A field comparison of nitrogen removal by on-site standard and pressure dosing septic systems in the New Jersey Pinelands

Pressure dosing is an alternative to standard gravity feed for waste water distribution in on-site septic systems. We completed a study comparing nitrogen removal in eight pressure dosing and eleven standard septic systems in the New Jersey Pinelands. For all systems, the native soil was replaced with select fill composed of sand. All systems served new, single family homes. Septic and pump tanks were sampled directly and suction cup lysimeters were installed to sample waste water at three depths within the disposal field. Each was sampled quarterly for three years. There was no significant difference in nitrogen removal between system types. Average system nitrogen removal rates of 40% and 48% were found for pressure dosing and standard systems, respectively. In both types of systems, most nitrogen removal occurred between the septic tank and the top zone of the disposal field. In most systems, there was little change in nitrogen between the top and bottom zones. At 1.5 m below the gravel/select fill interface, mean CI· corrected TN concentrations were 32.8 mg/l for pressure dosing systems and 34.0 mg/l for standard systems