Characterizing Groundwater Dynamics Based on Impact of Pulp and Paper Mill Effluent Irrigation and Climate Variability

Change in groundwater dynamics (in terms of changes in depth to watertable and its salinity) is a key environmental concern for agricultural production using pulp and paper mill effluent for irrigation purposes. At the study site, the treated effluent is delivered from the mill into a winter storage dam. This storage dam is also meant to provide an opportunity for runoff collection and recycling for irrigated areas. A natural creek also exists along the farm boundary. This paper presents, using field observation data and computer simulation results, the impact of using treated effluent from the pulp and paper mill on groundwater dynamics at the farm (covering areas both under and outside the effluent irrigation paddocks); and on the flows in the adjacent creek. The modeling results show that after 5 years of operations, the change in aquifer storage is more under average climatic conditions (−23.5 mm/year) as compared to −7.1 and −9.0 mm/year under dry and wet climatic conditions, .respectively. Under average climatic conditions, the combined effect of irrigation and rainfall creates more hydraulic gradient towards the creek thereby depleting the aquifer storage more as compared to wet and dry climatic conditions. Resultantly, the subsurface groundwater flows towards the creek becomes around 57.9 mm/year under average scenario as compared to 55.0 and 36.7 mm/year under wet and dry climatic conditions, respectively. During the average climatic condition, 456.6 mm evaporation from shallow groundwater was estimated under the current management practices; which was reduced to 399.1 mm under the best management practices due to better use of all sources of water and capillary upflow from shallow groundwater. Thus, with the adoption of best management practices, there would be less risk of salinisation due to evaporation from shallow groundwater tables.