Soil vapor studies are experiencing a resurgence in popularity with the increased focus on the Vapor Intrusion pathway and the introduction of new tools and analytical methods.  In this presentation we will discuss why understanding a site's soil vapor conditions is so important, how to collect and interpret soil vapor data, and how to use this information for site characterization, conceptual site model development, vapor intrusion assessment, and vapor mitigation.  Throughout the presentation we will present case studies based on sites where the understanding of the soil vapor conditions have helped to streamline the investigation and remediation processes leading to more successful outcomes.    

Sampling events for site investigations require careful planning to ensure the data collected will yield conclusive results.  Consultants and field teams understand their equipment and preparation are critical to human health risk determination. Are all sampling media created equal? Are they all “good enough”?  Data quality objectives provide direction for active vs passive sampling and there are several types of media within these two main categories. Dive deep into side-by-side comparisons of which work best and provide accurate results in a variety of situations. Understand what to consider for your next field event. 

Achieving remediation goals from high contamination levels, even in presence of NAPL  - Non Aqueous Phase Liquid - to concentrations in the micrograms range requires the integration of multiple proven technologies. This abstract presents a comprehensive overview of key remediation strategies: In Situ Chemical Oxidation (ISCO), In Situ Chemical Reduction (ISCR), bioremediation, adsorption/oxidation techniques, and the use of surfactants.

ISCO involves the injection of oxidizing agents (e.g., hydrogen peroxide, permanganate) to transform pollutants into less harmful compounds. ISCR, on the other hand, uses reducing agents (e.g., zero-valent iron) to chemically transform contaminants into benign substances. Bioremediation leverages microbial metabolism to degrade contaminants, utilizing either natural microbial communities or bioaugmentation with specialized strains. Adsorption and oxidation techniques, such as activated carbon and catalytic oxidation, effectively trap and break down contaminants. Surfactants can enhance the solubility and mobility of NAPLs, facilitating their subsequent treatment by other remediation methods.

These technologies are often used in combination to achieve synergistic effects, optimizing contaminant removal efficiency. Field applications have demonstrated their capability to reduce contaminant concentrations to regulatory-compliant levels. This integration of remediation strategies is essential for transforming highly polluted sites into environments that pose minimal risk to public health and the environment, showcasing a path from severe pollution to safe, sustainable land use.

Background/Objectives: 

This applied presentation will explain hydro-geo-chemical fundamentals of hydrophobic organic chemical (HOC) behavior including: petroleum hydrocarbons, chlorinated solvents, PFAS, 1,4 Dioxane, and pesticides, in saturated and unsaturated regimes. This encompasses their physical chemistry characteristics, what drives their tendency to phase partitioning from aqueous phases, what drives sorption (i.e. absorb and adsorb), the consequences of interfacial tension, between NAPL and aqueous phases, and how these kinetically limit the ‘availability’ of contaminants for physical, biological and chemical remediation. The objective in to specifically show how the application of selective, sub CMC, surfactant enhanced remediation (SER®) can overcome the limitation of sorption, phase partitioning and interfacial tension to measurably, and sustainably, enhance contaminant phase-desorption of VOC, SVOC, sorbed, globule and NAPL for enhanced remediation.

Approach/Activities: 

SER® case studies are presented explaining the hydro-geochemical conditions of each site which were hindering effective vapor, soil and groundwater remediation, through the clients’ in-situ SER® integration strategy, evidence based monitoring, with statistically evaluation to quantify the measurable benefits realized at each site. Such as coupling SER® with multi-phase extraction (MPE) and/or aggressive fluid vapor recovery (AFVR) strategies, which significantly truncated the duration of remediation, compared to the predictive models, to achieve regulatory objectives, and/or risk based closure for the involved sites.

The presentation will be technically underpinned by established scientific principles, supported by site data, figures, tables, and three-dimensional computer models for improve audience conceptual command of SER® for sustainable remediation of PFAS, Petroleum Hydrocarbons, and Chlorinated solvents.

Results/Lessons Learned: 

SER® remediation can be employed to overcome the principle hydro-geochemical factors that constrain the availability of NAPL, globule (ganglia), sorbed, and vapor phase contamination, for most physical, biological, and chemical remediation strategies, compared to when combined with SER® to realize synergistic benefits. Additional benefits included resolution of measurable and mobile LNAPL and DNAPL, significant project life-cycle time and cost savings, for achieve regulatory and/or risk-based closure.

Gasoline ether oxygenates (GEO), such as methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-amyl ethyl ether (TAEE), and diisopropyl ether (DIPE), are added to gasoline formulations to reduce vehicle emissions. Over the last 15 years,

ETBE has become the dominant ether oxygenate used in European gasoline, primarily because it can be synthesized from biomass and contributes to the EU Renewable Energy Directives;  requirements for biofuel use. GEOs may enter groundwater through releases during production, distribution, storage, and accidental spills, along with other gasoline hydrocarbons.

Thus, the remediation of these hydrocarbons through natural decontamination processes is of great importance. Bioremediation is a non-invasive and cost-effective technique for the cleanup of petroleum hydrocarbons. The presence of aerobic ETBE-degrading microorganisms has been observed at contaminated sites, though typically in low numbers and with low degradation rates. For this reason, the bioaugmentation approach presents an interesting alternative for the treatment of ETBE, as opposed to biostimulation or Monitored Natural Attenuation (MNA). 

The aim of this study was to enrich pure cultures from an ETBE-polluted site in northeast Spain, capable of degrading ETBE as the sole carbon source. We isolated and identified four pure strains with the ability to degrade ETBE and TBA, both individually and in consortium. Each

strain was identified by 16S rRNA gene sequencing, and their growth using ETBE or TBA as the sole carbon source was tested in mineral media. The strains were then used to define a synthetic consortium, and their synergistic interactions and degradation capabilities were

studied. This consortium was able to degrade 100 ppm of ETBE without any accumulation of TBA within 100 hours.

Once the ETBE-degrading culture has been obtained, a pilot test will be conducted to validate the laboratory results. This test will take place at a petrol station impacted by ETBE and will include a study of the degrading culture's effect on the contamination plume (with ETBE only) and in the focus area where TPH and BTEX are present.