Oslo kommune skal erstatte vegsalt med mer miljøvennlige alternativer, ønsker Bymiljøetaten å teste ut alternative miljøvennlige avisningsmidler på veg- og sykkelvegnettet. Fra februar 2018 ble natriumformiat benyttet som avisningsmiddel på Eterveien og en del av Østensjøveien langs Østensjøvannet i Oslo. Innløpsbekkene til innsjøen ble overvåket gjennom testperioden. Formiat forbruker oksygen ved nedbrytning, men ut fra sesongens resultater er det ingenting som tyder på at tilførsel av formiat har forårsaket oksygenmangel, hverken i sidebekkene eller i Østensjøvannet. Effektene av formiat på vegetasjon er vanskelig å si noe konkret om da det ble brukt vanlig vegsalt og formiat samme sesong. Systematiske undersøkelser av saltskader på vegetasjon gjennom vinteren, hyppigere prøvetaking i bekkene, samt kontinuerlig overvåking ved utløpet til Østesjøvannet er noen av tiltakene som foreslås for videreføringen av prosjektet vinteren 2018/2019.

Sammendrag

Som en del av Sykkelprosjektet i Bymiljøetaten i Oslo kommune ble det i 2017/2018 opprettet et pilotprosjekt for miljøvennlig salting av sykkelvegnettet. Et av delmålene i pilotprosjektet var å kartlegge miljøeffektene knyttet til bruk av formiater som et alternativ til vanlig vegsalt. Formiat brukes blant annet til drift av flyplasser, og skal være mer miljøvennlig og mindre korroderende enn vanlig veisalt. Denne rapporten er en sammenstilling av tilgjengelig litteratur om ulike effekter av vegsalt og alternative avisningsmidler, med hovedfokus på påvirkning av formiatbaserte avisningskjemikalier i naturen.

Til dokument

Sammendrag

A physically-based, distributed hydrological model (MIKE SHE) was used to quantify overland runoff in response to four extreme rain events and four types of simulated land use measure in a catchment in Norway. The current land use in the catchment comprises arable lands, forest, urban areas and a stream that passes under a motorway at the catchment outlet. This model simulation study demonstrates how the composition and configuration of land use measures affect discharge at the catchment outlet differently in response to storms of different sizes. For example, clear-cutting on 30% of the catchment area produced a 60% increase in peak discharge and a 10% increase in total runoff resulting from a 50-year storm event in summer, but the effects on peak discharge were less pronounced during smaller storms. Reforestation of 60% of the catchment area was the most effective measure in reducing peak flows for smaller (2-, 5- and 10-year) storms. Introducing grassed waterways reduced water velocity in the stream and resulted in a 28% reduction in peak flow at the catchment outlet for the 50-year storm event. Overall, the results indicate that the specific effect of land use measures on catchment discharge depends on their spatial distribution and on the size and timing of storm events.

Til dokument

Sammendrag

The recent flooding episode in Norway from May this year shows the necessity of understanding the processes of water discharge from small tributaries feeding the larger river systems. The major objective of the recently started ExFlood project is to define and analyze measures to combat negative impact of extreme weather events on infrastructure in small watershed areas in Norway and to incorporate this in a land use planning tool. Urban, agriculture, nature, and forest areas and infrastructure elements demands different approaches concerning impacts of and opportunities for extreme weather events. The approach of the ExFlood project is to reduce the peak flow and delay the peak time to avoid damages on infrastructure. Three municipalities from different climate regions in Norway contribute to the project where the planning tool will be tested, and an experimental catchment site is selected to conduct in depth process studies.

Sammendrag

In 1998 the new main airport of Norway was opened at Gardermoen, 40 km north of Oslo. The Gardermoen aquifer is the largest rain fed unconfined aquifer in Norway. The national pollution authorities demanded from the airport that there should be no pollution of the groundwater (e.g. from de-icing chemicals and jet-fuels) and the groundwater balance should be maintained. Several studies were conducted in order to examine the general geology in the area, unsaturated and saturated flow and transport. In this article, potential pollutants caused by winter operations will be discussed. Potassium Format (KF) is used for the de-icing of runways and Propylene Glycol (PG) is the active component of the de-icing chemical used for airplanes. Field monitoring of infiltration of meltwater using electrical resistivity was employed to characterise meltwater infiltration patterns at Gardermoen in 2001 (French et al., 2002B; French and Binley, 2004) and 2006. The formation of impermeable ice cover on the ground below the melting snowcover was observed at the field site in years with ground frost, while no ice was formed in 2006 when no ground frost was present until the last month of winter. More homogeneous infiltration conditions in 2006 were also confirmed by insignificant ponding at the airport site.

