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Activated Carbon-Based Technology for In Situ Subsurface Remediation

The U.S. EPA Office of Superfund Remediation and Technology Innovation recently published a fact sheet about an emerging remedial technology that applies a combination of activated carbon (AC) and chemical and/or biological amendments for in situ remediation of soil and groundwater contaminated by organic contaminants, primarily petroleum hydrocarbons and chlorinated solvents.  The technology typically is designed to carry out two contaminant removal processes: adsorption by AC and destruction by chemical and/or biological amendments.

With the development of several commercially available AC-based products, this remedial technology has been applied with increasing frequency at contaminated sites across the country, including numerous leaking underground storage tank (LUST) and dry cleaner sites (Simon 2015).  It also has been recently applied at several Superfund sites, and federal facility sites that are not on the National Priorities List.

The fact sheet provides information to practitioners and regulators for a better understanding of the science and current practice of AC-based remedial technologies for in situ applications. The uncertainties associated with the applications and performance of the technology also are discussed.

AC-based technology applies a composite or mixture of AC and chemical and/or biological amendments that commonly are used in a range of in situ treatment technologies.  Presently, five commercial AC-based products have been applied for in situ subsurface remediation in the U.S.: BOS-100® & 200® (RPI), COGAC® (Remington Technologies), and PlumeStop® (Regenesis) are the four most commonly used commercial products.  CAT-100® from RPI is the most recent product, developed based on BOS-100®.  One research group in Germany also developed a product called Carbo-Iron®.  The AC components of these products typically are acquired from specialized AC manufacturers.  These types of AC have desired adsorption properties for chlorinated solvents and petroleum hydrocarbons.  Different products also have different AC particle sizes, which determine the suitable injection approach and the applicable range of geological settings.

Example of powdered activated carbon “fracked” into the subsurface under high-pressure, causing preferential pathways into existing monitoring wells (Photo Credit: Regenesis)

 

In Situ Treatment Performance Monitoring: Issues and Best Practices

The U.S. EPA recently released an issue paper (EPA 542-F-18-002) that describes how in situ treatment technologies may impact sampling and analysis results.  The paper discusses the best practices to identify and mitigate issues that may affect sampling and analysis.

The utility of monitoring wells for performance or attainment monitoring is based on the premise that contaminant concentrations measured in the wells are representative of aquifer conditions. However, during in situ treatment, various biogeochemical and hydrogeological processes and sampling and analysis procedures may affect the representativeness of the monitoring well and sample quality, which may not be adequately considered in current remediation practice.

A properly designed monitoring network that anticipates the distribution of amendments after injection would minimize impacts to monitoring wells.  However, predicting amendment distribution prior to injection is challenging such that impacts to monitoring wells are likely.

The purpose of The U.S. EPA issue paper is to:
• describe how in situ treatment technologies may impact sampling and analysis results used to monitor treatment performance; and
• provide best practices to identify and mitigate issues that may affect sampling or analysis.

The U.S. EPA issue  paper discusses eight potential sampling or analytical issues associated with groundwater monitoring at sites where in situ treatment technologies are applied. These issues are grouped under three topic areas:
• Issues related to monitoring wells (Section 2).
• Representativeness of monitoring wells (Section 3).
• Post-sampling artifacts (Section 4).

The paper presents issues that pertain to collecting water samples directly from a monitoring well and does not discuss the use of other sampling techniques, such as passive diffusion bags or direct push groundwater sampling.