Opinion ID: 1176318
Heading Depth: 2
Heading Rank: 1

Heading: Use of a Mathematical Model

Text: Petitioners challenge on essentially two grounds EFSC's use of a mathematical model to predict radon-222 concentrations. First, petitioners note that the values used for the model variables were based on averages of measurements of those variables; some measured values greatly exceeded the averages used in the model. Thus, although the model predicts annual average radon-222 concentrations, actual concentrations of radon-222 in some houses built upon the waste may sometimes exceed the threshold value. They argue that EFSC's calculation of annual average concentrations is meaningless because it does not show what percentage of houses built upon the waste would be expected to have radon-222 concentrations exceeding the threshold set by OAR 345-50-035. Second, petitioners note that measurements of radon-222 concentrations taken from test houses built on the sludge ponds exceeded the radon-222 concentrations predicted by the model. They argue that EFSC cannot rely on model predictions when those predictions are contradicted by actual measurements. Petitioners' argument that a predicted annual average radon-222 concentration has little significance for determining the threat to public health posed by TWCA's waste may well be valid. This is especially true in this case because the predicted radon-222 concentrations depend upon a large number of variables. EFSC has made no effort to estimate the statistical variation of these variables or the effect that variation has on the significance of its predicted annual averages. But these are criticisms that are properly addressed to the rule and the legislation adopting that rule rather than to EFSC's interpretation of the rule. The rule explicitly refers to annual average concentration, and the very basis for this court's prior remand to EFSC was EFSC's reliance on an expected range of radon-222 concentrations rather than on an annual average. Teledyne Wah Chang v. Energy Fac. Siting Council, supra . Whether an annual average concentration has much meaning for public health is not an issue under the rule; the rule assumes that compliance with the rule protects public health. Petitioners' argument that EFSC could not ignore measured radon-222 concentrations in the test houses built on the waste in favor of concentrations predicted by the model is more properly characterized as a sufficiency of the evidence argument rather than an argument over the proper interpretation of OAR 345-50-035. The rule does not require radon-222 concentrations to be determined only on the basis of concentrations measured in actual test structures. [9] That concentrations measured in test structures are at variance with predicted concentrations may cast doubt upon the validity of the predictive model or upon the values used for the variables in the model, but the variance alone does not necessarily require a finder of fact to conclude that the model cannot be used in lieu of measurements obtained in the test structures. Indeed, as EFSC stated in its order, a mathematical model may better predict annual average concentrations because a model, not being limited to the unique circumstances and features of a test structure, can incorporate more information. [10]