Identification of lithology properties of groundwater by using resistivity method in Girimulyo, Kulon Progo, Yogyakarta

Identification of lithology properties of groundwater has been done in Nglengkeh and surrounding area, Pendoworejo Village, Girimulyo District, Kulon Progo, Special Region of Yogyakarta. There are 13 points survey (ST) with long of 80-250 meters spread across the surface. This measurement is done in Nanggulan Claystone and Old Andesit Intrusion which each have widh 71.8% and 6.3% of the total research area. Nanggulan Claystone consists of claystone, siltstone and sandstone while The Old Andesite Intrusion consists of andesites. The results of interpretation resistivity data indicate three lithology properties to groundwater are aquiclude, aquifer and aquifuge. This area are dominated by aquiclude that consist of siltstone with resistivity 12-25 Ωm and claystone 1-10 Ωm at depth 3 meters and 25 meters. Rocks, as aquifers, are sandstones and siltclay. The type of aquifer identified is unconfined aquifer of soil by the name of silt clay with resistivity 14-20 Ωm at a depth of about 23 meters. Sandstone as confined aquifer with resistivity 25-75 Ωm in depth of 25-45 meters. Aquifuge which consist of andesite intrusion has resistivity 380-1984 Ωm. It was found only in ST 11 at depth ± 35 meters and ST 12 at depth ± 80 meters. The variations lithology properties to groundwater and unconfirmity of a sedimentary layer in the reseach area are controlled by stratigraphic parameters and exogenic processes (weathering and erosion).