Groundwater contamination and clean-up, landfills

Environmental Geology - Lecture 8 outline - modified Sept. 2017

Content:


Contaminants and water quality

What might people want to know about the water they drink and use (water quality measures)?

What are examples of point sources in urban and/or rural environments?

This image is a mosaic taken from an overview stand right on the edge of the town of Butte, Montana. This is a large open pit (known as the Berkeley pit) at a copper mine no longer being worked directly for copper, but filling up with water with a distinct orange coloration. As the water migrates through the adjacent rock it has become very acidic with a pH of around 2 (the equivalent of vinegar), and with a very high concentration of dissolved heavy metals including copper, arsenic, cadmium, cobalt, manganese, iron and zinc. The water is so rich in copper (up to 187 ppm) that a plant on the far side of the pit and barely visible here actually extracts copper directly from the water, presumably at a profit. The dark object in the skyline to the right is a rafter from the viewing building that was incorporated into the mosaic. This is a Superfund site (more on Superfund later). Active mining occurs in an area in the background to the far right. This pit is a pretty large point source..

This is an image of part of the display material at the pit overview site. Note that at present the groundwater table (the blue line) slopes in toward the pit. This means that the shallow groundwater flow direction is in towards the pit, and this would suggest that the contaminants are not, at this point in time, flowing away from the pit. However, notice the critical water level depicted. A waste level higher than this could result in a groundwater table that slopes away from the pit, and a corresponding outward flow direction, at which time contaminants could begin to migrate away from the pit. Note also the depth of the water.

Common contaminants:

USGS diagram showing how a contaminant like PCB can increase in concentration up the food chain (biomagnification). Diagram source: http://pubs.usgs.gov/circ/circ1203/major_findings2.htm

Sampling bottom sediment in South Platte River for pharmaceuticals and other emerging contaminants. Source: http://toxics.usgs.gov/regional/emc/streambed_sediment.html .

EPA drinking water health standards website.


What do groundwater contaminant plumes look like, how do we map/understand them, and remediate them

Can't see groundwater directly (although springs, seeps and other landscape features give some insight as to what the shallow groundwater is doing), so must use multiple techniques to visualize what is going on underground.

Above is a simple schematic of point source, its associated contaminant plume and contours on the water table of a simple unconfined aquifer. This is a basic approach geohydrologists often use in some form. What direction is the groundwater flowing? Given the scale, and a ten year time span since the point source was created, at about what speed are the contaminants moving? How long before they might reach the surface drainage (stream)? Note that contours on the plume are sub-perpendicular to those of the ground water table.

View of an actual plume. The point sources are clear. As is often the case the shallow groundwater flow direction is towards the lake, down slope. If the groundwater recharges the lake (not an uncommon situation) then it come in contact with organisms, including people. Note how much more complicated it is in the 3rd dimension because of the different layers with their different permeabilities. The specific underlying geology is always crucial. Diagram source: http://wa.water.usgs.gov/pubs/fs/fs082-98/ .

 

What are some clean up methods? Have made tremendous progress in last two decades in this technology.

Image to the right is of a mix of microbes, microbial food and a tracer being injected in the ground to see how much TCE the microbes might degrade. The injection well is the red pipe in front of the blue barrel. This work is being done by the USGS at the Naval Air Warfare Center in Trenton New Jersey where a large TCE contaminant plume exists (over 100,000 gallons leaked). Source of additional information and of the picture can be found at: http://toxics.usgs.gov/highlights/bioaugmentation.html & http://toxics.usgs.gov/sites/nawc_page.html .

 


Legal and regulatory framework for water

This framework is extensive and complex, to the point that some people make a living just at helping industry stay in compliance. Below are just a few of the highlights, major pieces of legislation.

Environmental Protection Agency - federal agency with oversight on environmental issues.

Nebraska Department of Environmental Quality. This is our lead agency for environmental issues in Nebraska. Each state has an equivalent agency.

Superfund sites in Nebraska

Cost-benefit analysis and cleaning up toxic sites.

The above is a schematic graph showing assumed relationships between cost and the level of clean-up. It is a useful initial framework for considering the question of what level of clean-up should be undertaken for a given contaminated site. Perhaps consider two different perspectives: that of someone living next to the site, and that of the administrator with a fixed budget who has the responsibility of cleaning up many more sites than he has money for. Most important to note that it may be several times the cost to clean up the last 5% or so of contaminant compared to cleaning it up 95%. More recently, faced with large costs and limited resources, clean-up fund administrators are taking a cost-benefit approach. The basic trade off is between cleaning up a few sites to pristine levels versus cleaning a larger number of sites to lower levels. A risk assessment approach works well here.


Landfills and waste management

Methods of waste management?

Approaches taken:

Image of a landfill cell on Hawaii where land and groundwater are especially precious. Note the rubberized sheet on the side of the cell they are filling up. This is part of the landfill design discussed in greater detail below. Image source: http://commons.wikimedia.org/wiki/File:Landfill_Hawaii.jpg .

The landfill design and cost of course depends on the type of waste:

Where does your garbage go and what happens to it there?

Of the above options we will focus on sanitary landfills.

An exercise in estimating how much domestic garbage is produced in the Omaha metropolitan area in units of tons per day. Take the weekly weight in pounds of garbage you put out on the curb. Divide it by the number of people in your house/apartment. Divide it by seven. Now you have an estimate of the daily per capita domestic garbage production. Now multiply by the number of people in the Omaha metro area, and and then divide by 2000 (2000 lbs in a ton). Now you have the daily domestic garbage production in tons! What makes sure this is an underestimate of the total amount of garbage produced?

What are considerations during landfill siting?

Top 6 reasons people don't want to live next to a landfill?

Other related environmental concerns/considerations:

Image of leachate plume from a landfill studied by the USGS. Clearly the ground water flow direction is from left to right (this is the direction the plume extends). The black dots are portions of a well that is open to the surrounding geologic material and from which they can extract a sample.For more information and image source - http://pubs.usgs.gov/fs/fs-040-03/ .

Heflinger Park in Omaha is the site of an old landfill/dump and now of a popular dog park. The long trenches in which the garbage was buried are very evident as the cross beneath the road here. The garbage compacts and biodegrades, which means the surface subsides and that is why these elongate surface depressions that break up the road and parking lot are visible. This road has been 'repaired' multiple times. Methane vents can be found on the south side of the park.

Landfill design: Dumps were undesigned, unregulated and unmonitored holes in the ground where 'trash' was buried. The legacy was and is expensive, and now landfills are designed, engineered, regulated, and monitored.

Schematic cross section diagram of a landfill. Landfill designs vary dependent on geologic, climatic and other factors. The basic idea is to triple bag it, or more, and collect and control what does escape.

Designed landfills are expensive, which leads to reduce, reuse, recycle.

Link to Douglas County Landfill page.

Omaha's past and present landfills.