Contribution of Isotopic Techniques in the Hydrological Study of the Aquifers of Ica, Villacuri and Lanchas

Abstract

Ica Aquifer located at the coastal zone of Ica River Valley, supplies 40% of the water to a number of farms of Ica Region which is one of the most productive valley of Peru that covers an area of 30,000 hectares of area, in which a diverse agricultural product are grown for local and external market. In the last 15 years, water-table of the aquifer was lowering at an elevated rate that concerned to farmers and authorities of the Peruvian Government, so a number of studies was carried out to increase the water supply to the agriculture areas.

The main purpose of the study using isotope techniques, was to have a first insight of the hydrodynamics of Ica, Villacuri and Lanchas Aquifers and the possible interconnection between them and with Pisco River. For such purpose, 31 wells, lakes, rivers and springs of Ica and Pisco Basin where sampled during the years 2014 to 2016 both in rain and dry seasons, getting 189 samples for isotope and chemical analysis. The sampling schedule didn’t include rain sampling, instead of it, selected springs were sampled and nearby basin rain data was used.

¹⁸O,²H and ¹³C stable isotopes and ³H, ¹⁴C radioactive isotopes of the water samples were analyzed in the laboratory of “Isotope Tracer Technologies INC”; the results of the stable isotope analysis confirm the hydraulic interconnection of the three aquifers mentioned above; it also was confirmed that the main source of recharge was provided by Ica River and evidences were found about the contribution of Pisco River in the recharge of Villacuri and Lanchas Aquifers.

Analysis of ¹⁴C reveals that some wells are overexploited. All the results of ³H analysis were out of range, so it was not useful for the conclusions of the study, and a new sampling of water is required; the reason of this out of range result should be the possible contamination of the samples with no environmental Tritium.