Evaluation of Nitrate in the Ground War in the Delaware Coastal Plain

Abstract

ABSTRACTData from over 800 well samples collected and analyzed during a study of ground‐water quality in Sussex County, Delaware revealed that the water‐table aquifer contains excessively high concentrations of nitrate in several areas. Over 20 percent of the wells sampled contained concentrations that exceeded 45 milligrams per liter (mg/l), and in many areas, over 50 percent of the wells sampled exceeded 45 mg/l.Sussex County is part of the Atlantic Coastal Plain Province, geologically consisting of a series of unconsolidated sands, gravels, silts, and clays that contain extensive ground‐water reserves of generally high quality. On the basis of iron and nitrate concentrations, two major areas of differing water quality were delineated: one in which the ground water contained variable concentrations of nitrate with low concentrations of iron (<0.2 mg/l), and another in which it contained large concentrations of iron (>2.0 mg/l) and little detectable nitrate.Nitrate concentrations ranged from zero to 224 mg/l; average and median values determined for the area of nitrate occurrence were 33.9 mg/l and 25 mg/l respectively. Treatment of the nitrate data allowed depicting of 19 areas of possible excessive nitrate contamination. Nitrate occurrences were closely related to land use, soil permeability, water‐table depths and aquifer chemistry. The greatest incidence of high nitrate concentrations was associated with confined feeding operations. Other nitrate sources are septic tank effluent, natural and chemical fertilizers, foliage in forests, and precipitation.