277 Ill. App. The primary rule in statutory construction is to give effect to legislative intent. Ordinarily, the statutory language provides the best indicator of legislative intent, and where that language is plain and unambiguous, courts must give it effect without considering other indicia of legislative intent. Generally, courts give a great deal of deference to an agency's interpretation of a statute that it is charged with administering. However, an agency's interpretation is not binding and will be rejected if erroneous.
Sources belong to a single major industrial grouping when they have the same two-digit SIC code.
No party disputes that CCI owns and operates both plants. The SIC Codes CCI contends that the Board erred by concluding that the two plants constituted a single source even though they were classified under different two-digit SIC codes. The Board does not dispute that the two plants have different SIC codes, nor does it contend that the codes should be changed. In this case the plain language of the statute, as set forth above, clearly requires that if several stationary sources have the same two-digit SIC code, they must be considered to belong to a single major industrial grouping. Accordingly, an industrial grouping is defined by SIC codes.