The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO₃^-, N₂ from denitrification, O₂, Cl^-, and environmental tracers of groundwater age were matched to observations by adjusting the parameters for recharge rate, unsaturated zone travel time, fractions of N and Cl^- inputs leached to groundwater, O₂ reduction rate, O₂ threshold for denitrification, and denitrification rate. Model results revealed important interactions among biogeochemical and physical factors. Chloride fluxes decreased between the land surface and water table possibly because of Cl^- exports in harvested crops (averaging 22% of land-surface Cl^- inputs). Modeled zero-order rates of O₂ reduction and denitrification were correlated. Denitrification rates at depth commonly exceeded overlying O₂ reduction rates, likely because shallow geologic sources of reactive electron donors had been depleted. Projections indicated continued downward migration of NO₃^- fronts at sites with denitrification rates <0.25 mg-N L^-1 yr^-1. The steady state depth of NO₃^- depended to a similar degree on application rate, leaching fraction, recharge, and NO₃^- and O₂ reaction rates. Steady state total mass in each aquifer depended primarily on the N application rate. In addition to managing application rates at land surface, efficient water use may reduce the depth and mass of N in groundwater because lower recharge was associated with lower N fraction leached. Management actions to reduce N leaching could be targeted over aquifers with high-recharge and low-denitrification rates.