Derek Ross, head of museum construction, despaired as he stared into the colossal 80-foot pit where workers were digging out the basement for the new African American history museum. The huge excavators had broken into a hard clay soil that encased much of Tiber Creek, which was buried 150 years ago. Over the decades, the soil had formed a pressurized cushion around the underground aquifer that held up other buildings on the Mall. But now, it seemed in danger of collapsing.
The water was rushing out of the aquifer more quickly than it was being replenished by the creek. It was the same aquifer that flowed under the Washington Monument, a mere 800 feet away. Ross worried that if the cushion collapsed, the monument would shift or, worse, topple over. When he closed his eyes, he saw a giant sinkhole.