Garvey Reservoir Dam: Incident, Investigation and Repair

On November 14, 1989 the Metropolitan Water District of Southern California (MWD) notified the California Division of Safety of Dams (DSOD) that unusual seepage was being reported on Fulton Avenue, a residential street in the City of Monterey Park (City), adjacent to Garvey Reservoir Dam, shown in Figure 1. The Garvey facility is a major finished water reservoir owned and operated by MWD. A joint inspection of the dam, reservoir and surrounding area was made by DSOD and MWD staff on November 17, 1989. During the inspection it was confirmed that local groundwater was rising. Soggy lawns and free water within crawl spaces were observed at several houses. Piezometric levels around the southwest portion of the reservoir were also observed above normal and rising. There were, however, no visible defects or signs of seepage on the exterior of the hypalon covered reservoir. At the end of the inspection it was judged that if seepage was coming from the reservoir it was through the foundation and presented no immediate danger to residents located approximately 300 feet away from the downstream toe of the dam. Over the next few days MWD continued closely monitoring instrumentation while maintaining close surveillance of adjacent landscapes and increased investigative efforts to determine the source of seepage. Suspected sources were the reservoir, City of Monterey Park water tanks located next to the reservoir, distribution pipelines from the tanks, and an unexplained rise in the historically high regional groundwater table. On November 27, 1989 divers entered the reservoir and found an approximate 12 inch diameter hole in the asphaltic concrete lining in the southwest portion of the reservoir. DSOD was notified and semi-emergency reservoir evacuation was begun. The reservoir was completely drained by November 30, 1989. In the pages that follow, the investigations, theories for the cause of cracking, and plans for repairing the reservoir will be discussed. Also of interest to the state dam safety official will be a discussion of the public interest and opposition to placing the reservoir back in service and the steps taken to address public safety.