119 Recent Advances in Environmental Geoscience I

Monday, 26 September 2016
1:30 PM - 5:30 PM
Room 302

ASSESSING NATURAL RETARDATION OF CHROMIUM BY SEQUENTIAL LEACHING OF CONTAMINATED AND UNCONTAMINATED SEDIMENTS

Paper number: 119-11
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

Hexavalent chromium was used as a corrosion inhibitor in Los Alamos National Laboratory power-plant cooling towers between 1956 and 1972. It was released  as daily blowdown into effluent that discharged into a canyon. A complex infiltration pathway resulted in contamination within a deep alluvial aquifer approximately 1000 feet below ground surface. The highest concentration of chromium within the plume is ~1,000 ppb, compared to the New Mexico drinking water standard of 50 ppb. Natural retardation of Cr(VI) in the aquifer is being evaluated so that it can be properly accounted for in developing a remediation strategy. Elevated levels of chromium (III) in sediments taken from areas of high aqueous Cr(VI) concentrations in the aquifer are potentially an indicator of natural retardation. In a preliminary sequential leaching study, samples taken from chromium-contaminated areas of the aquifer were evaluated. Sample splits were leached three times with a weak alkaline solution (0.05 M sodium bicarbonate and 0.05 M carbonate), and the other split was leached three times with 0.01 M nitric acid. The samples that had been leached with 0.01 M nitric acid were sequentially leached three times with 0.1 M nitric acid. The alkaline solution was intended to desorb chromium (VI) from the sediments, and the acid solutions were intended to extract chromium (III) in successively greater amounts. The levels of chromium (III) leached from the contaminated sediments were barely elevated, if at all, above levels that were leached from similar sediments taken from uncontaminated regions of the aquifer, making it difficult to determine whether the leached Cr(III) was natural or anthropogenic. Therefore, a second leaching study was performed using a large number of uncontaminated samples to assess the variability in background levels of acid-leachable Cr(III) within the aquifer. We will present the results of this study and discuss their implications with respect to distinguishing between natural and anthropogenic Cr(III) in sequential leaching experiments.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-285516

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