Comparing soil found at a crime scene

A bike was stolen and the police dropped of a box of soil where the bike was stolen at, before we had the police soil, our group went out to collect some soil then we were to compare both soils and see if where we collected our soil was that of where the bike was stolen.

The purpose of this investigation is to compare the soils and the soil found at a crime scene and then see if these two soils then match up. We are trying to compare soil at a crime scene with the soil found around the school. Last week our group collected soil from around the school, we retrieved from the freshman court yard. We are using this soil to compare it to the crime scene soil.

Soil is important to Forensic Investigations because soils are like fingerprints because every type of soil that exists has unique properties that act as identification markers. The four categories of soil the loam, clay, silt, and sand. Our group was able to determine our soil texture by feeling our soil. We noticed that it was a mixture of clay and silt, possibly making it a silty clay loam.soils

pH is a measure of the hydrogen ion concentrated of a solution. pH test the acidity level and is tested on a zero- fourteen scale, zero being very acidic and fourteen being very alkaline. Between six and seven is a neutral pH. Soil analysis without a crime scene can also be helpful in finding the place where the crime was committed. Having acidic soil is the most common and is simply that the organic matter and minerals that break down in a soil overtime are acidic in nature, thus making the soil acidic. Having alkaline soil also referred to “sweet soil” soil that is alkaline usually contains large amounts of calcium, sodium, and magnesium, and it is less soluble than acidic soil.untitled

In the picture above this shows a comparison of pH levels of the two soils that we found. The soil on the left is our soil that we found at the crime scene was a pH of 8/9 which is more on the alkaline side but not drastic. The soil on the right is the soil that our group collected and had a pH level of 10/11 being even more alkaline than the soil found at the crime scene.

While comparing the soil at our crime scene to the soil we had collected is visually not the same. The soil at the crime scene feels gritty meaning it has sand in it. The soil our group collected is very chalky and a bit sticky with this information we can conclude that this soil contains silt and clay. The crime scene soil is a sandy loam and the soil our group collected is a silty clay loam.

soils

Top: Our group soil.    Bottom: Crime scene soil.

To determine our soil texture by using the soil texture triangle we measured the sand, silt and clay in mm. Then separately we took sand divided by the total amount of soil and then multiplied that by 100 and retrieved our percentage. The percentage for sand was 80%, silt was 16%, and clay was 0.0003%. As we calculate this on our Soil Texture Triangle we learned that our soil that our group retrieved was a sandy loam.

soil texture triangle2

 

We determined the soil texture by following the map above, In this map we determined the texture of the crime scene soil. When we did this with our soil that we got from around the school that came out to be a sandy clay loam. Clearly these two soils do not match and the soil that our group found was not at the crime scene.

Our group concluded that these samples do not match. I learned from this experiment that you can use soil to determine a crime scene by something as simple as a pH balance test. The question I still have about this soil analysis is that what if the soils do not match but have about the same pH balances? Is it possible that some of the crime scene soil and the soil that we collected have been in the same are? The next steps of this investigation should be to run more soil tests (chemical tests).

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