Principal Investigator: David Wenner (University of Georgia)
Sponsor: GWRI
Start Date: 1999-03-01; Completion Date: 2000-02-29;
Keywords: Groundwater Flow and Transport, Geomorphological and Geochemical processes, Groundwater, Nitrate Contamination
Problem and Research Objectives:
The presence of nitrate in groundwater in the Floridan Aquifer near Albany Georgia has prompted an investigation using nitrogen isotopic data to identify the source contamination. It is thought that the contamination originates from a farm and that nitrates were transported by groundwater flow to an adjacent residential community. This community’s water supply comes from homeowner wells, some of which exceed the MCL for nitrate in drinking water. A variety of materials capable of producing this contamination, such as cattle manure, biosolids (sewage sludge), and synthetic inorganic fertilizers are present or have been used on this farm. Biosolids were utilized as fertilizers over a twelve year period from 1984 to 1996 and a cattle feed lot was in operation from 1980-1984. Synthetic inorganic fertilizers were used prior to 1984. A hydrogeologic study conducted by the Georgia Geological Survey indicated that the most probable source of groundwater contamination is a disused cattle feed lot on the suspect property. To further assist in identifying the source of contamination, d15N values were measured for dissolved nitrate from nine wells both on the farm and within the residential community. The data from the contamination plume ranged from +5.5‰ to +2.3‰. This range is consistent with the idea that the major source of contamination stems from synthetic inorganic fertilizers. This conclusion is predicated on numerous studies indicating that different nitrate sources produce different ranges of d 15N values for dissolved nitrates. Typically, nitrates derived from inorganic fertilizers range from -5‰ to + 3.5‰, soil organic material from + 3.5‰ to +7.5‰, and manure and septic system effluent from +10‰ to +20‰. There are no known study of the d15N values of nitrates derived from biosolids. To reinforce this conclusion, d15N values were measured for grasses at sites where only cattle manure and biosolids were present. Analysis of plants serve as proxies for dissolved nitrate in soils because there is little or no isotope fractionation between plants and the dissolved nitrate that they uptake. The aim of this investigation was to directly assess the d15N values of dissolved nitrates in soils derived from decomposition of cattle manure and sewage sludge. A second investigation was initiated in order to constrain the age of nitrate contamination by measuring the tritium concentration of groundwaters within the area.