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Title: Removal of Carbon Tetrachloride from a Layered Porous Medium by Means of Soil Vapor Extraction Enhanced by Desiccation and Water Table Reduction

Abstract

A two-dimensional flow cell experiment was conducted to study the removal of the carbon tetrachloride component of a DNAPL mixture from a layered porous medium through soil vapor extraction (SVE) with moist and dry air. A dual-energy gamma radiation system was used at various times to non-intrusively determine fluid saturations. The mixture, which contained the volatile organic carbon tetrachloride, mimics the DNAPL disposed at the Hanford Site in Washington State. The flow cell, which is 100 cm long, 75 cm high and 5.5 cm wide, was packed with two sloped coarse sand and two sloped silt layers in an otherwise uniform matrix of medium-grained sand. A V-shaped fine sand layer was placed at the bottom of the flow cell to prevent DNAPL from exiting the flow cell. The water table was located 2 cm from the bottom, creating variably saturated conditions. A 500-mL spill was introduced at the top of the flow cell from a small source area. It was observed that the DNAPL largely by-passed the silt layers but easily moved into the coarse sand layers. Residual DNAPL was formed in the medium-grained sand matrix. The DNAPL caused a distinct reduction of the capillary fringe. Most of the DNAPLmore » ended up in a pool on top of the V-shaped fine sand. Through four treatments with moist air soil vapor extraction, most residual carbon tetrachloride was removed from the medium-grained matrix and the coarse sand layers. However, soil vapor extraction with moist air was not able to remove the carbon tetrachloride from the silt layers and the pool. Through a water table reduction and subsequent soil vapor extraction with dry air, the carbon tetrachloride in the silt layers and the pool was effectively removed. Based on gamma measurements and carbon tetrachloride vapor concentration data, it was estimated that after the final remediation treatment, almost 90% of the total mass was removed.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
877559
Report Number(s):
PNNL-SA-43627
4599a; 8196; KP1704020; TRN: US200608%%482
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Vadose Zone Journal, 4(4):1170-1182; Journal Volume: 4; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CARBON TETRACHLORIDE; GAMMA RADIATION; MIXTURES; REMOVAL; SAND; SILT; SOILS; WASHINGTON; WATER TABLES; DNAPL; soil vapor extraction; desiccation; remediation; Environmental Molecular Sciences Laboratory

