Evaluation of onsite sewage treatment and disposal systems in shallow karst terrain

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• 作者：Harmon S. Harden ; Eberhard Roeder ; Mark Hooks ; Jeffrey P. Chanton
• 关键词：Karst ; Groundwater ; Sulfur hexafluoride ; Fluorescein ; Septic tank ; Onsite sewage ; Tracer
• 刊名：Water Research
• 出版年：2008
• 出版时间：May 2008
• 年：2008
• 卷：42
• 期：10-11
• 页码：2585-2597
• 全文大小：509 K

文摘

Two conventional onsite sewage treatment and disposal systems (OSTDSs) at Manatee Springs State Park, Florida, USA, were studied to assess their impact on groundwater quality in a shallow karst environment. Sulfur hexafluoride (SF₆) and fluorescein were used as tracers to establish connections between the drainfields and monitoring wells. Elevated nutrients were found in all wells where significant concentrations of both tracers were observed, with the mean of the highest nitrate (NO₃) concentration observed at each well being 47.8±14.9 (n=11) mg/L NO₃-N. The most elevated nutrient concentrations were found directly in the flow path of the effluent. Fecal coliform densities above 10 colony-forming units (cfu)/100 mL were observed in wells with the most rapid connection to the drainfield. The proximity and connectivity of the 0.4–4 m thick sandy surficial soils and the underlying karst aquifer allow rapid contaminant transport and limit the ability of conventional OSTDSs to attenuate NO₃.