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A Dart Being Deployed
The Dart system is designed to quickly and inexpensively screen for polycyclic aromatic hydrocarbons (PAHs) in sediments and similar soft soils, where LIF, traditional soil boring, and other mechanized sampling are difficult, if not impossible.

The Dart sampler is comprised of a continuous rope or rod made from or coated with solid-phase extraction (SPE) media – the same type of materials used in labs for EPA-approved cleanup and “pre-concentration” of PAHs in traditional grab samples. PAHs are attracted to and sorb into the SPE media. Once they’ve migrated into the Dart, they’re held in “solid solution” and remain trapped there almost indefinitely.

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Dart Sampling Concept
The Darts are deployed by hand or manual slide hammer into the sediments, anywhere from 1 to 20 ft deep, depending on soil conditions or survey need. Once planted, any PAHs that are sorbed to sediment soil particles, dissolved in sediment pore water, or exist as a component of non-aqueous phase liquids in the sediments, will migrate into the Dart sampler. They migrate into the Dart sampler because of the PAHs’ high affinity for the SPE material versus its relatively low affinity for water or sediments, generating a considerable concentration gradient. Typically 24 hours of “equilibration” time is sufficient, after which the Darts are retrieved, packaged, and sent to Dakota for reading.

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A Dart Being Deployed
Technicians at Dakota run the Darts through an LIF reader which is very similar to UVOST. The result is an LIF log that looks nearly identical to a UVOST log. Similar to UVOST and TarGOST, the LIF response correlates to the “total available PAH” content of the sediment vs. depth. A graphical log in JPG format and high resolution data files are available to the client soon after reading.

Combined with DGPS position information, the numerical results are readily visualized with Dakota’s 3D conceptual site model service, allowing the client to visualize the “big picture” of their sediment PAH contamination at a fraction of the cost of traditional sampling/analysis.

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A Deployed Dart
The Dart system is particularly well suited for characterization work in shorelines, marshes, or shallow bodies of water adjacent to former MGP or creosote sites, where profiling PAHs sediments has been difficult and expensive.

Darts have been successfully applied to screening for PAH-containing NAPL (former MGP sites), but laboratory evidence suggest that Darts will also be effective for non-NAPL associated PAHs, such as the “black mayonnaise” that is commonly found to be plaguing large urban waterways.

Research by others also suggests that the Darts will be capable of acting as biological surrogates due to the SPE material’s similarity to biological tissues with regard to absorbing “biologically available” PAHs in sediments, allowing for surveys of biological uptake risk as opposed to total PAH analyses of sediment using aggressive Soxhlet extractions, which often overestimate risk. Dakota is continuing to investigate the efficacy of applying Darts to these and other screening applications.

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Diver Preparing to Deploy Dart

More Information

EPRI ID: 1014749 - A Continuous In-Situ Dart Profiling System for Characterizing MGP Coal Tar and PAH Impacts in Sediment

 
 
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