Citation Formats

Oostrom, Mart, Dane, Jacob H., and Wietsma, Thomas W. Removal of Carbon Tetrachloride from a Layered Porous Medium by Means of Soil Vapor Extraction Enhanced by Desiccation and Water Table Reduction. United States: N. p., 2005. Web. doi:10.2136/vzj2004.0173.
Oostrom, Mart, Dane, Jacob H., & Wietsma, Thomas W. Removal of Carbon Tetrachloride from a Layered Porous Medium by Means of Soil Vapor Extraction Enhanced by Desiccation and Water Table Reduction. United States. doi:10.2136/vzj2004.0173.
Oostrom, Mart, Dane, Jacob H., and Wietsma, Thomas W. Mon . "Removal of Carbon Tetrachloride from a Layered Porous Medium by Means of Soil Vapor Extraction Enhanced by Desiccation and Water Table Reduction". United States. doi:10.2136/vzj2004.0173.
@article{osti_877559,
title = {Removal of Carbon Tetrachloride from a Layered Porous Medium by Means of Soil Vapor Extraction Enhanced by Desiccation and Water Table Reduction},
author = {Oostrom, Mart and Dane, Jacob H. and Wietsma, Thomas W.},
abstractNote = {A two-dimensional flow cell experiment was conducted to study the removal of the carbon tetrachloride component of a DNAPL mixture from a layered porous medium through soil vapor extraction (SVE) with moist and dry air. A dual-energy gamma radiation system was used at various times to non-intrusively determine fluid saturations. The mixture, which contained the volatile organic carbon tetrachloride, mimics the DNAPL disposed at the Hanford Site in Washington State. The flow cell, which is 100 cm long, 75 cm high and 5.5 cm wide, was packed with two sloped coarse sand and two sloped silt layers in an otherwise uniform matrix of medium-grained sand. A V-shaped fine sand layer was placed at the bottom of the flow cell to prevent DNAPL from exiting the flow cell. The water table was located 2 cm from the bottom, creating variably saturated conditions. A 500-mL spill was introduced at the top of the flow cell from a small source area. It was observed that the DNAPL largely by-passed the silt layers but easily moved into the coarse sand layers. Residual DNAPL was formed in the medium-grained sand matrix. The DNAPL caused a distinct reduction of the capillary fringe. Most of the DNAPL ended up in a pool on top of the V-shaped fine sand. Through four treatments with moist air soil vapor extraction, most residual carbon tetrachloride was removed from the medium-grained matrix and the coarse sand layers. However, soil vapor extraction with moist air was not able to remove the carbon tetrachloride from the silt layers and the pool. Through a water table reduction and subsequent soil vapor extraction with dry air, the carbon tetrachloride in the silt layers and the pool was effectively removed. Based on gamma measurements and carbon tetrachloride vapor concentration data, it was estimated that after the final remediation treatment, almost 90% of the total mass was removed.},
doi = {10.2136/vzj2004.0173},
journal = {Vadose Zone Journal, 4(4):1170-1182},
number = 4,
volume = 4,
place = {United States},
year = {Mon Nov 14 00:00:00 EST 2005},
month = {Mon Nov 14 00:00:00 EST 2005}
}
  • A two-dimensional flow cell experiment was conducted to study the removal of the carbon tetrachloride component of a DNAPL mixture from a layered porous medium through soil vapor extraction (SVE) with moist and dry air. A dual-energy gamma radiation system was used at various times to non-intrusively determine fluid saturations. The mixture, which contained the volatile organic carbon tetrachloride, mimics the DNAPL disposed at the Hanford Site in Washington State. The flow cell, which is 100 cm long, 75 cm high and 5.5 cm wide, was packed with two sloped coarse sand and two sloped silt layers in an otherwisemore » uniform matrix of medium-grained sand. A V-shaped fine sand layer was placed at the bottom of the flow cell to prevent DNAPL from exiting the flow cell. The water table was located 2 cm from the bottom, creating variably saturated conditions. A 500-mL spill was introduced at the top of the flow cell from a small source area. It was observed that the DNAPL largely by-passed the silt layers but easily moved into the coarse sand layers. Residual DNAPL was formed in the medium-grained sand matrix. The DNAPL caused a distinct reduction of the capillary fringe. Most of the DNAPL ended up in a pool on top of the V-shaped fine sand. Through four treatments with moist air soil vapor extraction, most residual carbon tetrachloride was removed from the medium-grained matrix and the coarse sand layers. However, soil vapor extraction with moist air was not able to remove the carbon tetrachloride from the silt layers and the pool. Through a water table reduction and subsequent soil vapor extraction with dry air, the carbon tetrachloride in the silt layers and the pool was effectively removed. Based on gamma measurements and carbon tetrachloride vapor concentration data, it was estimated that after the final remediation treatment, almost 90% of the total mass was removed. Key Words: DNAPL; soil vapor extraction; desiccation; remediation« less
  • The purpose of this work is to identify the mechanisms that govern the removal of carbon tetrachloride (CT) during soil vapor extraction (SVE) by comparing multiphase flow simulations with a detailed data set from a well-defined two-dimensional flow cell experiment. The flow cell was packed with two sandy soils including an embedded fine-grained sand layer. Gas concentrations at the outlet of the flow cell and 15 sampling ports inside the flow cell were measured during SVE. A dual-energy gamma radiation system was used to measure an initial NAPL saturation profile in a fine-grained sand layer. Imaging result from a dual-energymore » gamma radiation system with dyed CT mark along CT migration was used to construct the distribution of initial NAPL saturation in the flow cell for input to numerical simulations. Gas concentration results and photographs during SVE were compared to simulation results using a continuum-based multiphase flow simulator, STOMP (Subsurface Transport Over Multiple Phases). The measured effluent gas concentration decreased quickly at first, and then started to decrease gradually, resulting in long-term tailing. CT mass was removed quickly in coarse sand, followed by a slow removal from the fine-grained sand layer. An analytical solution for a one-dimensional advection and first-order volatilization model matched the tailing well with two fitting parameters. However, given detailed knowledge of the permeability field and initial NAPL distribution, we can predict the tailing and gas concentration profiles at sampling ports using equilibrium NAPL volatilization. NAPL flow occurs in the presence of free NAPL, and must be accounted for to accurately predict NAPL removal during the SVE experiment. The model prediction was accurate within the uncertainty of the measured or literature derived parameters (i.e., dispersivity and soil parameters). This study provides insights into the physical mechanisms of NAPL removal from a low permeability zone, and use of the local equilibrium assumption for NAPL volatilization during SVE. In addition, this study demonstrates that lack of detailed information regarding NAPL distribution and heterogeneity pattern lead overall NAPL removal to a kinetically controlled system at a 2-D flow cell scale.« less
  • An existing multiphase flow simulator was modified in order to determine the effects of four mechanisms on NAPL mass removal in a strongly layered heterogeneous vadose zone during soil vapor extraction (SVE): a) NAPL flow, b) diffusion and dispersion from low permeability zones, c) slow desorption from sediment grains, and d) rate-limited dissolution of trapped NAPL. The impact of water and NAPL saturation distribution, NAPL type (i.e., free, residual, or trapped) distribution, and spatial heterogeneity of the permeability field on these mechanisms were evaluated. Two different initial source zone architectures (one with and one without trapped NAPL) were considered andmore » these architectures were used to evaluate seven different SVE scenarios. For all runs, slow diffusion from low permeability zones that gas flow bypassed was a dominant factor for diminished SVE effectiveness at later times. This effect was more significant at high water saturation due to the decrease of gas-phase relative permeability. Transverse dispersion contributed to fast NAPL mass removal from the low permeability layer in both source zone architectures, but longitudinal dispersion did not affect overall mass removal time. Both slow desorption from sediment grains and rate-limited mass transfer from trapped NAPL only marginally affected removal times. However, mass transfer from trapped NAPL did affect mass removal at late time, as well as the NAPL distribution. NAPL flow from low to high permeability zones contributed to faster mass removal from the low permeability layer, and this effect increased when water infiltration was eliminated. These simulations indicate that if trapped NAPL exists in heterogeneous porous media, mass transfer can be improved by delivering gas directly to zones with trapped NAPL and by lowering the water content, which increases the gas relative permeability and changes trapped NAPL to free NAPL.« less
  • /sup 103m/Rh in equilibrium with parent /sup 103/Ru was separated in yields of 94 percent of those theoretically possible. /sup 103/Ru chloride was first converted to the tetroxide which was then extracted from an aqueous solution of the equilibrium mixture with carbon tetrachloride.
  • In the extraction of uranyl nitrate from saturated calcium nitrate solutionsm a mixture of 64 vol % methyl ethyl ketone and 36 vol % carbon tetrachloride can be used in place of ethyl ether. This mixture is equiilalent to the ethyl ether, but is much less inflammable. The experimental conditions and results are the same as for the utilization of ethyl ether. The determination of the uranium extracted was made by use of arsenazo reagent. (tr- auth)