Rehabilitation of the Water Tower (AL-001), Alcatraz
The Alcatraz Water Tower is a 250,000 gallon elevated steel water tank designed in 1939 by the Chicago Bridge and Iron Works. It was purchased by the Federal Bureau of Prisons and erected by contractors in 1940. The empty steel water tank and tower has not been maintained since the Prison closed in 1963 and is badly deteriorated from exposure to the harsh marine environment. The Alcatraz Water Tower is a contributing structure to a National Historic Landmark District and work on the structure must meet the Secretary's Standards for the Treatment of Historic Properties. The tank is also an interpreted site of Indian Conscience in as much as it was used as a sign during the Indian Occupation and occupation graffiti will be re-painted and interpreted. The tank will not function to hold water for head pressure to the island's fire sprinkler system. Research into this notion by GOGA concluded that upgrades needed would be too costly and needed structural augmentations would have negative visual impacts. Alcatraz is also a nesting ground for regionally significant migratory sea birds that are protected from disturbance and harassment under the Migratory Bird Treaty Act. Limiting potential disturbance to nesting birds from construction activity on the Water Tower is a necessary constraint with cost implications and scheduling requirements.
Existing Conditions Summary
Since the structure is proposed to be empty, the tank is generally in sound structural condition. Deterioration is evident in rusted members and connections that have lost steel thickness and soundness. Lattice laces need to be removed, and in the case of the horizontal struts replaced in order to achieve structural performance in high winds and avert a safety hazards in the future. Deterioration has occurred in nuts connected to foundation bolts, foundation angle plates, rivets, and steel laces on columns. These elements were determined not to contribute to the structural integrity of the tank and will for the most part will either be repaired by welding or removed in order to minimize hazards to workers on the Project and the need for future maintenance. Deterioration appears at the connection of the tank to the columns (column caps) and on rivets connecting sections of the tank skin. Repairs to the skin, by welding new plates to the exterior, are required to extend the life of the structure. Components of the access ladder and cage and the roof eaves are in poor condition and were already mostly removed by the NPS in 2007 to avert closure of the east road and mitigate safety hazard from falling debris in high winds. The condition of the roof is poor and the roof will require complete replacement. The catwalk (tension ring) is an essential structural element and appears to be in good condition. Deterioration is evident in rusted members and connections that have lost steel thickness and soundness, particularly at the column caps, but this does not affect the ring's structural integrity. In general, repairs to deteriorated structural steel, stabilization of the bowl and tank, replacement of the roof, cleaning and re-coating the structure is required to extend the life of the resource and has become the revised scope of work of the Project.
The NPS contracted with MTM Builders, an 8a construction firm, to stabilize the iconic structure in a design-build project (the Project) in 2011. A notice to proceed limited to mobilization and scaffolding was issued on October 03rd, 2011 and a full notice was issued on October 28th, 2011. Work is in progress with a scheduled completion in July 2012.
NPS Project Manager