Menocal came from Cuba to the U.S. to attend Rensselaer where he graduated in 1862. Almost immediately he became assistant engineer and later chief engineer in charge of construction at the waterworks of Havana, Cuba. In 1872 Menocal entered the service of the U.S. Navy Department. He was commissioned chief engineer of all surveys made at Nicaragua. Menocal mapped the two most plausible routes for an interoceanic canal — initially working through the narrowest part of Nicaragua from 1872 to 1874. He favored a Nicaraguan canal, arguing that it possessed lower mountain passes and existing usable lakes and that a canal placed there would lie closer to American ports than one built across Panama. Menocal was invited to France in 1880 and was one of only a few American delegates asked to speak at the Congres International d’Etudes du Canal Interoceanic. He staunchly opposed Frenchman Ferdinand de Lesseps plan for a sea-level waterway through Panama.