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ABSTRAKAir tanah merupakan sumber utama cadangan air tawar yang bekerja dalam siklus hidrostatik. Air tanah disediakan untuk konsumsi manusia, pertanian, industri dan banyak ekosistem yang bergantung pada air tanah, terutama selama musim kemarau. Kecamatan Hulonthalangi secara geografis terletak bagian selatan Kota Gorontalo berbatasan langsung dengan Teluk Tomini terdiri dari 5 kelurahan yakni Donggala, Pohe, Siendeng, Tenda dan Tanjung Kramat. Jumlah penduduknya 16.304 yang dilalui tiga sungai yakni Sungai Bone, Bolango dan Tamalate. Penelitian ini bertujuan mengetahui kedalaman muka air tanah dangkal secara pasti dengan mengukur langsung sumur warga. Selain itu penelitian ini juga bertujuan mengetahui kualitas air tanah dengan analisis parameter fisika dan kimia. Metode yang digunakan adalah analisis secara kualitatif dan kuantitatif. Analisis kualitatif mengamati kualias air tanah berdasarkan parameter fisika seperti warna, bau, rasa dan keterdapatan endapan serta mewawancara warga. Untuk analisis kuantitatif mengukur dan memplot koordinat, elevasi, kedalaman air tanah dan kandungan kimia. Hasil dan pembahasan penelitian menunjukan kedalaman muka air tanah rata-rata 2,87 - 4,04 meter. Pola aliran air tanah terbagi dua yakni dari tenggara ke barat laut dan dari timur ke barat. Analisis kualitas air, untuk warna 16% sampel terindikasi perlu tindaklanjut analisis laboratorium. Parameter bau 12% sampel tidak memenuhi syarat, untuk rasa 24% sampel tidak memenuhi syarat dan untuk endapan 14% sampel terindikasi tindaklanjut analisis laboratorium. Pemanfaatan air tanah 24% untuk kebutuhan pokok temasuk air minum. Analisis kimia di Stasiun 46 Kelurahan Pohe merupakan depot air minum mengandung besi 0,02 mg/l, nitrat 1,2 mg/l dan arsen 0 mg/l memenuhi standar kesehatan. ABSTRACT Ground water is the main source of freshwater reserves that work in the hydrostatic cycle. Groundwater is provided for human consumption, agriculture, industry and many ecosystems that depend on ground water, especially during dry seasons. Hulonthalangi Subdistrict is geographically located south of Gorontalo City adjacent to Tomini Bay consists of 5 villages namely Donggala, Pohe, Siendeng, Tenda and Tanjung Kramat. The population of 16,304 passes through three rivers namely Bone, Bolango and Tamalate Rivers. This study aims to determine the depth of shallow groundwater face with certainty by directly measuring the residents' wells. In addition, this study also aims to determine the quality of groundwater with the analysis of physical and chemical parameters. The method used is qualitative and quantitative analysis. Qualitative analysis observes the quality of groundwater based on physical parameters such as color, odor, taste and sediment deposit and interviewing citizens. For quantitative analysis measures and ploting the coordinates, elevation, depth of ground water and chemical content. Results and discussion of the study showed the depth of groundwater averaging 2.87 - 4.04 meters. The pattern of groundwater flow is divided into two, namely from southeast to northwest and east to west. Analysis of water quality, for the color of 16% samples indicated need follow-up laboratory analysis. The odor parameter of 12% samples was not eligible, for a taste of 24% unqualified samples and for precipitation 14% samples indicated follow-up laboratory analysis. Utilization of ground water 24% for basic needs including drinking water. Chemical analysis at Station 46 Pohe Village is drinking water depot contain 0.02 mg/l iron, 1.2 mg/l nitrate and 0 mg/l arsen meets health standards.

The potential of reef limestone in Gorontalo Province is very large. The proof is in two research stations in Kelurhan Buli'ide and Tanjung Kramat Village. Research on the potential of reef limestone using two methods of analysis petrology and geochemistry of XRF. Based on the results of the research both stations have the name of the rock and the composition of the chemical compounds is different. The results of the study differ from previous studies. Differences are found in the composition of CaO compounds higher than 80%. The chemical composition of compounds in two research stations has the potential to be developed into industrial material. Use of reef limestone can be used as building stones, road stabilizers, agricultural lime, ceramic materials, water purification and the process of deposition of non-ferrous metal ores.

The research location is the northern part of the Basin of Limboto Lake; the focus of the research is the limestone outcrop with 24 meter thickness in Yosonegoro area. The purpose of the study is to find out facies, standard microfacies and depositional environment on Limboto limestone. The research method carried out consisted of three methods namely the measured section, petrographic analysis and biostratigraphy analysis. The limestone facies in the Yosonegoro area consist of two facies. Then, based on sedimentary structure, composition, color, precipitation texture, terrestrial origin components and the organism content, the two facies can divided into three different microfacies. Paleobathymetry shows a deepening from the middle shelf-upper slope to the upper slopelower slope due to the sea level rise. Compilation of standard microfacies and paleobathymetry types shows changes in depositional environment from the slope environment to the toe of slope environment. The result of this study will be led researchers to propose the name of the new formation, which is the Limboto Limestone Formation according to specific location and characteristics from the previous formation name of the Clastic Limestone Formation.

The research area is located in northern Limboto Lake in Gorontalo Province, which has complex geological characteristics. The geological complexities include stratigraphy and tectonics which influence the formation of the Limboto Basin. Limestone research in the Late Tertiary Limboto Basin is very intriguing to be done because of the lack of research in limestone. Gorontalo limestone outcrops, which become the focus of the research, have a total thickness of 30 meters. The research objective is to analyze facies, microfacies, and depositional environment of tertiary limestone. These two research objectives are attained by using two research methods, namely measurd section and petrography analysis. The research result exhibits that there are four Gorontalo limestones facies, including coralline rudstone intercalated with thin mudstone facies, sandy micrite intercession facies, coralline rudstone intercession facies and sandy allochem limestone intercession facies. According to the limestone micro- facies standard, the depositional environment of Gorontalo limestone is platform interior restricted (facies zone 8).