Impact of septic tank systems on local groundwater quality and water supply in the Pearl River Delta,China: case study

Located at southern coast of China, the Pearl River Delta (PRD) is facing serious water problems in both quantity and quality after its rapid urbanization in the last decade. Most remarkably, the local groundwater, that was used to be the source of drinking water before the urbanization was polluted due to poor management of the septic tanks. In order to study the effects of suburban development on local groundwater flow and water quality in the PRD region, Fengcun of Guangzhou has been chosen as the study area. In Fengcun, drinking water was groundwater before the 1990s, but now piped reservoir water is used by each family because the groundwater has been polluted. This study clarifies the source and process of the groundwater pollution from septic tanks using isotopic and geochemical characteristics, especially nitrate (NO₃^?) concentrations. Water samples were collected from the wells and ponds in Fengcun in March and July 2005 and in July 2006. Based on the pe–pH diagram, NO₃^? and ammonium of groundwater are from the effect of human activities, rather than from nitrification and ammonification of N₂. NO₃^? pollution of groundwater is from point sources, and NO₃^? concentrations decrease from northeast to southwest. Groundwater is polluted rapidly by the leakage of septic tanks. NO₃^? concentrations of pollution sources were lower than 20 mg l^?1 in March 2005, but had increased to about 120 mg l^?1 in July 2006. This implies that groundwater protection should be strengthened in rural areas of the PRD. Copyright © 2007 John Wiley & Sons, Ltd.