▁the ▁lay ing ▁of ▁the ▁sub structure ▁m ason ry ▁beginning ▁as ▁soon ▁as ▁each ▁section ▁of ▁concrete ▁was ▁cast . ▁The ▁opera ▁house ▁needed ▁a ▁much ▁deeper ▁bas ement ▁in ▁the ▁subst age ▁area ▁than ▁other ▁building ▁types , ▁but ▁the ▁level ▁of ▁the ▁ground water ▁was ▁unexpected ly ▁high . ▁Well s ▁were ▁s unk ▁in ▁February ▁ 1 8 6 2 ▁and ▁eight ▁steam ▁p umps ▁installed ▁in ▁March , ▁but ▁despite ▁operating ▁continu ously ▁ 2 4 ▁hours ▁a ▁day , ▁the ▁site ▁would ▁not ▁dry ▁up . ▁To ▁deal ▁with ▁this ▁problem ▁G arn ier ▁designed ▁a ▁double ▁foundation ▁to ▁protect ▁the ▁super structure ▁from ▁mo ist ure . ▁It ▁incorpor ated ▁a ▁water ▁course ▁and ▁an ▁enorm ous ▁concrete ▁c is tern ▁( cu ve ) ▁which ▁would ▁both ▁rel ieve ▁the ▁pressure ▁of ▁the ▁external ▁ground water ▁on ▁the ▁bas ement ▁walls ▁and ▁serve ▁as ▁a ▁res er voir ▁in ▁case ▁of ▁fire . ▁A ▁contract ▁for ▁its ▁construction ▁was ▁signed ▁on ▁ 2 0 ▁June . ▁So on ▁a ▁persistent ▁legend ▁arose ▁that ▁the ▁opera ▁house ▁was ▁built ▁over ▁a ▁sub ter rane an ▁lake , ▁insp iring ▁Gast on ▁L er oux ▁to ▁incorpor ate ▁the ▁idea ▁into ▁his ▁novel ▁The ▁Ph antom ▁of ▁the ▁Opera . ▁On ▁ 2 1 ▁July ▁the ▁corner stone ▁was ▁laid ▁at ▁the ▁sout heast ▁angle ▁of ▁the ▁building ' s ▁fac ade . ▁In ▁October ▁the ▁p umps ▁were ▁removed , ▁the ▁brick ▁v ault ▁of ▁the