For a proposed level of stress, ninety percent of consolidation occurred in 15.8 minutes (t90=15.8min) for a laboratory consolidation test of a 12.7 mm thick clay specimen. In the field a 6.5m layer of the clay is sandwiched between sand layers. How long will it take for 50% and 90% consolidation to occur in the field deposit of clay? How long will it take if the field clay layer is bounded on the bottom by an impervious material?