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NRS 212 Application Problem 11 - Contaminants Assignment
- Course
- NRS 212
- Institution
- University Of Rhode Island
Application Problem 11 - Contaminants Assignment with solutions.
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NRS 212 – Introduction to Soil Science Fall 2018______________________________________________________________________________
Application Problem #11
Please read and follow the rules provided in the Assignment Instructions
Honey BooBoo has a farm that has soil with a silt loam texture, an organic matter content
of 3.5%, a CEC of 8 cmol(+)/kg, and a pH of 5.0. Her farm overlies a shallow,
unconfined aquifer that is the source of drinking water for the town of South
Queenstown. A recent investigation by the State Police has revealed that for the past year
Ms. BooBoo has been charging for illegal disposal of a number of chemicals in her farm
(Table 1). The folks at the South Queenstown Water District have hired you to educate
them about the potential fate of these chemicals. Use the information in Table 1 to answer
the following questions:
1. Which contaminant is most likely to be retained in soil by partitioning into soil
organic matter? Explain
a. 4,4-dichlorobiphenyl is hydrophobic and is retained by proportioning into
the soil organic matter. This involves hydrophobic interactions between
the compound and the soil organic matter.
2. Which contaminant is least likely to be adsorbed to soil? Explain
a. 2,4-D will not be absorbed into the soil. It has a negative charge like soil.
It has very little affinity for soil indicated by the low value of KOC.
3. Which contaminant is most likely to be retained in soil by cation exchange?
Explain
a. Paraquat has a positive charge and since opposites attract it is the only one
that can be retained by negative soil particles.
4. Rank the contaminants with respect to risk of leaching to groundwater, from
highest to lowest, and explain the reasons for your ranking.
a. Absorption is the main process preventing the movement and transport of
compounds. The compounds can be ranked by their risk of leaching to
groundwater based on their KOC values. High values indicate that a
higher proportion of the chemical will be absorbed, with a lower
proportion left in the soil pore water, susceptible to leaching.
i. 2,4-D > DCBP > Paraquat
Table 1. Structure, solubility, Koc, and net charge of organic contaminants disposed of
illegally at Honey BooBoo’s farm.
Contaminant Structure Solubility in Koc Net
water (L/mg) charge
(g/L) at pH =
5.0
4,4’-dichlorobiphenyl
1 .0 X 10-6 1.6 X 104 None
Paraquat
6.2 X102 1.0 X 106 Positive
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