Sammendrag

In cases where snow is contaminated such as e.g. along highways and airports due to de-icing agents and other contaminants, it is important to be able to predict the zone of infiltration since this will determine the potential for retention and degradation in the unsaturated zone. The infiltration processes was monitored using time-lapse electrical resistivity measured in shallow electrodes in a glacial deposit near Oslo airport. TDR measurements were used to calibrate changes in water contents with changes in electrical resistivity values. In the first snowmelting event (April, 2006) there was hardly any ground frost, while in the second event (March, 2007) ground frost caused redistribution of meltwater and focussed infiltration

Sammendrag

For instance in France, the number of vertical flow constructed wetland has increased from 0 to more than 400 units between 1992 and 2005. There is a lack of relevant tools for monitoring their functionality and detecting potential failures in the systems. Electrical Resistivity Tomography (ERT) combined with Induced Polarization (IP) could potentially provide such a tool. Preliminary field studies have indicated that spatial variability in the flow pattern can be revealed by time-lapse measurements of electrical resistivity, however the interpretation of these results require better knowledge about the constitutive relationship between electrical properties and water content, water conductivity and biological clogging in typical filter media. A laboratory experiment was conducted using a four-electrode arrangement in soil sampling cylinders. Under controlled water contents the electrical resistivity and IP was measured for different levels of water conductivity and biofilm development. Finally, results were compared with empirical and theoretical relationships

Sammendrag

Bioforsk gjennomførte det strategiske instituttprogrammet: Transport og retensjon av forurensninger i små nedbørfelt- effekter av hydrologiske prosesser (2002- 2006 ). Dette var nært knyttet til miljøalliansens Felles SIP: Nedbørfeltforvaltning av store vassdrag, begge med finansiering av Norges Forskningsråd. I denne rapporten gis det en oversikt over aktiviteter og resultater fra delprosjektet "Romlig skalering av vassdragsinfromasjon" som omhandlet skalering og modelleringsarbeid. Oppskalering eller nedskalering er en nødvendig del av all modelleringsaktivitet, men fokus i denne rapporten er først og fremst knyttet til oppskalering av observasjoner enten til nedbørfelt skala (km2), skifte skala (ha), eller våtmarksfilter skala (m2). Rapporten gir en oversikt over geostatistisk faglitteratur og spesielt tema som er knyttet til heterogenitet og usikkerhet. Den omhandler prosesser som er viktig å studere i ulik skala når det gjelder avrenning fra dyrka mark i Norge. Det er gitt en oversikt over momenter fra lovgivningen i EU (EU Vanndirektiv ) der skalering av informasjon er en nødvendig forutsetning, men der dette ofte gjøres på en svært forenklet måte. Det referes i rapporten til eksempler på ulik metodikk for å beregne diffuse utslipp til overflatevannkilder i Europa dokumentert i EUROHARP prosjektet, som Bioforsk var en del av.

Sammendrag

Vansjø-Hobøl var et av nedbørfeltene som ble brukt til modellering av næringsstoff transport i EU prosjektet EUROHARP (2002-2005). EUROHARP (ledet av NIVA) var et prosjekt som hadde som mål å sammenlikne ulike modeller som brukes i ulike land i Europa for å estimere kilder til diffus forurensning eller for bergning av mengde nitrogen og fosfor som tilføres overflatevann. Ni ulike modeller ble testet i Vansjø-Hobøl. Modellene, og instituttene som har kjørt modellene, som ble testet er: NL-CAT(ANIMO/SWAP/SWQN/SWQL) ved ALTERRA, Nederland, MONERIS ved FV-IGB, Tyskland, NOPOLU ved IFEN / BETURE-CEREC, Frankrike, Source Apportionment ved NERI, Danmark, SWAT ved EC-JRC / NTUA / IRSA-CNR, Italia, Hellas og Spania, REALTA ved KMM, Irland, N-LES CAT ved NERI, Danmark, TRK(SOILNDB/HBV-N) ved SLU / SMHI, Sverige, EveNFlow ved ADAS, Storbritannia. Alle tilgjengelige data fra nedbørfeltet til Vansjø-Hobøl ble stilt til rådighet for modellørene. To målestasjoner for vannføring og næringsstofftransport (nitrogen og fosfor) var tilgjengelige i nedbørfeltet: Hobøl elva v. Kure og Mosselva. Selv om dette nedbørfeltet har relativt mye data sammenliknet med andre norske lokaliteter var det flere av modellene som manglet viktig informasjon, som f.eks. grunnvannsstand, og jordbeskrivelser for skogsområder (som dominerer i nedbørfeltet). En annen utfordring var at for den ene stasjonen ble vannkvalitet og vannføring målt på ulikt sted. Felles for alle modellene er at de har en rekke parametere som beskriver særtrekk ved nedbørfeltet de modellerer. Disse parametrene må justeres slik at de modellerte resultatene stemmer best mulig med observasjonene i feltet. Alle modellgruppene skulle først kjøre modellen uten å justere på parameterene, som om feltet ikke hadde noen tidsserier med observasjoner av næringsstofftransport. Kun TRK, NL-CAT, SWAT og Evenflow kunne utføre en slik test, bare TRK og SWAT har vist resultatene. Resultatene etter kalibrering illustrerer at alle modellene er relativt gode til å modellere vannføringen i området, total Nitrogen på en årlig basis simuleres tålelig bra, mens modelleringen av fosfor er problematisk. Det er svært liten forskjell mellom modellene til tross for at kun TRK og Moneris har evaluert sin modell som egnet for simuleringer av nordiske forhold.

