Technology - Environmental Site Assessment

The most difficult part of any environmental program for characterizing and remediating pollution in the soil or groundwater is obtaining an accurate site assessment and map of the plume. Because many polluted sites have supported multiple industries over the years, unknown sources often exist which will complicate monitoring and remediation.

In one case, the use of amplified geochemical imaging found an unknown TCE separator at a military site that, once identified, reduced the remediation time using soil vapour extraction by dozens of years and reduced costs by several million dollars (LaPlant, 2002).

This tool has been used successfully on industrial sites, airports, gas stations, dry cleaners, landfills, pipelines and terminals, and manufactured gas plants. Another use of this imaging tool is to document site status for property transfers to limit future seller liability for clean-up costs related to new spills.

Amplified geochemical imaging using a passive soil-gas survey will not only accurately map intensity of pollution but will also screen for indicators of natural attenuation pointing toward potential low-cost remediation solutions. This accurate map can in turn focus subsequent soil and water matrix sampling, monitoring well placement, layout, and design of remediation chemical injection, and monitoring and verification of site clean-up.

In all cases, using this tool to generate an enhanced view saves costs in the overall program.

A series of analytical techniques including thermal desorption, gas chromatography, and mass spectroscopy generate a quantitative measurement of most volatile compounds including chlorinated solvents, fuels, polyaromatic hydrocarbons, pesticides, water soluble compounds, explosive and chemical warfare agent breakdown products, and even mercury.

More recently, the compound specific sampling rates of GORE Modules are being characterized in both air and water allowing direct measurement of concentration. This allows their use in applications such as long term monitoring as well as vapour intrusion and human health risk assessment. Detection limits in air are typically about 1 ppb, but can be extended to ppt if necessary. Such sensitivity suggests possible application in monitoring sentinel wells and drinking water quality.

When placed in water, the unique hydrophobic ePTFE membrane of this sampler allows volatile compounds, dissolved in water, to partition from the water into the airspace inside according to Henry’s Law, and be captured by the hydrophobic adsorbent. It is essentially an in-situ purge and trap without all the lab work-up. This process is very fast allowing water exposure times of minutes for most applications to a few hours for low concentrations and measurement of a wide variety of compounds including VOC’s, SVOC’s, and water soluble compounds. Because it is a very simple passive approach, long-term well monitoring costs are slashed by dramatically reduced fieldwork costs, reduced sample handling, and eliminating costs to process purge water or to ship on ice.

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