Geology of Evangeline Equivalent Aquifers
The Evangeline aquifer is composed of unnamed Pliocene sands and the Pliocene-Miocene Blounts Creek member of the Fleming formation. The Blounts Creek consists of sands, silts, and silty clays, with some gravel and lignite. The sands of the aquifer are moderately well to well sorted and fine to medium grained with interbedded coarse sand, silt, and clay. The mapped outcrop corresponds to the outcrop of the Blounts Creek member, but downdip, the aquifer thickens and includes Pliocene sand beds that do not outcrop. The confining clays of the Castor Creek member (Burkeville aquiclude) retard the movement of water between the Evangeline and the underlying Miocene aquifer systems. The Evangeline is separated in most areas from the overlying Chicot aquifer by clay beds; in some areas the clays are missing and the upper sands of the Evangeline are in direct contact with the lower sands and gravels of the Chicot.
Recharge to the Evangeline aquifer occurs by the direct infiltration of rainfall in interstream, upland outcrop areas and the movement of water through overlying terrace deposits, as well as leakage from other aquifers. Fresh water in the Evangeline is separated from water in stratigraphically equivalent deposits in southeast Louisiana by a saltwater ridge in the Mississippi River valley. The hydraulic conductivity of the Evangeline varies between 20-100 feet/day.
The maximum depths of occurrence of freshwater in the Evangeline range from 45.7 m (150 ft) above sea level, to 685.8 m (2,250 ft) below sea level. The range of thickness of the fresh water interval in the Evangeline is 15.2 m to 579.1 m (50 to 1,900 ft). The depths of the Evangeline wells that were monitored in conjunction with the Baseline Monitoring Project range from 58.8 m to 522.7 m (170 to 1,715 ft).