Sammendrag

Climate changes will increase the frequency of extreme precipitation events, floods and snow melt periods experienced by the infrastructure. According to initial analysis by the Norwegian transport sector these changes will affect road maintenance, emergency planning, design of new roads and infrastructure. Increased frequency of floods is expected to cause more closed roads because of insufficient and badly maintained drainage systems. Increased ground frost and ice formation on ground surface cause large increases in surface runoff during snowmelt. Recently, in Norway the ClimRunoff project has started with the focus on quantifying discharge of catchment areas draining towards roads. The first priority of the project is to create a model that can evaluate the run-off situations under spring situation (i.e. overland flow due to snowmelt and partially frozen soils). The model is tested on a well-defined catchment under autumn situation. Preliminary results of the model calculations will be presented, together with the challenges to alter the model to be able to calculate snowmelt and frozen soil conditions. In close cooperation with the Norwegian road authorities, areas with historical flooding events are selected, and current and future climate data will be used to analyse the infrastructure of the road construction. Together with a risk analysis of the vulnerability of the transport infrastructure the model will be used to create guidelines for

Sammendrag

In the northern hemisphere, substantial amounts of de-icing chemicals are used to remove and prevent ice formation roads, runways and aeroplanes. Road and airport managers are therefore faced with the dual challenge of simultaneously maintaining public safety and meeting demands to protect the environment. De-icing fluids used on airports are commonly based on degradable organic solutes such as ethylene glycol, diethylene glycol or propylene glycol for aeroplanes, while de-icers for runways are based on urea, potassium formate or acetate. Sodium chloride (NaCl) is the most commonly used de-icing chemicals on Norwegian roads. At Oslo airport, Gardermoen, the accumulated amount of de-icers used at the airport is monitored and an upper threshold is defined according to potential degradation capacities and dilution in the unsaturated zone. There is so far, no such upper limit defined for road salting. The risk of contaminating the groundwater at Gardermoen is determined by several factors, the total consumption of de-icing chemicals, the infiltration conditions at the ground surface and the depth of the unsaturated zone. The monitoring of changes in electrical resistivities in 2000/2001 (French and Binley, 2004) documented a spatially variable infiltration pattern and basal ice played a significant role on melt water redistribution. Negative temperatures were measured in the top-soil throughout the entire winter period. In a similar study in 2005/2006 infiltration was more homogeneous and there was little ponding on the surface during snowmelt. Supporting the hypothesis that ground frost prior to snowfall plays a major role in the formation of basal ice, ponding and focused infiltration. The objective of the presented work, which is still ongoing (NFR 164946/S30, see: http://www.bioforsk.no/ViewPPP.aspx?view=project&id=659&ViewLanguage=English) is to: 1) Determine the use of de-icing chemicals as a result of climatic factors; 2) Model the changes in infiltration capacity as a function of weather and soil physical conditions throughout the winter period, and 3) Quantify the mechanism controlling focused infiltration and meltwater redistribution. Based on previously acquired knowledge on transport and degradation of de-icing chemicals in the unsaturated zone, prevailing boundary conditions and how they are affected by climatic conditions, a more probabilistic approach will be taken in order to determine the risk of groundwater contamination caused by different scenarios including climate change.

