**3. Results and discussion**

#### **3.1 Groundwater quality based on parameters**

Groundwater quality analysis in Kapas Island was done based on eight parameters, namely SAL, TDS, DO, BOD, COD, pH, NH3-N and TSS. The findings of this study described the value of groundwater quality parameters based on the four designated study areas in addition to comparing the values obtained during the Southwest Monsoon (SWM), monsoon transition (MT) and Northeast Monsoon


#### **Table 6.**

*Water quality calculation formula based on WQI [20].*

(NEM). **Figure 2** shows the level of water salinity of the groundwater solution for each sampling station. The salinity difference at each station has a natural factor in the soil cavity during the infiltration process occurring in the area. Observations were made on the total solubility of salts or groundwater salinity in the study area given the position of the observation station are located near the coastlines. It is clear that the salinity value at Station 1 (S1) was at a high position throughout three observations compared to other stations. The values obtained at S1 during the SWM were 1.1% and during the MT (1.09%) and during the NEM (1.17%).

Station 2 (S2) recorded the second highest reading among all observation stations. At S2 during the SWM, it was 0.68% while during the MT it recorded 0.6% and during the NEM it increased to 1.24%. Station 3 (S3) and Station 4 (S4) showed a flat average value between the two stations with the value obtained at S3 during the SWM and the MT was 0.48% and decreased during the NEM to 0.44%. While the readings recorded at Station 4 (S4) during the SWM was 0.48% and increased during the MT to 0.52% and during the NEM obtained a value of 0.51%.

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

#### **Figure 3.**

*Value of TDS parameter by station and season.*

In the essence, S1 recorded the highest reading of all three observations. This condition may result from seawater penetration into the aquifer system at S1. As pointed by [21], groundwater salinity can also be produced when the boundary between seawater and freshwater moves towards the land due to the leakage of saltwater zones found at the bottom of the aquifer that moves through the joints, fractures or faults. In addition, the locations of S1 and S2 were the closest to the coastlines and this influenced the high SAL value in the area. Overall, the SAL value at all stations exceeded Class I and II but did not exceed Class IV.

Meanwhile, **Figure 3** shows the value of TDS parameters obtained by station and observation by monsoon season in Kapas Island. These different value conditions were also influenced by the SAL content dissolved in groundwater and affected the TDS reading. This study found that the TDS value was in the range of 1573 mg/l and 591 mg/l. Observations showed that the TDS value in the groundwater of the study

area was high. NWQSM sets that the TDS for Class II water quality is 1000 mg/l and Class I is 500 mg/l. From the data obtained, the TDS value at S1 was high in all three observations compared to other stations. The values obtained in S1 during the SWM were 1404 mg/l, MT (1391 mg/l) and NEM (1495 mg/l).

Next, S2 recorded the highest reading on the third observation among all other observation stations. At S2 during the SWM, it was only 890.5 mg/l while during the MT it recorded a value of 793 mg/l and during the NEM, it increased to 1573 mg/l. However, S3 and S4 showed a flat horizontal value between the two stations with a small difference in values where S3 during the SWM recorded 643.5 mg/l and during the MT with 637 mg/l and showed a lower value during the NEM with 591 mg/l. While the values obtained in S4 during the SWM (637 mg/l), MT (689 mg/l) and decreased during the NEM (669.5 mg/l).

From the TDS analysis, the TDS was found in abundance at S1 and also showed significant changes at S2 during the NEM. This may be due to the presence of a mineral substance solution dissolved in the water as it is also influenced by SAL which co-exists in the groundwater. The SAL content analysis also increased at S1 and S2. According to Siti Fazilatul Husni et al. [22], this may be due to the rainfall phenomenon which had dissolved more soluble solids while transporting excess sediment and solutions found in the water. Overall, the TDS value at all stations exceeded Class I and II but did not exceed Class IV.

The following discussion is related to the parameters used in determining the WQI for the observation stations. **Figure 4** shows the values of the DO parameter by station and a comparison of different reading values recorded during different monsoon seasons. The study showed that the range of DO content was between 4.68 mg/l to 8.21 mg/l (**Figure 4**). Based on the observations between the stations for the three monsoons showed that there was a change in the DO value between the wet season and the dry season. In fact, the value reading was also constantly increasing from S1 to S4. Starting from the SWM, the analysis obtained showed that the DO value at station S1 which is 7.15 mg/l increased to 8 mg/l at S4. While the value at S2 was 6.77 mg/l and at S3 it was 7.66 mg/l. For observations during the MT, it was found that the DO value at S1 was 6.14 mg/l, increasing to 6.93 mg/l at S2. However, at S3 the DO value decreased to 6.44 mg/l and increased again at S4 which is the highest reading among the stations during the MT with a value of 7.1 mg/l.

**Figure 4.** *Value of DO parameter by station and season.*
