Advanced Environmental Interface

Here's the general idea of an environmental site investigation, in a simple example, with you as the investigator.

1. During the site assessment walkover, you observe a 55-gallon drum in the corner of a retaining wall. One of the bungs in the drum lid is missing. There's a smaller drum behind it; same situation. Looks like the drums were used to collect waste liquids from inside the facility.

2. You see wet rags with a petroleum odor sitting on top of the drum. The liquid (or rainwater, since the bungs were missing) has filled both drums up to the top. There are oily streaks down the side of each drum. The ground is visibly stained. Einstein's assistance is probably not going to be required here.

3. You take a sample from the large drum. This is best done with a coliwasa (half-inch diameter glass tube 36-inches long) to get a good view of layers. The coliwasa shows a 3-inch dark layer (probably oil) on top of a lighter layer (probably water). You repeat the sampling for the small drum. Small drum smells like petroleum solvent, large drum like cutting oil.

4. You pour the samples from both coliwasas into sample jars, and let them sit for awhile for the layers to fully separate. Both jars develop separate layers, but the sample from the large drum (on the right) tends to leave more color in the water layer. This implies some solubility, so the oil is probably water-soluble cutting oil.

5. The next logical questions are how much contamination has gotten into the soil, what is it, and how far down did it penetrate. You use an auger to core a hole down into the soil, and collect soil samples at depths of 6, 18, 36 and 48 inches below the surface. (Deeper than 6 ft with hand tools requires patience and strong shoulders.) You send these samples to the lab for analysis.

6. The lab analysis of the soil samples shows that the small drum contained waste petroleum solvent (mineral spirits), and the large drum contained a mixture of lubricating and cutting oils, with low levels of a chlorinated degreasing solvent (trichloroethylene). Total petroleum hydrocarbons (TPH) in the four soil samples decreases with depth.

7. From this investigation, you conclude that the soil is contaminated to a depth between 3 and 4 ft. By comparing the laboratory results to Connecticut cleanup standards, you conclude that soils from the surface down to the 3-ft depth should be excavated in order for this site to be considered clean.

Who needs an environmental site investigation?

A recipient of an environmental site assessment report that unequivocally recommends a site investigation, names specific areas of environmental concern, and says why;
A buyer or seller who wants to determine possible environmental liabilities;
A bank or other lender who wants to be sure that the assigned equity value reflects the environmental condition of the property.

Examples of site investigation methods. There are several methods and technologies typically used for site investigations. Use of hand tools as described above is rare for anything other than shallow depths; usually the equipment is a drivable sampler (GeoProbe), a drill rig or a backhoe. Two common methods are illustrated by:

A slide show sequence illustrating subsurface investigation by backhoe trenching (annotated to show the kind of features that geophysical scientists and engineers look for).
A slide show illustrating a soil gas survey (for an actual investigation), which show a method for defining areas of soil contamination by volatile compounds, such as solvents or gasoline.

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