Introduction

 

            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 Missouri landfill were responsible for higher concentrations of Ag, Zn, and Cu in the stream sediments.  In a similar study, Mantei and Foster (1991) showed that two landfills were responsible for increased concentrations of Cu, Pb, Zn, Cd, Ag, and Ba in stream sediments.  Mantei and Sappington (1994) showed that a sanitary landfill was the cause of increased concentrations of Cu, Zn, Cr, and Pb in the stream sediments. 

The purpose of our study was to ascertain if the Fullbright landfill had emitted Cu, Zn, Ag, and Pb into the nearby South Dry Sac River.  My hypothesis is that the Fullbright landfill is emitting Pb, Zn, Ag, and Cu into the river and that these metals are being concentrated in the stream sediments.  I believe that the sediment samples taken downstream from the landfill will show higher metal concentrations than the samples taken upstream from the landfill.      

 

Location and Geology

            The Fullbright landfill is located in southwest Missouri approximately 2 km north of the city of Springfield (figure 1).  It was in operation from 1962 to 1968 and was on the Environmental Protection Agencies Superfund clean-up list from 1983-1992.  The Fullbright landfill was removed from the superfund active sight list in 1992, but ground and surface water monitoring continues today (http://www.epa.gov/ superfund /sites /npl/npl.htm).  The study area is geographically located within the Springfield Plateau, which is located within the Ozark Plateau (Mantei and Coonrod, 1989).  This region of Missouri has a humid temperate climate.  It receives an average of 86.1 cm of precipitation and has an average mean temperature of 13˚ C (Mantei and Coonrod, 1989). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


The geology of the region includes the Burlington, Pierson, Elsey, and Compton limestone formations as well as the Northview silt-shale formation.  These rocks are all Mississippian in age.  The sight of the Fullbright landfill was chosen based on the presumption that the Northview formation would act as an aquatard to prevent leachate material from reaching the aquifer below.

            The sediment samples were taken along the South Dry Sac River, which flows west and joins the Little Sac River and eventually the Sac River.  The Fullbright Landfill is located proximally to the northeast of the South Dry Sac River and any runoff or seepage from the landfill will be drained via the study stream.  The aforementioned streams are important natural resources and are used for recreational activities, agricultural irrigation, and industrial uses.  The area around the study sight also contains a wastewater treatment plant and a police shooting range.

 

Methods

            The South Dry Sac River site was chosen due to its proximity to the Fullbright landfill and the fact that the landfill was once on the EPA’s Superfund cleanup list.  Information from government records shows that the Fullbright landfill received industrial and domestic waste, including plating waste, metals, and paint sludge (http://www.epa.gov/superfund/sites/npl/npl.htm).  Metals, including Pb, Cu, Zn, and Ag, emitted from the landfill could have been deposited and concentrated on the stream sediments. This information was used to choose the metals for which we would test the stream sediments. 

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.

 

 

 

 

 

 

 

 

Metals

Sample

Number

Ag

 

Zn

 

Cu

 

Pb

1

1.2

 

54.6

 

18.8

 

36.7

2

1.8

 

65.9

 

22.0

 

35.2

3

1.7

 

55.3

 

18.5

 

33.7

4

2.2

 

101.0

 

33.7

 

44.5

5

1.7

 

54.4

 

23.8

 

38.6

6

2.1

 

54.1

 

28.0

 

39.0

7

1.8

 

41.9

 

17.7

 

69.0

8

1.4

 

37.2

 

9.2

 

34.5

9

2.9

 

72.6

 

19.9

 

96.8

10

4.1

 

101.2

 

53.8

 

63.1

11

2.3

 

175.0

 

75.9

 

102.9

12

1.1

 

167.4

 

71.7

 

59.6

13

1.9

 

131.9

 

55.4

 

45.2

14

2.2

 

224.8

 

55.7

 

71.8

15

2.0

 

137.4

 

60.7

 

84.5

16

3.5

 

220.4

 

66.6

 

88.4

17

2.9

 

239.8

 

97.5

 

84.2

18

5.5

 

184.9

 

50.4

 

57.9

19

2.4

 

188.2

 

65.0

 

60.2

20

3.9

 

200.8

 

75.8

 

79.7

 

 

Table 2.  The mean concentration (in ppm) of the metals in the sediments of the study stream.

 

 

 

 

 

 

 

 

Metals

 

Ag

 

Zn

 

Cu

 

Pb

Control

2.1

 

63.8

 

24.5

 

49.1

Test

2.8

 

187.1

 

67.5

 

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.

Statistical T-Test 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

Alpha Number

Metal

0.05

 

 

0.01

 

Zn

X

 

 

X

 

Cu

X

 

 

X

 

Pb

X

 

 

X

 

Ag

----

 

 

----

 

X: Represents Significant Difference

 

CONCLUSION

            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 South Dry Sac River.  The results of the atomic analysis and the t-test showed that the mean concentrations of Zn, Pb, and Cu were significantly higher in the samples collected downstream from the landfill than those collected upstream of the landfill.  From this data we can say with confidence that the Fullbright landfill is emitting Zn, Cu, and Pb into the environment.  Although the atomic analysis showed the mean silver concentration was fractionally higher in the test samples than the control samples, the t-test showed that the difference was not statistically significant enough to confidently report that the landfill is emitting silver into the environment.  Further studies on different heavy metals and extended distances from the landfill might prove interesting and educational.