Introduction
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 absorb into the SPE media. Once they’ve migrated into the Dart, they’re held in solid solution and remain trapped there almost indefinitely.
Usage
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.
New Advancements in Dart Delivery
Dakota (with assistance from one of our more determined clients) has made advances in Dart delivery, including Vibracore and power post drivers. One client recently used a barge mounted Vibracore to deliver a portion of their Dart survey.
Vibracore delivery/retrieval went well (after some trial/error) and our client was able to deliver nine 6-foot Darts in water that was far too deep and had sediments much too firm for manual pole delivery. In addition, we recently field tested a gasoline powered post driver and found that it works great on 6-foot Darts on “terra firma.” We have a motivated client that we expect will be testing the system on bony creek bottom sediments very soon. So, if challenging Dart delivery logistics have prevented you from trying them, give us a call and we’ll discuss potential solutions to your sediment site coal tar and creosote NAPL delineation challenges.