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CHAPTER 4
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observed at sites S6 and S3, respectively. Furthermore, during summer, the highest groundwater temperature was measured at site S6 (26.9 ºC) whilst the lowest groundwater temperature was measured at sites S5 and LV (20.9 ºC). During spring, the highest and lowest groundwater temperatures were measured at sites S5 (20.4 ºC) and SG (34.2 ºC), respectively. Overall, the highest (26.48±4.31 ºC) and lowest (14.90±3.55 ºC) average groundwater temperatures were observed during spring and winter, respectively. Noticeably, the measured groundwater temperatures at all sampled sites were over 20 ºC during summer and spring. Additionally, the measured groundwater temperature at some sites during spring were above 30 ºC [S4 (33.4 ºC), DK (30.1 ºC), H (30 ºC) and SG (34.2 ºC)].
4.1.2 Total Dissolved Solids (TDS)
Total dissolved solids (TDS) are inorganic salts and small amounts of organic matter that are present in a water solution (Chang, 2005). During autumn the highest and lowest TDS values were measured at sites S6 (1482.37 ppm) and S4 (201 ppm), respectively. The TDS values of groundwater sampled during winter were also elevated with the highest and lowest values observed at sites S5 (1856 ppm) and BG (413.33 ppm), respectively. However, TDS values at sites BG, LS and LV were within the TWQR guideline. Additionally, the highest TDS value measured during summer was observed at site S6 (1399 ppm) whilst the lowest value was measured at site GM (121.3 ppm). Similar to the results observed in summer, the highest TDS values observed during spring were measured at site S6 (1302 ppm).
Nonetheless, the lowest TDS value during summer was measured at site S1 (340 ppm).
Thus, the measured groundwater TDS values were generally high during this study and exceeded the TWQR standards (0-450 ppm) (DWAF, 1996), Table 4.1.
4.1.3 Salinity
The amount of salt in water is measured as salinity. High salt levels in water interfere with the binding of dissolved oxygen consequently, reducing the amount of dissolved oxygen in the water. There are no TWQR guidelines available for salinity of groundwater. Site S4 (854 ppm) had the highest level of salinity during autumn, whilst site S7 (199 ppm) had the lowest salinity level in autumn. In winter, the highest and lowest nitrate levels were measured at sites S6 (855 ppm) and LS (213 ppm). Similar to the observations of winter, the highest salinity level measured during summer was observed at site S6 (700 ppm). The lowest salinity level during summer was observed at site GM (61.2 ppm). Lastly, groundwater from site S7 had the lowest measured salinity level (202 ppm) during spring. Overall, as depicted
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in Table 4.1, site S6 had the highest salinity level in winter, summer and spring. The trend witnessed during this study showed that the salt content was higher in colder seasons as compared to the warmer seasons.
4.1.4 pH
pH is a measure used to determine the acidity or basicity of an aqueous solution (Nola et al., 2002). All measured pH levels are presented in Table 4.1. Groundwater assessed at site S3 (8.2), during autumn, displayed the highest pH level whilst the lowest pH level was measured at site LV (6.7). Furthermore, the pH of groundwater during winter was highest and lowest at sites GM (7.89) and BG (6.5). These results were consistent during summer as both the highest and lowest pH levels were observed at sites GM (7.89) and BG (6.5) with the same pH measurements. In general, the pH measurements of groundwater collected during winter and summer, at the various sites, were in close proximity. Lastly, during spring, the highest and lowest groundwater pH levels were measured at sites S6 (7.43) and SG (6.58). Overall, the measured pH levels of all sampled groundwater, across the four seasons, were within the recommended TWQR standards (5.0 - 9.5) (DWAF, 1996). Also, there was no evident difference in the pH values when comparing the warmer (summer and spring) and colder seasons (autumn and winter).
