ENVIRONMENT

Plant Contamination Investigation Set: The U.S. Environmental Protection Agency said Shell Oil Co. and Dow Chemical Co. have agreed to investigate soil and ground water contamination at a proposed Superfund site in the Carson area. Shell and Dow estimate the cost for the work at the Del Amo plant site--bounded roughly by Del Amo Boulevard on the south, 190th Street on the north, Normandie Avenue on the west and Hamilton Avenue on the east--at $10 million, EPA officials said. The EPA will collect about $450,000 and the state of California another $450,000 in costs from Shell and Dow for work already performed at the site.