Investigation of groundwater aquifer at Noborejo, Salatiga using Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES) methods

Local Water Supply Utility (PDAM) of Salatiga, Indonesia planned to build three new wells to meet the needs for clean water and increase the number of customers in Salatiga. The plans for the construction of the new wells are located in Randuancir, Kumpulrejo and Noborejo Sub-Districts. The groundwater aquifer layer in Noborejo Village is detected using the Electrical Resistivity Tomography (ERT) method, while the determination of the depth of aquifer layer will be controlled by the results of Vertical Electrical Sounding (VES) data processing. 4 ERT lines and 4 VES points were acquired in 2017. The processing results showed that water-containing layer tends to have a lower resistivity value. In the study area, 2 types of aquifers were found, namely unconfined aquifer (usually exploited using dug wells), and confined aquifer which are generally located on the deeper depth. Unconfined aquifers were identified with a lower resistivity value than its surroundings (20-80 Ωm) with an average depth of 25 m on all lines. Whereas confined aquifer has a higher resistivity in the range of 90 Ωm. However, confined aquifers are only found with certainty in Line 1, while in other Lines the possibility of a confined aquifers existence is smaller.