The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .