A rapid failure of approximately 900,000 cubic yards of fill and lake bed foundation soil occurred sometime between 7:00 a.m. and 8:00 a.m., on August 6, 1997. The 45-acre landfill was approximately 100 feet higher than Lake Michigan and slid on a layer of weak silty clay located 55 to 60 feet below the water surface of Lake Michigan. The horizontally-translating slide mass nearly blocked the operating intake flume to the No. 2 Intake Pump House for the steel mill cooling water. Figure 1 shows the plan location of the slide mass and scarp location. The slide mass extended approximately 1,000 feet from the southwest fill area to a location east of the cofferdam that holds an oil boom along the south side of the landfill next to the intake flume. Pre-failure and failure conditions with estimated slide plane location and scarp geometry for failure sections A-A, B-B and C-C are shown on Figures 2 through 4. The slide extended 200 to 300 feet north from the flume up to a 30- to 40-foot high scarp. The slide mass moved approximately a a 30- to 40-foot high scarp. The slide mass moved approximately 30 feet into the canal and moved the cofferdam structure at least 10 feet south. In fact, the slide mass filled more than 400 feet of the 25-foot-deep, by 140-foot-wide flume and nearly blocked the flume with only 3 to 4 feet of water flowing when the channel was 20 to 25 feet deep
