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Previous HitDependenceNext Hit of the Wilcox Aquifer Water Chemistry

 on Stratigraphy, Spatial Distribution, and Proximity to Lignite

in Southern Caddo Parish, Louisiana 

Douglas Carlson and Thomas Van Biersel

Louisiana Geological Survey – Louisiana State University,

3079 Energy, Coast and Environment Bldg., Baton Rouge, Louisiana  70803




The Wilcox Aquifer is the principal source of groundwater for Bossier, Caddo, De Soto and Sabine parishes in northwestern Louisiana.  It appears, from examination of approximately 140 wells, that water chemistry within the Wilcox Aquifer is a function of sand horizon, spatial distribution and proximity to lignite seams. 


Water samples were collected from two sand layers located within the base of the Wilcox Aquifer south of Shreveport, Louisiana.  The upper sand (15 samples), as determined from the well screen centers, is located typically 50 to 100 ft below the surface.  The deeper sand (108 samples) is located typically 160 to 200 ft below the surface.  The lower sand has significantly difference concentrations of bromide, calcium, chloride, magnesium, manganese, pH, silica and sodium than the upper sand. 


Water chemistry within the lower sand, as a function of spatial distribution, was considered for a select set of quantifiable parameters (>100 values above detection Previous HitlimitNext Hit).  In general, for most species, the areas of higher concentration lied southeast and southwest of Shreveport.  Within some of these areas, a few concentrations of chloride, iron, and total dissolved solids (TDS) exceed the Environmental Protection Agency (EPA) national secondary drinking water standards. 


The samples were also categorized by the proximity to lignite into three categories:  wells without lignite; wells with lignite within borehole but not within screen interval; and wells with lignite within screen interval.  There were at least 30 wells sampled within in each category.  Lignite presence or absences was determined from review of the well completion reports submitted to the Water Resources Division of the Louisiana Department of Transportation and Development.  The presence of lignite within the well boring has a significant impact on concentrations of ammonia-nitrogen, boron, chromium, fluoride, phosphate, sodium, and strontium.

Carlson, D., and T. Van Biersel, 2009, Previous HitDependenceTop of the Wilcox Aquifer water chemistry on stratigraphy, spatial distribution, and proximity to lignite in southern Caddo Parish, Louisiana:  Gulf Coast Association of Geological Societies Transactions, v. 59, p. 145-157.


AAPG Search and Discover Article #90093 © 2009 GCAGS 59th Annual Meeting, Shreveport, Louisiana