Three lakes in the University of Waikato act as stormwater detention systems. Stormwater from various sources in the campus is directed into the Knighton Lake, Oranga Lake and Chapel Lake. As part of the detention system, the lakes are expected to allow some contaminants to be deposited into the sediments.
For each of the three lakes, sediment samples are taken from ten different locations within each of the lakes. The sediment samples are examined for five particular metals. These are Nickel (Ni), Copper (Cu), Zinc (Zn), Arsenic (As) and Lead (Pb).
The purpose of this report is to find out what the level of each metal contaminant in ...view middle of the document...
27 | 25.35 | 249.13 | 4.21 | 24.67 |
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The Oranga Lake results when compared against the guidelines showed that nickel and lead levels are below the trigger value and the arsenic, copper and zinc are above the trigger value. Zinc level is found to be at extremely high levels, it is 1,092 ppm higher on average in comparison to the ISQG-High value.
Table 3. Metals concentration in sediments from Chapel Lake,
University of Waikato, 2000
| Ni | Cu | Zn | As | Pb |
minimum (ppm) | 5 | 15 | 52 | 5 | 78 |
Maximum (ppm) | 8 | 26 | 247 | 9 | 177 |
Mean (ppm) | 6 | 20 | 106 | 7 | 137 |
standard Deviation | 0.92 | 4.17 | 60.06 | 1.37 | 35.11 |
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The Chapel Lake results when compared against the guidelines showed that nickel, copper, zinc and arsenic are below the ISQG-Low value. The level of lead in the sediment is found to be at a high level, below the ISQG-High value but is above the trigger value of 50 ppm.
In each of the three lakes, nickel is the only metal contaminant in the sediments that is below the levels recommended in the ANZECC, 2000 guidelines. Meaning that little or no further nickel metals are entering the lakes, we could conclude that nickel found in the lake is naturally forming. Zinc levels for both the Knighton and Oranga Lakes are very high. From the stormwater map the lakes that have high levels of zinc and arsenic has a lot of stormwater directed to it and has minimal amount of vegetation.
The zinc level in the two lakes is at a high level and I consider it to be a problem. One major effect of increased zinc level in the lakes is that the acidity level will increase. Another is that some fish can accumulate zinc in their bodies. A possible source for the amount of zinc in the lakes is the use of zinc as coating on steel to avoid corrosion. Many building in the campus have a corrugated roof coated with zinc to avoid rusting.
The Chapel Lake showed the least amount of contamination in all five metals tested, the only metal above the trigger level is the lead concentration (Table 3). Based on this, we can assume that the Chapel Lake is healthier than the other two lakes. This could be due to the smaller size and more vegetation...