Vapor intrusion (VI) is a chemical exposure pathway that refers to the migration of hazardous vapors from a subsurface vapor source, such as contaminated soil or groundwater, through the soil and into an overlying building or structure. Release and transport of these compounds through the VI pathway can result in health risks that are typically estimated by collecting and analyzing samples, representing the results as an average concentration over time, and then comparing these measurements to risk screening criteria established by regulatory agencies. These criteria determine which mitigation option, if any, is to be implemented, as well as the specified response timing. While spatial variability and temporal dynamics are well-documented, the most common VI risk assessment approaches consist of samples collected via random timing driven by practitioner convenience and scheduling constraints. Previous studies have demonstrated that randomly timed sample results do not typically represent conservative conditions and are susceptible to underestimation and false negative results. More recent studies demonstrated that samples collected during upward vapor flux conditions driven by advective transport can result in improved risk assessments and a reduction in the potential for false negative conclusions. The current study builds upon these findings by generating empirical building-specific correlations between barometric pressure patterns and exposure concentration measurements during upward flux conditions. These correlations are then used to predict past occupant exposure profiles by applying the building-specific relationships to historical barometric pressure records. Three examples are described, and considerations for future VI investigations are presented. For each of these, a linear relationship between the barometric pressure drop rate and indoor concentration was observed. Subsequently, the most rapid drop in historic barometric pressure corresponded with a prediction of the highest indoor air concentration. This study represents the first time this type of building-specific learning model has been developed and used to estimate occupant exposures. This novel exposure prediction approach has the potential to improve VI risk assessments and mitigation design and to expedite risk management decisions.

In this issue paper, the authors refine the definition of water sustainability to account for temporal dynamics and spatial variability, identify specific challenges that must be resolved in the very near future to avoid catastrophic outcomes on levels ranging from economic disruption to survival of mankind, discuss related policy changes and potential effectiveness, and describe several technologies available to achieve water security and sustainability. While water quality certainly poses formidable challenges, in this piece we emphasize and address challenges associated with dynamic water supply availability. Our future as a society will depend upon how well and how rapidly we navigate these challenges in the coming years. As such, the main objective is to encourage private and public sector practitioners to consider revising existing programs, and to update current industry business models in a manner that promotes expedited solutions, alignment of beneficial goals, and motivates the biggest consumers of water to adopt modern data collection and decision support technologies.

The US Environmental Protection Agency (USEPA) recommends basing vapor intrusion risk-related decisions on reasonable maximum exposure (RME). The RME can occur during conditions and factors that control advective vapor transport. The most common vapor intrusion assessment approaches consist of randomly timed sample collection efforts without regard to vapor transport controlling factors. As such, they often do not accurately yield RME estimates and are, therefore, inconsistent with USEPA recommended risk decision criteria. To address these challenges, continuous high-frequency monitoring platforms have been deployed to concurrently track indoor concentrations of key volatile constituents, climatic conditions, and nominal pressure differential conditions that can result in toxic vapor transport and entry into buildings. The objective of this article is to demonstrate how vapor intrusion RME-based risks can be successfully and efficiently characterized by documenting concentrations during advective chemical transport into the building. Time series analyses of data from selected sites and time increments were performed and compared to results expected from the most commonly employed sampling methods. These analyses indicate that time-weighted analyses and resulting conclusions and risk-based decisions can vary depending upon the sample timing. More specifically, these findings demonstrate that RME estimates will only be representative with a sufficient level of confidence when samples are collected at appropriate times. High-frequency monitoring of dynamic concentration and controlling factors, and determination of a time-weighted concentration average over a selected duration concurrent with advective flux conditions allows for the derivation of a representative RME-based risk estimate. Furthermore, these variable temporal data patterns can prove insightful regarding cause-and-effect relationships.

