The calculations of are summarized in Table 3 for the samples over 8 years. By comparing these calculations with the standard values of ⁠, Figure 4 demonstrates the results of water quality assessment in the INPI method. By using this method, the water quality evaluation of five wells in the study area 8 years in succession also analyzes the temporal variation of water quality. It is shown that Wells 1–3 remain at the same water quality grade respectively over 8 years. Well 4 has a slight change of water quality showing a better tendency year by year. Meanwhile, Well 5 has a sharp fluctuation due to uncertain causes, such as climate, the location of wells, human activities. Also, sampling methods could have some impact on the evaluation which should be taken into consideration. These factors interact in a complex way and result in spatial and temporal variation in groundwater quality parameters. Determination of processes affecting groundwater quality in a coastal aquifer is very complicated.