Sammendrag

In order to investigate the influence of biological growth on flow and transport patterns in horizontal subsurface flow constructed wetlands, bromide tracer experiments were conducted in two 3m long tanks. The tanks were filled with light weight aggregates and shell sand, respectively. The hydraulic conductivity, drainable porosity and dispersivity of the two filter mediawere determined before and after biological growth. The obtained breakthrough curves of bromide tracer showed that biological growth caused a pronounced reduction in drainable porosity, mainly for shell sand, whereas its effect on saturated hydraulic conductivity was negligible. The spatial distribution of the bromide after biological growth in the two filter media showed that the flow occurred preferentially along certain paths. However, in the light"weight aggregates filter medium, biological growth with possible clogging effects seems to reduce the efficiency of some preferential flow paths, increase the retention time, and hence, improves the system treatment efficiency. This study showed that selecting a filter medium including coarse fractions to some extent can mitigate the potential negative effects of bioclogging.

Sammendrag

Hydrology in the northern hemisphere is greatly affected by permafrost and seasonally frozen soils. In areas of permafrost only the top layer of the ground, as well as various thawed structures in the permafrost layer, are active from a hydrological point of view. Water supply is a big challenge in areas with permafrost. Changes in mechanical properties caused by changes in permafrost have also received much attention. Frozen ground near the surface will influence the distribution of melt-water and rain to run-off or infiltration. Changes in englacier and subglacier hydrology are important indicators of global warming. In this chapter examples of different geophysical methods applicable for charcterising flow and transport in cold regions are described. Case-studies carried out in Svalbard, Russia, Norway and Switzerland are presented. The examples relate to: leakages below frozen dams using electromagnetic (EM) soundings; EM soundings of saline permafrost and anomalous polarization; saltwater injection into permafrost zone; infiltration and solute transport in a partially frozen soil monitored by surface tomographic electrical resistivity techniques; drainage conditions beneath a glacier. The case studies presented (as well as examples from the literature) illustrate that most common geophysical methods are applicable in cold regions but may face problems with grounding or calibration of measurements with respect to hydrological meaningful properties such as water contents, etc. Temperature and phase change affect geophysical properties, and in combination with changes in solute concentration or changes in water content, the interpretation is made more complicated. Combining different geophysical and conventional methods may help to solve this problem.

Sammendrag

Mål Studenten skal ha innsikt i kvantitative metoder for å beskrive egenskaper av grunnvann inklusiv strømning av vann og spredning av forurensinger. Kvantitativ analyse av transport av vann og løste stoffer i porøse medier under mettede forhold. Kunnskapen er viktig i forbindelse med effektvurdering av menneskelig inngrep i grunnvannsystemer.Bruk av kvantitative metoder, inklusiv storskala grunnvannsmodeller som predikeringsverktøy. Å kunne vurdere risiko for irreversible endringer i grunnvannsressurser både når det gjelder kvantitet og kvalitet som en følge av menneskelig inngrep er viktig for en god ressursforvaltning. Rent grunnvann er en viktig naturressurs. Innhold 1. Forelesninger teori 2. Regneøvelser 3. Innleveringsoppgaver (teller for sluttkarakter) 4. Innføring i bruk av modellen MODFLOW 5. Innleveringsoppgaver MODFLOW (skal innleveres og godkjennes)

Sammendrag

Sigevann fra deponi med bunntetting, samt fra behandlingsanlegg for organisk avfall, samles opp og forbehandles i et lufte- og sedimenteringsanlegg. Etter forbehandling skal sigevannet infiltreres i grunnen. Det er gjennomført feltundersøkelser med formål og foreslå nytt anlegg for infiltrasjon og overvåking av sigevannet transport til og i grunnvannet. Strømningsforholdene under eksisterende infiltrasjonskummer samt lagdeling i løsmassene er kartlagt med geofysiske metoder. Forslag til nytt infiltrasjonsanlegg samt fremtidig overvåking er gitt. Anlegget foreslås som et todelt infiltrasjonsbasseng i grop ved siden av eksisterende behandlingsanlegg.

