Uncertainty Analysis of Nitrogen Transformation Parameters Used for Making Water Reclamation Predictions

Onsite wastewater treatment systems (OWTS) are used by approximately 20% of all households in the United States. The majority of these systems utilize a soil treatment unit (STU), which typically provide effective treatment of nutrients when located in appropriate soils. However, high OWTS density may result in an increase in wastewater nutrient loading into the underlying groundwater, especially in areas with a shallow water table or in environmentally sensitive areas. This work aimed to develop a tool that couples nitrogen transformation rates that are based on existing knowledge and data, with a simple numerical model (STUMOD) to estimate nitrogen removal with depth in the STU. Because both nitrification and denitrification rates were found to vary several orders of magnitude depending on soil hydraulic properties, texture, moisture and temperature, any modeling attempts will have a certain amount of uncertainty associated with it. This presentation will provide the results from the uncertainty analysis of the nitrogen transformation parameters that were used in STUMOD, and show the variability in expected nitrogen removal depending on soil texture. The results will greatly aid in the decision making process for OWTS design, and will provide a tool for water reclamation.