A large plume of produced salt water in the Chicot Aquifer is identified in the southwest Tomball Field area of north Harris County. The plume probably affects an area of 1/2 square miles or more and as much as 150 feet of the lower Chicot Aquifer. Historic oil field operations are the most probable surface point-source. Delta-plain sediments of the Pleistocene Lissie/Willis Formations influenced the contamination pathway and geometry. The Miocene-aged Evangeline Aquifer (Fleming Formation) is not impacted by the plume, as the Evangeline is geologically isolated from the Chicot by a regional paleo-Trinity Bay flooding sequence.

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