Sammendrag

During snowmelt Oslo airport has on repeated occations experienced the formation of large meltwater ponds due to impermeable ice forming below the snowcover. The airport is situated on a large glacial outwash plane with coarse sandy gravely sediments, hence the area normaly has a high infiltration capacity. Focussed infiltration can cause fast transport of contaminants to the groundwater, hence improved understanding of the processes determining where and how the focussed infiltration takes place is important. Previously the melting process has been monitored successfully on a small scale (4 m2) using a two dimensional grid of permanently installed electrodes (French and Binley, 2004). In the present work snowmelt infiltration was monitored by time-lapse measurements of electrical resistivity using grounded electrodes on 4 and 20 m2 plots and a capacitively coupled resistivity system (Ohmmapper, Geometrics) on a larger scale. While the smaller scale systems provide 3D images the capacitively coupled system was used to monitor changes in two dimensional vertical sections in a retention pond adjacent to one of the runways. The area covered by 4 lines was 170 m by 340 m. The initial data were collected late in the spring (2006) during the final stages of the snowmelt. The lines were repeated later in the year when the soil profile was dryer. The lines show good consistency in the description of the general geology of the subsurface and the time-lapse changes describe the infiltration pattern that occurred during snowmelt and subsequent drainage. The surveys provide useful information about the differences in spatial distribution of snowmelt infiltration at different scales. And there are good indications that capacitively coupled resistivity surveys can be used to describe infiltration processes at relatively large spacio-temporal scales. References French, H. and A. Binley, 2004, Snowmelt infiltration: monitoring temporal and spatial variability using time-lapse geophysics, J. Hydrology, 297, 174-186

Sammendrag

During snowmelt Oslo airport has on repeated occations experienced the formation of large meltwater ponds due to impermeable ice forming below the snowcover. The airport is situated on a large glacial outwash plane with coarse sandy gravely sediments, hence the area normaly has a high infiltration capacity. Focussed infiltration can cause fast transport of contaminants to the groundwater, hence improved understanding of the processes determining where and how the focussed infiltration takes place is important. Previously the melting process has been monitored successfully on a small scale (4 m2) using a two dimensional grid of permanently installed electrodes (French and Binley, 2004). In the present work snowmelt infiltration was monitored by time-lapse measurements of electrical resistivity using grounded electrodes on 4 and 20 m2 plots and a capacitively coupled resistivity system (Ohmmapper, Geometrics) on a larger scale. While the smaller scale systems provide 3D images the capacitively coupled system was used to monitor changes in two dimensional vertical sections in a retention pond adjacent to one of the runways. The area covered by 4 lines was 170 m by 340 m. The initial data were collected late in the spring (2006) during the final stages of the snowmelt. The lines were repeated later in the year when the soil profile was dryer. The lines show good consistency in the description of the general geology of the subsurface and the time-lapse changes describe the infiltration pattern that occurred during snowmelt and subsequent drainage. The surveys provide useful information about the differences in spatial distribution of snowmelt infiltration at different scales. And there are good indications that capacitively coupled resistivity surveys can be used to describe infiltration processes at relatively large spacio-temporal scales. References French, H. and A. Binley, 2004, Snowmelt infiltration: monitoring temporal and spatial variability using time-lapse geophysics, J. Hydrology, 297, 174-186

Sammendrag

Disposal of domestic sewage effluents in soil has been used for several decades in Norway and more than 100000 constructed systems for wastewater purification have been built with capacities between 5 and 8000 pe (person equivalent). However, the infiltration of wastewater effluents into soils and the estimation of application rates for a given system design and environmental setting are extremely complex and often poorly understood and oversimplified (Siegrist, 2004). The infiltration system presented here consists of 26 horizontal distribution pipes separated by 1.25 m over an area of 1100m2. The distribution pipes are placed in a coarse stone/gravel distribution layer at about 1m depth. A pump ensures regular injection of wastewater into the system. Below the distribution layer there is a 20 cm thick layer of local natural soil, which is a coarse gravely sandy soil, followed by a 25 cm thick layer of light weight aggregates (LWA). Below the LWA layer there is natural soil and the water drains freely to the groundwater at about 5m depth. Hence the retention time and flow pattern are key factors determining whether phosphates are retained and organic components are degraded before water leaves the filter system or enters the phreatic level. In this study a combination of time lapse electrical resistivity (ER) measurements and numerical modelling of an unsaturated system have been performed in order to examine the wastewater distribution and its potential effect on flow and transport in a 2D unsaturated layered profile. Measurements were performed in June 2005. In addition to the ER measurements, an inactive tracer was applied and the breakthrough curve monitored at three depths below the constructed filter. Changes in electrical resistivity with time revealed a distribution of water coinciding with the distribution pipes. The re is some consistency between measured changes in resistivity and changes estimated from unsaturated numerical simulations. Although a forward modelling based on the simulations were not done for this paper. The difference between the simulations and the field measurements indicate that the flow and transport in the system may be non uniform over the area, hence causing preferential flow paths in the filter system.

