Objectives

1. To determine the amount of nitrate in shallow groundwater beneath agricultural fields in the area of NC with the greateat potential for contamination.

2. To examine the likelihood of nitrate movement into deeper, confined aquifers.

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Accomplishments

1. Two sites were selected for this field and modeling investigation: one in Duplin and one in Sampson County. Commercial inorganic fertilizers are applied to the study area in Duplin County and pig waste is applied to the study area in Sampson County. Shallow groundwater in the surficial aquifer below agricultural at both sites was clearly contaminated with nitrate.

2. Differences in water table elevations between well nest locations at both sites indicate movement of this contaminated groundwater was predominantly lateral rather than vertical. No evidence of movement of nitrate below a finer textured sediment layer usually present 3060 feet below the soil surface was ever found.

3. The finer textured layer is discontinuous and it is possible that movement of contaminated water below this depth could occur even though it was not observed in this study.

4. Both the field and modeling study indicated that domestic wells located in the surficial aquifer immediately adjacent to agricultural fields or downstream of agricultural fields is likely to contain above the recommended drinking water level of nitrate-nitrogen.

5. Small streams draining areas where animal waste had been applied were observed to have elevated nitrogen levels although levels were not above drinking water standards.

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Significance

This study and related previous studies by the authors show that shallow groundwater below many agricultural fields in the Coastal Plain receiving even the recommended rates of fertilizer nitrogen are likely to contain greater than the recommended levels of nitrate nitrogen for drinking water. When the fields receive rates of nitrogen which exceed agronomic recommendations, nitrate levels in the shallow groundwater can be very high. Fortunately, much of the NC Coastal Plain contains a clay layer a few to several feet below the surface which prevents the migration of nitrate into the deeper aquifers. However, in some areas this clay layer may not be continuous and the potential for contaminate$on of deeper aquifers exists. In concentrated agricultural areas where the clay layer is 40 to 60 feet, it is probable that many shallow domestic wells contain more than the recommended levels of nitrate-nitrogen.

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