The movement of the subduction zone in the Southern Part of Java Islands, is impacted to the movement of Volcanic Arc in the West Java land. There are sign of a series of Tertiary Volcanic Craters observe in the South of Cianjur Regency (Kencana Mount (+1200 masl) and Gambong Mount (+675 masl). Samples of lavas flow taken from both those mountain shown that the lava types is basaltic. Based on the petrographic analysis this lava is a Porphyry Basalt. This Porphyry Basalt has been very high altered, means had been deformed several times during tectonic era. This discovery data then compared with the variation of lithology, product of Gede Mountain (Quartery Volcanic). The variation of lithology are dominantly by tuff, lapilli tuff, volcanic breccia and lava flow. Based on the petrographic analysis on this lava flow, the type of the lava is Porphyry Andesite (Intermediate Type). The correlation analysis between 2 (two) deep bore hole in the Lower Zone of research area, shown that there is barrier that separated these two of volcanic succession deposit era. It is interpreted that there is a big basin in between teritary volcanic and quartery volcanic. This basin then filled by eruption material of Gede Mountain.
Result of the hydrogeology mapping on the Upper Area shown that ranges of Temperature are 20o – 22oC, pH : 6,2 – 7,2 and Electric Conductivity : 90 – 280 S/cm. This physical parameter is associated with the interaction of the quartery volcanic deposit. It is also confirmed by the Piper analysis, that shown the groundwater chemical facies in the upper area is dominated by Ca HCO3 (calcium bicarbonate), Ca Mg HCO3, (Calcium-Magnesium bicarbonate), Mg Ca HCO3 (Magnesium bicarbonate) and Na HCO3 (Sodium bicarbonate). While the measurement on the Lower Area shown the result of physical parameter ranges has more wide variation. The measurement of Temperature are 24o – 28oC, pH : 5 – > 9 and Electric Conductivity :300 – > 1000 S/cm. Result from Piper analysis shown that ground water chemical facies is also varied, from Mg, Ca, HCO3 and existence of Mg, SO4 ,Cl, HCO3 . Based on this data result, it is confirmed that there is an interaction between ground water with old volcanic deposit. The existance of Sulphate and Chloride is also interpreted as the contact of ground water with the basement rock.