WATER SUPPLY WELL CONTAMINATION FROM FORMER DAIRY OPERATIONS AND LAND USE PLANNING IMPLICATIONS

In a rural North Carolina housing subdivision, several water supply wells were discovered to have nitrate levels exceeding the state and federal drinking water standard. The subdivision is located at the site of a former dairy farm that, in addition to having grazing land and feeding areas, used an unlined storage lagoon to contain animal wastes that were generated in areas where the animals were confined. An investigation was undertaken to determine the source of the nitrate contamination and the most appropriate remedial action to reduce the contaminant levels in the supply wells. Investigators sought to ascertain if the excess nitrate came from septic systems, lawn fertilizers, the former dairy waste lagoon, or residual animal waste on the former grazing fields. The investigation revealed that the former dairy waste lagoon was not the primary source of the contamination, as was first suspected. Chemical and isotopic data indicate that the majority of the water supply wells with nitrate levels above 10 mg/l were most likely impacted by nitrogen derived from residual waste products resulting from normal grazing and feeding activities at the site over a 35-year period. The investigation underlines the importance for planners to consider potential groundwater quality impacts from animal farming operations before changing land use to suburban housing development.