74 The 2 nd International Seminar on Science and Technology August 2 nd 2016, Postgraduate Program Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia Groundwater Analysis Using Vertical Electrical Sounding and Water Quality Tester in Sukolilo Area, Surabaya, East Java: Significant Information for Groundwater Resources Fuad Aulia Bahri 1 , Hasibatul Farida Rismayanti 1 , and Dwa Desa Warnana 1 Abstract This research purpose to find out groundwater quality and environmental pollution that has occurred in aquifer of Sukolilo, Surabaya, East Java. Vertical Electrical Sounding is a geoelectric method to measure the resistivity of the rocks. This instruments is used to obtain subsurface information about aquifer depth. Water quality tester is used to know water quality by measuring acidity, conductivity, salinity, Oxidation Reduction Potential, and Total Dissolved Solid parameter. The result shows that aquifer has about 3.17 m thickness and lied at 0.45 to 3.62 m with lithology of alluvium. Lithology changes toward the north shown by different depth of the layers of rock. There has been sea water intrusion in groundwater aquifer at Sukolilo area. It was shown by high salinity and high Total Dissolved Solid parameter of some water samples with the higher values approaching sea. Therefore, it can be concluded that water from the unconfined aquifer in Sukolilo was polluted and not worthy for consumption. KeywordsAquifer, Groundwater, Geo-electric, Water Quality. I. INTRODUCTION 1 Surabaya is the second largest city in Indonesia that become center of commerce and service with high inhabitant mobility. One of the district in Surabaya is Sukolilo. This area continues to develop significantly in commerce, industry, and education sector. The development of an area synonymous with the high number of people which indicates an increasing of water necessity. Therefore, ground water exploration will be higher and it will decrease ground water supply in aquifer layer. This condition can cause sea water (bigger mass) intrusion into aquifer and make ground water become brackish water or brine water. The decreasing of ground water supply that happen in coast aquifer makes hydrostatic imbalance between ground water and brine water. Sea water intrusion occur when ground water hydrostatic pressure is lower [1]. Sea water intrusion is a form of pollution and impact in various aspects of life such as health problems, declining soil fertility, damage to building foundations, etc. [2]. Therefore, it is necessary to study in order to determine groundwater aquifer layers that have been intruded by brine water. The use of geophysics for engineering studies and water groundwater exploration has been growing over the last few years due to the rapid advances in computer software and associated numerical modeling solutions. The 1 Fuad Aulia Bahri, Hasibatul Farida Rismayanti, and Dwa Desa Warnana are with Department of Geophysical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia. E-mail: Vertical Electrical Sounding (VES) has proved very popular with groundwater prospecting and engineering investigations due to simplicity of the techniques. The electrical geophysical survey method is the detection of the surface effects produced by the flow of electric current inside the earth. The electrical techniques have been used in a wide range of geophysical investigations such as mineral exploration, engineering studies, geothermal exploration, archeological investigations, permafrost mapping, and geological mapping. II. LITERATURE REVIEW A. Groundwater Groundwater is a water found beneath the surface, precisely at the fracture and the gaps which exist in soil particles, sand, and rocks under the earth's surface. Groundwater is stored below ground level and move slowly in a very low pressure through geological formations soil, sand, and rocks called the aquifer. The ground water will not always be in the ground, this is because at some point the water will return to the surface or washed out to sea. Therefore, aquifer is a point where the ground water back to the surface from underground. Aquifer is a rock that is able to drain water such as gravel, sand, or sandstone (Figure 1). Aquifer there are naturally occurring and some are made by humans. Aquifers can also be used as a water supply for the community. Figure 1. Groundwater Aquifer (Harlan et. al., 1989) B. Hidrogeology Surabaya Surabaya is a city with an area of approximately 33 048 ha and is divided into four regions, namely Central Surabaya, East Surabaya, West Surabaya, and South Surabaya. Surabaya has 31 districts with 163 villages, a ground height of 0-20 meters above sea level, and a height of beach from 0-3 meters above sea level Fuad13@mhs.geofisika.its.ac.id; farida13@mhs.geofisika.its.ac.id; dwa_desa@geofisika.its.ac.id.