The discharge of treated animal wastewater produced in concentrated animal feeding operations (CAFOs) on surface soil (within CAFOs borders) leads to groundwater degradation. In this research, groundwater degradation effects of an intensive hog farming operation, located in a Mediterranean area, were investigated. Treated animal wastewater was discharged on a small plot (~10.8 ha) with a geologic fault. Groundwater samples were taken from seven groundwater monitoring wells close to the farm. These wells were affected by the subsurface flow of waters, due to the presence of the geologic fault. In the summer, a significant increase of electrical conductivity values was noted in and attributed to falling water table levels. During the winter, significant increases in concentrations of ammonium nitrogen, nitrate nitrogen, and sulfate were noted and attributed to high precipitation, which assisted in the leaching of nitrogen and sulfur to groundwater.