*Seasonal Variability of Groundwater Quality in Kapas Island, Terengganu, Malaysia DOI: http://dx.doi.org/10.5772/intechopen.99863*

in agricultural areas. In this study, DOE's WQI Classification and Water Classes and Uses have been used in determining the status of groundwater quality in Kapas Island. Determination of groundwater WQI in Kapas Island used only six parameters, namely DO, pH, BOD, COD, TSS and NH3-N. These values of WQI reading are the result of each parameter analyzed based on the WQI formula as shown in **Table 6**. The findings of WQI analysis provided indicators about the current status of groundwater in the study area whether it belongs to Class I (> 92.7), Class II (76.5–92.7), Class III (51.9–76.5), Class IV (31.0–51.9) or Class V (<31.0). Next, based on DOE's Water Quality Classification, groundwater quality status is categorized into three, i.e. clean (81–100), slightly polluted (60–80) and polluted (0–59).

On average, the range of WQI was between 61 to 77, with the majority fell under Class II and III with slightly polluted status (**Table 7** and **Figure 10**). During the SWM, S1 and S3 recorded Class II and S2 and S4 recorded Class III. During the MT, three stations recorded Class II of water quality, namely S1, S3 and S4. Meanwhile, during the NEM, all stations recorded Class III of groundwater quality. Therefore, to be used as a supply of drinking water and other domestic uses, groundwater in this area needs to be treated using conventional and intensive methods. This is for the purpose of providing consumers, especially tourists, with clean water resources. This study is in line with previous studies where an area, especially


**Table 7.**

*WQI values and classes for each groundwater quality observation station in Kapas Island.*

**Figure 10.** *WQI for observation stations in Kapas Island by season.*

in the island area developed for various activities has contributed to the deterioration of groundwater quality [5, 8–9, 13]. Therefore, the values obtained during the NEM for all observation stations in the study area showed relatively the lowest WQI values compared to MT and SWM. This is due to the high concentrations of BOD, COD, TSS and NH3-N while the low DO value contributed significantly to the deterioration of water quality at all sampling stations taken during the NEM.
