oa The Determination Of Physical Properties Of Groundwater Aquifers Using Shallow Seismic Reflection Methods

A land-based shallow seismic reflection data set was<br>acquired along the barrier island complex of coastal New Jersey<br>for the purpose of understanding the physical properties and two<br>dimensional organization of four Tertiary hydrogeologic units:<br>the Kirkwood-Cohansey Aquifer System, the Rio Grande Water<br>Bearing Zone, the Atlantic City 800 Foot Sand, and the Piney<br>Point Aquifer. A series of 6-fold common depth point seismic<br>sections covering 5.0 km. was obtained. Data were acquired on<br>sandy beach areas, oceanward of the central island axis, to<br>depths of 600 feet. A detailed velocity analysis (5 m intervals)<br>revealed subtle vertical and lateral velocity variations<br>(detectable to 10 m/s) within the sediments. Dominant reflector<br>frequencies of ,200-250 Hz were observed leading to a theoretical<br>vertical resolution of 1.0 to 2.0 m. The seismic results were<br>combined with local well log information to make important<br>inferences regarding porosity, permeability, and aquifer<br>geometry. A synthetic seismogram generated from the Island Beach<br>State Park Test Well No.1 (sonic log) correlates well with field<br>sections, enabling a more precise definition of bed boundaries<br>and aquifer wavelet responses.<br>A linear multiple regression model was developed which<br>relates acoustic traveltime to relative gamma ray and relative<br>resistivity readings at the test well. The relation was then<br>applied to nearby wells possessing gamma ray and resistivity<br>logs, yet devoid of acoustic information. Pseudo-synthetic<br>seismograms were generated based upon the model and relative<br>gamma ray and relative resistivity readings from the new wells.<br>Comparison of the pseudo-synthetic seismograms with field seismic<br>sections shows good agreement, thereby enabling estimation of<br>lithology, velocity, and porosity. A characteristic seismic<br>signature for the aquifers of interest has been constructed from<br>the above information.