**2.2 Study method**

Water quality in Malaysia is measured by using the WQI set by the DOE Malaysia. According to Nurfadzlina et al. [17], this index is a measurement to give a comprehensive picture of the status of water quality for an area or water body. Meanwhile, Muhammad Fuad et al. [18] mentions that groundwater quality assessment consists of physical, biological and chemical parameters. In determining the status of groundwater quality in Kapas Island, only six water quality parameters were used as set by the DOE Malaysia in determining the quality status of a water body. The six parameters were pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N) and suspended solids (SS). In addition, two other parameters were also measured and analyzed, i.e., salinity (SAL) and the total dissolved solids (TDS).

Groundwater sampling in Kapas Island was carried out three times (August, October and November 2018). The three months were chosen to monitor for any possible difference in water quality levels following the season of monsoon winds, especially in Peninsular Malaysia. The observations of the groundwater quality in August represent the Southwest Monsoon winds, October (Monsoon Transition) and November (Northeast Monsoon winds). Sampling activities were carried out at four different locations and groundwater samples were tested in situ using YSI Multiparameter equipment. The parameters tested in situ including pH, SAL, TDS and DO. As for the other parameters, water samples were taken and analyzed ex situ (laboratory analysis), according to the procedure described by the American Public Health Association [19].

A quantitative approach was applied in analyzing the level of groundwater quality in Kapas Island. Descriptive statistics were used to describe the status of groundwater quality whether the observed parameters have exceeded the standards set by the DOE Malaysia. In this regard, the groundwater quality data obtained will be compared with the National Water Quality Standard for Malaysia (NWQSM) (**Table 2**), Water Uses and Classes (**Table 3**), DOE's WQI Classification (**Table 4**) and DOE's WQI Classification based on WQI (**Table 5**). Meanwhile, WQI formulas and calculations are shown in **Table 6**. The groundwater quality data of the four observation stations are presented in the form of tables and diagrams to provide an overall picture of the status of groundwater quality in Kapas Island.


#### **Table 2.**

*National water quality standards for Malaysia [20].*

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


#### **Table 3.**

*Classification of water quality and uses [20].*


#### **Table 4.**

*DOE's WQI classification Malaysia [20].*


**Table 5.**

*Range of water quality index based on WQI [20].*
