Artesian well | EPFL Graph Search

An artesian well is a well that brings groundwater to the surface without pumping because it is under pressure within a body of rock and/or sediment known as an aquifer. When trapped water in an aquifer is surrounded by layers of impermeable rock or clay, which apply positive pressure to the water, it is known as an artesian aquifer. If a well were to be sunk into an artesian aquifer, water in the well-pipe would rise to a height corresponding to the point where hydrostatic equilibrium is reached. A well drilled into such an aquifer is called an artesian well. If water reaches the ground surface under the natural pressure of the aquifer, the well is termed a flowing artesian well. Fossil water aquifers can also be artesian if they are under sufficient pressure from the surrounding rocks, similar to how many newly tapped oil wells are pressurized. Not all aquifers are artesian (i.e., water table aquifers occur where the ground

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

Widely used in industrial activities, chloroethenes have become common groundwater contaminants. Dehalorespiration is an anaerobic bacterial respiration coupling their sequential degradation to energy production. The interactions between the dehalorespiring bacteria and the other guilds and environmental variables are presumed to influence the dehalorespiration efficiency. Here, water and core samples were extracted from the PCE-contaminated site of Lyss (BE, Switzerland). Bacterial DNA was extracted and the 16S rRNA gene amplified by PCR. Terminal restriction fragment length polymorphism (T-RFLP) was used to assess the diversity of the bacterial communities. Core and groundwater environmental variables were analyzed as well. The T-RFLP profiles and the environmental data obtained were processed using statistical multivariate analysis. Within a period of two months, the bacterial communities remained relatively specific to their respective sampling origins. Communities from the oxic layer shared a similar set of bacterial species whereas piezometers from the anoxic layer had a specific one. The T-RFLP profiles obtained from single depth and multi-level piezometers were clearly distinct, probably due to differences in the pumping flow rates and their associated transport regimes, which can have an impact on i) the sediments extracted from the aquifer, ii) the hydraulic zone reached and iii) a potential selective bacterial adsorption onto the pumping tube wall. Environmental factors related to the groundwater redox state appeared as the major variables influencing the bacterial populations. Bacterial communities from core samples clustered into two distinct sets: i) samples from the strongly reductive silt layer, and ii) samples from the coarser and less reductive layer. Grain size distribution and redox state both had a major influence on the bacterial communities of core samples. Finally, it was shown that microbial populations extracted from groundwater differed from the ones extracted from core material, and thus were not representative of the overall aquifer microbial diversity.

2009

Contribution à l'étude du comportement thermo-hydraulique du stockage de chaleur en aquifère

Stéphane Dupasquier

In this work, a parametric study is done with computational methods for groundwater flow and heat transport in order to describe the dominant physical phenomena in an Aquifer Thermal Energy Storage (ATES). Optimum operating conditions and geological parameters are deduced from it. The intended use of the ATES is the domestic water or space heating. The stock is seasonal and functions without heat pump. Parametric study is organized as a series of reference simulations relating to the thickness of the aquifer and the injection flow rate. The other parameters and operating conditions of are kept constant. Other simulations are done and compared to the reference simulations in order to describe the influence of injection temperature, hydraulic conductivity, anisotropicity, injection frequencies, phases of rest, outflow rate and doublet wells. The cells of natural convection are strongly affecting the performances of an ATES. The thermal losses by conduction trough bedrock and caprock is an unfavourable factor as well, but to a lesser extent however. The increase of inflow rate always improves the efficiency, whereas an optimum aquifer thickness exists for each inflow rate. This optimum is characterised by weak natural convection phenomena. A greater thickness means strong density-viscosity effects, while a thinner aquifer forms a horizontally stretched stock, with increased conductive losses through the bedrock and cap rock. A maximum thermal recovery rate exists for a given flow rate. This maximum increases with inflow rate. The injection temperature behaves on the stock in the same way as the aquifer thickness for a given inflow: there is an optimal temperature. However it is in general preferable to increase the injection temperature instead of the inflow rate. In terms of optimization of the thermal power at disposal, the most favorable scenario is an increasing flow during the discharge. The precise scenario is different for each problem. The performances of a ATES are the complex result of the many parameters which enter in plays. One will recommend an inflow rate of at least 100m33/d during 6 months, and even rather 500 - 1000m3/d with an injection temperature of 80°C at least. An injection temperature of 60°C will have to be associated with an inflow of 1000m3/d at least. The geological targets proposed in Switzerland are the quaternary alluvial deposits filling the former glaciated valleys, fluvioglacial deposits and alluvial fans.

