Carbon Tetrachloride and Chloroform Partition Coefficients Derived from Aqueous Desorption of Contaminated

Riley Rg

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PNNL-15239








Carbon Tetrachloride and Chloroform
Partition Coefficients Derived from
Aqueous Desorption of Contaminated
Hanford Sediments



R. G. Riley J. E. Szecsody
D. S. Sklarew A. V. Mitroshkov
C. F. Brown C. J. Thompson
P. M. Gent






July 2005








Prepared for the U.S. Department of Energy
under Contract DE-AC05-76RL01830
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PNNL-15239







Carbon Tetrachloride and Chloroform Partition
Coefficients Derived from Aqueous Desorption of
Contaminated Hanford Sediments



R. G. Riley J. E. Szecsody
D. S. Sklarew A. V. Mitroshkov
C. F. Brown C. J. Thompson
(a)P. M. Gent




July 2005


Prepared for
the U.S. Department of Energy
under Contract DE-AC05-76RL01830




Pacific Northwest National Laboratory
Richland, Washington 99352

_______________

(a) Fluor Hanford, Inc.


Summary
Fluor Hanford, Inc. (FHI) has identified data needs important to locating, characterizing, and
assessing the impact of carbon tetrachloride (CCl ) contamination underlying the 200 West Area on the 4
Hanford Site. One need, which is described in this report, is to establish partition coefficients between
gas, liquid, and solid phases for CCl based on contaminated sediments and to use such data to refine the 4
fate and transport modeling performed to assess the impacts of the 200 West Area CCl plume. 4
Researchers at PNNL determined CCl and chloroform (CHCl ) groundwater/sediment partition 4 3
coefficients (K values) for contaminated aquifer sediments collected from borehole C3246 (299-W15-46) d
located in the 200 West Area adjacent to the 216-Z-9 trench. Having realistic values for this parameter is
critical to predict future movement of CCl in groundwater from the 200 West Area. It is best to obtain 4
such values from contaminated sediments because the values will reflect the long sediment/contaminant
contact times that are not possible to mimic in laboratory experiments. The K values used in modeling d
CCl are crucial to more accurate estimation of whether compliance limits may be exceeded outside the 4
Central Plateau waste management area.
CCl and CHCl partition coefficients for groundwater and sediment were determined in contami-4 3
nated aquifer sediments of the Ringold Formation collected at depths in the range of 230 to 430 feet from
the borehole 299-W15-46. The contaminants have been in contact with these sediments for up to
30 years. CCl and CHCl partition coefficients ranged from 0.106 L/kg to 0.367 L/kg and 0.084 L/kg to 4 3
0.432 L/kg, respectively. These values were 3 to 8 times and 12 to 23 times larger, respectively, than
would be predicted based on the organic carbon content of the sediments (0.017 to 0.059%).
These partition coefficients, along with groundwater concentrations of CCl and CHCl measured at 4 3
the same location of sediment collection, were used to estimate sediment concentrations of CCl . In some 4
cases, predicted values were significantly higher than observed sedim (e.g., 4
904 µg/kg calculated versus 31.8 µg/kg observed). A likely rationale for this difference is degradation of
CCl in the sediments. A significant fraction of CHCl (61% to 70% of the total solute mass) was 4 3
observed to be resistive to desorption from some of the sediments. The apparent sequestering properties
of these sediments suggest that a certain portion of the CHCl in Hanford aquifer sediments is migrating 3
more slowly in groundwater than would be predicted by simple partitioning between groundwater and
sediment.
Past modeling of the CCl transport in the Hanford groundwater aquifer has assumed conservative 4
values for contaminant partitioning (e.g., a K value of 0 and no degradation), resulting in predictions that d
CCl concentrations will exceed compliance limits on the 200 Area plateau and at the Columbia River 4
within a 1,000 year time frame. Use of the K values determined in this study in transport simulations d
would result in slower predicted migration rates and reduced uncertainty. The presence of significant
concentrations of CHCl in the presence of lower-than-expected concentrations of CCl indicated CCl 3 4 4
degradation in the sediment and the need to more accurately represent this process in transport modeling.
iii
Contents
Summary............................................................................................................................................ iii
1.0 Introduction.............................................................................................................................. 1.1
2.0 Sampling Methods ................................................................................................................... 2.1
2.1 Collection of Intact Sediment Cores............................................................................... 2.1
2.2 Conversion of Liners to Intact Core Transport Containers ............................................ 2.1
2.3 Conversion of Transport Containers into Desorption Columns ..................................... 2.3
2.4 Collection of Groundwater Samples .............................................................................. 2.3
3.0 Sample Preparation and Analysis Methodology ...................................................................... 3.1
3.1 Sediment Moisture Content............................................................................................ 3.1
3.2 Bulk Fraction Distribution Analysis............................................................................... 3.1
3.3 Carbon Analysis ............................................................................................................. 3.1
3.4 Analysis of Water Samples by Gas Chromatography/Mass Spectrometry .................... 3.2
3.5 Accelerated Solvent Extraction of Sediments ................................................................ 3.3
3.6 Analysis of Sediment Extracts by Gas Chromatography ............................................... 3.4
4.0 Experimental Desorption System and Solute Elution .............................................................. 4.1
5.0 Tracer/Solute Profile Simulations from 1-D Column Experiments ......................................... 5.1
5.1 Partition Coefficients from Profile Determination of Retardation Factors .................... 5.1
5.2 Model Simulations to Assess Tracer/Solute Behavior ................................................... 5.1
6.0 Results...................................................................................................................................... 6.1
6.1 Physical and Chemical Characteristics of Sediment Cores ............................................ 6.1
6.2 Desorption Experiments ................................................................................................. 6.2
6.2.1 CCl and CCl Behavior in Column Desorption Experiments .......................... 6.2 4 3
6.2.2 Simulation of Tracer Behavior in 1-D Column Experiments............................ 6.6
6.2.3 Simulation of CClnents................... 6.6 4
6.2.4 Simulation of Chloroform Behavior in Column Desorption Experiments........ 6.10
6.3 Carbon Tetrachloride and Chloroform Residuals in Sediment Cores ...................