Environmental activist Penny Newman said an independent study has found "extremely high levels" of a toxic chemical in the tap water of a law office near the Stringfellow Acid Pits in Riverside County. State officials dismissed the study because the laboratory that did it is not certified in California to test drinking water. Newman said an analysis of tap water from the Glen Avon area, conducted by National Testing Standards Inc. of Anaheim in April, turned up perchloroethelyne in levels of 593 parts per billion. That would be one of the highest results ever found in drinking water in California, state water experts said. Chet Anderson, regional sanitary engineer for the state Department of Health Resources, said, "In our opinion the results are invalid" because the test was "not done by a laboratory we have credence in." National Testing Standards President Lewis West refused to comment except to say, "I stand behind our work."