Nucleus (Jun 2019)
On the origin and residence time of water in the Lima aquifer
Abstract
Lima, the capital of Peru, and Callao form one of the largest urban centers in South America, with a total population of 10.9 million as of 2017. Three rivers supply water to Lima; however, water for municipal use is mainly taken from the Rimac and Chillon Rivers. Correlating the historic of Rimac flow with the static level of a well in Miraflores, 1 km from Pacific Ocean, was estimated that the residence time, this is the time passing after water infiltrates the ground during a rainfall event until it reaches the Miraflores well, is three years, which agrees with the permeability of the valley, which is in the order of 10-4 ms-1. The average age of water from Lima wells is 6 years, which is consistent with the hypothesis that wells have water from several soil shells. In other hand, the relative abundance of 2H and 18O in wells in the Lima aquifer are in agreement with the hypothesis that the aquifer is recharged with water from rainfall events that occur in the highlands between 3000 and 5000 m above sea level (a.s.l). The contents of 2H,18O, Ca and SO4 of the Graton tunnel sample suggest that it corresponds to water coming from altitudes of 4500 m a.s.l.
