Naval Facilities Engineering and Expeditionary Warfare Center

Transport of poly- and perfluoroalkyl substances (PFAS) at aqueous film-forming foam (AFFF)-impacted sites is limited by various processes that can retain PFAS mass within the source area. This study used concentration data obtained via a high-resolution sampling and analytical protocol to estimate the PFAS mass distribution in source and downgradient areas of a former firefighter training area. The total PFAS mass present at the site was approximately 222 kg, with 106 kg as perfluoroalkyl acids (PFAAs) and 116 kg as polyfluorinated precursors. Zwitterionic and cationic PFAS represented 83% of the total precursor mass and were found primarily in the source and up/side-gradient areas (75%), likely due to preferential hydrophobic partitioning, electrostatic interactions, and diffusion into lower-permeability soils. Based on the release history and the high percentage of total PFAS mass represented by precursors (primarily electrochemical fluorination-derived compounds), the estimated conversion rate of precursors to PFAAs was less than 2% annually. Eighty-two percent of the total PFAS mass was encountered in lower-permeability soils, which limited the potential for advection and transformation. This contributed to a 99% decrease in the mass discharge rate at the far-downgradient plume (0.048 kg/yr compared to the near-source area (3.6 kg/yr)). The results provide field-scale evidence of the importance of these PFAS retention processes at sites where AFFF has been released.

The relevance of multiple poly- and perfluoroalkyl substance (PFAS) fate and transport process across multiple sites was established through high-resolution characterization of the spatial distribution of PFAS within aqueous film forming foam (AFFF)-related source areas and the downgradient plumes. The maximum total PFAS concentrations in source area groundwater at the three study sites ranged from 6 to 51 mg/L but consistently decreased by several orders of magnitude with distance from the source area at all sites, indicating that non-destructive attenuation of PFAS occurred along each flow path. The relative distribution of different PFAS classes, including zwitterionic/cationic species, provided site-specific lines of evidence for retardation due to hydrophobic, air-water interfacial, and electrostatic partitioning processes, as well as impacts from biotransformation and matrix diffusion at multiple sites. The only site where one of these processes (air-water interfacial partitioning) was not supported by the data (Site 1) was attributable to disturbance of vadose zone soils as part of historic remedial efforts. In other cases, the magnitude that these processes influenced PFAS transport reflected site-specific conditions. This included apparent salting out of PFAS at Site 2 due to its elevated groundwater salinity, which has implications for plume migration in coastal areas. In addition, PFAS was present in lower-permeability soils at each site, suggesting that longer-term retention of PFAS is occurring in these zones. The finding that multiple processes were active at site-wide scales is consistent with expectations that these are naturally occurring reactions that should be relevant at most AFFF-impacted source zones.

Abstract Practical guidelines based on a three‐tiered lines of evidence (LOEs) approach have been developed for evaluating monitored natural attenuation (MNA) at per‐ and polyfluoroalkyl substances (PFAS)‐impacted groundwater sites using the scientific basis described in a companion paper (Newell et al., 2021). The three‐tiered approach applies direct measurements and indirect measurements, calculations, and more complex field and modeling methods to assess PFAS retention in the subsurface. Data requirements to assess the LOEs for quantifying retention in both the vadose and saturated zones are identified, as are 10 key PFAS MNA questions and 10 tools that can be applied to address them. Finally, a list of potential methods to enhance PFAS MNA is provided for sites where MNA alone may not effectively manage the PFAS plumes. Overall, a practical framework for evaluating PFAS MNA that can result in more efficient, reliable management of some PFAS sites is provided.

ABSTRACT Numerous polypropylene hollow fiber microfiltration membrane modules were severely degraded after utilization as pretreatment in a military water purification system. To determine the plausible causes of degradation, thermal, chemical, and mechanical material properties were initially evaluated by using differential scanning calorimetry, thermogravimetric analysis, 13 C solid‐state nuclear magnetic resonance, attenuated total reflectance infrared spectroscopy, and a tensile strength material testing system. The evaluation implied oxidation during the usage or storage of the samples. Protocols using more specialized techniques, micro‐Raman spectroscopy along with energy dispersive X‐ray spectroscopy and an atomic force microscope‐based nano‐thermal analysis, were developed to examine the chemical and thermal properties along the cross‐section of the samples at the micron and submicron‐scale. These results indicated that the degradation mainly took place at the outer and inner boundaries of the samples. Pristine samples exposed to several plausibly harsh environments did not evidence the same level of mechanical failure, but a few circumstances had similar test responses, leading to a hypothesis of high oxidative stress as the main failure etiology versus a slowly evolving one. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 41553.

