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.