EPFL2001

Fate of volatile fluorinated compounds in the subsurface

Christian Balsiger

Since their discovery around 1930, the synthetic compounds of the class of chlorofluorocarbons (CFCs) have been produced and used worldwide at very large scale. Their physico-chemical properties (non-flammability, chemical inertia, miscibility with water and oil, compatibility with many metals and plastics, solvent capacity) have made them ideal candidates for several applications, such as refrigerant fluids, aerosol propellants, foam blowing agents, or as solvents or intermediates of chemical synthesis. In the 70', it was demonstrated that following their release in the atmosphere, they are implicated in the process leading to the commonly called stratospheric ozone hole. The governments of several industrialised country have thus signed a protocol with the objective to stop the production and use of CFCs. CFCs have been increasingly replaced by compounds with similar structure, the hydrochlorofluorocarbons (HCFCs), but whose reactivity in the lower layers of the atmosphere is quite different from that of CFCs. Due to their chemical inertia, CFCs has been used as tracers for surface and groundwater datation. During such investigations, the biodegradability of these compounds and the existence of punctual pollution sources in soil and groundwater have been evidenced. It has been demonstrated that some of these compounds can be dechlorinated under anoxic conditions producing other compounds with sometimes higher toxicity and higher water solubility, and resulting in a risk linked to the consumption of natural groundwater. The goal of this thesis was to get indications about reductive transformations of CFCs and especially HCFCs in Swiss aquifers and landfills, on the potential of different microbial communities to reductively dechlorinate certain compounds, and under which redox conditions the transformations occur in aquifer systems. Data concerning the production, use, emission, regulation, as well as the biodegradability and toxicity of these compounds are presented in chapter 1 and in the appendix. The analytical methods developed and used during this work are presented in chapter 2. Particularly, a versatile analytical system allowing the measure of trace but also higher concentrations in different media, solid or aqueous, has been set up and used during this work. CFCs and HCFCs were analyzed at 3 sites in Switzerland. Samples were collected from a natural groundwater in which a chloroethene plume had been observed, from an old landfill closed in 1980, and from a more recent bioactive landfill constructed in horizontal layers. In addition, the behaviour of different CFCs and HCFCs was studied in microcosms inoculated with sludge originating from several sewage treatment plants in the canton of Vaud, and with a sediment originating from a contaminated aquifer in Holland. The studied CFCs and HCFCs were furthermore injected at the inlet of a 1.2 m height column filled with the aquifer sediment from Holland. In this quasi natural aquifer, the oxido-reductive conditions were modified during the experiment in order to investigate the conditions at which the biodegradation occurred. The field studies showed that CFCs and HCFCs are present in aquifers and landfills, and there were indications that their transformation also occurs there. Estimations of half-life times indicated that the reductive dechlorination occurred at slow rates. This could be due to the low temperatures of natural groundwater systems and other factors linked to the hydro-geological properties of the natural environment such as dispersion, sorption or partitionning. In the microcosms inoculated with sludge, CFC-11 was transformed to HCFC-21, the latter being further dechlorinated to HCFC-31. HCFC-123a and chlorotrifluoroethene (CTFE) were produced simultaneously from CFC-113. Inhibition of methanogesis with 2 bromoethane sulfonate decreased significantly the degradation rate of CFC-11, emphasizing the importance of the role of methanogens in the degradation process. In the microcosms inoculated with the contaminated sediment, the transformation of CFC-11 also occurred, but was not accompanied with methane production, as it was the case in the suldge microcosms. Moreover, the presence of acetate, lactate and butyrate in the microcosms containing CFC-11 suggested that methanogens were inhibited in the presence of CFC-11. CFC-113 was transformed in the same way as in the microcosms inoculated with the sludge; however, the produced CTFE was further transformed to trifluoroethene (TFE). Production of HCFC-151b from HCFC-141b was also observed. In the column filled with aquifer material, only the transformations of CFC-11 and CFC-113 were observed, which is probably due to the short residence time in the column (~10 days), during which the transformation of the other compounds was not sufficiently pronounced. The increasingly reducing conditions in the column were accompanied with an increase of the degradation rates of CFC-11 and CFC-113, with a maximum reached in presence of methanogenesis. The addition of sulfate in the artificial groundwater decreased the biodegradation rates of the two compounds, and the concentration of their transformation products was simultaneously increased. This suggests that these products become more persistent under sulfate-reducing conditions. Natural attenuation designates all the processes leading to the decrease of the concentration of organic compounds migrating from a pollution source throughout a natural environment. Whereas natural attenuation or enhanced natural attenuation seem adequate for several classes of compounds, the absence of defluorination reaction of CFCs and HCFCs reported in this work suggests the use of other remediation techniques for the decontamination of sites polluted with these compounds. Indeed, the transformation products of CFCs and HCFCs still contain a fluorine atom and are not less harmfull to the environment than the parent compounds. In addition, the use of CFCs as age-dating tracers in groundwater is not recommended under anoxic conditions, as it was demonstrated here that they are not stable in such environments. The HCFCs on the other hand seem to be more persistent, and it is primordial to decrease rapidly their production and release in the environment.

EPFL2004