The application of neural networks (NN) in groundwater (GW) level prediction has been shown promising by previous works. Yet, previous works have relied on a variety of inputs, such as air temperature, pumping rates, precipitation, service population, and others. This work presents a long short-term memory neural network (LSTM-NN) for GW level forecasting using only previously observed GW level data as the input without resorting to any other type of data and information about a groundwater basin. This work applies the LSTM-NN for short-term and long-term GW level forecasting in the Edwards aquifer in Texas. The Adam optimizer is employed for training the LSTM-NN. The performance of the LSTM-NN was compared with that of a simple NN under 36 different scenarios with prediction horizons ranging from one day to three months, and covering several conditions of data availability. This paper’s results demonstrate the superiority of the LSTM-NN over the simple-NN in all scenarios and the success of the LSTM-NN in accurate GW level prediction. The LSTM-NN predicts one lag, up to four lags, and up to 26 lags ahead GW level with an accuracy (R2) of at least 99.89%, 99.00%, and 90.00%, respectively, over a testing period longer than 17 years of the most recent records. The quality of this work’s results demonstrates the capacity of machine learning (ML) in groundwater prediction, and affirms the importance of gathering high-quality, long-term, GW level data for predicting key groundwater characteristics useful in sustainable groundwater management.

Vapor intrusion risk characterization efforts are challenging due to complexities associated with background indoor air constituents, preferential subsurface migration pathways, and representativeness limitations associated with traditional randomly timed time-integrated sampling methods that do not sufficiently account for factors controlling concentration dynamics. The U.S. Environmental Protection Agency recommends basing risk related decisions on the reasonable maximum exposure (RME). However, with very few exceptions, practitioners have not been applying this criterion. The RME will most likely occur during upward advective flux conditions. As such, for RME determinations, it is important to sample when upward advective flux conditions are occurring. The most common vapor intrusion assessment efforts include randomly timed sample collection events, and therefore do not accurately yield RME estimates. More specifically, researchers have demonstrated that randomly timed sampling schemes can result in false negative determinations of potential risk corresponding to RMEs. For sites experiencing trichloroethylene (TCE) vapor intrusion, the potential for acute risks poses additional challenges, as there is a critical need for rapid response to exposure exceedances to minimize health risks and liabilities. To address these challenges, continuous monitoring platforms have been deployed to monitor indoor concentrations of key volatile constituents, atmospheric pressure, and pressure differential conditions that can result in upward toxic vapor transport and entry into overlying buildings. This article demonstrates how vapor intrusion RME-based risks can be successfully and efficiently determined using continuous monitoring of concentration and parameters indicating upward advective chemical flux. Time series analyses from multiple selected 8- and 24-hr time increments during upward advective TCE flux conditions were performed to simulate results expected from the most commonly employed sampling methods. These analyses indicate that, although most of the selected time increments overlap within the same 24-hr window, results and conclusions vary. As such, these findings demonstrate that continuous monitoring of concentration and parameters such as differential pressure and determination of a time-weighted concentration average over a selected duration when upward advective flux is occurring can allow for a realistic RME-based risk estimate.

Groundwater Monitoring & RemediationVolume 39, Issue 1 p. 73-74 Letter to the Editor Comments in Response to “DyeLIF™: A New Direct-Push Laser-Induced Fluorescence Sensor System for Chlorinated Solvent DNAPL and Other Non-Naturally Fluorescing NAPLs” Mark Kram, Mark KramSearch for more papers by this authorArturo A. Keller, Arturo A. KellerSearch for more papers by this authorLorne Everett, Lorne EverettSearch for more papers by this author Mark Kram, Mark KramSearch for more papers by this authorArturo A. Keller, Arturo A. KellerSearch for more papers by this authorLorne Everett, Lorne EverettSearch for more papers by this author First published: 17 January 2019 https://doi.org/10.1111/gwmr.12313Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume39, Issue1Winter 2019Pages 73-74 RelatedInformation