Abstract The potential performance of a hypothetical colloidal‐activated carbon (CAC) in situ remedy for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in groundwater in coastal zones was evaluated using estimated hydrogeologic and geochemical parameters for a coastal site in the United States. With these parameters, a reactive transport model (ISR‐MT3DMS) was used to assess the effects of tidal fluctuations and near‐shore geochemistry on CAC performance. The average near‐shore ionic strength of 84 mM at the site was conservatively estimated to result in an increase in the adsorption of PFOA to CAC by about 50% relative to non‐coastal sites with ionic strength <10 mM. The modeling also confirmed the hypothesis that tidally induced groundwater flow reversals near the shore would result in the accumulation of PFOA at the downgradient edge of the CAC zone. Slow desorption of PFOA from this downgradient CAC boundary may sustain downgradient plume concentrations above a strict cleanup criterion (e.g., USEPA MCL of 0.004 μg/L), for decades; however, there was still a large PFOA mass flux reduction (>99.9%) achieved after several decades at the shore. CAC longevity was substantially greater for PFOS with a similar source concentration; however, the higher PFOS distribution coefficient ( K d ) in soil downgradient from the CAC zone resulted in substantially longer flushing times. It is recommended that short‐term remedial action objectives for CAC remedies at coastal sites be based on mass flux reduction targets over a period of several decades, given the demonstrated challenges in trying to achieve very low cleanup criteria downgradient of a CAC zone in the short term.

Separation Distances are used throughout the world to protect people and assets from the potential hazardous effects from propellants, explosives, and pyrotechnics. The current separation distances for Hazard Division (HD) 1.3 substances and articles used in the United States, in some cases, may not adequately protect against the effects from heat flux and debris when those substances and articles are ignited in a confined structure. Multiple tests in such a confined scenario with HD 1.3 substances have shown that the heat flux and debris hazards could result in injury at distances beyond the current specified explosives safety separation distance (ESSD). Herein are the recommended ESSDs for confined as well as unconfined HD 1.3 articles and substances based on the analysis of hundreds of tests. Recommended ESSDs include a smaller value for unconfined quantities less than 145 kg and ESSDs that are consistent with NATO distances for confined substances and articles.

A simple potentiostat was constructed as a strategy to enhance solvent production in a mediatorless and oxygen-exposed fermentation inoculated with the aerotolerant strain Clostridium sp. C10. Elevated n-butanol and acetone titers were recorded in all fermentations with either glucose or xylose in the presence of electrodes poised at + 500 mV (+ 814 mV vs SHE) relative to cells plus substrate only controls. Respective butanol titers and volumetric butanol productivities in studies performed with 30 g/L glucose or 30 g/L xylose were 1.67 and 2.27 times and 1.90 and 6.13 times greater in the presence of electrodes compared to controls. Glucose and xylose utilization in the presence of electrodes was 61 and 125% greater than no-electrode controls, respectively. Increasing substrate concentrations to 60 g/L decreased the butanol yields relative to the studies performed at 30 g/L. These data suggest that it may be more efficient to alter reactor reduction potential than increase substrate concentration for solvent output during industrial fermentations, which favors higher yield with few additional inputs.

The real-time identification of targets on small unmanned aircraft systems (UAS) is a challenging task. One approach to achieving this task is the use of image recognition in deep learning networks on embedded processors. While it has been well established that the use of deep learning networks can help increase the reliability of image recognition applications, less research has been performed on the requirements needed for selecting an appropriate embedded processor that can meet the speed and efficiency needs for real-time target identification. The embedded processor must fit within the size, weight, and power (SWaP) constraints of small UAS, while still meeting the computational and memory requirements of the detection algorithms. To determine whether embedded processors meet these form factor requirements and other performance considerations, we evaluated and compared several commercially available embedded processors based on their physical specifications, performance using lightweight benchmark machine learning models developed for commercial use, and performance using a Navy-developed deep convolutional neural network (CNN) used for identifying the California Least Tern. This evaluation will provide information on the necessary hardware and software requirements for performing complex computing tasks on a UAS in real-time using image recognition deep learning networks on embedded processors.

