Lecture 9b - Assessing a potential waste disposal site

Flashcards based on lecture notes about using geophysics to assess waste disposal sites, leachate plumes, and landfill structure.

What are leachates?

Fluids resulting from the breakdown and leaching of waste material within a landfill.

What was the task of the geophysical survey near Luderitz, Namibia, regarding fault and drift deposit identification?

To identify where faults may lie within the bedrock covered by drift deposits and to assess the thickness of these deposits.

What type of seal should waste disposal sites have to prevent leachate escape and minimize water ingress?

Impermeable seals at the bottom and top of the site.

What three geophysical methods were used in the case study to map subsurface features?

Horizontal loop electromagnetic, DC resistivity, and refraction seismics.

Why might faults be present as low resistivity or high conductivity anomalies?

Faults represent weaknesses within the rock, areas of higher permeability, and are more affected by weathering, leading to alteration to clay minerals.

How was the refracting data modeled in the seismic refraction profiles?

A two-layer model with an upper layer of lower velocities (drift deposits) and a lower layer of greater velocities (bedrock).

What is the typical resistivity depth plot observed in DC resistivity soundings?

A layer of relatively high resistivity at the very top, underlain by layers of decreasing resistivity, until a depth where resistivity increases again.

What do landfills that develop leaks produce?

They produce leachate plumes that are dispersed away from the location within groundwater.

What substances might leachates contain

Hydrocarbons, salts, solvents, and chemicals like cyanides, sulfates, and arsenates.

How does increasing salinity affect the resistivity of water?

The greater its conductivity and the smaller its resistivity.

What layers might be found in a vertical section through an old landfill site?

Topsoil over a clay cap, unsaturated spent fill, degrading fill with leachate, and potentially saturated fill.

What might a localized peak in conductivity represent at the top of a landfill site?

A peak in conductivity, representing the clay cap layer designed to minimize rainwater ingress.

What do conductivity variations typically reflect in leachate plumes?

The concentration of leachate; higher conductivity indicates higher concentrations of ions and total dissolved solids.

Why are subsurface fractures important in the context of leaking landfill sites?

Subsurface fractures are important as potential pathways for contaminant plumes under leaking landfill sites.

Why is leachate detectable through electrical and geophysical methods?

Leachate has high concentrations of total dissolved solids, leading to high conductivity.

How could geophysics be used to access insights on waste disposal sites?

To gain insights into fracture distributions underneath regions of drift deposits.

How does leachate material form

Water collecting and draining through the landfill site interacts with the waste and leachate material.

How was aerial photography augmented for a comprehensive investigation?

Aerial photography helped determine remote sensing data to allow photo based geological mapping.

Water contaminants result in what form?

A contaminant plume which is then dispersed within the substrate that potentially heads towards groundwater supplies or surface hydrological features (streams).

What does the conceptual model link?

Electrical geophysical signature linked to the anticipated formation processes of leachate and leachate distribution.