Vapor intrusion characterization and response efforts must consider four key interactive factors: background indoor air constituents, preferential vapor migration pathways, complex patterns of vapor distribution within buildings, and temporal concentration variability caused by pressure differentials within and exterior to structures. An additional challenge is found at sites contaminated by trichloroethylene (TCE), which in the United States has very low indoor air screening levels due to acute risk over short exposure durations for sensitive populations. Timely and accurate characterization of vapor intrusion has been constrained by traditional passive time-averaging sampling methods. This article presents three case studies of a robust new methodology for vapor intrusion characterization particularly suited for sites where there is a critical need for rapid response to exposure exceedances to minimize health risks and liabilities. The new methodology comprises low-detection-level field analytical instrumentation with grab sample and continuous monitoring capabilities for key volatile constituents integrated with pressure differential measurements and web-based reporting. The system also provides automated triggered alerts to project teams and capability for integration with engineered systems for vapor intrusion control. The three case studies illustrate key findings and lessons learned during system deployment at two sites undergoing characterization studies and one site undergoing thermal remediation of volatile contaminants.

Vapor intrusion characterization efforts can be challenging due to complexities associated with background indoor air constituents, preferential subsurface migration pathways, and response time and representativeness limitations associated with conventional low-frequency monitoring methods. For sites experiencing trichloroethylene (TCE) vapor intrusion, the potential for acute risks poses additional challenges, as the need for rapid response to exposure exceedances becomes critical in order to minimize health risks and associated liabilities. Continuous monitoring platforms have been deployed to monitor indoor and subsurface concentrations of key volatile constituents, atmospheric pressure, and pressure differential conditions that can result in advective transport. These systems can be comprised of multiplexed laboratory-grade analytical components integrated with telemetry and geographical information systems for automatically generating time-stamped renderings of observations and time-weighted averages through a cloud-based data management platform. Integrated automatic alerting and responses can also be engaged within one minute of risk exceedance detection. The objectives at a site selected for testing included continuous monitoring of vapor concentrations and related surface and subsurface physical parameters to understand exposure risks over space and time and to evaluate potential mechanisms controlling risk dynamics which could then be used to design a long-term risk reduction strategy. High-frequency data collection, processing, and automated visualization efforts have resulted in greater understanding of natural processes such as dynamic contaminant vapor intrusion risk conditions potentially influenced by localized barometric pumping induced by temperature changes. For the selected site, temporal correlation was observed between dynamic indoor TCE vapor concentration, barometric pressure, and pressure differential. This correlation was observed with a predictable daily frequency even for very slight diurnal changes in barometric pressure and associated pressure differentials measured between subslab and indoor regimes and suggests that advective vapor transport and intrusion can result in elevated indoor TCE concentrations well above risk levels even with low-to-modest pressure differentials. This indicates that vapor intrusion can occur in response to diurnal pressure dynamics in coastal regions and suggests that similar natural phenomenon may control vapor intrusion dynamics in other regions, exhibiting similar pressure, geochemical, hydrogeologic, and climatic conditions. While dynamic indoor TCE concentrations have been observed in this coastal environment, questions remain regarding whether this hydrogeologic and climatic setting represent a special case, and how best to determine when continuous monitoring should be required to most appropriately minimize exposure durations as early as possible. ©2017 Wiley Periodicals, Inc.

