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Mr. Kevin T. Haroff Page 4 According to Wadham's November 22, 1989 letter and the SWL reports, particle size was determined following "ASTM E-11" procedures. ASTM E-11 is not an analytical method, but rather, a specification for screen construction. In conversations with SWL, representatives of SWL have stated, and the Department concurs, that there are limitations associated with the use of ASTM E-11 screens (or any screening method) when attempting to measure very small silica particles. This is particularly true when screening silica because the electrostatic charges of the small particles cause them to adhere to the screens, as well as to larger particles in the sample. These electrical charges also cause agglomeration of the smaller silica particles. The degree to which mechanical shaking reverses this trend is not quantified in Wadham's letter. In the appendix to Wadham's November 22 letter, it was stated that "the sieve test involves a certain amount of mechanical shaking that can break up the test material [ash] into finer particles, thus tending to overstate the amount of small-sized particles present in the sample. " "Despite this fact," it was stated, "virtually no ash penetrated a 400 mesh, 37 micron screen, in any of the samples analyzed for Wadham and OEC [Operational Energy Corporation] . " The samples collected by the Department and analyzed by AIHL showed a m2an of 0.475 percent of the ash, by weight (from samples NR1 and NR2 ) are within the range of one and ten microns (µm) . The concentration at the upper 80 percent confidence limit is calculated to be 1. 16 percent. These results were derived using scanning electron microscopy and sonicating sifter techniques. The AIHL analysis did not, however, distinguish which portion of the ash samples were free crystalline silica and which were amorphous silica particles. Wadham's March 9, 1990 report (prepared by ENSR) , included results from RJ Lee for two ash samples. One of the samples was noted to have been taken from the "bag house, " and the other from the "surge bin." RJ Lee's January 30, 1990 analytical report, states that the samples were analyzed using a scanning electron microscope, and reports that in the surge bin sample, 97.2 percent of the particles were less than five gm in size, and in the bag house sample, 93.2 percent of the particles were less than five µm. No differentiation was made in this report between free crystalline silica and amorphous silica. RJ Lee performed additional analyses on these samples, reported in the March 3, 1990 analytical report. The additional analyses were 2 The remaining four samples taken by the Department on November 21, 1989 were not analyzed.