It is challenging to obtain degradation rate constants for chlorinated solvents (e.g., trichloroethene, TCE) that reside within low permeability formations such as fractured bedrock. Degradation rates are needed to evaluate remediation strategies. The overall objective of this research was to determine rate constants for degradation of TCE in rock core samples from fractured bedrock aquifers at three Department of Defense sites. In a prior study ( Wang et al., 2024 ), core samples were used in novel intact rock microcosms that were infused with TCE and carbon-14 ( 14 C-) labeled TCE. Uncontaminated groundwater was circulated through the headspace of the microcosms (i.e., the simulated fracture space) to induce diffusion out of the core that simulated back diffusion from a low permeability rock matrix. Four incubation conditions were evaluated based on the composition of the groundwater circulated through the simulated fracture space: unamended (i.e., no electron donor or sulfate added); lactate amended; lactate + sulfate amended; and mercuric chloride amended. In addition to monitoring the formation of cis -1,2-dichloroethene (cDCE) and vinyl chloride (VC), data were collected on non-chlorinated degradation products that accumulated in the microcosms, including dissolved gases (i.e., acetylene, ethene, ethane) and 14 C-labeled soluble compounds. The rates at which the non-chlorinated degradation products accumulated were used to estimate pseudo-first-order rate constants by inverting numerical simulations. Rate constants for unamended treatments that best represent in situ conditions ranged from 0.013 to 0.049 yr −1 and are statistically equivalent to the constants characterizing treatments that were amended with mercuric chloride to inhibit microbial activity. 14 C-labeled degradation products accounted for 75–90 % of the rate constants; not including these products would underestimate TCE degradation potential. Lactate and lactate + sulfate amended microcosms had statistically higher rate constants for TCE degradation (ranging from 0.034 to 0.13 yr −1 ) compared to unamended microcosms. Although numerical simulation of intact rock core microcosms infused with 14 C-labeled compounds is more time-consuming and complex than other methods to assess TCE degradation potential in low permeability media, the resulting rate constants provide a robust estimate of the potential for TCE degradation in situ. • 14 C-TCE used to determine degradation rate constants within fractured rock. • 14 C-labeled degradation products accounted for 75–90 % of the rate constants. • Numerically simulated TCE degradation rate constants ranged from 0.013 to 0.13 yr −1 . • Abiotic degradation rate constants were 2.2 to 5.5 times higher with lactate added. • Lactate effect is consistent with biologically mediated abiotic degradation (BMAD).

Separation Distances are used throughout the world to protect people and assets from the potential hazardous effects from propellants, explosives, and pyrotechnics. The current separation distances for Hazard Division (HD) 1.3 substances and articles used in the United States, in some cases, may not adequately protect against the effects from heat flux and debris when those substances and articles are ignited in a confined structure. Multiple tests in such a confined scenario with HD 1.3 substances have shown that the heat flux and debris hazards could result in injury at distances beyond the current specified explosives safety separation distance (ESSD). Herein are recommended ESSD’s for confined as well as unconfined HD 1.3 articles and substances based on the analysis of hundreds of tests. Recommended ESSD’s include a smaller value for unconfined quantities less than 145 kilograms and ESSD’s that are consistent with NATO distances for confined substances and articles.

Abstract Refrigerated gases have been used to store energy with limited success. This paper presents the results of an exploratory study of how the behavior of fluids compressed to high pressures can be used to increase the efficiency of refrigeration cycles and one possible application for renewable energy. This research presents the results of thermodynamic modeling and analysis of a novel Carbon Dioxide (CO2) cycle to be used for alternative energy production. The thermodynamic computational simulations are carried out in MATLAB and use the NIST REFPROP database for modeling the high pressure (on the order of 1000 MPa) CO2 state points. Preliminary results show that the maximum energy that can be recovered using the proposed high pressure cycle in on the order of 11,043 J, for each mole of CO2 flowing in the cycle. Thus the Coefficient of Performance is COP = 2.22, and the efficiency of the cycle is estimated as η = 35%. Future work will focus on the development of equipment such as the cryogenic turbo-expander that can operate at the ultra-high pressures studied.

