Rocky Mountain (66th Annual) and Cordilleran (110th Annual) Joint Meeting (19–21 May 2014)

Paper No. 5
Presentation Time: 9:25 AM

RED COLORATION WITH ELEVATED NO3, SE, SO4, TOC, AND U IN MANCOS SHALE SEEPAGE, SOUTHWESTERN UNITED STATES


MORRISON, Stan1, TIGAR, Aaron1 and BUSH, Richard P.2, (1)SM Stoller, Inc, 2597 Legacy Way, Grand Junction, CO 81503, (2)U.S. Department of Energy, Legacy Management, Grand Junction, CO 81502, stan.morrison@lm.doe.gov

Surface water in swamps and bogs is often colored yellow or brown from dissolved humic materials. While common in humid regions, such coloration is less common in arid desert areas. However, groundwater seeping from the Mancos Shale throughout much of its depositional basin in the arid southwestern United States has a distinctive yellow-red coloration. Field relationships indicate that the yellow-red color derives from contact with Mancos Shale. The seepage also has elevated concentrations of organic carbon, nitrate, selenium, sulfate, and uranium, but low iron concentrations. The sulfate is characterized by low δ34S values and the uranium by high 234U/238U activity ratios; both are consistent with a Mancos Shale origin. We used extraction and chemical oxidation methods to characterize the yellow-red color and to isolate the color-forming constituents. Filtering and dialysis tests indicate that organic carbon moieties smaller than 1000 Da cause the coloration. Tests with peroxide and bleach indicate that a portion of the color-forming constituents are readily oxidized. Adsorption to various resins suggests humic-based compounds. The combined results indicate that the color-forming constituents may be fulvic acid. The color‑forming moieties were isolated by adsorption to an acrylic ester‑based commercial adsorbent (DAX-8) followed by elution with NaOH and pH adjustment with a commercial resin (OnGuard II H). This method caused the color to increase by a factor of 5 and the salt content to decrease nearly 40-fold.