4.1.5 Chemical Oxygen Demand (COD)
The amount of dissolved oxygen required in water to oxidize chemical organic materials is known as the chemical oxygen demand (COD) (Christensen et al., 1992). The COD levels for the duration of the study are summarized in Table 4.1. During autumn, the highest COD level was observed at site DK (16.45 mg/L) whilst the lowest COD level was measured at site S6 (0.76 mg/L). In winter, the highest and lowest COD levels were measured at sites S7 (72 mg/L) and LV (0.33 mg/L). Similar to the observations of winter, the highest COD level measured during summer was observed at site S7 (111 mg/L). The lowest OCD level during summer was observed at site H (1.07 mg/L). Similarly, groundwater from this site (H) also had the lowest measured COD level (0.33 mg/L) during spring. Lastly, the highest COD level during spring was measured at site S6 (111 mg/L). The COD levels of the groundwater systems of interest fluctuated for most sites throughout the duration of the study. However, elevated COD levels were more prevalent during the warmer seasons (summer and spring) as compared to colder seasons (autumn and winter). No TWQR standards are available for COD levels in groundwater (DWAF, 1996).
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4.1.6 Phosphates (PO
42-)
Phosphates are chemicals that comprise the element phosphorus and have an impact on water quality by producing excessive algae growth (Carpenter et al., 1998). The phosphate levels recorded for the duration of this study are documented in Table 4.1. During autumn, the highest phosphate level was observed at site S5 (4.3 mg/L) whilst the lowest phosphate level was measured at site S3 (0.01 mg/L). In winter, the highest and lowest phosphate levels were measured at sites S6 (1.02 mg/L) and S7 (0.03 mg/L). Whilst, the highest phosphate levels were observed at site S7 (0.96 mg/L), during summer. The lowest phosphate level measured during summer were observed at site LV (0.01 mg/L). This is similar to the results observed in spring where the lowest phosphate levels were also measured at site LV (0.1 mg/L). Lastly, the highest phosphate level measured during spring was measured at site S6 (2.9 mg/L). There are currently no TWQR standards for acceptable phosphate levels in groundwater. Nonetheless, groundwater phosphate levels measured during this study were below 5 mg/L.
4.1.7 Nitrate (NO
3-)
Nitrate is a type of dissolved nitrogen that naturally occurs in soil and water. It is the principal source of nutrition for plants which can be used as fertilizer (Sasakova et al., 2018). All nitrate levels measured in this study are summarized in Table 4.1. Site S6 (20.23 mg/L) had the highest level of nitrates during autumn, whilst site S1 (0.12 mg/L) had the lowest nitrate level in autumn. In winter, the highest and lowest nitrate levels were measured at sites DK (4 mg/L) and S1 (1.01 mg/L). Similar to the observations of autumn, the highest nitrate level measured during summer was observed at site S6 (4.1 mg/L). The lowest nitrate level during summer was observed at site H (0.67mg/L). Lastly, groundwater from sites FD and LS had the lowest measured nitrate level (0.89 mg/L) during spring. Overall, as depicted in Table 4.1, the lowest levels of nitrates were measured in site S1 (0.12 mg/L) and the highest levels of nitrates were observed at site S6 (20.23 mg/L) respectively. In general, the measured nitrate levels in the sampled groundwater were below the TWQR (<10 mg/L) and suitable for irrigation purposes. This is with the except for nitrate levels measured at site S6 during autumn. This phosphate level exceeded the current TWQR (DWAF, 1996).
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Table 4.1. – The physico-chemical groundwater quality analysis of samples collected throughout the four seasons in May 2019, July 2019, February 2020 and September 2020.
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Values of levels at all sites, as well as average values of levels of all sampling sites per groundwater are presented and ± standard deviation values. TDS - Total Dissolved Solids; NO3- - Nitrate, PO42- - Phosphate, COD - Chemical Oxygen Demand. BG - Botanical gardens, SG - Sportsground, LV - LaVaria, LS -Lareus, GM - METSI, DK - Draak, FD - Fanie; H - Hombre. TWQR - Target Water Quality Range; AVG – Average.
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