A research has been carried Out to investigate the effects of below sea level mining on the cement raw material quality of a limestone quarry located adjacent to the shoreline near Darica-Kocaeli-Turkey. Field studies involved rock mass characterization through discontinuity surveys performed at the working benches of the quarry as well as on the core samples, monitoring of groundwater levels, performance of water pressure tests, and in-situ hydrochemical measurements. Hydrogeological data suggest that the carbonate sequence forms a poor unconfined aquifer having hydraulic conductivity values ranging between 10(-6) m/s and 10(-8) m/s. In the quarry, water seepages can only be observed at the shear zones. Electrical conductivity profiles taken from the boreholes located at various distances from the shore line indicated the present position of the salt water wedge.