The Pacific Journal of Science and Technology –505– http://www.akamaiuniversity.us/PJST.htm Volume 14. Number 2. November 2013 (Fall) Seismic Refraction Investigation for Groundwater Potential in Parts of Rivers State, Nigeria. Cyril N. Nwankwo, Ph.D. 1* ; Godwin O. Emujakporue, Ph.D.; Leonard I. Nwosu, Ph.D. Department of Physics, University of Port Harcourt, Nigeria. E-mail: cyrilnn@yahoo.com ABSTRACT A twelve channel digital signal enhancement Terraloc ABEM Seismograph was used in a continuous forward profiling to determine the depth to aquifer in Rukpokwu area of Rivers State, Nigeria. The geophones were fitted to the ground at an interval of 10m along the line which gives a total spread of 120m. The seismic spread was connected to the Seismograph which records the signal from the energy source. The first breaks seismic traces were picked with the aid of Reflex 2D Quick software, and the time-distance graph plotted. The results of the survey gave a three- layer model. The seismic P-wave velocity of the weak overburden sediments varies between 100 m/s and 200m/s with an average of 150 m/s. The thickness ranges between 0.69 and 3.32 m. The second layer has velocity that varies from 181.8 to 384.6 m/s with a simple average thickness of 17.68 m. The depth to bedrock (which is the aquifer layer) ranges from 12.52 to 26.56 m while the layer velocity varies from 275.0 m/s to 714.3 m/s. Comparison of this survey with the depths of existing water boreholes in the area and geoelectric resistivity data shows that the result is reliable. Therefore the seismic refraction method has proved to be a useful tool in defining the depth to aquifer in the study area. (Keywords: seismic refraction, groundwater, velocity, thickness, geoelectric section) INTRODUCTION Many geophysical methods find application in locating and defining subsurface water resources. They provide rapidly collected information on the geological structures and prevailing lithologies of a region without the large cost of an extensive drilling program. The geophysical survey results determine the location of the minimum numbers of exploration boreholes required for both essential aquifer tests and control of the geophysical interpretation (MacDonald et al., 2001; Milson, 1996, Nwankwo, et al., 2009). Seismic methods are very useful in hydrogeological investigations, but although the reflection technique would certainly provide more than adequate structural information, the method is uneconomically expensive. Seismic refraction methods, however, are widely used as they provide direct information on the level of water table since an increase in water content causes a significant increase of seismic velocity in a homogenous lithology (Murad et al., 2010; Ugwu and Nwankwoala, 2008). The study area, Rukpokwu is located within Port Harcourt, Rivers State Nigeria. The area lies on latitude 4 o 53 ′ and longitude 6 o 57 ′ (Figure 1), and forms part of the coastal plain of southern Nigeria. High productivity of many boreholes already drilled in the area supports the prolific nature of the coastal plain sands as an aquifer. This study is aimed at utilizing seismic refraction method to delineate the depth to aquifer that can be used for domestic and agricultural purposes in Rukpokwu town, Nigeria. GEOLOGY AND HYDROGEOLOGY OF THE STUDY AREA The underlying sediments in Rukpokwu forms part of the stratigraphic sequence in the Niger Delta complex. The Niger Delta has been described as a prograding depositional complex within the Cenozoic Formation of southern Nigeria (Etu- Efeotor, 1997; Ofodile, 1992). The Niger Delta is a sedimentary basin with complex regressive off lay sequence of clastic sediments ranging in thickness from 9000-12000 meters.