Domestic well water quality in rural Nebraska: focus on nitrate-nitrogen, pesticides, and coliform bacteria

For this statewide assessment, 1808 wells were sampled and a data base compiled that included water-quality data (NO3(-1)-N, pesticides, coliform bacteria) and site-specific data collected at each location. Domestic, rural water quality in Nebraska varies substantially from one ground water region to another and is a function of well characteristics, distances to potential contamination sources, and hydrogeologic and site characteristics. The percentage of wells exceeding the 10 ppm MCL for NO3(-1)-N ranged from 3 to 39 percent, depending on the ground water region. This large range of values indicates the inadequacy of stating that an average of 19 percent of domestic wells in Nebraska are contaminated by nitrates. This statistic does not describe the nature, extent, and variability of the contamination problem. Depending on the ground water region, the degree of nitrate contamination in rural domestic drinking-water wells has remained generally unchanged or has only slightly increased since the last statewide assessment conducted from 1985 to 1989. Bacterial contamination has either remained the same or has decreased. The percentage of wells affected by bacteria ranged from 8 to 26 percent, depending on the ground water region. Statewide, about 70 wells, or 4 percent of the wells sampled, had detectable-pesticide levels, of which atrazine was the most common. Eighty-two percent of the detections were in the Platte River Valley or in the South Central Plains, both of which are characterized by heavily irrigated corn and a statistical association between nitrate and atrazine contamination. To improve the quality of domestic drinking water will require a combination of activities, including the application of best management practices specific to a ground water region and individual action at rural households, such as conducting sanitary surveys of existing wells before installing new wells.