Summary for Monday February 8th

After briefly discussing our homework assignment for the weekend on fish consumption advisories, we looked at the pollution and water quality implications of the combustion and post-combustion stages of the coal to power life cycle. Here are the highlights (or low lights):

Americans used 4119 million megawatts of electricity in 2008 (EIA)

~50% of this came from burning coal (EIA)

The NAS estimates that the burning coal costs the United States about $60 billion a year in health costs, mostly because of thousands of premature deaths from air pollution. Not only does this dwarf the coal mining industry's annual revenue of $25 billion (an oft-quoted number for which I was unable to find a reliable citation), it amounts to 7 cents per kWh which is actually greater than the utilities price!

In order two reduce the air pollution that results from coal combustion, ~50% of the CFPP in the US have been modified with scrubbers that substantially reduce emission of SO_X, NO_X, fly ash, and PM_2.5 into the air. The trade off is that the process leaves the plant with dirty water that must be treated (to varying degrees) before being released back into the environment.

In order to understand the pollution that is produced from coal combustion, it is useful to know the composition of coal (major elements = C,O,H,N,S with a wide range of many different elements present at minor and trace level). During coal combustion, C and O combine to make CO₂ (and CO), S and O combine to form SO_X, N and O to form NO_X, H and O to form H₂O, et cetera. This means that the major elements, for the most part form gasses that go out into the atmosphere and the residue (called coal ash) is a highly concentrated assemblage of all of the materials that did not burn. Most of this ash is composed of common (and relatively benign) oxides such as SiO₂, Al₂O₃, and Fe₂O₃; however, coal ash also contains toxic heavy metals such as Pb, As, and Hg (though Hg has a very low vaporization temperature and can go up the chimney quite nicely as well). Since coal ash represents about 0.1% of the original volume of pre-combustion coal, these toxic elements are now concentrated 1000 times their original abundances. The high surface area to volume ratio also increases the availability of any toxic material to percolating water and anyone who eats fly ash. Coal ash can be recycled, moved to a landfill or stored on site in large ponds. According to the American Coal Ash Association, 43% of the 130 million tons of coal ash produced in the US is recycled each year into building materials (mostly concrete). For an alternative look and recycled coal ash see here. Ash that is not recycled is commonly stored on site in open air ponds. The impermeable lining of these ponds prevents water from percolating through the ash and into the ground water carrying toxic material with it; however, the lining also affects the volume and mobility of the impounded coal ash. The incident in Kingston, TN that some are calling the worst environmental disaster in US history involved a very large coal ash pond whose dike failed spilling 5.4 million cubic yards of coal ash sludge. Preliminary reports from the TVA and the EPA both suggest that the spilled ash sludge contains low levels of many of the toxic elements commonly associated with coal ash. The independent study (.pdf)that we reviewed in class today, however, suggests otherwise.

Slides shown in lecture today have been posted as a .pdf to Sakai.

The my maps page has been updated with the locations mentioned in today's lecture.

For Wednesday, please read Chapter 9 in Applied Principle of Hydrology (Chemical Quality of Natural Water).