A study of groundwater transport in the effluent-dominated reach of the Santa Cruz River, Arizona

The Upper Santa Cruz Basin has experienced population growth and industrial development resulting in increased water demand and greater risk of groundwater contamination. Contaminant occurrence and transport in the subsurface were examined in the Upper Santa Cruz Basin by creating conceptual models and using a groundwater flow model coupled with a contaminant transport model to determine the movement of contaminants. Water-quality data from numerous sources were collected and compiled into a database for the area, which was aggregated to identify major contaminants and their distribution. Using this data and a numerical model (MT3DMS, Zheng and Wang, 1999), simulations have been conducted for nitrate to evaluate its movement in the aquifer and to determine if this is an appropriate tool to use in the Santa Cruz Basin. Results show that the model was not able to capture the nitrate movement and that additional sources need to be considered.