Investigation of the groundwater reservoir in the tropical coastal island of Sumatra to help mitigate the wildfires: a study case in Siak Regency-Riau

The wildfires are often triggered by drought and human activity, one of the main challenges when the wildfires happen is to access to freshwater sources. The aim of this research is to estimate the depth of groundwater stored in different surficial aquifers as the source of water to suppress the wildfires in the East part of Siak-Regency. Collecting the dataset using water level measurements in wells, 2D-resistivity, and ground-penetrating radar (GPR). These data were used to estimate the aquifer properties and provide additional information which can be used to identify optimal locations to install new groundwater wells. The research was conducted over a two-year period from 2016 to 2017. utilizing the resistivity method, GPR, and auger data all showed four easily identifiable subsurface layers. The surface soil in the study area is predominantly peat, with a depth ranging between 2m to 5.8m (bgs), resistivity values ranging from 80Ω-m to 100Ω- m, and EM velocities between 0.038m/ns and 0.048m/ns The sandy-clay loam is relatively impermeable and acts as a confining layer, with resistivity values between 40Ω-m to 80Ω- m. GPR signals in this confining layer are attenuated, The EM velocity values in the confining unit range between 0.12m/ns and 0.15m/ns. the auger was unable to penetrate further. Below the confining unit lies a sandy layer at depths between 8m and 14m (bgs) with resistivity values lower than 20Ω-m, the fourth layer was deeper than 16m (bgs), had resistivity values from 70 Ω-m-100Ω-m and was consistent with the Pleistocene clayey-gravels of the Kerumutan Formation (Qpke). The other results of our study indicate that the surface water from the studies area has quite a low PH (1.5 to 2.5), making them unsuitable for domestic use. Based on the results of this study is recommended that groundwater in the study area in eastern Siak Regency be screened in the confined aquifer, at a depth from approximately 8m to 12m.