EVIDENCE FOR FRACTURE-CONTROLLED INFILTRATION TO THE SPARTA AQUIFER, NORTHERN LOUISIANA

Fractures within the Cook Mountain confining unit above the Sparta Sand have been postulated based on stream patterns and are observed locally in outcrop, but their effect on the hydrology of the Sparta aquifer has not been established. Preliminary analysis of the geometry of the fresh water - salt water interface in the Sparta, as recorded in gas well logs, shows a depression of the interface directly beneath the Bayou de Loutre channel in southeastern Union Parish, Louisiana. The Bayou de Loutre channel above the depressed zone follows a prominent geomorphic lineation that apparently marks a major fracture zone with an orientation compatible with the regional systematic fracture pattern. Since there are no other apparent factors to account for this depression, the depression is interpreted as resulting from enhanced infiltration of surface water along the fracture. The existence of fracture-controlled infiltration affects the range of possible remedial actions being considered to restore the health of this highly stressed aquifer.