A methodology was developed to assess the impact that changes in groundwater recharge, nitrate leaching from the root zone of crops, and pumping rates for irrigation have on groundwater quality and quantity. The methodology is based on the use of four simulation models. EPIC model is use to simulate the water and nitrogen balance in the root zone. The vadose zone model was developed and linked to existing models for groundwater flow (MODFLOW) and solute transport (MT3D) generating the recharge files used by those models The methodology was applied to an area in the Central Platte Valley of Nebraska, near the town of Shelton. The groundwater system in the area is a shallow, sand-gravel aquifer that is highly contaminated by nitrate-nitrogen. The groundwater flow model was calibrated using historic groundwater level data for 1981-1996. The combined models were used to predict changes in groundwater quality resulting from reduced nitrate leaching at a farm scale. Simulations showed concentration reductions on the order of 10 percent in the upper third of the groundwater body after 10 years of improved irrigation and nitrogen fertilizer management.