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

Observations conducted during the NEM showed high-value readings at S1 (7.38 mg/l) and S4 (8.21 mg/l). However, the readings of the DO content decreased at S2 (5.31 mg/l) and decreased to 4.68 mg/l at S3. A low level of DO content can clearly be seen during the NEM at S3 with a value of 4.68 mg/l while the highest DO content was recorded during the same monsoon at S4 which is 8.21 mg/l as there was a heavy rainfall when the observation was made during the NEM. Based on the DO value recorded at all stations, it was found to be in Class I and II except at S3 with a DO value of 4.68 mg/l which is in Class III. It is proven that the rate of DO is dependent on the presence of organic wastes or organic matters that require oxygen causing the level of DO content of the water to be low and it is also influenced by the strength of water convection [23].

Next, the values of the pH parameter were 7.15 to 7.85 (**Table 5**). The results showed that the pH values recorded at all of the observation stations were in Class I as according to the DOE's WQI classification. From the pH values recorded, it showed that the pH of groundwater was in a stable condition for each station according to the monsoon season. High pH readings were recorded at S4 (7.67) during the SWM, NEM (7.61) and MT (7.5). The second highest value recorded was at S2 (7.69) during the NEM and increased to 7.85 during the MT and decreased during the NEM to 7.15. For S3, the MT was high at 7.74 and followed by the value during the SWM (7.56) and decreased during the NEM (7.27). The pH value of 7 obtained showed that the reading is neutral, therefore, the water is neither acidic nor alkaline [24]. While S1 recorded the lowest pH value among all stations during the SWM (7.45), followed by MT (7.43) and the lowest value was during the NEM (7.22). This fluctuation in pH value may be due to the environmental factors of the island as well as the influence of seawater with a higher pH as compared to the pH of freshwater (**Figure 5**) [25].

**Figure 6** showed the values of the BOD parameter in Kapas Island that were within the range of 0.38 mg/l to 3.66 mg/l, which was in Class I to III based on the DOE's WQI classification. From the analysis, the differences in BOD readings at all sampling stations during the NEM were the highest compared to other seasons. The data obtained during the NEM at S1 which recorded the highest value of 3.66 mg/l

**Figure 5.** *Value of pH parameter by station and season.*

**Figure 6.** *Value of BOD parameter by station and season.*

followed by S3 (3.58 mg/l), S2 (2.98 mg/l) and S4 (2.2 mg/l). During the SWM, all observation stations showed different values and the highest reading of all stations were recorded at S2 with 3.02 mg/l. Meanwhile, the BOD value was recorded as low at S3 (0.64 mg/l), S4 (0.6 mg/l) and S1 (0.38 mg/l). While during the MT, the highest reading values were recorded at S2 (1.34 mg/l) and S1 (0.48 mg/l). The BOD value showed low readings at S3 (0.46 mg/l) and at S4 (0.42 mg/l).

All of the observation stations comparatively showed a high average of BOD values during the NEM. These high BOD values give the impression that there were organic matters that could be broken down by microorganisms and more oxygen was being used because this decomposition process requires oxygen. The high BOD values at all of the stations during the NEM give the impression that the water quality was in Class III based on the DOE's WQI classification. Therefore, the water quality in the area requires further treatment before it can be used and according to Nurfadzlina et al. [17], BOD parameter is used as an indicator for the degree of water pollution. High BOD values indicate that the water tested was in a contaminated status.

Meanwhile, **Figure 7** showed the COD value according to observation station by season. It was found that the COD concentration of the groundwater in the study area appeared to be not polluted with the majority of the analysis showed notdetected value (nd value) or below the WQI classification. During the study period, the values of COD for all observation stations was within the range of 0 mg/l to 2 mg/l (**Figure 7**). Water quality samples for all stations and seasons were in Class I i.e., below 10 mg/l. Class I indicate that the water analyzed is free from organic pollutants especially from sewage.

The COD values obtained according to stations during the SWM at S2 and S3 were not detected with a reading of nd values followed by S1 (0 mg/l) and S4 (1 mg/l). During the MT, all stations showed that the groundwater is currently not contaminated with an nd reading of the analysis. Next, the COD value during the NEM recorded the highest value at S1 which is 2 mg/l followed by S4 (0 mg/l). While at S2 and S3 readings were obtained with an nd status for both stations. With that value, the COD parameter is in Class I where the quality of groundwater in

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

**Figure 7.** *Value of COD parameter by station and season.*

Kapas Island showed no organic pollutants that exist from domestic sewage from residents or tourists. This is due to the widespread usage of COD to determine the concentration of sewage wastes and is used mainly for a mixture of pollutants such as domestic, industrial and biological sewage [25].

**Figure 8** shows the readings of the NH3-N parameter with the NH3-N concentration for each observation station ranging from 0.01 mg/l to 3.5 mg/l. The majority of the sampling taken and analyzed obtained Class I which is a reading of <0.1 mg/l and only one outlier sample recorded Class V with a reading of 3.5 mg/l as based on the DOE's WQI classification. NH3-N parameter usually indicates that a body of water has been contaminated by domestic sewage waste, that is, human feces [5, 9].

**Figure 8.** *Value of NH3-N parameter by station and season.*

#### **Figure 9.** *Value of TSS parameter by station and season.*

It is possible that at S2, groundwater had been polluted as a consequence of tourism activities which is sewage waste that was not well managed causing the NH3-N value to be high in the observations made during the NEM. Nevertheless, the analysis of the study found that the majority of the sample obtained an nd status. During the SWM observation, all stations from S2 to S4 obtained an nd reading while during the MT at S1 and S3 as well as during the NEM at S3 and S4.

**Figure 9** showed the laboratory analysis on TSS and found that the values of TSS were within the range of 0–0.0012 mg/l. Based on the DOE's WQI classification, the TSS values for all stations were in Class I which is <25 mg/l. The maximum value recorded was during the SWM at S2 (0.0012 mg/l), followed by S1 (0.0005 mg/l) while at S4 (0.0001 mg/l) and at S3 no TSS was recorded which is 0 mg/l. TSS values were also recorded during the NEM with readings of 0.0005 mg/l at S4 followed by S3 (0.0004 mg/l), S1 (0.0002 mg/l) and S2 (0.0001 mg/l). The average value during the MT was recorded at 0.0005 mg/l at S4 followed by the same values recorded at S1 and S2 which is 0.0002 mg/l as well as at S3 (0.0001 mg/l). The results of this analysis found that the sample obtained through the observations analyzed was water that was not contaminated and also contained less suspended solids.

Furthermore, this situation may be due to the groundwater taken had already gone through suspended solid filtration treatment before the water was being channeled to the tourist accommodation area. The results of the TSS test done in the laboratory may also come from fragments of suspended particles that exist or the condition of contaminated pipeline in the study area because the suspended matter in the water contained inorganic material or organic particles or water-insoluble. Inorganic solids are like clay, silt and other particles in the soil while organic matter includes plant fibers and microorganisms such as algae and bacteria [17].

#### **3.2 Determination of groundwater quality based on DOE's WQI Malaysia**

WQI is a very important indicator in knowing the quality status of surface or groundwater. This is carried out to ensure the suitability of water for various purposes such as domestic water supply sources, industrial activities and irrigation