Vapor intrusion characterization efforts are challenging due to complexities associated with indoor background sources, preferential subsurface migration pathways, indoor and shallow subsurface concentration dynamics, and representativeness limitations associated with manual monitoring and characterization methods. For sites experiencing trichloroethylene (TCE) vapor intrusion, the potential for acute risks poses additional challenges, as the need for rapid response to acute toxicity threshold exceedances is critical in order to minimize health risks and associated liabilities. Currently accepted discrete time-integrated vapor intrusion monitoring methods that employ passive diffusion–adsorption and canister samplers often do not result in sufficient temporal or spatial sampling resolution in dynamic settings, have a propensity to yield false negative and false positive results, and are not able to prevent receptors from acute exposure risks, as sample processing times exceed exposure durations of concern. Multiple lines of evidence have been advocated for in an attempt to reduce some of these uncertainties. However, implementation of multiple lines of evidence do not afford rapid response capabilities and typically rely on discrete time-integrated sample collection methods prone to nonrepresentative results due to concentration dynamics. Recent technology innovations have resulted in the deployment of continuous monitoring platforms composed of multiplexed laboratory grade analytical components integrated with quality control features, telemetry, geographical information systems, and interpolation algorithms for automatically generating geospatial time stamped renderings and time-weighted averages through a cloud-based data management platform. Automated alerts and responses can be engaged within 1 minute of a threshold exceedance detection. Superior temporal and spatial resolution also results in optimized remediation design and mitigation system performance confirmation. While continuous monitoring has been acknowledged by the regulatory community as a viable option for providing superior results when addressing spatial and temporal dynamics, until very recently, these approaches have been considered impractical due to cost constraints and instrumentation limitations. Recent instrumentation advancements via automation and multiplexing allow for rapid and continuous assessment and response from multiple locations using a single instrument. These advancements have reduced costs to the point where they are now competitive with discrete time-integrated methods. In order to gain more regulatory and industry support for these viable options, there is an immediate need to perform a realistic cost comparison between currently approved discrete time-integrated methods and newly fielded continuous monitoring platforms. Regulatory support for continuous monitoring platforms will result in more effectively protecting the public, provide property owners with information sufficient to more accurately address potential liabilities, reduce unnecessary remediation costs for situations where risks are minimal, lead to more effective and surgical remediation strategies, and allow practitioners to most effectively evaluate remediation system performance. To address this need, a series of common monitoring scenarios and associated assumptions were derived and cost comparisons performed. Scenarios included variables such as number of monitoring locations, duration, costs to meet quality control requirements, and number of analyses performed within a given monitoring campaign. Results from this effort suggest that for relatively larger sites where five or more locations will be monitored (e.g., large buildings, multistructure industrial complexes, educational facilities, or shallow groundwater plumes with significant spatial footprints under residential neighborhoods), procurement of continuous monitoring services is often less expensive than implementation of discrete time-integrated monitoring services. For instance, for a 1-week monitoring campaign, costs-per-analysis for continuous monitoring ranges from approximately 1 to 3 percent of discrete time-integrated method costs for the scenarios investigated. Over this same one-week duration, for discrete time-integrated options, the number of sample analyses equals the number of data collection points (which ranged from 5 to 30 for this effort). In contrast, the number of analyses per week for the continuous monitoring option equals 672, or four analyses per hour. This investigation also suggests that continuous automated monitoring can be cost-effective for multiple one-week campaigns on a quarterly or semi-annual basis in lieu of discrete time-integrated monitoring options. In addition to cost benefits, automated responses are embedded within the continuous monitoring service and, therefore, provide acute TCE risk-preventative capabilities that are not possible using discrete time-integrated passive sampling methods, as the discrete time-integrated services include analytical efforts that require more time than the exposure duration of concern. ©2016 Wiley Periodicals, Inc.

