Search

Low temperature heating of the subsurface (increases of about 5–20 °C) can substantially increase rates of biotic and abiotic destruction of dissolved contaminants such as chlorinated solvents. Low‐temperature heating can be sustainably and cost‐effectively achieved using solar thermal collectors coupled with closed‐loop borehole heat exchangers. This technology has been implemented at several sites in the United States and abroad with favorable results. The design of a solar thermal remediation system requires a quantitative understanding of heat transfer from the array of borehole heat exchangers. We present an easy‐to‐use design tool that is based on a transient three‐dimensional analytical heat transfer solution and is programmed in Visual Basic in Excel. This tool can be used to quickly explore the effect of design variables on the forecast temperature field. Typical design variables would include the site‐specific average and monthly solar insolation data, solar collector configuration, borehole heat exchanger geometry and spacing, and the effects of environmental variables such as groundwater velocity, background subsurface temperature, and thermal conductivity. The design tool has been verified by comparisons with the TOUGH2 multiphase heat transfer code for a three‐dimensional multi‐heater system with seasonally variable thermal power rates. The code has been validated by comparisons to observed temperatures measured at a solar thermal field remediation application at a site in Colorado. Article impact statement: A straightforward mathematical modeling tool is presented for designing solar thermal remediation systems using borehole heat exchangers. [ABSTRACT FROM AUTHOR]

A simple analytical model is presented for predicting subsurface gas flow to a vadose-zone well in response to atmospheric pressure fluctuations (barometric pumping). The effective radial permeability ([k.sub.r]) in the vicinity of the well is determined during model calibration using less than two weeks worth of data. By combining the flow solution with a solution for the vertical gas pressure, only atmospheric pressure data are required to predict the induced flow through a well. The ability to quantitatively predict naturally induced flow in vadose-zone wells by simple and inexpensive measurements is invaluable for systems using barometric pumping for remediation., Joseph Rossabi (1) Ronald W. Falta (2) Introduction The prevalence and persistence of subsurface contamination by volatile organic compounds (VOCs) and the shortage of funds to remediate this contamination below [...]

Some errors could be introduced when partitioning interwell tracer tests (PITTs) are employed to measure subsurface contamination by nonaqueous phase liquids (NAPLs). The PITTs should use a corrected partitioning coefficient when measuring NAPLs using a solubilization mechanism. Ideally, PITTs technology can be used to measure contamination effectiveness for a variety of remediation processes.

Introduction Nonaqueous phase liquids (NAPLs) present a common subsurface pollution problem. When introduced into the subsurface, NAPLs will travel downward through the unsaturated zone under the force of gravity, and [...]

Introduction Soil vapor extraction (SVE) is a widely used method for removing volatile organic compounds (VOCs) from the unsaturated zone. With this technique, a vacuum is applied to wells screened [...]

Introduction Soil vapor extraction is a popular method for removing volatile organic contaminants from the unsaturated zone. A soil vapor extraction system consists of one or more pumping wells screened [...]

In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two-dimensional, homogeneous sand pac with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady-state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser-than-air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil.

A general semianalytical technique helps analyze a volatile organic compound (VOC) for its advective transport to a soil vapor extraction. An initial VOC distribution, employed in the process, involves one-, two- or three-dimensions. The availability of information on gas travel time distributions and stream functions limits the applicability of this technique.