We discussed quite a variety of topics just based on the visit to the landfill/quarry.
A single, half-day, visit to the landfill and quarry brought up quite the variety of topics, ranging from the quarry itself, to the reason for the red colors of the cliff walls, to the uses of the gases that come out of the landfill. I still have not gotten to the details about the landfill itself, but I’ve put together a page that links all my posts about the quarry and landfill so far.
The water cycle, at the quarry.
The water cycle is intricately tied to all the other topics that came up on our visit to the quarry/landfill. For some things, the tie to water is direct and inextricable.
It’s groundwater that dissolves the pyrite in the coal seam and then precipitates an orange iron stain on the quarry cliffs.
Rainwater seeping into the landfill leaches out chemicals that have to be prevented from getting into the groundwater, rivers or lakes.
Gases like hydrogen sulfide can react with water (and oxygen) in the air to produce acid rain. Not to mention that water is needed for the decaying processes that produce the hydrogen sulfide, and other landfill gases like methane, to begin with.
For other things the link to water is not necessarily so obvious:
The sediment that was compressed into the limestone that is being quarried, was formed beneath the shallow seas that once covered this region in the geologic past. Limestone is also dissolved by rainwater to create caverns, underground rivers and spaces for geodes.
Methane gas not only requires water for it to be released via decomposition of garbage, but also produces carbon dioxide when burned. Carbon dioxide is a greenhouse gas, so it affects the global temperature and contributes to the melting glaciers, rising sea levels and changes in climatic patterns such as the amount of rain we’re going to receive in the midwest.
The water cycle picture starts simply, but gets complicated very quickly.
A bigger, fuller picture of the water cycle as it interacts with the quarry.
Dan Frommer has posted a guide called, “10 steps to better blogging“. His rules are aimed at commercial bloggers/journalists, but even for the hobbyist/student there are some noteworthy points (certainly ones I try to follow):
1. Accuracy is essential: Be forthright about errors and fix them.
4. Cite your sources: It’s honest, and honorable to give credit where it’s due.
7. Grammar and spelling are important: You don’t necessarily have to use the Queen’s English but use language intentionally.
10. Try new things: It’s a new medium so there are lots of areas for discovery.
Most of these are just the basic elements of good writing.
I’d also suggest that it’s important to include your perspective wherever you can. There are a number of great places that aggregate a lot of good information, but for the aspiring writer, adding your unique point of view should help find your voice.
The quarry's primary purpose is to extract limestone for construction.
The landfill/quarry we visited was originally a limestone quarry; once they had the hole in the ground they needed to fill it with something so why not trash (and why not get paid to fill it).
Shoveling boulders. The rock pieces look small but only because the shovel is so big.
The limestone bedrock is blasted daily to create some massive boulders. The boulders are then loaded on some equally massive dumptrucks. There are scarce few minutes between trucks, so a lot of rocks are being moved.
Dumptruck moving rocks. Massive boulders in the foreground. Unloading dumptruck.
The trucks then dump their load into a large building where the rocks are crushed. Our guide made us stop the bus to watch the process. While watching a dumptruck unloading might seem mundane, the enormous size of the truck and its boulder load did seem to captivate the students.
Once the rocks are crushed, the resulting sediment is sorted by size (sand, pebbles and gravel, I think) and piled up. The piles are massive. I’ve been wanting a good picture that shows the angle of repose; I got several.
The angle of repose of a pile of sediment. Also notice the greenish color of the water in the pond to the bottom left. Water with lots of fine limestone particles (silt) and dissolved limestone, tends to have that color.
The pebbles and gravel are used for road construction and provide a matrix for concrete.
Since limestone dissolves fairly easily in rainwater, the sand-sized and smaller particles (< 2mm diameter) aren't used for construction -- hard, insoluble quartz sand is preferred.
Limestone: calcium carbonate (CaCO3)
However, the limestone sediment piles sit out in the open and some the finer grains (silt sized particularly), and any dissolve calcium carbonate, get washed into the nearby ponds, which turn a beautiful, bright, milky green.
