GROUNDWATER RESOURCES ALONG THE NATCHEZ TRACE PARKWAY IN NORTHERN MISSISSIPPI

Groundwater resources along the Natchez Trace Parkway (Trace) in northern Mississippi include springs, shallow unconfined aquifers and deeper confined aquifers. The geologic units containing the groundwater are Quaternary age modern stream alluvium; Quaternary age stream terrace deposits; Cretaceous age sedimentary units; and Paleozoic age sedimentary rocks. The Quaternary age modern stream and terrace alluvium are surficial deposits occurring on outcropping Cretaceous age units in many places along the route of the Trace in north Mississippi. These alluvial deposits contain groundwater in unconfined conditions. Several Cretaceous age geologic units occur along the Trace in north Mississippi. In descending age as well as positional order they are: Demopolis Formation; Coffee Sand Formation; Mooreville Formation (where present); Tombigbee member of the Eutaw Formation; lower portion of the Eutaw Formation; Gordo Formation; and McShan Formation. In some areas the Gordo and McShan are combined as the Tuscaloosa Group. Each unit in this sequence contains groundwater with the exceptions of the Demopolis and Mooreville Formations. The Cretaceous age units are sedimentary deposits that dip to the west at about 30 feet per mile. In the areas where these units outcrop groundwater is in unconfined conditions. As the units dip to the west they become confined and groundwater is in artesian conditions. This is due to the fine grained components within the units’ sequence and due to the Demopolis and Mooreville Formations which are low permeability chalk and clay marl. The remainder of the Cretaceous age units are composed of sand and gravel beds with interbedded clays and silts. Directly underlying the Cretaceous age sediments are Paleozoic age sedimentary sandstones, shales, and limestones. The Paleozoic rocks had been an exposed surface upon which the Cretaceous age sediments were deposited. Due to the exposure, the Paleozoic age rocks were weathered and fractured and the Cretaceous contact is irregular. Because the upper Paleozoic surface was weathered and fractured it also contains groundwater that is in confined conditions. Due to the variability in the nature of the groundwater containing geologic units along the Trace in north Mississippi, both quantity and quality of the groundwater are also variable.