Description:

"Additional Case Studies Vadose Zone Science and Technology Solutions EDITED BY Brian B. Looney, Ph.D. AND Ronald W. Falta, Ph.D. Electromagnetic Imaging of Chemical and Mixed Waste Landfills David J. Borns Geophysics Department Sandia National Laboratories Albuquerque, NM 87185-0750 We have demonstrated the use of electromagnetic imaging for waste site characterization and monitoring in arid alluvial environments. The approach is based on the radio imaging method. This continuous waveform technique measures the amplitude and phase relative to the transmitter waveform (15 MHz) as the signal propagates from borehole-to-borehole or borehole-to-surface. At one site, we used a pulsed ABEM system (radar >20MHz) for imaging in the same borehole configuration as the continuous wave system for comparison between methods. One demonstration utilized test boreholes at the Chemical Waste Landfill, Sandia National Laboratories, Albuquerque, NM. Another was performed under a complex of burial pits named RB-11 on Kirtland Air Force Base (KAFB), Albuquerque, NM. At the Chemical Waste Landfill, we obtained tomographic data from four vertical boreholes (30 m deep and 6 to 15 m separation) that straddle a chromic acid pit. Analysis of the tomographic data delineates boundaries between alluvial facies (e.g., zones of granitic and limestone cobbles; variations in soil density and grain-size). Such variations may control contaminant migration at the site. The surveys also detect portions of the contaminant plumes beneath the pit. Another survey configuration at the Chemical Waste Landfill and RB-11 used slant boreholes for borehole-to-borehole and borehole-to-surface surveys through a series of disposal trenches. Regions of varying conductivity in resulting images delineate pits and contaminant plumes. An advantage of the borehole-to-surface approach is that a waste site can be characterized using only one slant or directional borehole. Adaptive Sampling Approach to Environmental Site Characterization Grace Bujewski, Sandia National Laboratories A technology demonstration that optimizes sampling strategies and real-time data collection was carried out in August 1994 at the Kirtland Air Force Base (KAFB) RB-11 Radioactive Burial Site, Albuquerque, New Mexico. The project, funded by the Strategic Environmental Research and Development Program (SERDP), involved application of a geostatistics-based adaptive sampling methodology and software with on-site field screening of soils for radiation, organic compounds, and metals. The software, known as Plume, was developed at Argonne National Laboratory as part of the DOE OTD-funded Mixed Waste Landfill Integrated Demonstration (MWLID). During the field demonstration, a SunSPARC workstation containing the geostatistical program was successfully linked via the Internet with an identical workstation at Argonne. The objective of the investigation was to compare an innovative adaptive sampling approach that stressed real-time decision-making with a conventional Resource Conservation and Recovery Act (RCRA)-driven site characterization carried out by the Air Force. The latter used a standard drilling and sampling plan as mandated by the Environmental Protection Agency (EPA). To make the comparison realistic, the same contractors and sampling equipment (Geoprobe soil samplers) were employed. In both investigations, soil samples were collected at several depths at numerous locations adjacent to burial trenches. These trenches contained low-level radioactive waste and animal carcasses; some might also have contained mixed waste. Neither study revealed contaminants appreciably above risk-based action levels, indicating minimal to no migration away from the trenches had occurred. The combination of adaptive sampling with field screening achieved a level of confidence similar to the RCRA investigation regarding potential migration of contaminants at the site. By comparison, according to the adaptive sampling program, drilling was conducted at 28 locations (vs. 36 for the conventional investigation), 81 samples were collected (vs. 163), and 15 samples (vs. 163) were sent off-site for laboratory analysis for confirmation. In addition, field work took 3½ days compared to 13 days for the RCRA investigation. These figures translate into large cost savings, because 22 percent fewer boreholes were drilled, 50 percent fewer samples were collected, and 91 percent fewer samples were analyzed off-site. Of these costs, the most significant savings involved laboratory analyses, which typically cost over $1000 per