Finally, in addition to the limestone sediment piles, there is also one enormous pile of broken up concrete. One of the things that stuck with the students was that fact that you can recycle concrete.
The freshwater lens beneath small islands is fed by rainwater and maintained because the freshwater is less dense than the surrounding saltwater.
One of the questions that came up when we were talking about dealing with the highly contaminated leachate that drains out of landfills, is what would happen to it if it was just put into a lake or the ocean. Would the liquid just mix into the water, or would it stay separate.
Rainwater seeping through a landfill picks up a lot of nasty chemicals, and by the time it gets to the bottom it is a highly contaminated leachate.
I’m afraid I did not go with an easy answer. It depends after all on two things: how different the density is of the leachate from seawater; and how turbulent is the water.
Turbulent water will make the leachate more likely to mix, while a greater density difference would cause them to “want” to remain separate. An extremely dense leachate might just settle to the bottom of a lake and stay there.
Small Islands
One example of two fluids that are in contact but stay separate is in the groundwater beneath small islands. Rain water falls on the island and seeps into the ground. It’s fresh, but the water in the surrounding ocean and the water that’s already underground are both salty. Salty water is more dense than the fresh so the freshwater will float on top of the salty water creating a thin lens.
Dimensions of a freshwater lens. Image via the USGS.
How thick is the lens? For every meter that the fresh groundwater is above sea level, there are 40 meters of fresh water below sea level (1:40). This is because saltwater has density of about 1.025 g/cm3, while freshwater has a density of about 1.000 g/cm3 (note that I use four significant figures in each of these values).
The freshwater lens can be a great source of drinking water on these isolated small islands, but like the islands themselves, they are threatened by rising sea levels due to global warming.
The flames in this image came from the free svg blog.
I needed a little icon of flames to show the methane from the landfill being burned for heat. So I googled, “svg flames” and ran into the free svg blog. Their svg images are aimed at scrapbookers, but they’ve got some good ones, and they’re free.
NASA thinks their rover has found veins of gypsum on Mars. If they have, it will be an excellent indication that there was once standing water on Mars — gypsum is usually precipitated in evaporating lakes — and will excite the search for life on Mars.
What gypsum veins on Earth look like: white gypsum veins from Somerset, UK. Image by Ashley Dace. (via Wikipedia)
Methane in a landfill. It's produced by decomposing organic material, is extracted via wells, and is then burned to produce heat (for a school and a set of greenhouses) and electricity (soon anyway).
Decomposing waste in landfills produces quite a lot of methane gas (CH4). Perhaps better known as natural gas, methane is one of the simplest hydrocarbons, and a serious atmospheric pollutant (it’s a powerful greenhouse gas). In the past the methane produced was either released into the atmosphere or just burned off.
Greenhouses that are warmed by methane produced by the landfill. It's a cheap, close source of energy.
I remember seeing the offshore oil rigs burning natural gas all night long — multiple miniature sunrises on the horizon — in the days before the oil companies realized they could capture the gas and sell it or burn it to produce energy. The landfill companies have realized the same thing. So now, wells pockmark modern landfills and the methane is captured and used.
Looking down the slope of the landfill to see the Pattonville High School, which uses natural gas from the landfill for heating.
First, of course, the hydrogen sulfide gas (H2S), is separated from the methane — H2S produces acid rain, so it’s emissions are limited by the EPA — then, the gas from the landfill we visited, is piped to:
greenhouses, where it’s burnt to produce heat;
the Pattonville High School, which is right next to the landfill and burns the gas for heating;
and (soon) to a electricity generating power plant that will burn the gas to produce heat which will boil the water that will produce the steam that will turn the turbines that will generate the electricity.
Electric power plant -- still under construction -- that's fueled by methane from the landfill.
You may have noticed the common theme of all these uses of natural gas: it has to be burned to be useful. The combustion reaction is:
CH4 (g) + 2 O2 (g) —-> CO2 (g) + 2 H2O (g)
which produces carbon dioxide (CO2) that is also a greenhouse gas, but is, at least, not nearly as powerful at greenhouse warming as is methane.
