Implementation plan of an aquifer storage & recovery (ASR) pilot at the Nga Bay water treatment plant of HAWASUCO Hau Giang Province

We believe that the location and set up at the water treatment plant of HAWASUCO in Nga Bay, Hau Giang province, meets all requirements for an aquifer storage and recovery (ASR) pilot based on the following success factors: Source water quantity: There is sufficient surplus source water available from the water treatment plant. • Source water quality: The water quality of the treated water is of high quality and does not pose any risk for the operation of the system (clogging) and the contamination of the aquifer. • Suitable aquifer: Results of sediment analysis show the presence of a hydrogeological favorable aquifer qp1 consisting of 20 m of medium sand with only a 2.5 m thick layer of sandy loam. The overlying aquitard provides a very good protection against upward leakage as it consists of at least 5 m of stiff clay. The underlying aquitard provides a good protection against downward leakage as it consists of at least 5 m of silt loam. • Storage capacity: As the groundwater level has dropped significantly over the last decades due to over abstraction and low natural recharge rates of the confined aquifer system, there has been sufficient storage space created in the aquifer to recharge water artificially. • Recovery: The hydraulic gradient of the groundwater and hence groundwater velocity (estimated 3-8 m/year) on a regional scale is low. In the vicinity (1.5-2 km) downstream of the pilot there are only one smaller (170 m³/day) active licensed wells abstracting water from qp1. Hence, it is not expected that the recharged water will move quickly away from the pilot site and reach other users in the near future. Based on sedimentary analysis of the aquifer material physical clogging due to the mobilization of clay minerals and the precipitation of iron hydroxides should be monitored. The risk of aquifer contamination due to the release of trace elements especially for As, Cr, Ni and Zn seems low, but will be further investigated and monitored. • Method: The ASR method using a single well for recharge and recovery of water is the most suitable method for deep confined aquifers and has been proven successful in many cases worldwide. • Demand: In cases that the surface water is of insufficient quality (e.g. due to saline intrusion or pollution), the recharged groundwater provides an additional emergency storage to supply the water treatment system with source water. While currently the saline intrusions into the surface water system have not reached Nga Bay Town, it is expected that factors like climate change and riverbed incision will lead to years with saline intrusion also affecting the surface water salinity in the dry season at Nga Bay town. If this pilot is successful, it could be a model to be transferred to other locations in the Mekong Delta that are already experiencing saline intrusion during the dry season now. • Monitoring: The pilot will be set up with a comprehensive monitoring scheme to allow detailed evaluation of the tests with respect to water quantity (infiltration rate, recovery efficiency) and water quality (source water quality, recovered water quality), as well as cost-benefit analysis (energy consumption, operational costs, infrastructure costs). • Institutional arrangements: This project combines the operational capacities of the ASR well owner HAWASUCO, who has an interest in a secure water, with the scientific and technical expertise from a number of international organizations (Deltares, VEI, BGR, WWF), and the local expertise for well drilling of the Division of Water Resources Planning and Investigation in the South (DWRPIS).