QUESTIONS FROM A FALL SEMESTER FINAL EXAM

Geology and Geophysics 392: “Environmental Geochemistry, Living Dangerously”—Assistant Professor Kevin G. Harrison

1. A pond contains small, medium, and large fish. The medium fish eat the small fish, while the large fish eat the medium fish. The pond is contaminated with PCBs. To minimize the ingestion of PCBs, what size fish should you eat? Explain.

2. In 2002, you discover that your well water is contaminated with the toxic form of chromium (Cr VI). The recharge zone for your aquifer is a small pond located near an industrial site that changed ownership in 1964. Both of the owners of the site made chrome bumpers, so either could have been the source of the chromium. You take a core of the pond sediments and discover a Cr VI spike at 50 cm and a Cs-137 spike at 27 cm. Assuming a constant sedimentation rate, in what year was the Cr VI dumped into the pond? Explain.

3. Suppose Julia Roberts added 400 kilograms of nitrate to Lake Waban and Kirsten Dunst added 150 kilograms of phosphate to Lake Waban. How many moles of oxygen would be produced? Hint: You have to determine which nutrient is more limiting. The molecular weights: P=31, O=16, N=14.


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