Aliso Beach, a popular recreation area in Laguna Beach on the south Orange County coast, remained closed for a fourth straight day after a spill of 900,000 gallons of raw sewage. Lifeguards have posted signs warning of the possible danger of contamination, turning away beach-goers and sun worshipers while county health officials take water samples. "They will run the samples through tests to determine the bacteria count in each," said Art Tsuji, a South Coast Water District engineer. "Based on the results of those tests, the Health Department will decide whether or not to instruct the lifeguards to reopen the beach." Further samples were to be collected today and officials said the beach would probably remain closed at least until Tuesday.