Sammendrag

Vann i anlegg og drift (vanndirektivet, etc) Anleggsfase: Krav til utslepp frå anleggsområder. Søknad om utslepp. Aktuelle problem (olje, partiklar, ammonium, etc). Korleis få krav inn i kontrakten, oppfølging. Praktiske løysingar. Fylling i vassdrag, forhold til strandsoner, Driftsfase: Krav til overvatn frå veg og tunnelar. Behandling av vaskevatn frå tunnel. Rensedammar/fordrøyningsbasseng. Korleis få krav inn i kontrakten, oppfølging. Praktiske løysingar.

Sammendrag

Mål Studentene skal ha kunnskaper om prinsippene i økologisk ingeniørarbeid og forstå hvordan forbindelsen mellom natur og samfunn kan utnyttes i planleggingen av desentraliserte systemer for vannforsyning, bioenergi og gjenbruk av organisk avfall og avløpsvann. Studentene skal kunne identifisere parametere som er nødvendig i planleggingen av systemer for grunnvannsforsyning, bioenergi og gjenbruk av organisk avfall og avløpsvann og bruke dette til å planlegge slike systemer. Innhold Emnet dekker grunnleggende begreper for å forstå økologisk konstruerte systemer. Nøkkelord: biogeokjemisk resirkulering, analyse av livssykluser, forvaltning av nedslagsfelt, grunnvannshydrogeologi, eksempler på moderne økoteknologi. Emnet vil også ta for seg de innbyrdes forholdene til den institusjonelle og sosiale settingen, begrensninger og potensialet ved konstruksjon av økologisk tilpassete systemer. Det er mulig å skrive en semesteroppgave innen et av temaene som gis i dette kurset. Dette vil gi et tillegg på 5 studiepoeng, se beskrivelse av THT299.

Sammendrag

Fosforbindingsegenskapene til de to filtermaterialene Filtralite-PTM og Fosen skjellsand er blitt sammenlignet i et pilotskala-anlegg. Anlegget bestod av to kar i plexiglass (3m x 0,8m x 0,29m), ett for hvert materiale. De to karene ble tilført en kunstig P-løsning (6 mg P l-1) i 18 måneder. Fosforkonsentrasjonen i innløp, utløp og i grunnvannsrør jevnt fordelt i karene ble målt igjennom hele forsøksperioden. Mengden akkumulert total P (TP) ble målt i prøver fra filtermaterialet ved forsøkets slutt. Resultatene viser at TP i første del av karet var mye høyere for Filtralite-PTM enn for Fosen skjellsand, henholdsvis 4000 og 330 mg P kg-1. Dette tilsvarer 2000 og 330 g P m-3 filtermateriale. I begge karene sank konsentrasjonen av TP mot utløpet. De første 0,9 m av karet med Fosen skjellsand var mettet med P, mens bare 0,3 m av karet med Filtralite-PTM var mettet. Resultatene viser også at for å beregne en realistisk levetid for et filteranlegg, må en gjennomsnittelig bindingskapasitet (basert på målinger av TP i materi-alprøver fra hele anlegget) brukes. Dette fordi bare materialet i de fremre deler av et anlegg vil ha oppnådd maksimal bindingskapasitet når utløpskonsentrasjonen er høyere enn kravet (ofte satt til 1 mg P l-1). En slik gjennomsnittlig bindingskapasitet bør baseres på målinger av TP i materiale fra et anlegg der utløpskonsentrasjonen nettopp har nådd 1 mg P l-

Sammendrag

More than 50% of the groundwater recharge in Norway takes place during snowmelt. Given the possible threat to groundwater quality caused by potentially rapid transport through the unsaturated zone, it is important to understand the infiltration processes that take place during snowmelt, and the factors that control the temporal and spatial variability of such processes. Here, we report on the results of an experimental study of infiltration during the snowmelt period of 2001. The study was carried out at a well-characterised field plot, close to Oslo Airport. In order to examine the spatial and temporal variability of snowmelt infiltration, a series of electrical resistivity surveys were carried out using electrodes installed below the ground surface and in shallow boreholes. The results from this time-lapse survey reveal significant changes over time, and suggest that localised infiltration takes place. The patterns of inferred increases in saturation are consistent with observed reductions in snow cover and appear to be principally controlled by variations in microtopography. Resistivity changes observed at depth, using the borehole-based electrodes, show rapid percolation through the unsaturated profile. Such behaviour is consistent with observed rapid changes in local groundwater levels. The results confirm the potential threat to groundwater quality during snowmelt and illustrate the spatial scale of processes that require adequate attention in groundwater management in vulnerable areas.

