4.3 Ephemeral Dam Water Quality Water quality sampling of the ephemeral dam occurred on 3 November 2025 with results summarised in Table 18. These results have been compared to Australian and New Zealand Guidelines for Fresh Water Quality (ANZECC & ARMCANZ, 2000) default trigger values for toxicants for the 80% protection of aquatic ecosystems with exceedances highlighted in bold. Table 18. Ephemeral Dam Water Quality
Analyte
Unit
Value
Guideline Value
pH
pH unit
3.12
6.5-8
EC
µS/cm
4840
30-350
TDS
mg/L
3150
-
Sulfate as SO4
mg/L
3530
Aluminium (total) (ph < 6.5)
mg/L
45.1
-
Arsenic (AsV) (total)
mg/L
0.004
0.140
Cadmium (total)
mg/L
0.0007
0.0008
Chromium (total)
mg/L
<0.001
0.040
Copper (total)
mg/L
0.035
0.0025
Cobalt (total)
mg/L
0.321
-
Nickel (total)
mg/L
0.058
0.017
Lead(total)
mg/L
0.004
0.0094
Zinc (total)
mg/L
0.384
0.031
Manganese (total)
mg/L
55
3.6
Selenium (total)
mg/L
<0.010
0.034
Boron (total)
mg/L
0.21
1.3
Iron (total)
mg/L
14.7
-
Mercury
mg/L
<0.001
0.0054
Sampling results indicate that the ephemeral dam is highly disturbed characterised by a low pH, that is consistent with the water quality in the OCP and groundwater, elevated EC and exceedance of trigger values for some metals. Sulfate concentrations are elevated and consistent with sulfate measurements in the OCP and collected seepage water. Given the lack of contamination sources from any upstream location, it can be reasonably concluded that the Western Dump mine feature the only source of contamination that is contributing to the degraded water quality in the ephemeral dam. The sampling suggests that the western dump is a source of contamination, that if left unmanaged, will continue to contribute contaminants to surface water, groundwater and land receptors.
Project number: 25B061
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