Groundwater Monitoring & RemediationVolume 36, Issue 3 p. 84-87 Letter to the Editor Comments and Corrections to: “The Emperor's Old Clothes: An Inconvenient Truth About Currently Accepted Vapor Intrusion Assessment Methods,” and “Emperor's Old Clothes Revisited,” Two Recent Editorials by Mark Kram by Todd McAlary, Todd McAlarySearch for more papers by this authorTom McHugh, Tom McHughSearch for more papers by this authorBart Eklund, Bart EklundSearch for more papers by this authorChris Lutes, Chris LutesSearch for more papers by this authorEric Suuberg, Eric SuubergSearch for more papers by this authorHeidi Hayes, Heidi HayesSearch for more papers by this authorKelly G. Pennell, Kelly G. PennellSearch for more papers by this authorDavid Folkes, David FolkesSearch for more papers by this authorHelen Dawson, Helen DawsonSearch for more papers by this authorRobert Truesdale, Robert TruesdaleSearch for more papers by this authorLila Beckley, Lila BeckleySearch for more papers by this authorChase Holton, Chase HoltonSearch for more papers by this author by Todd McAlary, Todd McAlarySearch for more papers by this authorTom McHugh, Tom McHughSearch for more papers by this authorBart Eklund, Bart EklundSearch for more papers by this authorChris Lutes, Chris LutesSearch for more papers by this authorEric Suuberg, Eric SuubergSearch for more papers by this authorHeidi Hayes, Heidi HayesSearch for more papers by this authorKelly G. Pennell, Kelly G. PennellSearch for more papers by this authorDavid Folkes, David FolkesSearch for more papers by this authorHelen Dawson, Helen DawsonSearch for more papers by this authorRobert Truesdale, Robert TruesdaleSearch for more papers by this authorLila Beckley, Lila BeckleySearch for more papers by this authorChase Holton, Chase HoltonSearch for more papers by this author First published: 20 July 2016 https://doi.org/10.1111/gwmr.12166Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume36, Issue3Summer 2016Pages 84-87 RelatedInformation

With continuous high-frequency monitoring, each of the challenges listed above can be directly addressed. In addition, one can immediately respond when an exceedance is recorded. This brings into question the use of time-weighted averaging versus concentration, which again would be subject to the regulatory exposure duration of concern. I believe there is a need for more comprehensive comparisons with continuous high-frequency monitoring techniques such as Gas Chromatograph/Electron Capture Detector (GC/ECD). The Hapsite control data presented in McAlary (2014) recorded -concentrations just before and just after the passive collectors were deployed, and the mean value was used as a -statistical reference. Since the Hapsite results exhibited concentration variabilities that have yet to be directly attributed to real conditions or operator or protocol causes, and measurements were not collected during the sampler deployments, questions remain regarding the actual range of concentrations encountered, detailed temporal patterns, and therefore the representativeness of the passive samplers during dynamic concentration conditions. Comparisons between the sorbents and a continuous monitoring GC/ECD system under carefully controlled dynamic concentration scenarios and durations could help resolve several remaining uncertainties and concerns. I must also confess that I was under the incorrect assumption that EPA was funding the development of Dr. Truesdale's TCE and Tetrachloroethylene sensors. While EPA personnel strongly endorse and encourage this effort (and should be commended for doing so), I have since learned that EPA has not directly sponsored this important sensor development program. I would like to acknowledge Drs. McAlary and Truesdale for their productive exchanges following receipt of the opinion piece.

The Environmental Protection Agency (EPA) has just released its long-awaited vapor intrusion (VI) guidance (USEPA 2015a). While this represents a very thorough overview of key considerations that practitioners should be aware of, and the document warns of the many ways that concentrations can vary over time and space in both the indoor and subsurface environments, the guidance unfortunately widens several critical gaps that currently exist between recent scientific evidence as it relates to VI risk phenomenon and EPA’s own policies regarding acute exposure based response criteria. For instance, very little is mentioned about EPA’s relatively new policy changes associated with trichloroethylene (TCE), where it was recently determined that very low levels of short-term exposure to TCE in pregnant women during their first trimester of pregnancy can result in serious impairment to their unborn children (USEPA 2011). More specifically, the new VI guidance advocates for the use of assessment and monitoring methods that are not capable of yielding short-term worst case exposure concentration under dynamic risk conditions, which is precisely what is needed to be able to appropriately protect receptors. This is particularly applicable when women of child-bearing age can be exposed. As such, there remains a huge gap between EPA exposure policy and its position regarding what constitutes acceptable decisionquality data. Similar concerns apply to petroleum contaminant releases, as the same methods advocated for in the VI guidance are not capable of yielding correct conclusions when acute exposure and explosion conditions are of concern. As with TCE, the objective should be to determine site-specific worst-case risk conditions associated with VI. Given our current understanding regarding widely ranging risk dynamics and episodic concentration increases driven by natural and anthropogenic factors, continued use of the methods endorsed in this guidance will most likely result in flawed conclusions and people being exposed to harmful environmental risks without their knowledge.

