Sediment analysis of M1 monitoring well samples : ASR pilot in Nga Bay, Hau Giang Province, Vietnam

An aquifer recharge and recovery (ASR) pilot is being implemented in Nga Bay (Hau Giang province, Vietnam) where a monitoring well M1 was drilled in January 2024. Eighteen samples from 150–201 m bgl were analysed for grain size distribution, mineral content, elemental composition and cation exchange capacity (CEC). Results show the presence of the hydrogeological favourable aquifer qp consisting of 20 m of medium sand with only a 2.5 m thick layer of sandy loam. The overlying aquitard, made of at least 5 m of stiff clay, provides a very good protection against upward leakage. The underlying aquitard, made of at least 5 m of silt loam, provides a good protection against downward leakage. Physical clogging due to the mobilisation 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 arsenic was investigated further and seems to be limited.