The study area comprises about 3,200 square miles of the Mississippi Alluvial Plain in southeast Arkansas. About 90 percent of the area drains south to the Ouachita River in Louisiana.The alluvial aquifer and the streams are hydraulically connected and are studied as an aquifer-stream system. Bayou Bartholomew is a principal stream of the system. The aquifer is underlain by confining strata of the J ackson Group and Cockfield Formation. The m ean annual surface-water yield of the area that drains to the Ouachita River basin is nearly 2 million acre-feet. Floodcontrol projects have significantly reduced flooding in the area. Basin boundaries and low-flow characteristics of streams have been altered as a result of the flood-control projects and streamflow diversion for irrigation. The direction of ground-water flow generally is southward. Bayou Bartholomew functions mostly as a drain for ground-water flow from the west and as a recharge source to the aquifer east of the bayou. As a result of navigation pools, the Arkansas River is mostly a steady-recharge source to the aquifer. Pumpage from the aquifer and streams increased from about 20,000 acre-feet in 1941 to 237,000 acre-feet in 1970. Estimates of flow, derived from analog analysis but lacking field verification, indicate that recharge to the aquifer in 1970 was about 161,000 acre-feet. About 70 percent of the recharge was by capture from streams as a result of ground-water pumpage. Discharge from the aquifer was about 233,000 acre-feet. About 80 percent of the discharge was through wells. Stream diversion in 1970 from capture and open channel, excluding capture from the Arkansas and Mississippi Rivers, was about 110,000 acre-feet. Return flow to streams from rice irrigation and fishponds was about 60,000 acre-feet. The chemical quality of streamflows is excellent for irrigation. Water from the aquifer generally ranges from permissible to excellent for irrigation. The use of water from the aquifer in the flood-plain area, exclusive of irrigation, is severely limited unless it is treated to remove the iron and reduce the hardness.

This is Part I of a series of reports being prepared by the U.S. Geological Survey in c o n s u l t a t i o n with S t a t e s in t h e Basin and Range Province. filgflfWmON OF T t X C%U?Efl 1s alMm DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced fmrn the best available original document.

The geologic and hydrologic factors in selected regions of the Basin and Range province were examined to identify prospective areas for further study that may provide isolation of high-level radioactive waste from the accessible environment. The six regions selected for study were characterized with respect to the following guidelines: (1) Potential repository media; (2) Quaternary tectonic conditions; (3) climatic change and geomorphic processes; (4) groundwater conditions; (5) groundwater quality; and (6) mineral and energy resources. The repository medium will function as the first natural barrier to radionuclide travel by virtue of associated slow groundwater velocity. The principal rock types considered as host media include granitic, intermediate, and mafic intrusive rocks; argillaceous rocks; salt and anhydrite; volcanic mudflow (laharic) breccias; some intrusive rhyolitic plugs and stocks; partially zeolitized tuff; and metamorphic rocks. In the unsaturated zone, the permeability and hydrologic properties of the rocks and the hydrologic setting are more important than the rock type. Media ideally should be permeable to provide drainage and should have a minimal water flux. The groundwater flow path from a repository to the accessible environment needs to present major barriers to the transport of radionuclides. Factors considered in evaluating the groundwater conditions include groundwater traveltimes and quality, confining beds, and earth materials favorable for retardation of radionuclides. Groundwater velocities in the regions were calculated from estimated hydraulic properties of the rocks and gradients. Because site-specific data on hydraulic properties are not available, data from the literature were assembled and synthesized to obtain values for use in estimating groundwater velocities. Hydraulic conductivities for many rock types having granular and fracture permeability follow a log-normal distribution. Porosity for granular and very weathered crystalline rock tends to be normally distributed; porosity of fractured crystalline rock probably follows a log-normal distribution. The tectonic setting needs to prevent an increase in radionuclides to the accessible environment. Data on historic seismicity and heat flow, Quaternary faults, volcanism, and uplift were used to assess the tectonic conditions. Long-term late Cenozoic rates of vertical crustal movement in the Basin and Range province range from less than 2 meters per 104 years to greater than 20 meters per 104 years. Shortterm rates of vertical movement may be more than an order of magnitude greater, based on geodetic leveling. Changes in tectonic and climatic processes may potentially cause changes in hydrologic Idaho Department of Water Resources. Manuscript approved for publication, January 16, 1985. BASIS OF CHARACTERIZATION AND EVALUATION A3 EXPLANATION BOUNDARY OF REGION BOUNDARY OF GROUNDWATER UNIT~May coincide with regional boundary 100 200 300 MILES STUDIES OF GEOLOGY AND HYDROLOGY FOR ISOLATION OF HIGH-LEVEL RADIOACTIVE WASTE 120°116...

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The position and shape of the water table .under certain conditions may be considered to be the sum of two components of head, namely, the boundary component and the accretion component. In an aquifer of given hydraulic characteristics, the boundary component of head is determined by the stream stage and areal shape of the aquifer; the accretion co.mponent of head is determined by vertical gain or loss of water to the aquifer and by the areal shape of the aquifer. The boundary component may be obtained by electric-analog methods. By subtracting the boundary component from the observed position of the water table, the accretion component can be obtained. A change in river stage impo•s a new boundary component on the system. The effect of changed stream stages on the water table may be obtained Publication authorized by the Director, U.S. Geological Survey. •,EFERENCES Slichter, C. S., Theo,retical investigations of the motion of ground waters, U.S. Geol. Survey 19th Ann. Rept., pt. 2, 295-384, 1898. Southwell, R. V., Relaxation Methods in Theoretical Physics, Oxford University Press, 248 pp., 1948.Stallman, R. W., Numerical analysis of regional water levels to define aquifer hydrology, Trans.