The president of a Ventura chemical company was arrested for investigation of illegally dumping toxic wastes into the Ventura River, authorities said. There was no major threat to the coastal city's drinking water supplies, but some private water supplies for local ranches and industry will be tested, said Gary Gilday, a Ventura County Environmental Health Department supervisor. Arrested was Ray Earl Martin, 53, president of oil field chemical producer Chem-O-Lene Inc., Deputy Dist. Atty. Barry Klopfer said. Martin, the first Ventura County businessman to be arrested under a revised state law that took effect Jan. 1, was released on his own recognizance pending arraignment April 15. The company is accused of allowing petroleum hydrocarbons, benzene, toluene, xylene and methyl alcohol and other contaminants to flow into the river.