Controlling Mercury Release from Source Zones to Surface Water: Initial Results of Pilot Tests at the Y-12 National Security Complex

Southworth, George R ; Brooks, Scott C ; Peterson, Mark J ; Bogle, Mary Anna ; Miller, Carrie L ; Liang, Liyuan ; Elliott, Mike

Oak Ridge National Laboratory

关键词: Surface Waters;    Mass Balance;    Management;    Breakdown;    Chlorides;   

DOI  :  10.2172/969971
RP-ID  :  ORNL/TM-2009/035
RP-ID  :  DE-AC05-00OR22725
RP-ID  :  969971

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report presents initial results obtained during year 2008 and satisfies a deliverable listed in the work breakdown structure (WBS) element OR081301. Broad objectives of the multi-year project are: (1) evaluation of remediation technologies for waterborne mercury, (2) development of treatment methods for soil mercury, and (3) source identification, characterization and analyses to improve mass balance on mercury estimates. This report presents the results of pilot tests, conducted in summer and fall 2008, which focused on remediation of waterborne mercury. The goal of this task is to develop strategies and treatment technologies that reduce the concentration and loading of waterborne mercury discharges to the UEFPC, thus minimizing mercury uptake by fish. The two specific studies are: (1) reducing flow augmentation in UEFPC to lessen mercury mobilization from contaminated stream sediments, and (2) treatment of contaminated source waters with a chemical reductant to convert dissolved mercury to a volatile form that can be removed by air stripping or natural evasion. Diversion of 50% of the flow currently added to UEFPC by the flow management system appeared to reduce mercury inputs from a localized, highly contaminated streambed by 0.6-1.5 grams per day (g/d). A reduction of 0.6 g/d represents {approx} 7-10% decrease in mercury input to UEFPC. Mercury concentrations within UEFPC did not rise proportionately with the loss of dilution, in part because of the reduction in input from the streambed source and in part because of reduced flow from the Y-12 NSC storm drain system. A longer-term test that includes seasonal variability will be the next step to validate these initial field observations of the flow diversion experiment. Preliminary laboratory experiments show that a large fraction ({approx} 90%) of the mercury can be chemically reduced to Hg(0) by addition of low concentrations of tin, Sn(II). Conversion of mercury to volatile Hg(0) in UEFPC was also demonstrated in the field by in-situ addition of low levels of Sn(II) in the headwaters. A substantial fraction ({approx} 30% of baseline mercury levels by the end of the experiment) of the mercury was converted from oxidation state II to 0. The addition of the dechlorinating agent sodium thiosulfate mobilized a small amount of additional mercury from the pipe through which EFPC flowed, but the excess Hg largely disappeared by the end of the chemical addition period. No excess tin was observed at the regulatory monitoring point, mercury levels in air were low, and no in-stream toxicity was observed. At a Hg(II) reduction efficiency of {approx} 30%, in-situ reduction coupled with air stripping has the potential to remove large quantities of mercury from the UEFPC flow. Air stripping has not been implemented, but a demonstration is planned for the next phase of field experiments. The initial results from this 2008 study suggest a combination of reducing augmented flow volume and chemical reduction using stannous chloride will produce at least a 35% reduction in baseflow mercury loading to UEFPC, from approximately 8 g/d to 5 g/d. The goal of research in 2009 and beyond will be to gain further improvements in each of these approaches.