If anybody is interested in the computer modeling technique used by Calpine to determine the concentrations of pollutants at ground level, there is a document at the EPA web site named 40 CFR Part 51, Appendix W: Guideline on Air Quality Models at http://www.epa.gov/docs/epacfr40/chapt-I.info/subch-C/40P0051/40P051 XW.pdf. The most interesting part of the document is section 10.0 Accuracy and Uncertainty of Models. I found the following paragraph from the section worthy of more investigation:

"As noted in paragraph a of this section, poor correlations between paired concentrations at fixed stations may be due to ��reducible�� uncertainties in knowledge of the precise plume location and to unquantified inherent uncertainties. For example, Pasquill 82 estimates that, apart from data input errors, maximum ground-level concentrations at a given hour for a point source in flat terrain could be in error by 50 percent due to these uncertainties. Uncertainty of five to 10 degrees in the measured wind direction, which transports the plume, can result in concentration errors of 20 to 70 percent for a particular time and location, depending on stability and station location. Such uncertainties do not indicate that an estimated concentration does not occur, only that the precise time and locations are in doubt."

My understanding is there are two sets of meteorological data, one from the IBM plant and the other from the PG&E substation with differing wind patterns. I was told Calpine used the data from the IBM plant.

Sincerely,

Steven Nelson