Aquifer properties, measured

As discussed before, groundwater samples can be collected when a sufficient volume of water has been removed from the well (e.g., three to five well volumes) and groundwater parameters have stabilized. If parameters have not stabilized after five well volumes have been removed, then the well may be sampled (acceptance of sampling following the fifth purge volume is dependent on the study objectives). Table 1 summarizes the criteria used for establishing the stability of groundwater parameters. The time intervals between the parameter measurements depend on the well characteristics and the hydraulic properties of the aquifer and must be sufficiently spaced to provide results representative of aquifer properties. ... 

Important issues in groundwater model validation are the estimation of the aquifer physical properties, the estimation of the pollutant diffusion and decay coefficient. The aquifer properties are obtained via flow model calibration (i.e., parameter estimation see Bear, 20), and by employing various mathematical techniques such as kriging. The other parameters are obtained by comparing model output (i.e., predicted concentrations) to field measurements a quite difficult task, because clear contaminant plume shapes do not always exist in real life. 

A model was built using the best estimates of the variables including volumetries, stratigraphy, leak window area, hydrocarbon and aquifer properties. By producing hydrocarbons, the pressure in one block was depleted at the measured rate while the depletion profiles of the non-producing block were monitored. The least known parameter, the transmissibility of the faults, was varied until a history match was achieved between the modelled and observed depletion profiles. Comparison for different faults showed that faults with small displacements had to be modelled with higher transmissibilities than faults with large displacements. 

Conventionally, the sample is initially saturated with one fluid phase, perhaps including the other phase at the irreducible saturation. The second fluid phase is injected at a constant flow rate. The pressure drop and cumulative production are measured. A relatively high flow velocity is used to try to negate capillary pressure effects, so as to simplify the associated estimation problem. However, as relative permeability functions depend on capillary number, these functions should be determined under the conditions characteristic of reservoir or aquifer conditions [33]. Under these conditions, capillary pressure effects are important, and should be included within the mathematical model of the experiment used to obtain property estimates. 

Use of these equations to predict future production from a recovery project is described by the following example. An abandoned refinery property is being dismantled and the underlying aquifer remediated. Substantial LNAPL product accumulations occurred overlying the fine silty sand aquifer. Preliminary investigation indicated that a four-well system would effectively remove most of the product within a reasonable time at a modest cost. The production rate over time is illustrated in Figure 11.4. Peak production occurred on day 78 of operation, then declined. Final measurement occurred on day 141. 

You are interested in the hydraulic and geochemical properties of an aquifer, particularly in its dispersivity and average organic matter content. Fortunately, at your disposition you have long-term time series of water temperature and tetrachloroethene (PCE) measured in two adjacent wells, 15 m apart from each other along the main flow direction in the aquifer. From earlier tracer experiments you are pretty sure that the two wells are located on the same streamline, that is, they see the same water passing by, although not at the same time. 

The selection and preparation of sites for any of these gas stores is a fairly delicate process, because tightness can rarely be guaranteed on the basis of geological test drillings and modelling. The detailed properties of the cavity will not become fully disclosed until the installation is complete. The ability of the salt cavern to keep an elevated pressure may turn out not to live up to expectations. The stability of a natural rock cave, or of a fractured zone created by explosion or hydraulic methods, is also imcertain until actual full-scale pressure tests have been conducted. For the aquifers, the decisive measurements of permeability can only be made at a finite number of places, so surprises are possible due to rapid permeability change over small distances of displacement (Sorensen, 2004a). 

The fact that Rn is omnipresent in all soils, and is measurable down to very low concentrations, makes it an ideal, naturally occurring tracer gas. This property may be used e.g. in exploration techniques, or in the detection of subsoil fissures and aquifers. 

Based on exact process studies in selected validation areas (like the redox studies in the Oderbruch region) chemical indicator elements can be used to characterize the environmental conditions with sufficient accuracy. Using the GIS data model, the interpretation of the region by characterizing distinct geohydraulic properties of the different catchment parts in connection with the derived hydrochemical conditions enables a comprehensive spatial hydraulic-chemical characterization on basis of the main chemical characteristics in the identified aquifer complexes. Considering the results of the hydrochemical calculations in the anoxic aquifer in the Oderbruch and at the interface between this aquifer to surface waters, iron measurements in connection with the common hydrochemical parameters can be used to characterize the redox con-... 

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