Hydrogeological feasibility of disposal of treated effluent in coastal dunes near Auckland, New Zealand

This paper describes the methodology developed to investigate the feasibility of disposing of treated wastewater into a dune sand aquifer via surface infiltration. The findings show that the main limitation for disposal of treated wastewater into coastal dunes is topographic depressions behind the foredunes. The existing shallow water tables within these depressions provide limited allowance for water table rise in response to wastewater infiltration. In this study, where a shallow water table (less than 2 m) is not desirable (due to the forestry landuse and potential effects on tree health), the maximum disposal rate that could be sustained is only 1250 m³/d/km of coastline. However, the study shows that under different landuse conditions it would be possible to adopt less restrictive criteria with respect to water level rise. In such scenarios, disposal rates of 3000 to 4500 m³/d/km of coastline are tenable with some minor impact by way of localized ponding in depressions.