title: The spatial variability of nitrogen and phosphorus concentration in a sand aquifer influenced by onsite sewage treatment and disposal systems: a case study on St. George Island, Florida.
abstract: Groundwater from a shallow freshwater lens on St. George Island, a barrier island located in the Panhandle of Florida, eventually discharges into Apalachicola Bay or the Gulf of Mexico. Nutrient concentrations in groundwaters were monitored downfield from three onsite sewage treatment and disposal systems (OSTDS) on the island. Estimates of natural groundwater nutrient concentrations were obtained from an adjacent uninhabited island. Silicate, which was significantly higher in the imported drinking water relative to the surficial aquifer on St. George Island (12.2+/-1.9 mg Si l(-1) and 2.9+/-0.2 mg Si l(-1), respectively), was used as a natural conservative tracer. Our observations showed that nitrogen concentrations were attenuated to a greater extent than that of phosphorus relative to the conservative tracer. At the current setback distance (23 m), both nitrogen and phosphate concentrations are still elevated above natural levels by as much as 2 and 7 times, respectively. Increasing the setback distance to 50 m and raising the drainfields 1 m above the ground surface could reduce nutrient levels to natural concentrations (1.1+/-0.1 mg N l(-1), 0.20+/-0.02 mg P l(-1)).
authors.affiliation: Department of Geology, East Corolina University, Greenville, NC 27858, USA. corbettd@mail.ecu.edu
authors.forename: D Reide
authors.initials: DR
authors.lastname: Corbet
authors.forename: Kevin
authors.initials: K
authors.lastname: Dillon
authors.forename: William
authors.initials: W
authors.lastname: Burnett
authors.forename: Geoff
authors.initials: G
authors.lastname: Schaefer
mesh_terms: D004784:Environmental Monitoring; D005431:Florida; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D012037:Refuse Disposal; D012722:Sewage; D012822:Silicon Dioxide / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply
chemical_list: D012722:Sewage; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus; D012822:Silicon Dioxide; D009584:Nitrogen