A comparative study of a conventional and a mound on-site wastewater disposal system in a coastal environment
Wastewater effluents from two absorption systems were studied in the Assateague Island National Seashore Park, during 1993. The study focused on the wastewater effluents from a mound and a conventional on-site wastewater disposal system (OSWDS). The site was characterized by coastal beach soils. Ave...
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| Format: | Others |
| Language: | en |
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Virginia Tech
2014
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| Online Access: | http://hdl.handle.net/10919/46416 http://scholar.lib.vt.edu/theses/available/etd-12232009-020649/ |
| Summary: | Wastewater effluents from two absorption systems were studied in the Assateague Island National Seashore Park, during 1993. The study focused on the wastewater effluents from a mound and a conventional on-site wastewater disposal system (OSWDS). The site was characterized by coastal beach soils. Average wastewater loadings to each drainfield were 10,800 liters per day. The density of the ground water varied due to changes in salinity and the hydraulic gradients fluctuated due to tidal effects. The OSWDS’s were used between four to five months of the year, with three to four months at near full capacity.
Dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) immediately adjacent to the conventional drainfield were correlated with bath house usage. The average DIN concentration was 0.76 mg/L in January-March, before the season started, increased to 80.78 mg/L by August, and decreased to 26.41 mg/L in October-November, once the season ended. Likewise the DIP increased from 1.20 mg/L before the season started, to 7.36 mg/L during the season, and decreased to 1.86 mg/L once the season ended.
Conversely, the DIN and DIP in the ground water immediately adjacent to the mound drainfield were not well correlated with bath house usage. The DIN increased from 1.01 mg/L during off-season, to 39.95 mg/L during September and showed almost no appreciable difference after fall closure. The DIP did not show a significant difference from off-season values, with an average value of 0.29 mg/L.
Transport of the wastewater through the ground water toward the surface waters was suggested by increasing DIN concentrations with distance from both drainfields over time with increasing bath house usage.
Elevated <i>Escherichia coli</i> concentrations were measured in the ground water immediately adjacent to the conventional drainfield. Concentrations of <i>E. coli</i> ≥ 16,000 MPN/100 ml were measured up to 2 meters from this drainfield. On the other hand, the mound did not show, on average, ground water fecal contamination. There was no indication of fecal coliform contamination to the ocean waters in either site. On only three occasions were <i>E. coli</i> concentrations, with values between 30 and 130 MPN/100 ml measured at distances greater than 40 meters from the conventional drainfield. At the mound site on only one occasion was a E. coli concentration with a value of 23 MPN/100 ml measured at distance of 50 meters from the drainfield.
The conclusions from this study were: 1) the mound drainfield had a better performance in wastewater treatment than the conventional drainfield, 2) direct transport of <i>E. coli</i> to surface water via ground water could not be detected or measured, 3) both systems showed direct loadings of nutrients to the ground water, 4) there was some evidence of nutrient transport to surface waters, and 5) the conventional system showed high loadings of <i>E. coli</i> to ground water. === Master of Science |
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