Conventional vapor intrusion characterization efforts can be challenging due to background indoor air constituents, preferential subsurface migration pathways, sampling access, and collection method limitations. While it has been recognized that indoor air concentrations are dynamic, until recently, it was assumed by many practitioners that subsurface concentrations did not vary widely over time. Newly developed continuous monitoring platforms have been deployed to monitor subsurface concentrations of methane, carbon dioxide, oxygen, hydrogen sulfide, total volatile organic constituents, and atmospheric pressure. These systems have been integrated with telemetry, geographical information systems, and geostatistical algorithms for automatically generating two- and three-dimensional contour images and time-stamped renderings and playback loops of sensor attributes, and multivariate analyses through a cloud-based remote project management platform. The objectives at several selected sites included continuous monitoring of vapor concentrations and related physical parameters to understand explosion risks over space and time and to then design a long-term riskreduction strategy. High-frequency data collection, processing, and automated visualization have resulted in greater understanding of natural processes, such as dynamic contaminant vapor intrusion risk conditions potentially influenced by localized barometric pumping. For instance, contemporaneous changes in methane, oxygen, and atmospheric pressure values suggest there is interplay and that vapor intrusion risk may not be constant. As a result, conventional single event and composite assessment technologies may not be capable of determining worst-case risk scenarios in all cases, possibly leading to misrepresentation of receptor and explosion risks. While dynamic risk levels have been observed in several initial continuous-monitoring applications, questions remain regarding whether these situations represent special cases and how best to determine when continuous monitoring should be required. Results from a selected case study will be presented and implications derived.

Environmental monitoring, data processing, and reporting methods are expensive, labor- and resource-intensive, time-consuming, and often inaccurate. An innovative project management platform was developed for integrating environmental monitoring sensors, telemetry, geographical information systems, models, and geostatistical algorithms for automatically generating contour maps and time-stamped renderings of sensor attributes and multivariate analyses. More specifically, algorithms converting sensor-derived head and solute concentration values allow for automated monitoring of mass flux and discharge to evaluate groundwater remediation system performance and contaminant discharges from aquifers to surface-water receptors. Life-cycle costs and carbon footprints were reduced due to the elimination of energy and labor expenditures associated with transportation, data collection, laboratory efforts, report generation, and information dissemination. A brief summary of two demonstrations of this sensor-based water resources management application is presented. (C) 2011 Wiley Periodicals, Inc.

: During environmental site characterization, remediation, and compliance efforts, groundwater monitoring wells have served as the conventional tool-of-choice for accessing groundwater samples. Recently developed direct pushed (DP) technologies provide the means for collecting faster, less expensive groundwater samples when compared to conventionally drilled wells. The most extensive use of these cost-effective technologies, initially used almost exclusively as temporary installations for characterization purposes, have not been widely accepted for long-term monitoring at remedial action sites. For broad acceptance of DP well long-term monitoring applications, comparisons between conventionally drilled wells and DP wells needed to be conducted to validate these innovative approaches. The purpose of this project was to rigorously compare the results of laboratory analyses conducted on samples obtained from DP wells to those obtained from wells installed utilizing conventional techniques (e.g., hollow-stem auger [HSA] wells). The demonstration consisted of these side-by-side comparisons followed by comprehensive statistical analyses over several years of quarterly monitoring. Five sites (located in New Hampshire, Delaware, California, Massachusetts, and Florida) comprised of various geologic regimes and contaminants of concern were included in this demonstration. Ultimately, the goal of this demonstration was to determine whether DP wells can yield representative data for long-term monitoring applications.