Using Solid-Phase Extraction in the Field
Barr Engineering recently conducted its first screening using solid-phase extraction samplers (otherwise known as Darts) from Dakota Technologies. The Darts were used at a crude oil release site in a peat bog, and they were found to be a quick, inexpensive and effective method of identifying NAPL.
Darts are one of the latest products from Dakota Technologies. Each Dart sampler is made of a fiberglass rod that is covered in a solid-phase extraction media to absorb and trap the polycyclic aromatic hydrocarbons (PAHs) found in crude oil, coal tar, and creosote NAPLs. The Darts can be deployed anywhere from 1 to 20 feet deep into the sediment under as deep as 15 ft of water, and they are usually given 24 hours to absorb PAHs from any NAPL-affected horizons. Once the Darts are removed they are shipped to Dakota (no ice necessary) where the Dakota Technologies crew uses LIF to delineate PAH contamination versus depth. The data can be combined with GPS positioning information to provide 3D visualization of the sediment NAPL at the site.
On August 12th, 2011, Barr Engineering used a number of Darts on a suspected crude oil release site near Deer River, Minnesota. The engineers coupled 3-foot Dart segments to standard-length, 6-foot Darts, and they drove the samplers 9 feet into the ground. The crew was able to install and remove most Darts by hand, although a few required the use of a slide hammer for a short distance. Investigating with the Darts in this dense undergrowth was quick and simple compared to core sampling.
To maximize sensitivity the Darts were left in the ground for three days to absorb any existing PAHs before being removed (and they could also enjoy the weekend). Then they were pulled out, wrapped in tin foil, and sent to the Dakota Technologies lab which had results completed in less than two days. The results were emailed back to Barr which helped the engineering firm quickly and accurately confirm/delineate crude oil contamination of the area.
From this project, Barr Engineering also concluded that Darts may be particularly useful for work in shorelines, marshes or shallow bodies of water where screening for NAPL in sediments with conventional motorized direct-push technology may be difficult, expensive, or impractical.