Lecture 9c - Mapping pollutant plumes

Flashcards about using geophysical techniques for mapping pollutant plumes.

Winthrop Landfill Site

Gravel extraction site used for waste disposal from the 1930s to 1980s, located in Maine, USA.

What triggered the investigation at the Winthrop Landfill Site?

Reported leaking drums and complaints of unpleasant odors in local residents' drinking water.

What was the overall aim of the USGS investigation at the Winthrop Landfill Site?

To identify the source and extent of leaks from the landfill.

What did the investigation need to directly determine regarding the pollution?

Locating the specific regions of the landfill where leaks originated and defining the extent of the affected areas

What is natural gamma logging?

Radiation-based method used in boreholes.

Which geophysical techniques were used to gain insight into the hydrogeological characteristics and subsurface fluid composition?

Electrical and electromagnetic techniques.

Why were magnetic surveys carried out at the Winthrop Landfill Site?

To identify metal objects and metal-rich deposits associated with surface seeps.

What was the purpose of the boat-based seismic reflection profile?

To get a more detailed model of the geology and lithologies under the lake.

How do seismic results contrast with electrical methods in subsurface investigation?

They reflect the mechanical properties of the rocks, providing insight into geological details.

What does natural gamma logging measure?

Maps gamma radiation emitted from rocks down the depth of the borehole, useful for identifying different rock types and mineralogies.

What did the DC resistivity survey reveal in profile SF4?

A region of low resistivity, indicating high conductivity near the surface.

What do the different colors of the electromagnetic profile data represent?

Different coil orientations associated with different effective depths of investigation

How does profile SF1 differ from SF4 in location?

It is located nearer the lakeshore than SF4.

What did the resistivity section along profile SF1 reveal?

It showed a localized area of high conductivity that increased in depth, moving away from the surface.

What did the vertical logs from Well 13 show?

Elevated conductivity near the surface (within 4 meters) and a rapid increase in gamma signal at 12-13 meters, indicating metamorphic bedrock.

Where is Well 8A located?

Located between the two surface profiles.

What did the conductivity signal in Well 8A reveal?

Showed increasing conductivity at depths below about 7 meters, potentially indicating a pollution plume.

Why were two wells (212A and 212B) drilled adjacent to each other?

Problems with debris inside Well 212A.

What did the magnetic data from the waterborne surveys indicate?

Suggests seeps were present within the lake bed near the base of the landfill.

According to seismic reflection data, what geological features could be potential subsurface routes for pollutant plumes?

Paleochannels within the bedrock paleosurface.