A data mule is a vehicle used to physically transfer data between locations, providing asynchronous connectivity without the expense of establishing traditional networking solutions (e.g., cellular, mesh, wired broadband, etc.). In remote areas, field personnel often act as "human data mules," retrieving data from ground sensors (e.g., camera traps, data loggers, audio recorders) on foot, which is time-consuming and exposes individuals to safety risks. This paper provides an overview of the novel UAS Data Mule technology as an effective alternative for manual data retrieval of ground-based sensor data used in a broad range of applications including wildlife and environmental monitoring, disaster response, and security.

The accurate assessment of repaired airfield pavements, particularly crater repairs in military airbases, is critical for ensuring operational safety and structural integrity. This study evaluates pavement profiling methods and quality criteria, focusing on small-area repairs under 152.4 m (500 ft) in length. Existing standards such as the Tri-Service Pavement Working Group (TSPWG), Unified Facilities Criteria (UFC), and Federal Aviation Administration (FAA) guidelines are reviewed for applicability to localized repairs. A full-scale pavement test conducted at Tyndall Air Force Base compared four profiling methods to select the better-performing one for small repair areas: a 3.65 m (12 ft) straightedge, a customized straight bar, a walk-behind profiler, and an inertial profiler. While the inertial profiler excelled in rapid data collection for full-length runways, it lacked the accuracy and repeatability needed for localized repairs. The walk-behind profiler demonstrated superior precision and repeatability, albeit with longer measurement times. Additional data analysis was conducted using arbitrarily created bumps and simulated aircraft responses on them, revealing that current deflection thresholds for repaired areas are overly conservative. The study proposes refined threshold values for bump height and length to better align with realistic operational conditions, enhancing both the accuracy and efficiency of pavement evaluation. Results inform recommendations for revising airfield pavement management guidelines to improve quality assurance (QA) and quality control (QC) processes for repaired and newly constructed surfaces. These findings contribute to the optimization of profiling tools and methods, addressing gaps in current practices and improving the performance and reliability of airfield pavements in both civilian and military contexts.

Input values used in existing airfield pavement design methods are all assumed to be consistent for 20 years of their whole pavement design life without allowing for any potential changes during the pavement life. This paper presents research efforts the Naval Facilities Engineering and Expeditionary Warfare Center (NAVFAC EXWC) made to characterize pavement damages caused by traffic condition changes such as emerging new aircraft types with excessive stresses that were not considered in the original pavement design. Selected military aircraft operations under the expeditionary environments were implemented by the California Bearing Ratio (CBR) design method in the US Department of Defense (DoD) Pavement Computer Assisted Structural Engineering (PCASE) program to characterize pavement damages which has been adopted for civilian airport pavement design as well. A procedure was developed to estimate in-service airfield pavement damages under given aircraft operations in expeditionary (military) and overload (civilian) environments and adopted for remaining pavement life computations.

Abstract DoD organizations such as the Naval Facilities Engineering Command (NAVFAC), the Air Force Civil Engineering Center, and the US Army Corps of Engineers provide design and analysis of structures to resist blast effects from accidental explosions and terrorist or foreign threats. Current code provisions for designing structures under accidental blast conditions and dynamic loading are given in UFC 3-340-02 (Change 2, 1 September 2014). The field of structural blast safety is uniquely and acutely more relevant to DOD agencies due to the nature of both malicious and accidental risks. Obviously, terrorist incidents address one component, but the requirement to safely store munitions on DOD installations sparked the formation of the DOD Explosives Safety Board in 1928 after the major accidental explosion at the Naval Ammunition Depot, Lake Denmark, New Jersey. The requirements persist, as all services face the challenges posed by explosives safety. Beginning in the fall of 2019, researchers at the NAVFAC Expeditionary and Engineering Warfare Center (EXWC) in Port Hueneme, CA and faculty at the US Military Academy in New York began partnering in search of mutually beneficial research and education opportunities. This paper presents a unique research project and capstone experience at the undergraduate level that will benefit DOD research, active duty service members, and undergraduate civil engineering students from June 2020 through May of 2021. Three civil engineering students embarked on a project-based study to support NAVFAC EXWC in their role as subject matter experts in protective construction for explosives safety for multiple military construction (MILCON) projects on Navy installations. Cadet work has extended learning on reinforced concrete, delved into new blast engineering design knowledge, incorporated the generation Mathcad-based engineering tools, and investigated performance-based alternatives to support rotation limits for one-way structural members identified in the UFC 3-340-02. The project has provided a wealth of opportunities to prepare cadets for graduate level experiences and learn new content, while the analysis and results from this capstone project will arm DoD engineers with new tools for design. This paper reports on the results of this effort leveraging DoD expertise and research with undergraduate experiential learning. The authors will demonstrate that the synergies associated with the DoD interests substantively improved the student capstone experience, resulting in enhanced achievement of broader ABET student outcomes, while simultaneously providing useful tools and better trained engineers to the profession.

