Hydrochemical Study of Groundwater in Sidoarjo Mud Volcano Area, East Java Indonesia

Mudflow phenomena that was occured in the Porong, Sidoarjo since May 29, 2006 has resulted in environmenta l impacts. One of the impact is the decline in groundwater quality and the presence of gas bubbles in the wells of the population Hydrochemicha l analysis is used to evaluate the quality of groundwater, to know the genesis systems and groundwater aquifers. Hydrochemichalanalysis by Piper diagram show there are three groups of groundwater facies first is bicarbonate chloride facies, chloride bicarbonate facies and chloride facies. Analysis of isotope deuterium (δ2H) and oxygen-18 isotope (δ18O) showed that the water coming from the bubble is related to the hydrological cycle or meteoric water and groundwater around the center of the water spray is included in formation water. Multivariate analysis resulted in two groups: the groundwater in the area of wate r bursts originate from magmatic hydrothermal process while groundwater in wells comes from surface water. Compilation parameters total dissolved solids and dissolved ion of groundwater contamination is divided into three zones, namely a low polluted zone, middle polluted zone and high polluted zone with groundwater pollution spread pattern trending east/northeast in the direction of unconfined groundwater flow. The water that comes out with mud from the center bursts are thought to origina tefrom the volcanic sandstone confined aquifer lithology, the Upper Kalibengformation,Pliocene age.