Hoover Dam was a monumental accomplishment for its era which set new standards for post-construction performance evaluations. Reclamation based many of their decisions on surveys of previous high dams to compare their physical, geologic, and hydrologic features with those proposed at Hoover Dam. Perhaps the greatest triumph was the hydroelectric power generation, which repaid the cost of the project with interest over a term of 50 years, which quickly became the economic model for similar high dam projects, world-wide. In the aftermath of the behemoth project, the project did suffer a number of unexpected failings, principally, the failure of the grout curtain to function as intended (requiring retrofitting between 1936 and 1948) and severe cavitation of the spillway elbows in 1941 and 1983 (requiring installation of air ducts in 1983-84). Along the way Hoover Dam was the first dam to be singled out as a terrorist target (by German agents) and provided electricity for the world's largest magnesium production facility from 1942 onward.