In situ hydraulic conductivity of clay and silty-clay fluvial-deltaic sediments, Texas Gulf Coast

Two aquifer pumping tests (13 and 24 hours) and a tracer injection test were performed on shallow (7.5 m) clay and silty-clay sediments of the fluvial-deltaic Beaumont Formation from the U.S. Gulf Coast. The in situ horizontal hydraulic conductivity determined from these tests is found to be approximately 10(-3) cm/sec. This value is one to three orders of magnitude larger than that of typical silts and clays, and two to four orders of magnitude larger than the vertical hydraulic conductivity measured on core in laboratory permeameter experiments. A uniformity of the drawdown curves from different observation wells strongly suggests that hydraulic conductivity is relatively homogeneous and isotropic in the horizontal plane at the scale of the test. This relatively large in situ horizontal hydraulic conductivity for these clay-rich sediments is attributed to macroporosity rather than matrix porosity.