A groundwater study has been conducted in the Semarang City in August 2014, aiming to determine the source of shallow groundwater salinization using stable isotopes (18 O, 2 H) and water chemistry approach, and supported by local hydrogeological data. A number of shallow groundwater samples were taken at several locations with a depth of 0-35 m. Based on geological data, shallow groundwater of Semarang alluvium is dominated by insertion of sand-gravel and sandy-clay with average porosity of around 56.0 %. This layer is thinning towards the south and then increasingly thickening to the north and northeast of the studied area. The results of the analyses show that the characteristics of shallow groundwater, i.e. approximately 51% of groundwater, still have the original composition as meteoric water and the remaining approximately 49% obtained a shift in the isotopic composition as caused by interaction with seawater and the little influence of evaporation. The results of chemical analysis of water indicates that in dry seasons, shallow groundwater aquifers in the Semarang City is dominated by chloride (Cl-) with NaCl of water type. While the parameters of bicarbonate, chloride, and Na/Cl ratio, shallow groundwater can be classified into two groups, namely unintruded groundwater around 51% spread from the foot hills to the south towards the hills with elevations of 9-142 m above sea level and intruded groundwater around 49% spread from the coastline to the urban direction.

Bantar Gebang landfill located in Bekasi regency is a biggest sanitary landfill in Indonesia which comes up some refusals from local people because of its bad impact on their environment. Major ion contents in leachate and fresh groundwater were investigated during the rainy and dry season to determine contamination by leachate released from Bantar Gebang and Sumur Batu landfill. Leachate contained high concentrations of all major ions that was mainly characterized as a NaKHCO3 water type. On the other hand, most fresh groundwater samples were predominated by CaMgHCO3 and CaMgCl water type. Concentrations of K+, Ca2+, Mg2+, Na+, SO42-, Cl-, HCO3- and NO3- in leachate were to be in a maximum factor of 2110; 7; 6; 143; 20; 112; 349 and 20, respectively than its contents in groundwater. Leachate from Bantar Gebang was detected have a higher concentration than those contained in Sumur Batu that was probably due to its mature leachate. An estimated mixture of leachate to fresh water in monitoring wells (5 m and 15 m depth) was in the range of 20 to 34%, related to Na+ and Cl- signatures, while the shallow groundwater located in residents in the vicinity of these landfills exhibited maximum leachate about 2%.

Subsurface flow is one of the available water sources in the Karsts area such as in GunungKidul. The study of the pattern of the variations of stable isotopes content as a function oftime and its interaction with other water sources such as rain waters, groundwater, riverwater will be a very good tool to assess the potential of the subsurface flow as a water source.For this purpose, the variations of stable isotopes content of subsurface flow around GunungKidul Karsts area and its interactions with other local water sources have been studied for thelast two years. From the comparison of stable isotopes variations pattern of the subsurfaceflow with monthly rain water, the interaction of the subsurface flow with other water sourcesin the area has been quantified. Based on hydro-chemical data, it was found that the rechargearea of subsurface flow were relatively further than other samples and it was also found thatSeropan and Bribin subsurface flow systems originate from different geologic structures.Based on stable isotopes relative contents, it was found Ngobaran and Baron Caves have beenmixed with domestic sewerage water or other surface water.Keywords : Karsts area, stable isotopes, subsurface flow

ABSTRAK Gunung Tampomas merupakan salah satu daerah di Jawa Barat yang memiliki manifestasi panas bumi berupa mata air panas di sekitarnya. Penelitan potensi dan karakterisasi reservoar panas bumi Gunung Tampomas telah dilakukan dengan menggunakan metode kimia serta isotop alam 18 O dan 2 H (deuterium) dari mata air panas dan dingin di sekitar Gunung Tampomas dengan temperatur mata air berkisar antara 20ºC hingga 50ºC. Interpretasi hasil analisis tersebut dimaksudkan untuk mengetahui karakteristik reservoar seperti asal-usul fluida, temperatur reservoar dan evolusi fluida. Hasil analisis menunjukkan bahwa sebagian mata air panas Gunung Tampomas yaitu Ciseupan dan Ciuyah memiliki kandungan klorida tinggi yang mengindikasikan fluida berasal dari reservoar panas bumi. Sementara berdasarkan perhitungan geotermometer daerah panas bumi Gunung Tampomas memiliki potensi panas bumi yang tergolong medium entalpi dengan temperatur berkisar 120-220°C. Fluida panas bumi berasal dari air meteorik dengan sedikit pencampuran dengan air magmatik. Berdasarkan data geokimia, reservoar Gunung Tampomas diperkirakan memiliki reservoar yang terletak cukup dalam.Kata kunci: Gunung Tampomas, panas bumi, reservoar, metode kimia, metode isotop. ABSTRACT Mount Tampomas is one of many areas in West Java that has several geothermal manifestations. A study about geothermal potential and reservoir has been done using chemistry and natural isotopes methods taken from hot springs and cold springs around Mount