sample. Additional costs associated with increased field screening and use of adaptive sampling software were relatively minor compared to the savings achieved. The UFA Method for Characterization of Vadose Zone Behavior James L. Conca and Judith Wright, UFA Ventures, Inc., 2000 Logston Blvd, Richland, Washington 99352 james@ufaventures.com http://www.ufaventures.com A newly-developed Unsaturated Saturated Flow Apparatus (UFA) decreases the time required to obtain direct measurements of most transport parameters for any porous media, even in unsaturated or relatively impermeable materials. These properties include hydraulic conductivity (K) or intrinsic permeability (ka), diffusion coefficient (D), matric potential (ψ), electrical conductivity (σ), vapor diffusivity (Dv), distribution coefficient (Kd), retardation factor (Rf), dispersivity (α) and thermal conductivity (λ). All are strong, non-linear functions of the volumetric water content (θ). The UFA achieves steady-state in hours, uniformly at any water content in any porous media, by using an adjustable body force together with precision fluid flow. Detailed, complete and economic characterization of subsurface and engineered systems is provided by using the UFA in combination with other methods such as electrical conductivity, gas permeametry or thermal probes. This case study describes the UFA Method and comparisons to traditional methods. The UFA instrument consists of an ultracentrifuge with a constant, ultra-low flow pump that provides fluid to the sample surface through a rotating seal assembly and microdispersal system (Figure 3.3.3.2-1). The ultracentrifuge can reach accelerations of up to 20,000 g (soils are generally run only up to 1,000 g (3,000 rpm), an effective hydrostatic pressure of only 2.5 bars), temperatures can be adjusted from -20°C to 150°C, and constant flow rates can be reduced to 0.001 ml/h. Ключевые слова: permeability, surface, soil sci, fracture, hydraulic potential, raman, aeration zone, unsaturated, air, function, zone, sample, constitutive relationship, nonwelded tuff, moisture, bauer hagan, martins, national, rotary jet, content, site, capillary conduction, remediation, geologic setting, cold trap, sudden surge, point, darcys law, cost, process, cofferdams wall, instrument, climatic condition, period, prior pdfs, princeton illinois, measurement, purging event, high, trac tion, largest pore, potential discontinuity, electromagnetic imaging, electrical pulse, data, flow, pressure, annual symposium, medium, livermore, carbon dioxide, location, secondary mineral, moisture content, type, clay, funded, number, sheffield ill, nonequilibrium condition, porous, storm event, artificial smoothing, simulation, midnight prior, environmental, water, infiltration, guidance tool, wavenumber, condition, table, las nutrias, stary shepelichi, vadose zone, landfill, water content, porous cup, alluvial valley, savannah river, model, salinity laboratory, capillary fringe, technique, le ng, ha, level, references, observed, jd ay, reactive ribbon, transport, subsurface, building soils, emanation profiling, foot, conductivity, drip event, layer, sampling, decided, reactive chemistry, driving force, approach, result, fitting, gas, soil water, sandia corporation, change, depth, centrifugal force, collected, ft, protozoan grazing, van genuchten, soil, relative humidity, wa, street sacramento, cm, chlorinated ethenes, ft ft, parameter, tensiometer, sci, hydraulic conductivity, humidity characteristics, national laboratory, ecological condition, analysis, time, property, groundwater, aq fe, no-flow condition, animal intrusion, beavertail straps, science, hydraulic, georgia institute, multiple solute, plot, circuit board, waste, boreholes, parts-per-trillion-by-volume pptv, redox potential, day, unit, georgia tech, extraction, monitoring, radioactive decay, technology, matric potential, phase, vadose, madison, ineral abundance, contaminant, material, visualization tool, coffer dam, saturation, potential, concentration, se, field, design, carbon tetrachloride, water-borne delivery, optical window, test, posterior pdfs, flux, sediment, raman spectroscopy, scintillation counter, body force, barrier, laboratory, roughly orthogonal, vedose zone, tce, porous media, bandelier tuff, relationship, borehole, capillary force, c f, retention, water-salt regime, sanitary landfills, vapor, sulfur hexafluoride, advisory scientist, rubble zone, water potential, plant succession, nuclear chimney, vertical, soc, measured, study, basalt, cone permeametertm, distribution, range, rate, area, method