It
has been shown in numerous studies that landfills, point sources, and non-point
sources emit concentrations of undesirable materials into the environment. Mantei and Coonrod (1989) showed that
emissions from a southwest
The purpose of our
study was to ascertain if the Fullbright landfill had emitted Cu, Zn, Ag, and
Pb into the nearby
Location and Geology
The
Fullbright landfill is located in southwest
The geology of the
region includes the
The
sediment samples were taken along the
Methods
The
Sample Collection
Twenty sediment samples were collected from the study stream. The locations of the collection sites are shown in figure 1. These sites were chosen based on the location of the landfill and the direction of water flow. The samples one through nine are the control samples that were collected up stream from the landfill. Samples ten through twenty are the test samples that were collected adjacent to the landfill. The samples were collected at sites with abundant amounts of available fine sediments and at significant but random distances from each other.
The latitude and longitude of each site was found and saved on a handheld GPS device. Sediments from each site were then wet sieved in situ to a grain size between 0.105mm-0.074mm. Mantei and others (1993) found that controlling the grain size in testing for heavy metals resulted in more significant results. Metals adhere preferentially to finer-grained sediments, which will generate more accurate and significant data in our study. The sieved sediments were placed into sealed sample jars and labeled with the corresponding site number. By this method, we hoped to show metal concentrations that were constant upstream from the landfill and then increased sharply as the emissions from the landfill affected the stream sediments, suggesting an epigenetic source.
Preparation and Chemical Extraction of Metals
The sediment samples were taken back to the lab where they were prepared for analysis. The samples were dried and disaggregated and one gram of each was weighed out and placed in a clean sample bottle. 20 mL of 3M HNO3 was then added to each bottle and the bottles were placed in an 80.0˚C water bath at 40 rpm for twenty hours. The samples were then centrifuged at 4500 rpm for three minutes and the solutions were poured into clean sample bottles for analysis. The concentration of Ag, Pb, Cu, and Zn in each sample was determined using an inductively coupled plasma atomic absorption spectrometer.
Results and Discussion
Metal Content of Samples and Trends of Analysis
The concentrations of Ag, Cu, Zn, and Pb in each sediment sample are shown in table 1. Figures 2 and 3 show the trends of the concentrations of metals versus the sample sites. The mean content of Ag, Zn, Cu, and Pb are shown in table 2, with sites 1 through 9 and the control sites and sites 10 through 20 as the test sites. Zinc, Cu, and Pb all show significantly higher mean concentrations in the test samples than in the control samples. The mean Ag concentration is higher in the test than the control samples, but only fractionally.
Table 1. Concentrations (in ppm) of the metals in
the sediments of the study stream. |
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Metals |
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Sample Number |
Ag |
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Zn |
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Cu |
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Pb |
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1 |
1.2 |
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54.6 |
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18.8 |
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36.7 |
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2 |
1.8 |
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65.9 |
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22.0 |
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35.2 |
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3 |
1.7 |
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55.3 |
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18.5 |
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33.7 |
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4 |
2.2 |
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101.0 |
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33.7 |
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44.5 |
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5 |
1.7 |
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54.4 |
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23.8 |
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38.6 |
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6 |
2.1 |
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54.1 |
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28.0 |
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39.0 |
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7 |
1.8 |
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41.9 |
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17.7 |
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69.0 |
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8 |
1.4 |
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37.2 |
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9.2 |
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34.5 |
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9 |
2.9 |
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72.6 |
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19.9 |
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96.8 |
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10 |
4.1 |
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101.2 |
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53.8 |
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63.1 |
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11 |
2.3 |
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175.0 |
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75.9 |
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102.9 |
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12 |
1.1 |
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167.4 |
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71.7 |
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59.6 |
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13 |
1.9 |
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131.9 |
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55.4 |
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45.2 |
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14 |
2.2 |
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224.8 |
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55.7 |
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71.8 |
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15 |
2.0 |
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137.4 |
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60.7 |
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84.5 |
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16 |
3.5 |
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220.4 |
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66.6 |
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88.4 |
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17 |
2.9 |
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239.8 |
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97.5 |
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84.2 |
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18 |
5.5 |
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184.9 |
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50.4 |
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57.9 |
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19 |
2.4 |
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188.2 |
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65.0 |
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60.2 |
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20 |
3.9 |
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200.8 |
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75.8 |
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79.7 |
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Table 2. The mean concentration (in ppm) of the
metals in the sediments of the study stream. |
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Metals |
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Ag |
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Zn |
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Cu |
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Pb |
Control |
2.1 |
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63.8 |
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24.5 |
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49.1 |
Test |
2.8 |
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187.1 |
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67.5 |
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73.4 |
Landfill
Trends, Comparisons, and Specific Metal Comparisons
The Zn, Cu, and Pb
concentrations show a significant increase beginning at site 10 and remaining
high through site 20. As I hypothesized,
this would be expected if the Fullbright landfill were emitting these heavy metals
into the stream. While the mean Pb
concentration was higher for the test sights than the control sites, sample
sites 9 and 11 had the highest concentrations of Pb. I believe that the police shooting range just
upstream from these sights may have something to do with this result, but more
testing would have to be done.
Landfill
The silver concentrations for each sample site do not show a steadily higher amount of silver in the test sites versus the sample sites. This may be a result of the clean up efforts that took place from 1983 – 1992. If the majority of the sources emitting Ag were terminated and the stream sediments were purged of most of their silver content, then sporadic results such as ours might be expected. It is also possible that Pea Ridge Creek, which flows into the South Dry Sac River between the control and test sample sites (see figure 1) has diluted the stream sediments which would cause lower than expected results.
A two-sample t-test assuming an equal variance in the samples was run on the mean control and test values for each metal. The results of this test are used to determine if there is a statistically significant difference between the test and control mean concentrations in each metal, the results are displayed in table 3. The t-test was performed at an alpha level of 0.05 and 0.01. A significant difference using the 0.05 alpha number results in a 95% confidence level that the landfill is responsible for the increased concentrations of metals found. A significant difference using the 0.01 alpha number results in a 99% confidence level that the results of the concentration analysis are significant.
The results of the t-tests support the concentration analysis results. Copper, Pb, and Zn show significant differences in the control and test mean values at the 0.05 and 0.01 alpha numbers. Silver does not show a significant difference in the control and test values for either the 0.01 or the 0.05 alpha numbers.
Table 3. T-Test Results for Two Sample Comparison
with Equal Variance |
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Alpha Number |
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Metal |
0.05 |
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0.01 |
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Zn |
X |
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X |
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Cu |
X |
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X |
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Pb |
X |
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X |
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Ag |
---- |
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---- |
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X: Represents Significant
Difference |
The
purpose of this study was to show whether or not the Fullbright landfill was
emitting Pb, Zn, Cu, and Ag into the environment through analysis of sediments
taken from the nearby