Peter M. Kearl

Observations of particle movement in a monitoring well using the colloidal borescope

Abstract The colloidal borescope consists of a set of lenses and miniature video cameras capable of observing natural particles in monitoring wells. Based on field observations of these particles, it appears possible to measure in situ groundwater velocity in a well bore. Field observations have shown that directional measurements using the colloidal borescope are generally in good agreement with expected flow directions. However, the magnitude of flow velocity is higher compared with values based on conventional test methods. High relative flow velocities, even after correction factors have been applied to compensate for well bore effects, are believed to be due to preferential flow zones in the surrounding aquifer. Low flow zones exhibit swirling multidirectional flow that does not allow for a linear velocity measurement. Consequently, groundwater flow velocities measured by the colloidal borescope in heterogeneous aquifers will be biased toward the maximum velocity values present in the aquifer. A series of laboratory experiments was conducted to assess the reliability of the instrument. Based on this work, a seepage velocity correction factor ( α ) of 1–4 was found for quantifying groundwater seepage velocity in the adjacent aquifer from observations in a well bore. Laboratory measurements also indicate that preferential flow in the surrounding aquifer dominates flow in the well. Results of this work suggest the possibility of quantifying higher-flow velocities associated with preferential flow zones in the subsurface.

Vapor extraction experiments with laboratory soil columns: Implications for field programs

Abstract As part of a site remediation project, laboratory soil column experiments were conducted to evaluate the effectiveness of a field vapor extraction system. Different soil types were placed in specially designed soil columns and saturated with 1,1,1-Trichloroethane and Jet-A fuel. The soil columns were connected to a vacuum pump and removal rates were monitored using mass balance, a portable photoionization detector, and a gas chromatograph. Results of the laboratory experiments indicated that the technique is useful for designing and monitoring field vapor extraction systems. Guidelines were developed for flow rate versus removal times, the effects of varying lithologies on removal rates and efficiencies, and the removal characteristics of organic mixtures consisting of varying volatile components.

Air permeability measurements of the unsaturated Bandelier tuff near Los Alamos, New Mexico

Abstract The Bandelier Tuff near Los Alamos, New Mexico, is located approximately 200 m above the regional water table. Because of the distance to the water table, organic and radioactive wastes were disposed of in unlined trenches and shafts within the tuff. Concerns regarding the movement of the contaminants, particularly in the vapor phase, prompted a site investigation. Part of that investigation included the determination of the permeability of the tuff. Three methods which measure the intrinsic permeability were used — air injection, vacuum testing, and laboratory testing of rock core samples. Dual packers were used to isolate specific zones for the air injection and vacuum tests. Klinkenburg and dynamic methods were used to measure permeabilities in the laboratory. Comparison of the results shows that vacuum tests produce results which are in good agreement with the laboratory permeabilities for unfractured zones. Permeabilities measured with air injection tended to be as much as an order of magnitude higher than the other methods. For estimates of the intrinsic permeability in the unsaturated zone, however, both air injection and vacuum tests are reliable methods.

State-of-the-art approach to hazardous waste site characterizations

A state-of-the-art characterization of a hazardous waste site provides significant benefits over a conventional program because it defines the hydrogeologic framework that governs contaminant transport, rather than merely confirming the existence of contamination State-of-the-art programs are commonly believed to be substantially more expensive than conventional programs. Such is not the case, however, for properly planned investigations Indeed, a state-of-the-art program can be substantially cheaper than a conventional one in some circumstances Costs remain comparable even under conditions unfavorable to the comparison These conclusions are illustrated by examples of field activities conducted at a variety of study sites.

Should restoration of small western watersheds be public policy in the United States

Additional research is needed to determine whether restoration of degraded watersheds in the western United States should become large-scale public policy. Numerous small projects have demonstrated that vegetation can be restored, sediment losses halted, and, in some cases, formerly ephemeral streams made perennial. But if all watersheds in a basin were restored, what would be the overall effects both ecologically and economically? For example, if large-scale restoration of small watersheds were conducted in a western river basin, what would be the effects on water yield and quality for the basin as a whole? Would implementing basin-wide watershed restoration be cost-effective? A means of examining this question is to monitor a watershed prior to and during the restoration process and to compare the results to a control watershed. The watersheds would be instrumented such that the ecological processes and water balance could be monitored both instream and within the associated groundwater system. Overall effects would then be subjected to economic and policy analysis, and modeling would be used to extrapolate the new information over the entire basin. These results would then be available to political leaders and government agencies for determining whether large-scale watershed restoration should be public policy.

The inadequacy of commonly used risk assessment guidance for determining whether solvent‐contaminated soils can affect groundwater at arid sites∗

Commonly used risk assessment guidance is not adequate when applied to solvent-contaminated soils in arid environments. The equations that are recommended for calculating how such soils will affect groundwater assume that liquid phase leaching controls contaminant migration. If vapor phase migration is considered at all, diffusion is assumed to be the dominant process. In contrast, a field study performed at an industrial site in Southern California demonstrated that leaching could not account for the transport of contaminants to the water table and the recent technical literature suggests that gravity-induced vapor migration may be the principal mechanism for vapor phase migration. Thus, regulatory guidance provided by the United States Environmental Protection Agency and the State of California could result in a significant underestimate of the amount of chlorinated solvent that could contaminate the groundwater at arid sites. 14 refs., 2 figs.

Plume management—An inexpensive long-term strategy for groundwater contamination at low-risk sites

Abstract The costs of full-scale groundwater treatment and source removal and the unrealistic goals of many groundwater treatment projects have prompted a reevaluation of long-term remediation strategies. This report has presented a plan that manages the groundwater contamination and is sensitive to the changing regulatory and technical climate. The groundwater treatment system is inexpensive to install, operate, and maintain. Plume migration has been stopped. Treatment time is exceedingly long, but the site operator is now free to evaluate new technology or the development of a risk-based clean-up strategy. We believe that implementing such a strategy at low-risk sites can result in significant cost savings to the hazardous waste clean-up problem.