MODELING OF THE FUNDAMENTAL MECHANISMS OF AN INJECTED WASTEWATER PLUME IN THE MARSHLAND UPWELLING SYSTEM

Migration and development of a wastewater plume within the marshland upwelling system (MUS) are a function of various mechanisms: background salinity, permeability, injection flow rate, injection pressure, and biofilm growth. Accurate representation of the system for variable-density flow modeling requires quantification of these mechanisms. Observation wells situated around the injection well were routinely monitored to track the movement of the wastewater plume within the saline subsurface. Background salinity values at the site increased over a 15 ft depth. Intermittent injection of wastewater created a transient plume of low salinity that expanded with decreasing depth. Assuming no lateral dispersion upon injection, the average linear velocity of the wastewater was estimated to be 0.42 ft/day, which corresponds to a minimum hydraulic retention time of approximately 35 days. The two-dimensional wastewater front can be modeled based on the governing equations and boundary conditions commonly used in saltwater intrusion models.