Method for obtaining key parameters for pollutant transportations under coupling effects of temperature and hydrodynamics based on site

A method for obtaining key parameters for pollutant transportations under coupling effects of temperature and hydrodynamics based on a site scale, wherein the method comprises following steps:

• 1) arranging a water injection well H1, a pumping well H4, observation wells H0, H2, and H3 on a contaminated site, conducting pre-experiments on each of the wells, including geotechnical tests, pumping tests, and micro water tests, and obtaining an initial permeability coefficient for an aquifer of the site, and taking the initial permeability coefficient as a calibration standard for subsequent models;
• 2) conducting, on a basis of the pre-experiments, coupling tracing tests including the pumping tests, thermal tracing tests and salt tracing tests on each of the wells, wherein the pumping tests are to calculate a permeability coefficient by observing water level variations of the aquifer, the thermal tracing tests are to calculate a thermal conductivity coefficient by observing a relation between depth and temperature variations in each of the wells, and the salt tracing tests are to convert a conductivity into a concentration calculation dispersion coefficient by observing a relation between the depth and conductivity variations, and arrange probes according to positions of test wells and observation wells, and monitoring a temperature, a conductivity, and a permeability coefficient for aquifers at different depths;
• 3) constructing a three-dimensional groundwater flow field model, processing contaminated site data in an experimental area into spatial coordinates, setting an initial condition and a boundary condition, and inputting the permeability coefficient, the thermal conductivity coefficient, and a dispersion coefficient obtained from on-site experiments into a simulation software COMSOL Multiphysics 5.6 for a three-dimensional modeling, and dividing, according to the positions of the test wells and the observation wells, the three-dimensional groundwater flow field model into three layers to obtain a three-dimensional groundwater flow field model of the contaminated site;
• 4) collecting groundwater level data from the observation wells H0, H2, and H3 on the contaminated sites, obtaining groundwater level data during a same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site, comparing actually measured water level values with simulated water level values to obtain a root-mean-square error of the groundwater level, and adjusting, according to the initial permeability coefficient for the aquifer obtained from the pre-experiments, model parameters, to ensure that the root-mean-square error of the groundwater level is within a preset range;
• 5) conducting, by utilizing a corrected three-dimensional groundwater flow field model of the contaminated site, multi field coupling simulations of a groundwater flow field, a temperature field, and a solute concentration field, selecting a Darcy's law module in the software COMSOL Multiphysics 5.6 for a groundwater flow field simulation, selecting a porous medium thermal transfer module in the software for a temperature field simulation, and selecting a porous medium dilute matter transfer module in the software for a solute concentration field distribution, conducting multi physical field simulations of the groundwater flow field and the temperature field, the groundwater flow field and the solute concentration field, as well as the groundwater flow field and the temperature field solute and the concentration field, respectively, and obtaining influence relations between each of the fields under a full coupling condition;
• 6) adjusting and correcting, by utilizing monitoring data at different depths in the tracing tests, the permeability coefficient, the thermal conductivity coefficient, and the dispersion coefficient in the groundwater flow field model, and determining an optimal model for the contaminated site;
• 7) predicting, according to the optimal model for the contaminated site, pollutant transportation parameters, inputting a water level, a temperature, a conductivity or a concentration of the aquifer into the optimal model, and obtaining the pollutant transportation parameters, that is, the permeability coefficient, the thermal conductivity coefficient, and the dispersion coefficient.