Sammendrag

Constructed wetlands remove pollutants by physical, chemical, and biological processes. The pollutant removal efficiency is strongly dependent on the hydraulic characteristics of the wetlands. Hydrology highly affects the hydraulic flow regime and thus has a huge effect on the treatment processes. The current design criteria based on the simplifying assumptions of plug flow and first order decay of pollutants do not accurately predict wetland performance. The lifetime of a filter material may also be strongly affected by a non-uniform flow pattern. In this paper, the effects of different hydrological factors on the transport and removal of pollutants in subsurface-flow (SSF) constructed wetland are reviewed from the research literature, and is examined by experiments and numerical simulations. Results from tracer experiments (Br-) in small-scale subsurface-flow wetlands, with and without vegetation, are presented. Analytical and numerical solutions were used to describe the experimental observations. A three-dimensional finite-difference flow model (MODFLOW) coupled to the transport model (MT3DMS) was used to obtain the numerical solutions. In a series of transport simulations, hydraulic parameters, hydraulic conductivity, effective porosity, and longitudinal dispersivity, were estimated. Results showed that the estimated hydraulic conductivity values were reasonably close to the laboratory-measured values. Although the simulations gave a good representation of the effluent breakthrough curve in the experimental containers, it did not describe the flow pattern within the volume very well. Non-isotropic effects or heterogeneities in the Ks values and/or Kd values could be the cause of inconsistencies in local observations. The field scale experiment showed a large variability in soil physical properties, which gave, rise to unexpected breakthrough curves at the observation wells and at the outlet. Thus, at a field scale it was even more difficult to capture the observed phenomena in Visual modflow, heterogeneities might have given rise to preferential flow paths, data from this experiment have not yet been fully analysed, and further simulations are planned to include heterogeneity. Although we have not yet been able to describe sufficiently the factors, which give rise to the heterogeneous flow pattern, simulations in Modflow are very useful to improve understanding and design of constructed wetlands. To be able to solve the transport equations analytically the system has to be simplified to a larger degree than in a numerical model, but the analytical solutions are still useful to get a rough idea of the flow and transport processes.

Sammendrag

The flow and transport of a non-reactive tracer and melt water was monitored in a heterogeneous coarse sandy unsaturated zone in southeastern Norway, during the snowmelt of 2001. Electrical resistivity tomography (ERT) as well as conventional suction cup techniques was employed. A frozen solution of NaBr in water was supplied as a line source on the ground surface above two parallel vertical profiles monitored by the two measurement systems prior to the onset of snowmelt. The two monitored vertical profiles were separated by approximately 1 m. The results were analysed by visual comparison of images and by the use of spatial moments analysis. The two measurement approaches showed that the system was affected by the presence of preferential flow paths during the early stages of the snowmelt, perhaps due to ice near the surface, but the major part of the plume moves uniformly later in the snow-melting period. After most of the tracer plume has reached the depth monitored by both systems (i.e. below 0.4 m depth) there is a good consistency between the two datasets. Spatial moment calculations on the basis of ERT cannot be used to describe the movement of tracer alone, as the resistivity is affected by changes in both saturation levels and tracer concentration. Nevertheless, ERT appears to be an appropriate method to characterise regions of localised high infiltration in this type of soil. The method therefore constitutes a possible alternative and supplement to suction cups in a monitoring system.

Sammendrag

De-icing chemicals used during the winter season are potential pollutants for the groundwater underneath the new main airport of Norway. Several field experiments examining the transport and degradation of propyleneglycol (PG), potassium acetate (KAc) and non-reactive tracers were performed in a lysimeter trench under natural snowmelting conditions. Chemicals were applied underneath the snow cover and the transport in a heterogeneous coarse sandy soil was examined by extracting soil water from 30 or 40 suction cups placed at five depths between 0.4 and 2.4 m depth. Transport and degradation was analysed by spatial moment calculations. The de-icing chemicals showed the same basic displacement as chemically inactive tracers, an initial fast transport during the melting period followed by a period of stagnation throughout the summer season. PG seemed to be displaced to greater depths compared to non-reactive tracer after the first application. However, computer simulations of transport and degradation in a heterogeneous unsaturated soil showed that decreasing degradation constants with depth can generate a downward movement of the centre of mass without any flow occurring in the system. Potassium acetate showed some adsorption, with calculated retardation factors of approximately 1.3 and 1.2. The degradation rate constant for PG was calculated to be 0.015 day"1 in 1994 and increased to 0.047 day"1 in the second application made in 1995. The degradation rate constant for acetate was estimated to be 0.02 day"1. Increased manganese concentrations seem to be a good indicator of degradation of PG and Ac.

