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Mr. Robert Graulich Page 5 disintegrate into smaller particles) . Wadham, therefore, had to design a test method which would simulate the forces expected to be exerted upon the ash. To accomplish this, Wadham employed the services of ENSR and RJ Lee. The test method, detailed in the February 1991 ENSR report, involved placing varying amounts of ash into a cylindrical press and exerting forces up to 90 pounds per square inch (psi) on the ash (in a uniform compression method) . This method of testing was chosen because it was anticipated that "the most prevalent condition that might impose high, localized, forces that exceed the fracture stress of the ash is direct compression from heavy vehicles.2#v The results of this testing demonstrated that there was no consistent or significant increase in the amount of particles with a size of <10 microns. What the testing did demonstrate is that fracturing of the particles did occur, but was primarily observed in the larger particles, which fractured into particles from 11 ® 45 microns in size. Assessment of Risk: In determining whether a waste indeed poses a hazard which would warrant its regulation as hazardous waste, it is necessary to assess whether a risk is posed by that waste. Typically this risk is assessed by comparing the waste's characteristics to the criteria for identifying hazardous waste (the Article 11, 22 CCR criteria) . In this case, there is no specific numeric criterion to which the ash's silica concentrations may be compared. The definition of hazardous waste found in §2'5117, HSC states that a waste is hazardous waste if it, "because of its quantity, concentration, or physical, chemical, or infectious characteristics may either: (A) Cause, or significantly contribute to an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or (B) Pose a substantial present or potential hazard to human health or environment when improperly treated, stored, or disposed of, or otherwise managed" (emphasis added) . The terms "significantly" and "substantial" are not defined in statute or regulation, but are key to interpreting whether a waste is hazardous. Regulatory thresholds for compounds and constituents in wastes are created with these terms in mind, and incorporate risk assessment when they are established. The exposure scenarios envisioned are 2ENSR calculated the maximum forces which would be brought to bear on the ash by heavy equipment to be approximately 42.5 psi, the load anticipated from a truck loaded with ash.