It took two-and-a-half decades, a handful of prior trials, and multiple trips to the California Court of Appeal and back, but last week The Dow Chemical Co. and PPG Industries Inc. finally got the result they were seeking. After a six-week trial in San Francisco Superior Court, the companies secured a defense verdict in a lawsuit brought on behalf of the City of Modesto alleging perchloroethylene, or PCE, made by the companies and used by a local dry cleaner contaminated the city's groundwater.