deployment-and-retrieval-of-mineral-samplers

Deployment and Retrieval of Mineral Samplers

Subsurface chemical, geochemical, and microbiological interactions, such as reactive mineral formation, gas generation, and contaminant sorption, play a ...

Arcadis

The primary goals for most ground water capture systems (i.e., pump-and-treat systems) are that (1) all contaminants within zones of interest will eventually be captured and (2) the extraction and reinjection wells are best located and operated at optimal flow rates, creating hydraulically efficient flow systems. A new tool, MODular ALLocation (MODALL), is presented to aid in the design and assessment of capture systems. MODALL uses the MODFLOW-calculated cell-by-cell flow terms to evaluate internodal flow balances to determine the percentage of flow in each cell which has either originated from a given source(s) or flows to a specified sink(s). Output from MODALL can be easily displayed in isopleths of "capture fraction" (CF) to indicate the certainty or strength of capture in various areas. MODALL results are compared to the results from an analytical solution, a pathline analysis using MODPATH, and solute transport simulation with MT3DMS. A brief case study is also presented where MODALL is used to optimize an existing pump-and-treat system to more effectively and more efficiently contain a 5000-m long plume.

MODALL: a practical tool for designing and optimizing capture systems.

Evaluation of chemical risks to threatened and endangered species is a requirement for Superfund ecological risk assessments; however, screening levels to evaluate the potential for toxicity associated with ecological receptor exposure to per- and polyfluoroalkyl substances (PFAS) are lacking. Therefore, PFAS risk-based screening levels (RBSLs) were developed. Wildlife RBSLs were developed using surrogate receptors selected to be representative of threatened and endangered species with different habitat types, feeding guilds, and trophic levels. Published uptake and toxicity data were combined with receptor exposure factors to derive RBSLs for terrestrial and aquatic wildlife for several PFAS, including perfluorononanoic acid, perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorohexanoic acid, perfluorobutanesulfonic acid, and pentafluorobenzoic acid. Uptake information for surrogate PFAS were considered to calculate RBSLs for PFAS with toxicity data and insufficient bioaccumulation data to develop an RBSL. Both no-observed-adverse effect level (NOAEL)- and lowest-observed-adverse effect level-based wildlife RBSLs were calculated to allow for a range of risk estimates appropriate to individual threatened and endangered species and populations of nonlisted wildlife receptors, respectively. Recommended water quality RBSLs protective of aquatic life were developed for 23 PFAS based on published literature reviews and peer-reviewed aquatic toxicity studies and Great Lakes Initiative methodology. For wildlife receptors, NOAEL RBSLs ranged from to 0.013 to 340 mg/kg for soil, 0.0014 to 370 mg/kg for sediment, and 0.000075 to 1600 mg/L for surface water. For aquatic life, chronic RBSLs ranged from 0.00022 to 3.4 mg/L. For terrestrial plants and soil invertebrates, the no-observed-effect concentration screening levels range from 0.084 to 642 mg/kg and from 1 to 50 mg/kg, respectively. Environ Toxicol Chem 2021;40:921-936. © 2020 SETAC.

Development of Per and Polyfluoroalkyl Substances Ecological Risk-Based Screening Levels.

The Horizontal Reactive Media Treatment Well (HRX Well®) is a technology capable of collecting and treating groundwater passively. To monitor the internal flow rate, ensuring it remains at an acceptable level and maintains the desired capture zone size in the aquifer, Point Velocity Probes (PVPs) were adapted for the task. The modified PVP was assessed for its performance in a mock-HRX Well setting, which consisted of a laboratory sand column, similar in diameter to the HRX Well cartridges that would house the PVP in the field, with flow directed along the longitudinal axis of the probe. Experiments were conducted to assess 1) the effects of friction between the fluid and the probe surface, which could bias a velocity measurement low, and 2) the effect of gas in the porous medium, potentially generated by some reactive media, on PVP signals and measurements of velocity. It was determined that PVP length exerted no discernable effect on the quality of the PVP performance. However, the effects of gas in the porous medium were varied. Compared to velocity estimates assuming a fully saturated porous medium, the bias to velocity measurements was negative if gas was limited to locations near a PVP's injection-detection array, such as might occur by inadvertent bubble injection during the tracer pulses. The bias was positive if the gas was generated uniformly throughout the porous medium, such as might occur in a reactive porous medium like granular iron, or one featuring vigorous biological activity. A field trial of the HRX Well was subsequently undertaken with internal PVPs. The PVPs identified a missing seal that was later retrofit, and documented flow in the HRX Well at velocities in the range of 1.3 to 4.0 m/d, which compared well with expectations based on a site model that predicted velocities of 1.3 to 2.3 m/d. The results of this study demonstrate that HRX Wells perform hydraulically as designed, and that PVPs are effective devices for tracking flow rates within them in near real-time.

