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GeoInsighter Spring 2004 Newsletter
Real Time Field Data Saves
Time and Money Return to the Newsletter Index A large percentage of a consultant’s time is spent helping clients identify and characterize the magnitude and extent of environmental impacts. We take very seriously the objective of obtaining data that are necessary to adequately characterize a site, and upon which, we can develop project strategies while keeping project costs as low as possible. This objective requires that data be collected efficiently to get as much "bang-for-the-buck" as possible. The value of real time analytical data is becoming more and more apparent. As an added plus, it is also apparent that the regulatory community is finally coming on board with the idea that quality field data can be used to supplement more traditional laboratory analytical approaches.
For example, let’s look at a recently delineated plume of dissolved chlorinated hydrocarbons approximately 500 feet off-site into an area that was not previously investigated. Once access to the potential downgradient parcels was granted, a discrete ground water sampling program was initiated within a median strip of a bounding highway and on three downgradient parcels. Ground water samples were analyzed in the field using a field GC calibrated to two signature compounds. By evaluating ground water concentrations along the highway median, the axis and direction of plume migration were defined. Ground water sampling on the downgradient parcels was then conducted to delineate the downgradient extent of the plume and evaluate potential impacts to sensitive receptors, including a wetland area and commercial property. Over two days, 24 discrete water samples were collected and analyzed in the field. Using the field GC technique, the focus was on successive borings in the direction of actual plume migration based upon the relative concentration of the two signature compounds detected in previous borings. Based upon data obtained during the field GC event, the best locations to install standard monitoring wells can be selected (i.e., wells can be placed in precise locations with respect to the orientation and extent of the plume). The relative cost savings using this approach as opposed to the standard well approach are significant. The field event described above was conducted over two days using a geoprobe discrete water sampler. The standard monitoring wells approach would likely have resulted in several phases of well installation activities (i.e., you rarely “get it right” with well location selections on the first try). It is estimated that based upon the areal extent of the plume, to obtain the same data set with standard wells would have required the installation of 10 to 15 wells over 4 to 6 days. To verify the field GC results and provide supporting data for regulatory acceptance, a percentage of the samples analyzed in the field are typically submitted for laboratory confirmatory analyses. Generally, approximately 10 to 20 percent of the total samples collected are submitted for confirmatory laboratory analyses. It is a good idea to include samples that are representative of “hot” conditions and of areas with no apparent impacts. For the project described above, the field GC results were within 15 percent of the reported laboratory value (which is a very good degree of precision). Concentrations detected in the plume using the field GC technique ranged from 1 part per billion (ppb) to 1,000 ppb. The next article regarding the use of field GC techniques will focus on how site conditions affect the quality of data collected in the field.
Christene A. Binger Return to the Newsletter Index |
This article explains
how collecting real time data using a gas chromatograph (GC) saves time
and money. The value of field chromatography is the ability to identify
specific target compounds and quantify their relative concentration in
the field. Real time data analysis provides in-field flexibility to
focus investigation activities in response to actual, rather than
anticipated, site conditions.