A physical model to make short-term management decisions at effluent-irrigated land treatment system

Timely prediction of water and nitrate–nitrogen (NO3–N) movement through the soil–water matrix is an essential pre-requisite for the operation and management of a land treatment system (LTS). Groundwater monitoring at a LTS is usually performed to determine how well the LTS is functioning and to ensure that groundwater contamination is not occurring. This paper describes (a) the management issues at a LTS, (b) the concept and approach used to establish a physical model to make short-term management decisions (i.e. to check the short-term effects of land application of wastewater on groundwater quality) at a LTS, and (c) to provide an overview of the importance and practical feasibility of monitoring site specific factors (SSF, e.g. relevant to climate, effluent, soil, plant) and groundwater quality at a LTS. This study showed that when the soil moisture content (SMC) approached a level that was close to or at field capacity (FC) in response to rainfall, the NO3–N leakage occurred and exceeded the maximum permissible level (i.e. MPL=11.3 mg/l) at this site. Monitoring the ability of soil to absorb the designed irrigation volume and rainfall possibility in the immediate future is a cost-effective approach to check the potential of NO3–N leakage through the soil–water matrix into groundwater. This approach would enable the manager of a LTS to determine how well the system is functioning and that groundwater contamination is not occurring. The study showed that the short-term management decisions could be made at a LTS based on monitoring SMC and rainfall, and that continuous monitoring of groundwater may not be necessary. The study admits the truth that monitoring of SMC, rainfall, and groundwater quality data was important, practicable, and feasible at the site.