Demonstration of Mineral Traps to Passively Evaluate and Monitor In Situ Reactive Minerals for Chlorinated Solvent Treatment

Dr. Craig Divine | Arcadis U.S., Inc.

ER19-5190

Objective

Many in situ groundwater treatment technologies for chlorinated solvents, as well as many other contaminants, rely upon the formation, dissolution, and/or transformation of target solid-phase minerals either to degrade or sequester groundwater contaminants. However, evaluation of these solid phase minerals and/or processes is often only inferred from aqueous phase conditions (i.e., groundwater sampling) because of the significant challenges and costs associated with the collection of solid phase samples. Traditional approaches for the collection of solid-phase samples include the use of high cost drilling/coring techniques, and sub-sampling of discrete zones within the core material for analysis. In addition to the high costs and health and safety risks, drilling/soil sampling examines discrete points/depths within the subsurface, often requiring a relatively large sample number to characterize the subsurface area of interest and account for the high heterogeneity observed across very small scales at most sites.

The objective of this project is to field-validate the Min-Trap™ technology, a new in situ monitoring tool that offers distinct advantages over traditional approaches for collecting mineralogical data to evaluate and manage in situ groundwater remediation programs. The Min-Trap is an adaptable tool that may be integrated into a broad range of remediation programs in diverse geologic environments.

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Technology Description

The Min-Trap is a sampling device consisting of a solid medium (e.g., silica sand, iron oxide sand, site soil) contained within a water permeable mesh that is deployed inside a monitoring well and allowed to incubate over time. Non-reactive media within the Min-Trap provides a carrier substrate upon which target minerals can form passively. Reactive media/site soil provides iron minerals that can be transformed into reactive minerals. Analysis of the medium through microscopic or spectroscopic means gives direct evidence of the formation of target minerals in situ. The degradation of CVOCs via the reducing power stored in reactive minerals (e.g., iron sulfides, sorbed ferrous iron, etc.) is recognized as a very important process, and cost-effective tools to support field applications are needed.

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Benefits

Min-Traps provide direct mineralogical data using the existing well network, allowing for an expanded set of sampling locations, repeated time series data, and the ability to evaluate consistent locations during modifications to the treatment program – without the need for repeated drilling events. In addition to potential improved data quality and decreased costs compared to traditional drilling methods, Min-Traps could also decrease field hours and health and safety risks, provide more efficient remedial operations, and improve communication with regulatory agencies and stakeholders. Min-Traps may improve the management of CVOC treatment programs by providing a reliable and cost-effective method for measuring reactive minerals that facilitate CVOC degradation in the subsurface (currently an unmet need). For CVOC sites, the formation of reactive minerals in situ can be a key line of evidence to evaluate the synergy between biological and abiotic processes, support remedy optimization, and provide a basis for the transition from active treatment to a monitored natural attenuation (MNA) approach. For many sites, it is anticipated that data from Min-Traps will provide a basis for ending active in situ treatment and transitioning to MNA several years earlier than they would otherwise, potentially saving hundreds of thousands of dollars per site.

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Points of Contact

Principal Investigator

Dr. Craig Divine

ARCADIS-US, Inc.

Phone: 720-308-5367

Program Manager

Environmental Restoration

SERDP and ESTCP

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