Dense Non-Aqueous Phase Liquids (DNAPLs)

[Guest]

And they say you can't find it. Ha !!

Pictures are taken from a dig I was at where a thin clay unit within the surficial aquifer was hiding the 'source' of the leak into the lower (more transmissive) aquifers.

JR

 

[udpolo15]

We are working on a site out east that has free phase mercury in the soil. I'll see if I can find some pictures of the cores that show the silver globs.

 

[RIP - VTEnviro]

JR - what was it that you found? Or was it an uknown contaminant.

My first ethical dilemma as a PE happened last summer at a site where we found fuel oil in a test pit we were investigating.

We were doing both a structural and environmental study of a particular municipal site where the town wanted to either upgrade or replace some of their buildings. It was me on the envl stuff and a structural guy evaluating the buildings. He is by far the senior engineer and a talented one at that.

I discovered a batch of free product in a test pit. I stopped the work and got the senior guy on the scene. The town DPW guys who dug the pit were half seriously contemplating covering the whole back up. Fortunately, the senior engineer took charge and said if you don't call it in, I am obligated to. They ultimately called it in, avoiding an ugly standoff.

Susburface investaigation are one of the most interesting things I deal with, you never know what you'll find.

 

[Guest]

We knew that site was contaminated - it was an old Dept of Transportation asphalt testing laboratory. There were numerous drums of spent trichloroethylene (TCE) and waste asphalt landfilled on the property.

The remedation was an aggressive over-excavation of the landfilled drums and other waste products. The generated media was sent to a staged soil burner for thermal treatment. The thought was that once the source had been removed the remainder of the dissovled phase plume would 'naturally' degrade. Based on observations after the first dig, it was obvious there was still a 'source' continuing to contribue to the groundwater plume.

A second mobilization broke into one of the intermediate fat clay formations thought to have been serving as a barrier. That excavation revealed an ever-so-slight fracture within the clay that allowed for a migration pathway into the lower surficial aquifer. It just so happened that the excavator provided a cut at that fracture facie. The picture is the resulting 'ooze' from the formation.

I love subsurface investigation - unfortunately, these days, many of my investigation projects have matured to we dug it or we are restricting it projects. My mind works in an abstract way and I love the fact that there is a certain sense of 'art' that comes into play when making interpretations. Turd tumbling was just about puncing in numbers for length, diameter of pipe to figure out where the next lift station needed to go - not that exciting as far as I am concerned.

I am making a long trip starting next Friday to inspect some construction and evaluate some investigation work. I will get some more pics to post.

JR

JR