In U.S. Gulf Coastal areas, clay-rich fluvial- deltaic sediments comprise the surficial sediments that overlie, and are thought to protect, the Coastal Lowlands Aquifer System, which is one of the larger domestic-use aquifers in the U.S. (Williamson et al., 1990). The Beaumont Formation is one of these fluvial-deltaic clays that extends along much of the north Texas Gulf Coast.

Fluvial-deltaic sediments are dominated by thick units of silty clay and clay, with irregular and discontinuous sand layers. While the sands in fluvial-deltaic sediments are known to have a relatively high hydraulic conductivity, they are often considered unimportant in transporting contaminants because of their irregular and discontinuous nature. In contrast, permeameter testing of the thick layers of silty clay that enclose the sands generally show the silty clays to have hydraulic conductivities on the order of 10^-5 to 10^-7 cm/sec or less, and thus the silty clays are thought to act as a barrier to flow.

Pumping and tracer tests conducted on a 70-foot-thick section of clay-rich (no sand beds) Beaumont Formation, however, indicate that the silty clays are 2 to 4 orders of magnitude more permeable than indicated by permeameter tests and thus can have a hydraulic conductivity on par with that of the sands. This study was conducted at the hydrogeology research facility at the University of Houston Coastal Center Preserve located approximately 50 miles southeast of Houston, in Galveston County, Texas. The tracer and pumping tests were conducted on closely spaced wells and multilevel piezometers. Detailed information on the site and the results of these studies are presented in a series of papers listed below. Funds for this work were provided by the Gulf Coast Hazardous Substance Research Center (U.S. EPA cooperative agreement R815197 and Texas Hazardous Waste Research Center funds), the University of Houston Coastal Center, and the Environmental Institute of Houston.

References

Bunge, G. C., and Capuano, R. M., 1995, Importance of crawfish burrows to infiltration in clay-rich sediments: Geological Society of America, Abstracts with Program, Annual Meeting, v. 77, no. 6, p. A- 99.

Capuano, R. M. and Hinks, A. W., 1996, Hydrochemical communication between clay and silty clay layers in shallow fluvial-deltaic sediments: Geological Society of America, Abstracts with Programs, Annual Meeting, v. 28, no. 7, p. A73.

Capuano, R. M., and Jan, R. Z., 1996, In-situ hydraulic conductivity of clay and silty clay fluvial-deltaic sediments: Ground Water, v. 34, no. 3, p. 545-551.

Capuano, R. M., Siringan, M. A., Jan, R. Z., and Jurtshuk, P., Jr., 1996, Enhanced activity of oligotrophic endogenous bacteria in clay-rich sediments by nutrient injection: Geomicrobiology Journal, v. 13, p. 165-179.

Hinks, A. W., and Capuano, R. M., 1995, Spatial and tenlporal variations in the hydrogeologic properties of the Upper Beaumont Clay: in. R. Jensen ed., Proceedings of the 24th Water for Texas Conference: Texas Water Development Board, pg. 147-156.

Mills, S. D., and Capuano, R. M., 1995a Infiltration of rain water through clay-rich soil of the Beaumont Formation. Galveston County. Texas: in. R. Jensen ed.. Proceedings of the 24th Water for Texas Conference: Texas Water Development Board, pg. 161-170.

Mills, S. D., and Capuano, R. M., 1995b, Transpiration-induced chloride enrichment of pore water in shallow, variably saturated, clay-rich sediments: Geological Society of America, Abstracts with Program. Annual Meeting, v. 27, no. 6, p. A-41.

Williamson, A. K., Grubb, H. F., and Weiss, J. S., 1990, Ground-water flow in the Gulf Coast Aquifer Systems, South Central United States - A preliminary analysis: U.S. Geological Survey, Water Resources Investigations Report 89-4071, 124 p.

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