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Milnes, Ellen

Nom
Milnes, Ellen
Affiliation principale
Email
Ellen.Milnes@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/145

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  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    Process-based groundwater salinisation risk assessment methodology: Application to the Akrotiri aquifer (Southern Cyprus)
    (2011)
    Milnes, Ellen 

    Groundwater salinisation is a major groundwater contamination issue world-wide and can be caused by different processes, such as seawater intrusion, agrochemical pollution, geogenic contamination and irrigation-induced salinisation. In many areas, several salinisation processes are superimposed. Since remedial measures vary for different salinisation processes, correct identification is fundamental for adequate design of management strategies: different strategies may be required in one and the same aquifer, depending on which salinisation process is active where in the domain.

    A simulation-based salinisation risk assessment methodology is proposed, based on the principle of linear superposition of total dissolved solutes in groundwater. In a first step, the measured bulk salinity distribution is used to calibrate a numerical groundwater flow and transport model, accounting for all identified salinisation processes. Then, the bulk salinity distribution is decomposed into different salinity components by adapting the boundary conditions, running a simulation for each salinisation process separately. These simulation results yield the necessary components to calculate the risk index distributions, which are a measure of the respective future potential salinity increase. Overlaying the risk index distributions with a defined threshold concentration reveals risk areas requiring remediation or conservation measures with respect to each process. The risk area maps resulting from this methodology are a promising tool for the design of groundwater management schemes. They condense relevant information from complex dynamic processes obtained from numerical simulations and visualise the results in simple and static maps, accessible to decision makers who are not familiar with groundwater dynamics.

    The different steps of the salinisation risk assessment procedure are first described and illustrated on a synthetic example and then applied to a real aquifer system in Southern Cyprus (Akrotiri), where three major salinisation processes are superimposed.
  • Publication
    Accès libre
    Markierungsversuche und Modellierung zur Bewertung der Gefährdung eines Trinkwasserbrunnens
    (2008)
    Goldscheider, Nicola
    ;
    Milnes, Ellen 
    ;
    Fries, W.
    ;
    Joppen, M.
    In einem Porengrundwasserleiter aus Niederterrassenschottern bei Pratteln, Schweiz, wurde ein Markierungsversuch mit Uranin durchgeführt, um die Gefährdung eines Trinkwasserbrunnens durch ein 760 m talaufwärts gelegenen Ablagerungsstandort zu bewerten. Dabei wurde eine maximale Abstandsgeschwindigkeit von 127 m/d und ein Wiedererhalt von 0,93 % festgestellt. Der Tracer wurde auch in zwei intermediären Beobachtungsbrunnen nachgewiesen. Diese Studie diskutiert die Ursachen dieser hohen Fließgeschwindigkeit. Durch drei verschiedene analytische Modelle konnten die Durchgangskurven simuliert und Transportparameter bestimmt werden. Erst die Anwendung eines zweidimensionalen numerischen Modells (FEFLOW) mit vereinfachter Geometrie liefert aber eine hydrogeologisch konsistente, mögliche Erklärung aller Versuchsergebnisse. Demnach handelt es sich vermutlich um einen relativ homogenen Grundwasserleiter. Der steile Gradient (6 ‰) und die hohe Durchlässigkeit (3 • 10–2 m/s) verursachen die hohen Fließgeschwindigkeiten. Der Hauptteil der Tracerwolke strömt seitlich an den Brunnen vorbei. Durch später durchgeführte Kleinpumpversuche wurde diese Modellvorstellung weitgehend bestätigt. Diese Befunde sollten bei Schutz- und Sanierungskonzepten berücksichtigt werden., A tracer experiment with uranine in a gravel aquifer aimed to assess the risk of a drinking water well near Pratteln, Switzerland, resulting from a contaminated site 760 m further upgradient. The experiment revealed a maximum linear flow velocity of 127 m/d and a mass recovery of 0.93 %. The tracer was also detected at two intermediate monitoring wells. This paper discusses the causes of this high flow velocity. Three different analytical models allowed simulation of the breakthrough curves and determination of transport parameters. A two-dimensional numerical model (FEFLOW) with simplified geometry provided a hydrogeologically consistent and probable explanation of all results. The aquifer is most likely relatively homogeneous, the steep hydraulic gradient (6 ‰) and high conductivity (3 • 10–2 m/s) cause high flow velocities, and most of the tracer passed northeast of the wells. Recently conducted small scale pumping tests largely confirmed this conceptual model. These findings should be considered for future protection measures.
  • Publication
    Accès libre
    Simultaneous identification of a single pollution point-source location and contamination time under known flow field conditions
    (2007)
    Milnes, Ellen 
    ;
    Perrochet, Pierre 
    A theoretical framework is presented that allows direct identification of a single point-source pollution location and time in heterogeneous multidimensional systems under known flow field conditions. Based on the concept of the transfer function theory, it is shown that an observed pollution plume contains all the necessary information to predict the concentration at the unknown pollution source when a reversed flow field transport simulation is performed. This target concentration C0 is obtained from a quadratic integral of the observed pollution plume itself. Backwards simulation of the pollution plume leads to shrinkage of the C0-contour due to dispersion. When the C0-contour reduces to a singular point, i.e. becomes a concentration maximum, the position of the pollution source is identified and the backward simulation time indicates the time elapsed since the contaminant release. The theoretical basis of the method is first developed for the ideal case that the pollution plume is entirely known and is illustrated using a synthetic heterogeneous 2D example where all the hydro-dispersive parameters are known. The same example is then used to illustrate the procedure for a more realistic case, i.e. where only few observation points exist.
  • Publication
    Accès libre
    Direct simulation of solute recycling in irrigated areas
    (2006)
    Milnes, Ellen 
    ;
    Perrochet, Pierre 
    Solute recycling from irrigation can be described as the process that occurs when the salt load that is extracted from irrigation wells and distributed on the fields is returned to the groundwater below irrigated surfaces by deep percolation. Unless the salt load leaves the system by means of drains or surface runoff, transfer to the groundwater will take place, sooner or later. This can lead to solute accumulation and thus to groundwater degradation, particularly in areas where extraction rates exceed infiltration rates (semi-arid and arid regions). Thus, considerable errors can occur in a predictive solute mass budget if the recycling process is not accounted for in the calculation. A method is proposed which allows direct simulation of solute recycling. The transient solute response at an extraction well is shown to be a superposition of solute mass flux contributions from n recycling cycles and is described as a function of the travel time distribution between a recycling point and a well. This leads to an expression for a transient ‘recycling source’ term in the advection–dispersion equation, which generates the effect of solute recycling. At long times, the ‘recycling source’ is a function of the local capture probability of the irrigation well and the solute mass flux captured by the well from the boundaries. The predicted concentration distribution at steady state reflects the maximum spatial concentration distribution in response to solute recycling and can thus be considered as the solute recycling potential or vulnerability of the entire domain for a given hydraulic setting and exploitation scheme. Simulation of the solute recycling potential is computationally undemanding and can therefore, for instance, be used for optimisation purposes. Also, the proposed method allows transient simulation of solute recycling with any standard flow and transport code.