Monitored natural attenuation forum: The case for abiotic MNA

The environmental fate and transport of chlorinated volatile organic compounds (VOCs) is controlled by the physical and chemical properties of the compound and the nature of the subsurface media through which the compound is migrating. Several processes (advection, dispersion, diffusion, biodegradation, and abiotic degradation, to name a few) result in a reduction in concentration and/or mass of contaminants in groundwater. Of these processes, biodegradation is often considered the dominant destructive attenuation mechanism for chlorinated VOCs. However, chlorinated VOCs can also degrade through abiotic processes and, in some cases, may be the primary or only destructive process occurring. © 2007 Wiley Periodicals, Inc.     

Monitored natural attenuation forum: The use of carbon isotope analysis at MNA sites

Stable carbon isotopes have been used in various applications for approximately 50 years, in many applications including the fields of medicine, criminology, and biology and recently has been used in the remediation field to track the degradation of various organic compounds. It is a commercially available investigation technology that is gaining in popularity and has unique applications related to monitored natural attenuation (MNA). To further discuss this technology and how it is used at MNA sites, we presented the following question to five guest panel members. © 2007 Wiley Periodicals, Inc.     

Monitored natural attenuation forum: State of the practice—Highlights from a breakfast discussion

The Monitored Natural Attenuation (MNA) Forum is published as a column in each issue of Remediation. The format typically includes one or two questions related to MNA with responses from several MNA Panel members. This column highlights MNA topics discussed at a breakfast held in support of the MNA Forum. It includes thoughts from various MNA Panel members and other environmental professionals who attended the breakfast on the “state of the practice.” © 2005 Wiley Periodicals, Inc.     

Evaluation of natural attenuation at a 1,4‐dioxane‐contaminated site

1,4‐Dioxane entered the environment as a result of historic leaks and spills in the production area at an industrial facility in the southeastern coastal plain. The areal extent of the 1,4‐dioxane plume is several hundred acres and is largely contained on the site. Land use adjacent to the plant property is primarily undeveloped (wetlands or woods) or industrial, with a small area of mixed land use (commercial/residential) to the southwest and north. The surficial aquifer is a relatively simple hydrogeologic system with well‐defined boundaries and is comprised of a 50‐ to 70‐foot‐thick deposit of alluvial/fluvial sand and gravel that overlies an aquitard in excess of 100 feet thick. A groundwater flow model, developed and calibrated using field‐measured data, was used for the fate‐and‐transport modeling of 1,4‐dioxane. The flow‐and‐transport model, combined with the evaluation of other site geochemical data, was used to support the selection of monitored natural attenuation (MNA) as the proposed groundwater remedy for the site. Since the active sources of contamination have been removed and the modeling/field data demonstrated that the plume was stable and not expanding, the proposed MNA approach was accepted and approved by the regulatory agency for implementation in 2004. Subsequent accumulated data confirm that concentrations in the 1,4‐dioxane plume are declining as predicted by the fate‐and‐transport modeling. © 2008 Wiley Periodicals, Inc.     

Accelerating environmental cleanup at DOE sites: Monitored natural attenuation/enhanced attenuation—A basis for a new paradigm

The U.S. Department of Energy is conducting a project to accelerate remediation through the use of monitored natural attenuation and enhanced attenuation for chlorinated ethenes in soils and groundwater. Better monitoring practices, improved scientific understanding, and an advanced regulatory framework are being sought through a team effort that engages technology developers from academia, private industry, and government laboratories; site cleanup managers; stakeholders; and federal and state regulators. The team works collaboratively toward the common goals of reducing risk, accelerating cleanup, reducing cost, and minimizing environmental disruption. Cutting‐edge scientific advances are being combined with experience and sound environmental engineering in a broadly integrated and comprehensive approach that exemplifies socalled “third‐generation R&D.” The project is potentially a model for other cleanup activities. © 2004 Wiley Periodicals, Inc.     

Equipment choices for dredging contaminated sediments

This article describes the selection and field evaluation of dredging equipment and techniques for removal of highly contaminated sediments from the upper estuary of the Acusbnet River, a portion of the New Bedford Harbor Supetfund Project. Site conditions as related to dredge selection and operation, factors considered in selection of equipment, and various dredge types considered for use are described. Each of the dredge types is ranked according to the following criteria: availability, safety, potential for sediment resuspension, maneuverability, cleanup precision, cost and production, flexibility, required water depth for operation, ability to access the site, and compatibility with disposal options. A field pilot study comparing three dredge types indicated that dredging could be conducted at the site without a significant increase in the contaminant release from the upper estuary to the lower harbor.