The goal our Experiment, was to find a relationship between the level of arsenic in the ground top soil, and its distance away from Ames Creek. What we hoped to do was take samples of top soil, at set distance intervals away from the creek. Then measure the level of arsenic in the soil samples by using INAA (neutron activation analysis), and then enter the information into a GIS database, so that others doing research could pull from the research we did.

The reason we want to do this experiment, is because it’d be useful to the people of Sweet Home, to know what the general concentrations of arsenic are along the creek. Useful specifically to farmers raising live stock, or growing plants, because arsenic is poisonous to both and it would be good for them to know the general safe distance to plant or let animals graze. It’s helpful also to people building houses along the creek, because once you reach a point out of the main city, wells have to be dug to supply water to the house, and it’s a good thing to know if you need to put in a filter to take out the arsenic.

Past research of arsenic let us know something about it already that were very useful to know about ahead of time. Arsenic occurs naturally in the environment, it cannot be destroyed, only change form. Arsenic mixes with other molecules, creating inorganic arsenic when coupled with oxygen chlorine and sulfur. Arsenic in things like plants and animals mix with carbon and hydrogen and make organic arsenic (Hilari’s Proposal). One way that the arsenic gets into the water is that the water will erode away things like rocks, and during this process, the arsenic gets into the water that broke it down (Hilari’s Proposal).

We thought that this experiment could also be very useful to scientists, because it would set up a method for other creeks and streams, that if it’s suspected that there are high levels of arsenic, can not only find out if there is. But can also make a way that would help people in areas up and down the creek, stream or river.

We thought that Ames Creek was carrying in the arsenic, and that it was depositing the arsenic in the soil as it went. Our hypothesis was that the levels of arsenic would be greatest near the creek, and become lower as the distance away from Ames Creek increased.

Materials List:

• Tape ruler at least 50m in length
• Comapass
• Shovel
• Plastic ziplock bags(sandwich size)
• GPS reader
• Sharpie pen
• INAA Facilities

Methods:

1. Traveled to Sweet Home where we took soil samples (Ames Creek area).
2. Chose the sites along the shore of the creek where we took the samples.
3. Identified the sites as site numbers (e.g 1, 2, 3 Etc…).
4. Used shovels to gather the topsoil from three different areas in close proximity to the center of the site. Got enough to fill the sandwich bag with a little soil from all three areas.
5. Placed the soil into the plastic bags and sealed the bags.
6. Marked the plastic bags with the corresponding site numbers and the sample numbers.
7. Took GPS readings at each of the site’s origin and recorded it.
8. Repeated steps 4 though 8 two more times at the same site for a total of three samples from one site.
9. Moved 50 meters in the direction going away from the creek (Used the tape ruler to measure the distance of 50 meters).
10. Did the same procedure as numbers as 3 through 9 twice more
11. Lastly, for the three spots along the river, we repeated steps 1 through 10 to complete the field part of the experiment.
12. Delivered the samples back at the CVHS Science department, where another class got the samples ready.
    1. Weighed the samples wet
    2. Set the Samples into a drying oven
    3. Measured the weight again to get a dry weight
    4. Mixed all the soil from each site to get a homogenous sample.
    5. Took about a gram of soil and placed into a special container provided by OSU
    6. Sent to the OSU Nuclear Reactor to be irradiated
    7. After irradiation, levels of arsenic were measured using INAA
13. Analyzed the data gathered, and made conclusions

Timeline:

Designing the experiment (7 days)

Crating all materials needed (2 months)

Gathering samples (1 day)

Getting samples ready to go to reactor (3 days)

Irradiation at the reactor (3 months)

Analysis of the data back from reactor (2 weeks)

List of Data:

• Arsenic levels of soil (in ppm)
• GPS coordinate locations
• Distance away from the creek

Now, many changes were made to the experiment. Because of the fact that we couldn’t send a whole lot of samples, our samples were not collected because there was not enough space. So because of this, we used other people’s samples to get data. Because of this we were limited to only 3 usable samples. All 3 were gathered by the other group, by taking a shovel to the ground, getting some top soil, and placing it in a bag from each sample site, then step 12 (a – g) and 13 were done to those samples. We took the data we could from the 3 samples and made our conclusions.

To find the levels of arsenic in the soil, we used a method called Neutron Activation Analysis (INAA). This process involves creating samples (by the procedures in step 12 of our methods) that were sent to the nuclear reactor at Oregon State University. There, they placed the samples inside the reactor for about an hour where they were bombarded by neutrons which stuck to all the atoms in the samples. After the hour, they were taken out, and placed inside a special lead box with a special counter, that counts not only the number of electrons that shoot off from samples, but the energy level at which they are shot off at. A standard was already tested, so that there was something to compare with so that we knew that the levels in Sweet Home soil samples were unusual, and this standard went through the same irradiation that the Sweet Home samples did. Using the explanation and formula given to us from Erwin who works at the reactor. The explanation is as follows: 2 samples are irradiated, a standard, and an unknown. After they are irradiated, they start to give off gamma radiation. This gamma radiation is counted using special detectors. The rate and energy level (or activity) of the gamma radiation is counted by the detectors. If the concentration (in ppm) and the mass (in grams) are known for the standard, and if the mass of the unknown sample is known, the concentration of the element (in this case arsenic) in the unknown sample can be calculated. This is done by equating the ratio of the concentration of arsenic in the unknown and the standard to the ratio of the activities of the unknown and the standard

After collecting our samples, measureing distances from the GPS coordinates, taking the samples to the reactor to get irradiated, and then using INAA to get the amount of arsenic (in ppm) in the top soil, we got our data. There isn’t however a lot of data because of the circumstances that happened after everything got under way (as explained in the methods section) and also because their wasn’t much data needed to answer our question and hypothesis. Attached on separate sheets of paper to the back of this report, are the data tables and graphs. The data sheet states in a pretty self explanatory way, all the data. The graph shows the amount of arsenic (in ppm) over the distance from Ames Creek.

The distances were measured after the samples were taken using a map and the GPS coordinates, giving the distances a large amount of error. The distances were also completely up surd to use because they were miles away and would’ve had no effect from Ames Creek. Because of this hypothetical data was used for the distances (also stated on the data table)

According to our data, the soil closer to the creek had more arsenic in it than that of soil farther away, which supports our hypothesis. However, because it only 3 samples, a definitive statement of universal truth can not be stated.

We think this happened because somewhere there is a large concentration of arsenic in rocks or some other source, which is being broken down by water. Arsenic is known to be carried by water and in this case, carried down Ames Creek, depositing the arsenic in the soil along the way since the concentration is less in the soil than in the water. This process of having once thing in high concentration going into a low concentration is known as diffusion.

Some things that would’ve made our experiment better would have been the ability to take our own samples first of all, instead of trusting someone else. Another way would be to take more samples. The samples would be extending from both banks of the creek, and at different intervals along the creek’s path.

The best and most logical step in our study would be to do what our ideal experiment would have been (as stated in last paragraph). Continuing far enough down stream to find the point where the arsenic levels are back at a safe level. And also upstream to find the general area that the arsenic is coming into Ames Creek.

Pauk, Hilari. (2004) Hilari’s Intro. [Online] Available:

http://www.geocities.com/soilcblock2003/intro.htm [January 28, 2004]