Concept for initial water quality assessment and water monitoring plan during implementation for ASR pilot in Hau Giang province

The project ASR application for Domestic Fresh Water Supply in the Vietnamese Mekong Delta was made possible by a grant under RVO's Partners for Water program. This report describes general water quality considerations during Managed Aquifer Recharge (MAR) operation. These are based on three main aspects: operational risk due to clogging, risk of contamination of the ambient groundwater and aquifer, and risk of water quality deterioration during storage, such as due to redox reactions. Surface water quality in Hau Giang province is affected by domestic and industrial untreated wastewater discharges, agricultural runoff, and discharges from aquaculture. The water quality of the treated water meets the Vietnamese technical guidelines for drinking water. Ambient groundwater quality is variable, ranging from fresh to brackish, and may contain elevated concentrations of iron, ammonium, and coliforms. The main recommendations are: 1. Injectant should be of high quality to prevent chemical, mechanical, and biological clogging. 2. Injectant should meet the Vietnamese technical guidelines for groundwater and should not be lower than the ambient groundwater quality. 3. Injectant should be sourced from the fully treated surface water before disinfection to prevent the development of disinfection by-products. 4. Before pilot development, water samples should be taken from the treated surface water and ambient groundwater of the selected site during rainy and dry seasons and analyzed for a broad range of parameters. 5. Sediment sampling during the drilling of the monitoring well and further data acquisition is required to estimate geochemical reactions in the underground. 6. During operation, water quantity monitoring should be done to assess the recovery efficiency and well performance, and provide data for the cost-benefit analysis. 7. During operation, water quality monitoring should be done for parameters critical for clogging, potential contamination of the groundwater, and geochemical reactions in the subsoil relevant for recovered water quality.