Design, testing, and implementation of a real-time system for monitoring flow in horizontal wells.

The use of aqueous film forming foam (AFFF) in the United States has caused concern about the potential effects of per- and polyfluoroalkyl substances (PFAS) on ecological resources. Moreover, the limited availability of scientific information and a lack of guidance have collectively resulted in significant challenges for ecological risk assessors supporting site-specific investigations and management decisions at PFAS-impacted sites. To address these needs, the environmental science and technology program of the Department of Defense (DoD), the Strategic Environmental Research and Development Program (SERDP), began funding four desktop review projects in 2018. Project teams were tasked with developing strategic guidance for assessing ecological risk at AFFF-impacted DoD sites. The projects focused specifically on ecological risk assessment practices for threatened and endangered (T&E) species; however, the recommendations and approaches presented in the projects are also applicable and adaptable to common species. The present review provides risk assessors and site managers an overview of how the resources provided in these projects can support ecological-risk-based management decisions at AFFF and other PFAS-impacted sites. Additionally, we synthesize perspectives offered by the four projects on a path forward for PFAS ecological risk assessment, including research needs that we recommend should be prioritized by the scientific community. Integr Environ Assess Manag 2021;17:746-752. © 2021 SETAC.

Strategic resources for assessing PFAS ecological risks at AFFF sites.

Fire suppression systems are known to be impacted with residual, entrained per- and polyfluoroalkyl substances (PFASs) because of historical use of aqueous film forming foam (AFFF) and fluoroprotein foam. Amphiphilic PFASs aggregate at liquid:solid interfaces creating a hydrophobic layer which reduces the effectiveness of water to remove PFAS from layered surfaces. When fire suppression systems are transitioned to fluorine free foam (F3) without appropriate cleaning, residual PFASs associated with the surfaces of the fire suppression system can contaminate the replacement F3. Release of residual PFASs from fire suppression systems into F3 has been documented; however, little is known about the residual PFASs associated with the surfaces of the fire suppression systems. More information is needed to develop methods to appropriately remove PFASs from fire suppression systems to prevent costly and inefficient foam transitioning and preserve the PFAS-free benefit of F3. The objective of this work was to evaluate the distribution and composition of PFASs on hangar piping exposed to PFAS-containing firefighting foam for a prolonged period. Two assessment methods were used: 1) extractions with methanol, water, and a proprietary aqueous organic solvent (Fluoro Fighter™); and 2) direct imaging methods of the surface. Extractions were analyzed with mass spectrometry and combustion ion chromatography. Results indicate pipe in contact with PFAS-containing firefighting foam can amass approximately 10 μg/cm of surface-associated PFAS residual following decades of exposure. Fluoro Fighter demonstrated higher PFAS removal per surface area of pipe than methanol (p = 0.007) or water extraction (p < 0.0001). Scanning electron microscope (SEM) images of the hangar piping reveal deposits suspected to be self-assembled PFAS layers, as evidenced by examination of pipe surfaces using X-ray photoelectron spectroscopy (XPS), which revealed atomic fluorine on the surface of the pipe.

Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods.

Low temperature heating of the subsurface (increases of about 5-20 °C) can substantially increase rates of biotic and abiotic destruction of dissolved contaminants such as chlorinated solvents. Low-temperature heating can be sustainably and cost-effectively achieved using solar thermal collectors coupled with closed-loop borehole heat exchangers. This technology has been implemented at several sites in the United States and abroad with favorable results. The design of a solar thermal remediation system requires a quantitative understanding of heat transfer from the array of borehole heat exchangers. We present an easy-to-use design tool that is based on a transient three-dimensional analytical heat transfer solution and is programmed in Visual Basic in Excel. This tool can be used to quickly explore the effect of design variables on the forecast temperature field. Typical design variables would include the site-specific average and monthly solar insolation data, solar collector configuration, borehole heat exchanger geometry and spacing, and the effects of environmental variables such as groundwater velocity, background subsurface temperature, and thermal conductivity. The design tool has been verified by comparisons with the TOUGH2 multiphase heat transfer code for a three-dimensional multi-heater system with seasonally variable thermal power rates. The code has been validated by comparisons to observed temperatures measured at a solar thermal field remediation application at a site in Colorado.

