11. Walden Pond is a perfect glacial " kettle, " fed by underground spring and rainwater. 12. The cause was thought to be underground springs released during the pile driving and excavations. 13. When digging the foundation, excavators discovered an underground spring . 14. It is nicknamed " the city of waters ", because of its abundant underground springs . 15. The lake salinity increases towards the middle and northern parts due to underground spring waters. 16. It may also be found near underground springs . 17. It continued until the 1960s when small underground springs made the extraction too expensive to continue. 18. "When they were moving dirt to build what's now turn 11, they found an underground spring ," 19. The source of much of the water comes from cold underground springs rising from a bedrock aquifer. 20. Upon return all that was there was pools fed by an underground spring but no vigorous water.
