Gromadzki, Gregory A.1, Stanley T Paxton1, Robert W Puls2,
Jamie L Schlottmann3
(1) Oklahoma State University, Stillwater, OK
(2) USEPA, Ada, OK
(3) Consultant, Edmond, OK
ABSTRACT: Outcrop-Based High Resolution Gamma-Ray Characterization of Arsenic-Bearing Lithofacies in the Permian Garber Sandstone and Wellington Formation, Central Oklahoma Aquifer (COA), Cleveland County, Oklahoma
The COA supplies drinking water to a number of municipalities in central Oklahoma. Two major stratigraphic units in the COA, the Garber Sandstone and Wellington Formation, contain naturally occurring arsenic that exceeds government mandated drinking-water standards (EPA, 2001). Previous work in the COA (Schlottmann et al., 1998) has shown that arsenic concentrations in the aquifer vary with lithofacies. Isolated sandstones (encased by thick shale intervals where flow is reduced) tend to yield water with elevated arsenic levels. In order to better constrain the distribution of arsenic with lithofacies, we have constructed numerous high-resolution spectral gamma-ray profiles of the outcrops using a portable gamma-ray scintillometer. In addition, rock samples associated with each gamma ray reading taken from outcrops were returned to the laboratory for textural analysis. We find that many of the arsenic-bearing lithofacies are characterized by high total gamma-ray counts (associated with K, U and Th). This result is because arsenic in the rocks is associated with iron oxide that appears to be enriched in the finer-grained, clay-rich lithofacies. Calculated permeability profiles mimic fining-upward grain-size profiles characteristic of fluvial depositional settings. Data from previous USGS studies (cores, geochemistry, petrography, and x-ray diffraction) are being incorporated into the evaluation of the gamma-ray responses as well. Results of this work are being integrated with other on-going companion studies to constrain subsurface well log correlation and the reconstruction of paleodepositional environments in the Garber-Wellington interval of the COA. (This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.)
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.