WRRCTR No.125 Numerical Modeling of Liquid Waste Injection into a Two-Phase Fluid System

Abstract

The injection of liquid wastes into a groundwater environment saturated with density-stratified fluid is simulated by a finite-difference numerical model. The fluid transport equation is simultaneously solved with the convective-dispersion equation for salinity. The migration of the injected liquid waste effluent is then tracked by solving a second convective-dispersion equation for an ideal tracer dissolved in the effluent. The convective-dispersion equation for the ideal tracer is solved with the flow velocities obtained from the simultaneous solution of the fluid transport and the salinity convective-dispersion equations. The equations are solved for the two-dimensional case of a line of injection wells set close together parallel to the coastline. Total length of the line of injection wells is considered to be much longer than the distance to the ocean so that any vertical cross section taken normal to the coastline will appear the same. Results are presented in a time-series of contour maps in the vertical plane: one map for each time-step, with lines of equal concentration for the salinity (isochlors); and the effluent tracer (isopleths). The more concentrated effluent is found to migrate vertically upward around the injection well due to buoyant force, while dilute effluent solutions migrate horizontally, displaying very little buoyant rise.