environmental geoscience test 3

features of historical carbon cycle

magma outgassing, seafloor spreading (sources)

sedimentation of calcium carbonate, chemical weathering, basalt alteration (sinks)

evapotranspiration

returns water from soils to atmosphere (through leaves, usually)

chemical weathering

2CO₂ + 3H₂O + CaAl₂Si₂O₃ —> Ca²⁺ + 2HCO₃^- + Al₂Si₂O₅(OH)₄

(kaolinite/clay)

albedo

reflected light from Earth’s surface and clouds

greenhouse effect

trapped heat from molecular resonant gasses reradiates onto Earth’s surface, raising temperature

breakdown of greenhouse gases in atmosphere

60% water vapor and clouds

26% Carbon dioxide

8% Ozone

4.4% methane

1.5% N₂O

rest “other”

keeling curve

shows increase in atmospheric CO₂ over time, measurements from mauna loa observatory in hawaii. has been accelerating in growth.

thermohaline circulation

high salinity water cools and sinks in north atlantic, deep water returns to surface in Indian and pacific oceans through upwelling, “global conveyer belt”

travel time is about 1000 years

Particulate Inorganic Carbon

calcite and aragonite, fluxes in global ocean. depends on temperature, depth, and acidity for saturation.

at depth, concentration increases until it decreases. eventually progresses to undersaturation at large depths bc of lower stability of minerals.

Aragonite compensation depth (ACD)

since __ is more soluble, this is shallower.

depth at which no more of this compound is found (completely dissolved)

calcite compensation depth (CCD)

since __ is less soluble, this is deeper

depth at which no more of this compound is found (completely dissolved)

saturation index

above 1 is supersaturated, below 1 is undersaturated

resource

inferred, indicated, or measured. may be there, probable

reserve

probable or proven, with a plan to access/use. able to be extracted.

ocean

where is there currently a net uptake in carbon dioxide, acting as a buffer?

developments in extraction tech (fracking, etc.)

why did oil & gas reserves increase from 1993-2003?

gas

“cleanest” fossil fuel

energy generation

what is most coal used for?

82%

share of world’s energy consumption mix that is fossil fuels (same as 25 years ago)

reservoir rocks

permeable rocks that contain oil and gas within, have lots of interconnected pores and absorb gas & oil like a sponge.

50 C

minimum temp for oil generation

180 C

minimum temp for gas generation

seal/cap rocks

keep trap integrity, any rock that is impermeable (mudstone?). Acts similarly to an aquitard in a confined aquifer.

enhanced oil recovery

use of CO₂ to mobilize residual oil. Oil takes up CO₂ in the miscible zone, expands, and becomes mobilized. The goal is to reduce to viscosity of oil.

fracking steps

1. pump fluid & make cracks

2. extract fluid, leave sand there to hold cracks open

3. gas migrates upward through cracks to well

fracking risks

fault slip, water contamination, earthquakes, lowered groundwater and acid sulfate soils

water treatment and reuse

drinking water

irrigation

dust suppression

industrial use (drilling, cooling)

supporting environmental flows

underground disposal

Carbon Capture & Storage

GRAB THE CARBON AND STICK IT IN THE GROUND

elements of a good CCS site

places where CO₂ is a supercritical fluid: temps higher than 31 C and pressure greater than 7.39 MPa.

also good to have a seal and reservoir (porous) rock, mimic natural hydrocarbon deposits (container and lid)

800m

good depth for CCS, usually

wireline well logging

records subsurface rock formation properties, including natural gamma ray (radioactivity, mainly used for rock id), density, sonic porosity, and resistivity

sources of groundwater contamination

leaking sewers, landfills, septic tanks, oil, petrol stations, pesticides, fertilizers, ploughing, road salt

point source

from a single contamination site, like a septic tank, leak, or landfill.

reverse wells, plant waste discharge

non-point/diffuse source

environmental contaminant, like fertilizer, rain, atmospheric fallout

nitrate

incredible groundwater contaminant, non-point. comes from beef and coal, and can affect red blood cells and reduce oxygen carrying capability. Blue baby syndrome.

