No abstract

Groundwater is an essential resource which is influenced by salt water due to the groundwater exploitation in Holocene aquifer of Quang Nam - Da Nang. Hence, the measures for preventing saltwater intrusion and better groundwater management are required. In this study, GALDIT method was utilized to identify the salt water intrusion (SWI) vulnerability zones using monitoring data in Holocene aquifer of Quang Nam - Da Nang. The results of GALDIT method indicated that Da Nang and Hoi An cities were in the high SWI vulnerability zones. The moderate SWI zones were dominant and low vulnerability zones were at the southern part of the study area. The analysis of the monitoring data showed the occurrence of SWI far inland, up to the distance of 12.5 km from the sea shore and suggested the impact of human activities on SWI. The analysis of monitoring data together with GALDIT index indicated that the important of the groundwater abstraction depth or the occurrence of fresh-salt groundwater interface should be considered to improve the result of GALDIT method for the prevention of SWI. In short, the GALDIT used in this study is an important approach for the prevention of SWI in the study area.

Groundwater quality is vulnerable to various processes. In this study, processes affecting groundwater quality were evaluated in coastal aquifers of Quang Nam - Da Nang (QNDN). A chemical data of 426 groundwater samples from 27 monitoring wells in the period 2011-2018 were analyzed. Principal Components Analysis (PCA) and Base Exchange Indices (BEXD) were applied for the evaluation. The PCA results suggested the influences of natural processes and anthropogenic activities on the groundwater quality. Seawater influence contributed to the dominant ions in groundwater; mineral weathering and dissolution mainly increased the alkalinity, Ca2+, and Mg2+; SO42- reduction explained the low SO42- in the groundwater; and reductive dissolution of Fe (hydroxides) caused Fe exceeding WHO’s drinking standard. Intensive groundwater abstraction generated up coning of saline groundwater; discharge from agricultural practices, industrialization, and urbanization were considered as sources of high NO3- in groundwater. The integration of monitoring data and BEXD gave a better interpretation of salinization and freshening, which can be masked by the memory effects of seawater transgression and regression in history.

No abstract