Unconfined Groundwater Dispersion Model on Sand Layers in Coral Island

The research objective is to analyze the sand layer to determine the characteristics of the unconfined groundwater aquifer on coral island and found the dispersion model of unconfined groundwater in the sand layer in the coral island. The method used is direct research in the field, laboratory analysis and secondary data. Observations geological conditions, as well as the measurement and interpretation of geoelectrical potential groundwater models based on the value of the conductivity of groundwater from 20 wells dug and 15 test wells in Satando Island the rainy season, the transition season and the dry season with Groundwater Modelling software. Geological mapping indicates Satando Island area is a coastal plain that is still active with the type of alluvial coast and the elevation of 0, 0 to 2, 3 meters. Interpretation of geoelectrical cross-section resulted in the composition of soil and rock layers vertically in the central part of the island consists of overburden (0 0, 5 m), fine sand - coarse (0, 5 3, 5 m), limestone reefs (3, 5 12 m), fractured limestones (12 39 m), limestone (39 57 m) and a solid limestone (57 78.8 m). Freshwater needs Satando Island residents 32.22 meter3/day. Dispersion model unconfined groundwater coral island in the rainy season to produce a layer thickness of fresh water in the central part of the island is 2.74 meters (-1.33 m below sea level), which produces the potential for fresh water in the sand layer is 10588.2 m3, which can be used only 2117.62 m3 are able to meet the needs of fresh water island residents. As the season transitions freshwater layer thickness in the central part of the island is only 2.10 meters (-0.93 m below sea level), which produces the potential for fresh water in the sand layer is 4688.9 m3, which can be used only 937.78 m3 are still able to meet the fresh water of the island residents but have had to wait 2-3 hours to get fresh water. During the dry season the thickness of the layer of fresh water in the central part of the island is only 1.54 meters (-0.53 m below sea level), which produces the potential for fresh water in the sand layer is 1375.9 m3, which can be used only 275.18 m3 ( water that is above a depth of 1.75 meters), supply of fresh water on the island is not able to meet all the needs of the residents of the island, so that should bring fresh water from the mainland to meet the needs of fresh water.