Vapor Intrusion Monitoring Method Cost Comparisons: Automated Continuous Analytical Versus Discrete Time‐Integrated Passive Approaches |
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| Authors: | Mark L. Kram Blayne Hartman Cliff Frescura |
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| Affiliation: | 1. Groundswell Technologies, Inc.;2. Consultant and Expert on Soil Vapor Sampling, Soil Vapor Analysis, and Vapor Intrusion |
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| Abstract: | 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. |
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