Deep convolutional neural networks (CNNs) have proven to be successful for learning task-specific features that achieve state-of-the-art performance on many computer vision tasks. For object detection applications, the introduction of region-based CNNs (R-CNNs), and its successors, Fast R-CNN and Faster R-CNN, has produced relatively high accuracies and run-time efficient results. With Faster R-CNN, a region proposal network (RPN) is employed to share convolutional layers for both object proposals and detection with no loss in accuracy. However, these approaches are trained in a fully supervised manner, where a large number of samples for individual object classes are required, and classes are pre-determined by manual annotation. Large-scale supervision leads to limitations in utility for many real-world applications, including those involving difficult-to-detect, small, and sparse target objects in variable environments. Alternatively, exemplar learning is a paradigm for discovering visual similarities in an unsupervised fashion from potentially very small numbers of examples. Surrogate classes or outliers are discovered via the inherent empirical characteristics of the objects themselves. In this work, we merge the strengths of CNN structures with pre-processing steps borrowed from exemplar learning. We employ a semi-supervised approach that combines the ability to use generically-learned class-relatedness with CNN-based detectors. We train and test the approach on a set of aerial imagery generated from unmanned aircraft systems (UAS) for challenging real-world, small object detection tasks.

This paper evaluated the performance and durability of leading structural shading materials to be used in the Super Containerized Living Units (Super-CLU’s) project. Fifteen unique shading fabrics were tested in five different experiments in order to evaluate their strength, resistance to wind, abrasion, and heat and to assess their heat transmissivity and breathability. A current United States Navy material was used as a control material for the evaluation of the other tested materials. Samples of each fabric were first tensile tested in both their warp and weft orientation to create an ‘as-received’ baseline condition. Then, additional samples of each fabric were exposed to wind, abrasion, or heat and subsequently tensile tested in order to show the degradation in tensile strength as compared to the as-received samples. The heat transmissivity and breathability testing was conducted separately.

Separation Distances are used throughout the world to protect people and assets from the potential hazardous effects from propellants, explosives, and pyrotechnics. The current separation distances for Hazard Division (HD) 1.3 substances and articles used in the United States, in some cases, may not adequately protect against the effects from heat flux and debris when those substances and articles are ignited in a confined structure. Multiple tests in such a confined scenario with HD 1.3 substances have shown that the heat flux and debris hazards could result in injury at distances beyond the current specified explosives safety separation distance (ESSD). Herein are recommended ESSD’s for confined as well as unconfined HD 1.3 articles and substances based on the analysis of hundreds of tests. Recommended ESSD’s include a smaller value for unconfined quantities less than 100 kilograms and ESSD’s that are consistent with NATO distances for confined substances and articles.

The knowledge of live load spectra is needed for the development of rational design criteria for piers and wharves at port terminals. Unbiased truck axle weights and configurations are collected using Weigh-in-Motion (WIM) sensors installed at various access points and locations within the Port Terminal. Records of trucks and other types of heavy vehicles are processed to determine statistical distributions of gross vehicle weights, axle loads, and other parameters. This paper presents a methodology for developing a live load model for the design of piers and wharves at port terminal using “heavy” representative (i.e., upper tail) data. The recorded trucks are run through influence lines to calculate load effects. The obtained load spectra are compared with those from truck surveys and permit records in the vicinity of port areas. The approach includes calibration of live load factors and performing reliability-based analysis for predicting future live load levels for pier design.

This paper discusses a study using several analysis tools to make pre-test predictions of blast loads from an internal explosion test of a cased charge. The objective of the calculations was to generate best estimates of the blast loads, and because of the uncertainties associated with the different analytic tools, account for these uncertainties when analyzing or designing for the structure's response. The codes used included two fast-running models (FRM's) and two high-fidelity physics-based (HFPB) computational fluid dynamic (CFD) codes. The predictions from the simulations are compared to data from an actual blast test that was performed in a test structure that was designed to resist the loads while incurring only low levels of damage. The results of these comparisons are presented and the accuracy of the analysis tools is discussed