1,720,966 research outputs found
Recovery the release history and source location of a pollutant in groundwater using data collected in laboratory
No full textThis work shows the application of an innovative procedure that is able to simultaneously identify the release history and the source location of a pollutant injection in groundwater using a dataset obtained experimentally. The methodology follows a geostatistical approach and it requires a preliminary delineation of a probably source area. The dataset was provided through an experimental installation developed at the hydraulic laboratory of the University of Parma (DICATeA). The equipment represents a 2-D unconfined aquifer controlled through two constant head levels (upstream and downstream); it consists of a Plexiglas sandbox filled with a porous medium (1 mm glass beads). An injector was placed inside the porous medium and sodium fluorescein salt was used as tracer during the tests. The standard test consists of releasing a constant and known concentration with a variable flow rate. The injection rate and the mean flow rate inside the sandbox are stored by means of a data acquisition system, meanwhile the concentration distribution inside the sandbox is observed through the processing of side wall images collected by means of a digital camera.
The digital camera and the sandbox are placed in a dark room lightened by blue light in order to excite the fluorescein and easily evaluate the concentration distribution. A Matlab routine was developed to cut and to correct images by a projective transformation in order to obtain pictures with same size and orientation. Each pixel of the image has known coordinates on the sandbox. After a calibration process, the relationships between the luminosity of the emitted fluorescence and the tracer concentration have been identified in each pixel of the picture and consequently in each point of the domain. Initially a series of simple tests (with constant injection) were carried out with the aim at validating the experimental equipment comparing the observed data to those collected through the images, such as mass balance or mass flow rate. Once that the equipment was considered reliable, the tracer was injected with a variable flow rate in order to test and validate a geostatistical procedure that it is able to simultaneously recover the release history and the source location with a dataset provided under known and controlled condition.
20 concentration values at different times, obtained from the photographic technique, of 2 monitoring points were used to recover the flow rate injected in the porous media in time. A numerical model was developed to support the procedure, in particular, considering a constant injection, it allowed to identify the transfer functions between the source and the monitoring points. At first only the true source was considered and the injected flow rate was well recovered. Then the release history was recovered simultaneously for 4 potential sources (one true and three false). The geostatistical approach showed at the true source the actual release history and null concentration at the other sources. This demonstrated the capability of the method and the reliability of the experimental equipment
Stima dei coefficienti di dispersività mediante prove sperimentali condotte in vasche di filtrazione
No full text
Identification of the release history of a groundwater contaminant in non-uniform flow field through the minimum relative entropy method
No full textThe recovering of the contaminant release history in heterogeneous and partially known flow field
No full textLaboratory sandbox validation of pollutant source location methods
Full text linkInverse methods can be used to recover the pollutant source location from concentration data. In this paper, the relative effectiveness of two proposed methods, simultaneous release function and source location identification (SRSI) and backward probability model based on adjoint state method (BPM-ASM) are evaluated using real data collected by using experimental equipment. The device is a sandbox that reproduces an unconfined aquifer in which all the variables are controlled. A numerical model was calibrated using experimental observations. The SRSI is a stochastic procedure which finds the source location and the release history by means of a Bayesian geostatistical approach (GA). The BPM-ASM provides the backward probability location of the pollutant detected at a monitoring point by means of a reverse transport simulation. The results show that both methods perform well. While the simultaneous release function and SRSI method requires a preliminary delineation of a probable source area and some weak hypotheses about the statistical structure of the unknown release function, the backward probability model requires some hypothesis about the contaminant release time. A case study was performed using two observation points only, and despite the scarcity of data, both methodologies were able to accurately reconstruct the true source location. The GA has the advantage to recover the release history function too, whilst the backward probability model works well with fewer data. If there are many observations, both methodologies may be computationally heavy. A transfer function approach has been adopted for the numerical definition of the sensitivity matrix in the SRSI method. The reliability of the experimental equipment was tested in previous laboratory works, conducted under several different conditions
Application of Multi-frequency Oscillatory Hydraulic Tomography for estimating the transmissivity on a well field
No full textThe recovery of contaminant release history in groundwater: identification of the minimum required characterizationof the aquifer
No full textRicostruzione della posizione della sorgente e della storia di rilascio in mezzi porosi utilizzando dati di laboratorio
No full textEvaluation of dispersivity coefficients by means of a laboratory image analysis
Full text linkThis paper describes the application of an innovative procedure that allows the estimation of longitudinal and transverse dispersivities in an experimental plume devised in a laboratory sandbox. The phenomenon of transport in porous media is studied using sodium fluorescein as tracer. The fluorescent excitation was achieved by using blue light and the concentration data were obtained through the processing of side wall images collected with a high resolution color digital camera. After a calibration process, the relationship between the luminosity of the emitted fluorescence and the fluorescein concentration was determined at each point of the sandbox. The relationships were used to describe the evolution of the transport process quantitatively throughout the entire domain. Some check tests were performed in order to verify the reliability of the experimental device. Numerical flow and transport models of the sandbox were developed and calibrated comparing computed and observed flow rates and breakthrough curves. The estimation of the dispersivity coefficients was carried out by analyzing the concentration field deduced from the images collected during the experiments; the dispersivity coefficients were evaluated in the domain zones where the tracer affected the porous medium under the hypothesis that the transport phenomenon is described by advection-dispersion equation (ADE) and by computing the differential components of the concentration by means of a numerical leap-frog scheme. The values determined agree with the ones referred in literature for similar media and with the coefficients obtained by calibrating the numerical model. Very interesting considerations have been made from the analysis of the performance of the methodology at different locations in the flow domain and phases of the plume evolution
- …
