Water samples from 10 tail water recovery (reuse) pits and 18 irrigation wells were analyzed for nitrate-nitrogen (NO//3-N) and atrazine to ascertain concentrations of these heavily utilized products in surface runoff of irrigation water and ground water beneath irrigated land in Merrick County, Nebraska. Atrazine concentrations in the reuse pit samples ranged from 1. 02 to 23. 1 mu g/liter and in the gound water samples ranged from less than 0. 005 to 6. 96 mu g/liter. The significant correlation between NO//3-N and atrazine in the ground water samples indicated that atrazine probably enters the ground water by infiltrating the soil. Addition of bromide (Br** minus ), **1**5N, and atrazine as spikes to water in an established reuse pit in hydraulic connection with the gound water indicated that the pit loses water by seepage.; Water samples from 10 tail water recovery (reuse) pits and 18 irrigation wells were analyzed for nitrate-nitrogen (NO3-N) and atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-s-triazine) to ascertain concentrations of these heavily utilized products in surface runoff of irrigation water and ground water beneath irrigated land in Merrick County, Nebraska. Atrazine concentrations in the reuse pit samples ranged from 1.02 to 23.1 μg/l and in the ground water samples ranged from < 0.005 to 6.96 μg/l. The significant correlation (r = +0.48) between NO3-N and atrazine in the ground water samples indicated that atrazine probably enters the ground water by infiltrating the soil. Addition of bromide (Br-), 15N, and atrazine as spikes to water in an established reuse pit in hydraulic connection with the ground water indicated that the pit loses water by seepage. Eighteen days after spiking, Br- and δ15N in downgradient shallow wells had approached one-half the pit values, and atrazine concentrations had increased at least 100 times above background concentrations. These results indicated that seepage from reuse pits during late spring and early summer can increase the concentration of both NO3-N and atrazine in ground water. However, throughout the remainder of the year, when water in the reuse pits generally contains much less NO3-N and atrazine, seepage generally dilutes already contaminated ground water.
