The Oceanside Water Pollution Control Plant is a wastewater treatment plant operated by the San Francisco Public Utilities Commission, in San Francisco, California, United States. The award-winning facility is noted for its mostly underground construction inside a hollowed-out hill. It is located between Ocean Beach and Lake Merced in the far-southwest corner of the city, near the San Francisco Zoo, and the California National Guard. OWPCP is a secondary treatment plant handling one-third of the city's wastewater. The maximum treatment plant capacity is 65 million US gallons per day, with the average daily dry weather flow of 17.5 million US gallons. Construction on the US$200 million, 12-acre facility began in January 1990 and was completed in June 1994. 70 percent of the structure is underground covered with 6 ft of earth and landscaping.