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The goal of ENVIRO.wiki is to make scientific and engineering research results more accessible to environmental professionals, facilitating the permitting, design and implementation of environmental projects. Articles are written and edited by invited experts (see Contributors) to summarize current knowledge for the target audience on an array of topics, with cross-linked references to reports and technical literature.

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Featured article / Contaminated Sediments - Introduction

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are mobile in the subsurface and highly resistant to natural degradation processes, therefore soil source areas can be ongoing sources of groundwater contamination. Soil standards issued for protection of groundwater are in the single digit part per billion range. Well developed soil treatment technologies are limited to capping and excavation with incineration or disposal. Soil stabilization with sorptive amendments and soil washing have been applied at limited locations. At present, no in situ destructive soil treatment technologies have been demonstrated at full scale.

Excavation and off-site disposal or treatment of PFAS-impacted soils may be acceptable for small quantities of soil. Disposal in non-hazardous landfills is allowable in most states. However, some landfill operators are choosing to restrict acceptance of PFAS-containing waste and soils as a protection against future liability. Various amendments have been manufactured to sorb PFAS to reduce leaching from soil. Although this is a non-destructive approach, stabilization can reduce mass flux from a source area or allow soils to be placed in landfills with reduced potential for leaching. Amendments sorb PFAS through hydrophobic and electrostatic interactions and are applied to soil through in situ soil mixing or ex situ stabilization. Incineration is a well-developed technology for organics destruction, including PFAS-impacted soils. Incineration is generally defined as high temperature (>1,100°C) thermal destruction of waste, and PFAS are thought to mineralize at high temperatures. Generally, incinerators treat off-gasses by thermal oxidation with temperatures as high as 1,400°C, and vaporized combustion products can be captured using condensation and wet scrubbing.

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Enviro Wiki Highlights

Molecular diffusion slowly transports solutes into clay-rich, lower permeability zones

Typical subgrade biogeochemical reactor (SBGR) layout. The SBGR is an in situ remediation technology for treatment of contaminated source areas and groundwater plume hot spots

An Hydraulic Profiling Tool (HPT) log with electrical conductivity (EC) on left, injection pressure in middle, and flow rate on the right

Diagram of mineral surface exchanging hydrogen ions with varying pH. The surface of most aquifer minerals carries an electrical charge that varies with pH

Comparison of the longitudinal redox zonation concept (A) and the plume fringe concept (B). Both concepts describe the spatial distribution of electron acceptors and respiration processes in a hydrocarbon contaminant plume

Schematic of an Hydraulic Profiling Tool (HPT) probe. HPT were developed to better understand formation permeability and the distribution of permeable and low permeability zones in unconsolidated formations

In situ chemical oxidation using (a) direct-push injection probes or (b) well-to-well flushing to delivery oxidants (shown in blue) into a target treatment zone of groundwater contaminated by dense nonaqueous phase liquid compounds (shown in red)

High-resolution 3D cross-borehole electrical imaging of contaminated fractured rock at the former Naval Air Warfare Center in New Jersey. Cross-borehole resistivity tomography imaging is a geophysical technique that can be used for site characterization and monitoring by observing variations in the electrical properties of subsurface materials

Stable isotope probing (SIP) in use: Loading, deployment and recovery of Bio-Trap® passive sampler with 13C-labeled benzene. Stable isotope probing (SIP) is used to conclusively determine whether in situ biodegradation of a contaminant is occurring

Summary of anticipated, primary reaction pathways for degradation of 1,2,3-Trichloropropane (TCP). TCP is a man-made chemical that was used in the past primarily as a solvent and extractive agent, a paint and varnish remover, and as a cleaning and degreasing agent

Distribution of BTEX plume lengths from 604 hydrocarbon sites. Monitored Natural Attenuation (MNA) is one of the most commonly used remediation approaches for groundwater contaminated with petroleum hydrocarbons (PHCs) and certain fuel additives such as fuel oxygenates or lead scavengers

No-purge and passive sampling methods eliminate the pre-purging step for groundwater sample collection and represent alternatives to conventional sampling methods that rely on low-flow purging of a well prior to collection. The Snap SamplerTM is an example of a passive grab sampler

Conceptualization of Vapor Transport-related Natural Source Zone Depletion (NSZD) processes at a Petroleum Release Site

Conceptual diagram of basic Soil Vapor Extraction (SVE) system for vadose zone remediation. (SVE) is a common and typically effective physical treatment process for remediation of volatile contaminants in vadose zone (unsaturated) soils

Emulsified Vegetable Oil (EVO) mixed in field during early pilot test. EVO is commonly added as a slowly fermentable substrate to stimulate the in situ anaerobic bioremediation of chlorinated solvents, explosives, perchlorate, chromate, and other contaminants