A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers.

A field study was completed to assess the effectiveness of in-situ soil stabilization (ISS) to immobilize per- and polyfluoroalkyl substances (PFAS) impacted soil, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), in a former burn pit at the Cavalier Space Force Station, North Dakota. Only a few field ISS studies have been published to-date and this work provides important practical considerations and performance data. Based on the results of a laboratory treatability study, RemBind® 100X, which consists of an aluminum hydroxide/carbon blend (amorphous aluminum hydroxide, kaolinite clay, and activated carbon), was applied at 3 percent by dry weight as a stabilizing material (or fixant) to impacted soil to reduce PFAS leaching from soil to groundwater. The fixant was distributed and mixed over a 3-foot vertical zone across a 100- x 100-foot area gridded into 18 test cells. Four performance monitoring events were completed throughout 19 months, during which soil samples were collected to assess PFAS leaching using Leaching Environmental Assessment Framework (LEAF) analysis, and vadose zone moisture was monitored using downhole nuclear magnetic resonance (NMR) imaging and in-situ moisture probes. For all PFAS analyzed, leachate concentrations following leachate testing, were reduced by at least 95 percent (±5.1 %) for each of the four sampling events and concentrations were measured at levels less than the United States Environmental Protection Agency's (USEPA's) regional screening levels (OSD 2023) and maximum contaminant levels (EPA 2024) for PFOS, PFOA, perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), perfluorononanoic acid (PFNA), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), and hexafluoropropylene oxide dimer acid (HFPO-DA). Furthermore, the approach was effective at reducing leaching from the stabilized soils, while still allowing infiltration of precipitation. Overall, this study confirms the efficacy of this technology and therefore should be consideration at other similar PFAS-impacted sites.

Field demonstration of in situ stabilization (ISS) of per- and polyfluoroalkyl substances in soil with remBind®.

Groundwater contaminated with organic chemicals can be treated by raising the subsurface temperature, thereby enhancing the rate of microbial degradation. This process requires careful monitoring through space and time to ensure that heat is being delivered to the most contaminated regions of the groundwater system. Here, we demonstrate the effectiveness of a fiber-optic distributed temperature sensing (DTS) system as a high spatial and temporal resolution monitoring strategy. The DTS sensing system required the installation of fiber optic cable in the subsurface. Boreholes were drilled with hollow casings, a fiber optic cable was inserted into the casings, and then, the casings were withdrawn to allow the formation to collapse around the fiber. The fiber was then fusion-spliced into a single continuous fiber that could be interrogated by a Raman-based DTS unit. Temperature measurements were collected at 30 min intervals over a 575 m span with 0.25 m spatial sampling, resulting in over 110,000 temperature data points per day. With this high resolution monitoring the development of thermal plumes emanating from solar-heated borehole heat exchangers could be closely monitored. The pseudo-3D monitoring network showed the lateral and upward migration of the induced thermal plumes over time. This information was valuable for assuring the heated groundwater was contacting the intended treatment zone.

Article	Year
MODALL: a practical tool for designing and optimizing capture systems. Ground water\| PubMed ID: 18194317	2008
Development of Per and Polyfluoroalkyl Substances Ecological Risk-Based Screening Levels. Environmental toxicology and chemistry\| PubMed ID: 33369775	2021
Design, testing, and implementation of a real-time system for monitoring flow in horizontal wells. Journal of contaminant hydrology\| PubMed ID: 33545531	2021
Strategic resources for assessing PFAS ecological risks at AFFF sites. Integrated environmental assessment and management\| PubMed ID: 33751777	2021
Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods. Chemosphere\| PubMed ID: 36108758	2022
A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers. Ground water\| PubMed ID: 36250992	2023
Field demonstration of in situ stabilization (ISS) of per- and polyfluoroalkyl substances in soil with remBind®. Journal of hazardous materials\| PubMed ID: 41110319	2025
Monitoring Groundwater Thermal Treatment Using a Fiber-Optic Distributed Temperature Sensing Network. Sensors (Basel, Switzerland)\| PubMed ID: 41374480	2025

Craig Divine

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