title: Mass Balance of Water and Nitrogen in the Mounded Drainfield of a Drip-Dispersal Septic System.
abstract: Quantitative assessment of nitrogen (N) loading from septic systems is needed to protect groundwater contamination. We determined the mass balance of water and N in the mounded drainfield of a drip-dispersal septic system. Three lysimeters (152.4 cm long, 91.4 cm wide, 91.4 cm high, with 1:1 side slope) were constructed using pressure-treated wood to mimic mounded drainfields. Of total water inputs, septic tank effluent (STE) added 57% water and natural rainfall added 43% water from January 2013 to January 2014. Outputs included leached water (46%) from the lysimeters over 67 sampling events ( = 15 daily and = 52 weekly flow-weighted), potential evapotranspiration (28%), and water stored in the drainfields (26%). Over 13 mo, each drainfield received 227 g of total N (STE, 99%; rainfall, 1%), of which 33% leached, 23% accumulated in the drainfield, and 6% was taken up by grass, with the remainder (38%) estimated to be gaseous N loss. Using these data, the leaching of water from 2.5 million drip-dispersal drainfields in the state of Florida was estimated to be 2.29 × 10 L yr, which would transport 2.4 × 10 kg of total N yr from the drainfields to shallow groundwater. Further reduction of N below drainfields in the soil profile could be expected before STE reaches groundwater. Our results provide quantitative information on the water and N loading and can be used to optimize drainfield conditions to attenuate N and protect groundwater quality.
authors.forename: Mriganka
authors.initials: M
authors.lastname: De
authors.forename: Gurpal S
authors.initials: GS
authors.lastname: Toor
mesh_terms: D005431:Florida; D060587:Groundwater / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D012037:Refuse Disposal; D012987:Soil; D014867:Water; D014874:Water Pollutants, Chemical
chemical_list: D012987:Soil; D014874:Water Pollutants, Chemical; D014867:Water; D009584:Nitrogen