Abstract. The effect of microscale surface roughness in fracture walls is shown to accelerate colloid transport relative to a tracer and to increase colloid capture. These results are from experiments on duplicate laboratory experiments using synthetic, neutrally buoyant, abiotic, colloidal particles and two dense rhyolitic tuff cores. One core has a single, rough-walled fracture with an average aperture of 450/am. We have used a profilometer to measure the fracture topography and calculate aperture distributions and surface areas in the reconstructed core. The other core has a smooth, channelized slit that is a parallel-plate analogue to the fractured core. Identical tracer and particle pulses were injected into each core. Particle capture b• electrostatic attachment in the parallel-plate core gives a retention capacity of 55 x 10 • particles m -2. In the rough-walled fracture core, average particle transport rates are a full fracture volume faster than average tracer transport rates. Reynolds flow simulation indicates the presence of highly channelized fluid flow that likely contributes to this accelerated particle transport. Capture in the fractured core was 90 x 109 particles m-2; retention capacity is unknown because particle concentrations in the effluent achieved a steady state value of only 85% of the injected concentration.

A field test of hydrous pyrolysis/oxidation (HPO) was conducted during the summer of 1997, during a commercial application of thermal remediation (Dynamic Underground Stripping @US)) at the Visalia Pole Yard (a super-fund site) in southern California. At Visalia, Southern California Edison Co. is applying the DUS thermal remediation method to clean up a large (4.3 acre) site

The development of in situ thermal remediation techniques requires parallel development of techniques capable of monitoring the physical and chemical changes for purposes of process control. Recent research indicates that many common contaminants can be destroyed in situ by hydrous pyrolysis/oxidation (HPO), eliminating the need for costly surface treatment and disposal. Steam injection, combined with supplemental air, can create the conditions in which HP0 occurs. Field testing of this process, conducted in the summer of 1997, indicates rapid destruction of polycyclic aromatic hydrocarbons (PAHs). Previous work established a suite of underground geophysical imaging techniques capable of providing sufficient knowledge of the physical changes in the subsurface during thermal treatment at sufficient frequencies to be used to monitor and guide the heating and extraction processes. In this field test, electrical resistance tomography (ERT) and temperature measurements provided the primary infijrmation regarding the temporal and spatial distribution of the heated zones. Verifl-ing the in situ chemical destruction posed new challenges. We developed field methods for sampling and analyzing hot water for contaminants, oxygen, intermediates and products of reaction. Since the addition of air or oxygen to the contaminated region is a critical aspect of HPO, noble gas tracers were used to identify fluids from different sources. The combination of physical monitoring with noble gas identification of the native and injected fluids and accurate fluid sampling resulted in an excellent temporal and spatial evaluation of the subsurface processes, from which the amount of in situ destruction occurring in the treated region could be quantified. The experimental field results constrain the destruction rates throughout the site, and enable site management to make accurate estimates of total in situ destruction based on the recovered carbon. As of October, 1998, over 400,000 kg (900,000 lb) of contaminant have been removed from the site; about 18% of this has been destroyed in situ.

The development of in situ thermal remediation techniques requires parallel development of techniques capable of monitoring the physical and chemical changes for purposes of process control. Recent research indicates that many common contaminants can be destroyed in situ by hydrous pyrolysis/oxidation (HPO), eliminating the need for costly surface treatment and disposal. Steam injection, combined with supplemental air, can create the conditions in which HP0 occurs. Field testing of this process, conducted in the summer of 1997, indicates rapid destruction of polycyclic aromatic hydrocarbons (PAHs). Previous work established a suite of underground geophysical imaging techniques capable of providing sufficient knowledge of the physical changes in the subsurface during thermal treatment at sufficient frequencies to be used to monitor and guide the heating and extraction processes. In this field test, electrical resistance tomography (ERT) and temperature measurements provided the primary infijrmation regarding the temporal and spatial distribution of the heated zones. Verifl-ing the in situ chemical destruction posed new challenges. We developed field methods for sampling and analyzing hot water for contaminants, oxygen, intermediates and products of reaction. Since the addition of air or oxygen to the contaminated region is a critical aspect of HPO, noble gas tracers were used to identify fluids from different sources. The combination of physical monitoring with noble gas identification of the native and injected fluids and accurate fluid sampling resulted in an excellent temporal and spatial evaluation of the subsurface processes, from which the amount of in situ destruction occurring in the treated region could be quantified. The experimental field results constrain the destruction rates throughout the site, and enable site management to make accurate estimates of total in situ destruction based on the recovered carbon. As of October, 1998, over 400,000 kg (900,000 lb) of contaminant have been removed from the site; about 18% of this has been destroyed in situ.

Investigation of the Behavior of VOCs in GroundWater Across Fine-and Coarse-Grained Geological Contacts using a Medium-Scale Physical Model F. Hoffman, M.L. Chiarappa March 1998This is an informal report intended primarily for internal or limited external distribution. The opinions and conclusions stated are those of the author and may or may not be those of the Laboratory. Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W-7405-ENG-48. DISCLAIMERThis document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.This report has been reproduced directly from the best available copy. Executive SummaryOne of the serious impediments to the remediation of ground water contaminated with volatile organic compounds (VOCs) is that the VOCs are retarded with respect to the movement of the ground water. Although the processes that result in VOC retardation are poorly understood, we have developed a conceptual model that includes several retarding mechanisms. These include adsorption to inorganic surfaces, absorption to organic carbon, and diffusion into areas of immobile waters. This project was designed to evaluate the relative contributions of these mechanisms; by improving our understanding, we hope to inspire new remediation technologies or approaches.Our project consisted of a series of column experiments designed to measure the retardation, in different geological media, of four common ground water VOCs (chloroform, carbon tetrachloride, trichloroethylene, and tetrachloroethylene) which have differing physical and chemical characteristics. It also included a series of diffusion experiments designed to measure the diffusion of VOCs in aquifer materials. To establish parameters that constrain the model, we compared the data from these experiments to the output of a computational model.For the column experiments, we modified a chromatographic glass column with Teflon and with stainless-steel end fittings and packed it with a fine-grained, well-sorted sand that contained no detectable organic carbon. We ran the experiments by (1) simultaneously injec...