can spread relatively quickly through groundwater if it’s flowing.

urea

from cattle, converts to ammonia, ammonium, and then nitrate where it is then taken up by crops

nitrification

NH₄⁺ —> NO₃^-

GAIN in electrons: this is a reduction

dispersion

water in subsurface has to travel around sediment grains, makes spread larger but also decreases concentration (plume)

hydrocarbon contamination stages

free

trapped

vapor

dissolved

LNAPL

light non-aqueous phase liquids.

less dense than water, float on top of groundwater and disperse downward as they slowly dissolve. get carried by flow as well.

includes gasoline, light oils

DNAPL

dense non-aqueous phase liquids

more dense than water, sink to bottom of aquifer and accumulate between sediment grains due to high viscosity

includes organic solvents, turpentine, TCE, degreaser: highly toxic and carcinogenic

Natural Attenuation

different processes that reduce the concentration of a contaminant

vitalization (votalization)

transition to gas phase and subsequent upward degassing

chemical reactions

change contaminants into compounds that are less toxic/harmful through chem processes

biodegradation

bacteria eat contaminants

sorption

contaminant binds to mineral surfaces (often IRON OXIDES), reducing contaminant plume

dispersivity

dilution from going around grains (attenuation one, with -ity)

steps of MNA (monitoring natural attenuation)

1. preliminary assessment of feasibility

2. initial evaluation of natural attenuation

3. detailed characterization of NA (bulk monitoring here)

4. verification of NA performance

5. closure: goal setting, stewardship, etc.

how to monitor & predict contaminants

regular sampling along groundwater flow path, gas and water analysis

develop groundwater flow model, account for chemical reactions along flow path

ex-situ remediation

moving contaminated material to a secondary location, either to be dumped or treated (using chem reactions, heat, or bacteria)

in-situ remediation

more knowledge needed to assess impact on local environment: injection of bacteria/reagents into soil to treat contamination at the site.

includes things like adding FE OXIDES (for adsorption), alkaline substances (pH adjustment)

works best with homogenous subsurface systems

permeable reactive barrier

inserted into groundwater flow path in order to collect contaminant as water flows past. Often uses FE-OXIDES or carbonate. Can be used over and over, just switch out barrier material.

Acid Mine Drainage

AMD

when exposed to atmosphere or oxygenated water, sulfides (PYRITE) oxidize and leave behind acid. Also leave behind heavy metals, metalloids, metal colloids

active and abandoned

two types of mine sites

50,000

apprx. number of abandoned mines in Australia

mine water

unwanted/unused water from mineral processing, coal washing, etc.

can dissolve elements and carry minerals/colloids

can be toxic to plants and animals

can also be ALKALINE (high pH)

tailings

unwanted mine byproducts

crushed rocks and processing fluids, can contain toxic dissolved elements

environmental impact of mine waste

acidic water (erosion, dead flora, low life potential)

heavy metals (TOXIC)

high dissolved solids/salinity, bad for vegetation and cattle

physical/chemical techniques for mine waste

soil vacuum/air injection (to physically move contaminant)

neutralization (pH)

Oxidation (for cynaide, but may generate sludge)

adsorption (IRON OXIDES)

permeable reactive barrier (use of zero-valent iron)

green technology

bioremediation, use of microbes to break down contaminants.

factors to consider in bioremediation

rate of growth/decay

rate of consumption

solubility of contaminants

food for microbes

environmental conditions

inhibitors

recreation lakes

what you can turn an old coal mine into, if you neutralize acidity and have high evaporation and cover the surrounding are with appropriate vegetation

fracking

process used to extract coal seam gas and shale gas

coal seam gas

much shallower

requires extensive water production (to reduce pressure)

concerns: lowered groundwater level due to water extraction (acid soils?), extra fracturing of rocks outside of production area leading to aquifer contamination

shale gas

deeper under the surface

requires LESS water

thiocyanide

used for leaching gold from rocks in mining operations. a very strong contaminant. can be adsorbed by iron oxides or eaten by bacteria (bioremediation)

forest fires and burning hydrocarbons

two largest anthropogenic sources of carbon dioxide