Dist. Ct. did not err in finding that attorney work product exemption applied so as to deny plaintiff’s FOIA request for copy of report prepared by consultant hired by govt. to assess responsibility of plaintiff and other entities accused of contaminating Fox River in Wisconsin. Plaintiff agreed that consultant’s report qualified as work product, and fact that govt. disclosed certain portions of report in prior consent decrees involving other entities accused of instant contamination did not serve as waiver of all related material in report. Ct. also rejected plaintiff’s claim that underlying factual material used to support author’s opinion in report was subject to disclosure under FOIA after noting that “factual” and “opinion” materials were both covered by FOIA work product exemption.