and vegetation. The nutrient balance used here is based on the simplistic DLG (1998) methodology, but improves this by more accurately accounting for natural nutrient cycles and processes. It acknowledges that a proportion of nitrogen will be retained in the soil through processes such as ammonification (the conversion of organic nitrogen to ammonia) and a certain amount will be lost by denitrification, microbial attack and volatilisation (Patterson, 2003, Geary & Gardner 1996). Patterson (2002) estimates that these processes may account for up to 40% of total nitrogen loss from soil. In this case, a more conservative estimate of 20% is adopted for the nitrogen loss due to soil processes. Table 4 presents the key data used and results of the water and nutrient balances. Table 4: Data Used and Results of the Water and Nutrient Balance Modelling DATA Parameter Units Value Comments Average effluent load L/day 700 Max anticipated from 3 bedroom dwelling on each lot (assuming no pool backwash water) Precipitation mm/month Girraween From BoM Data Drill (Girraween) mean Pan Evaporation mm/month Middle Point From BoM station (Middle Point) mean Retained rainfall unitless 1 Proportion of rainfall that remains and infiltrates the soil; i.e. 1 assumes nil rainfall will run off and is the most conservative approach Crop Factor unitless 0.7 0.8 Conservative annual value for turf – grasses adjusted for season – Design percolation rate mm/week 25 Nominated rate for Category 4 soil, (DPR) based on DIR values given in AS/NZS 1547:2012. Effluent total nitrogen mg/L 50 Conservative target effluent quality for concentration typical biological filter systems. Nitrogen lost to soil annual 20 Patterson (2002) processes (denitrification and volatilisation) Effluent total mg/L 12 Conservative target effluent quality for phosphorus typical biological filter systems. concentration Soil phosphorus mg/kg 300 Estimated P-sorption capacity for the sorption (P-sorption) sandy clay loam topsoil, based on capacity known P-sorption values for similar soil types elsewhere in the NT. Nitrogen uptake rate by kg/Ha/yr 200 Approximately half the rate expected plants of effluent irrigated pasture grasses (NSW Agriculture, 1997).
and vegetation. The nutrient balance used here is based on the simplistic DLG (1998) methodology, but improves this by more accurately accounting for natural nutrient cycles and processes. It acknowledges that a proportion of nitrogen will be retained in the soil through processes such as ammonification (the conversion of organic nitrogen to ammonia) and a certain amount will be lost by denitrification, microbial attack and volatilisation (Patterson, 2003, Geary & Gardner 1996). Patterson (2002) estimates that these processes may account for up to 40% of total nitrogen loss from soil. In this case, a more conservative estimate of 20% is adopted for the nitrogen loss due to soil processes. Table 4 presents the key data used and results of the water and nutrient balances. Table 4: Data Used and Results of the Water and Nutrient Balance Modelling DATA Parameter Units Value Comments Average effluent load L/day 700 Max anticipated from 3 bedroom dwelling on each lot (assuming no pool backwash water) Precipitation mm/month Girraween mean From BoM Data Drill (Girraween) Pan Evaporation mm/month Middle Point mean From BoM station (Middle Point) Retained rainfall unitless 1 Proportion of rainfall that remains and infiltrates the soil; i.e. 1 assumes nil rainfall will run off and is the most conservative approach Crop Factor unitless 0.7 – 0.8 Conservative annual value for turf grasses – adjusted for season Design percolation rate (DPR) mm/week 25 Nominated rate for Category 4 soil, based on DIR values given in AS/NZS 1547:2012. Effluent total nitrogen concentration mg/L 50 Conservative target effluent quality for typical biological filter systems. Nitrogen lost to soil processes (denitrification and volatilisation) annual 20 Patterson (2002) Effluent total phosphorus concentration mg/L 12 Conservative target effluent quality for typical biological filter systems. Soil phosphorus sorption (P-sorption) capacity mg/kg 300 Estimated P-sorption capacity for the sandy clay loam topsoil, based on known P-sorption values for similar soil types elsewhere in the NT. Nitrogen uptake rate by plants kg/Ha/yr 200 Approximately half the rate expected of effluent irrigated pasture grasses (NSW Agriculture, 1997).
guidelines-land-capability-assessment-onsite-wastewater-management.docx