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LOCK, BRIAN E., University of Southwest Louisiana, Lafayette, LA

ABSTRACT: The Proposed Cade II Landfill Site, South Louisiana: Threat to the Chicot Aquifer

A national solid waste management company has been attempting for several years to open a new sanitary landfill in the St. Martin/Iberia/Lafayette tri-parish area of south Louisiana. The first permit application, for a site near Cade, St. Martin Parish (Cade I), was rejected by the Louisiana Department of Environmental Quality (DEQ) in 1987 in the interests of protecting the Chicot Aquifer, an "important source of drinking water," which is close to the surface in the area.

In 1988, the company submitted a new permit application for a second site (Cade II), less than 2 mi from the first. Despite geological and technical criticisms of the site voiced by local geologists, by the Louisiana Geological Survey (in its role as consultant to DEQ), and by members of the Solid Waste Division of DEQ, a permit was granted in early 1992.

Geological objections to the site fall into two main categories. First, the site selection process should have given high priority to optimizing geologic protection for the aquifer. DEQ apparently ignored this consideration and chose a location within the area shown by published studies to have the thinnest clay cover. Cade lies very close to a major recharge area for the Chicot aquifer, which is the main source of domestic and municipal water supplies for southwestern Louisiana.

Second, site characterization was done to engineering standards with no geologic insight. Fifty-five borings were sampled and five geologic units recognized. Lithological logs clearly reveal that the units are highly variable and that gradational contacts exist between units 1 and 2 and between units 3-5, numbered from the surface down. Units 1 and 2 are here interpreted as loess, and units 3-5 as representing the upper parts of a late Pleistocene (Prairie Terrace) point bar, a component of the Chicot Aquifer system. The clays of unit 3 constitute the main natural protection for the aquifer relied upon in the permit application, and were assumed by the engineering consultants to he homogeneous and characterized by the measured sample permeabilities of 1 x 10{-7} cm/sec or less through ut. As might be anticipated from numerous point-bar studies, the detailed boring descriptions mention very fine- to fine-grained sand pockets and interbeds that must have higher permeabilities and are likely to be oblique to the unit boundaries, providing potentially rapid access to the silts and sands of the lower units.

An early and unbiased geologic evaluation would have introduced an element of realism to the assessment of the barrier potential of the delay and probably would have condemned the site as a suitable landfill location. This case history provides a good example of the wrong approach to landfill site selection.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.