Sammendrag

A small number of measuring points may inflict a bias on the characterisation of flow and transport based on field experiments in the unsaturated zone. Simulation of pure advective transport of a Gaussian plume through a setup of 30 regularly placed measuring points revealed regular temporal fluctuations about the real spatial moments. An irregular setup predicted both irregular fluctuations and larger discrepancies from the real value. From these considerations, a regular setup is recommended. Spatial moments were sensitive to the plume size relative to the distance between individual measuring points. To reduce prediction errors of the variance, the distance between the measuring points should be less than twice the standard deviation of the examined plume. The total size of the setup should cover several standard deviations of the plume to avoid mass being lost from the monitored area. Numerical simulations of a dispersing plume (comparing calculations based on 9000 nodes with 30 measuring points) revealed that vertical and horizontal centres of mass were predicted well at all degrees of heterogeneity, and the same was the case for horizontal variances. Vertical variances were more susceptible to prediction errors, but estimates were of the same order of magnitude as the real values.

Sammendrag

Five tracer experiments have been performed in a coarse-textured soil near the new main airport at Gardermoen, Norway. In two lysimeter walls, 30 and 40 measuring points form the basis for spatial moment calculations. Although experiments were performed under different meteorological conditions (autumn and snowmelt) and at two different sites, the ratios of centres of vertical mass over cumulative infiltration were of the same order of magnitude, indicating a gravity-dominated flow. Two-dimensional transport simulations with SUTRA (Voss, 1984), with a priori estimated input parameters and random fields of soil hydraulic properties revealed a relatively good agreement with the experimental results. Three possible sources of heterogeneity affecting the vertical displacement of solute during snowmelt were identified: variability of soil physical properties, soil surface elevations and variability of ground frost during the melting period. To obtain accurate predictions, soil heterogeneity was the most important factor to characterize for the coarse-textured soil under consideration.

Sammendrag

Outline of the thesis Chapter 1 Introduction Chapter 2 was published in an international proceedings (French et al., 1994) at an early stage of this Ph.D work and describes the experimental field set-up at Gardermoen; instrumentation and installation procedures. As more installations have been included at the experimental site, the publication has been slightly modified to include these changes in the presented chapter. Chapter 3 evaluates the uncertainty of spatial moments calculations from a limited number of measuring points. This is done by theoretical simulations of flow and transport in a 2D model (SUTRA, Voss, 1984). Spatial moment calculations of a plume distribution based on 9000 nodes and a set up of 30 measuring points are compared and the situation for various degrees of heterogeneity of the permeability fields tested. A regular and an irregular set-up is examined. The simulations of this chapter are based on a groundwater level at 2.7 m depth which is similar to the monitored depth interval in the field (2.4 m deep). The simulations revealed that predictions of the vertical centres of mass were quite good. A larger difference between the depth of the monitored area and the depth to the groundwater, may inflict larger prediction errors of the vertical centres of mass. This point is not examined in chapter 3. An idea of what the prediction error of the vertical centre of mass might have been at the field site Moreppen, is provided from the simulation where the groundwater level is defined at the more realistic level of 4 m depth (Fig. 4, only one realisation is shown). Chapter 4 examines the heterogeneity of the snowmelt/drainage pattern at the field site and relates it to the local microtopography. The range of infiltration variation is quantified from melting plates and indirectly from breakthrough curves observed in the uppermost part of the monitoring zone. Chapter 5 compares numerical simulations of solute transport in a heterogeneous or homogeneous soil with field results performed during autumn rains and snowmelting conditions. Different combinations of heterogeneities, of infiltration and soil hydraulic conductivities are tested numerically and their relative importance is determined. Chapter 6 shows calculations of degradation rates and retardation factors on the basis of spatial moment analysis of field results. The plume evolution of a reactive and an inert chemical are compared, and the difference quantified by vertical centres of mass. Simulated development of concentration distribution is shown in figure 3. The use of average manganese concentrations as an indicator of degradation in the unsaturated zone is also evaluated.