AP Environmental Science

## Learning Outcomes

- Define **tar sands** or **oil sands** and explain why they are considered an unconventional fossil fuel source
- Distinguish between **bitumen**, **synthetic crude oil**, **diluted bitumen**, and **conventional crude oil**
- Compare **surface mining** with **in situ extraction**, including how **SAGD** works
- Explain why crude oil from tar sands has a lower energy return and higher environmental cost than conventional oil
- Identify major environmental impacts, including habitat loss, water use, tailings ponds, and greenhouse gas emissions
- Apply these ideas to AP Environmental Science multiple-choice and free-response questions

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand crude oil from tar sands, with a focus on the following syllabus points:

- Know that **oil sands** and **tar sands** are interchangeable terms for deposits containing **bitumen**
- Identify **bitumen** as a heavy, sticky, highly viscous form of petroleum that does not flow easily like conventional crude oil
- Explain the difference between **surface mining** and **in situ extraction** for oil sands
- Understand how **steam-assisted gravity drainage (SAGD)** works as an in situ method
- Distinguish **bitumen**, **synthetic crude oil**, **dilbit**, and **conventional crude oil**
- Explain why tar sands oil has higher energy demands and generally higher greenhouse gas emissions than conventional crude
- Identify major environmental impacts including boreal forest destruction, water use, tailings ponds, toxic runoff, and habitat fragmentation
- Recognise Canada as the major APES example associated with oil sands reserves and development

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What is the main petroleum substance found in tar sands?
2. How does surface mining differ from in situ extraction?
3. Why is oil from tar sands usually considered more environmentally damaging than conventional crude oil?
4. What does SAGD stand for, and how does it help extract bitumen?
5. Why must bitumen be upgraded or diluted before transport or refining?

## Introduction

Crude oil from tar sands is a high-yield APES topic because it sits at the intersection of **energy resources**, **land use**, **pollution**, and **global change**. On the exam, it can appear as a definition question, a comparison question, or part of an environmental trade-off prompt asking whether a fuel source should be expanded.

Tar sands matter because they are a huge fossil fuel reserve, especially in Canada, but they are not extracted or processed as easily as conventional crude oil. That difference is the heart of the topic. Students need to understand not just what tar sands are, but why their extraction has higher energy costs, lower efficiency, and bigger environmental impacts.

> **Key Term: oil sands (tar sands)**
> Deposits of sand, clay, water, and bitumen from which petroleum can be extracted; in AP Environmental Science, oil sands and tar sands are treated as equivalent terms.

### What tar sands actually are

Oil sands are not pools of liquid oil waiting to be pumped out like many conventional crude reserves. Instead, they are mixtures of mineral material and a very heavy form of petroleum.

> **Key Term: bitumen**
> A thick, heavy, sticky, highly viscous form of petroleum found in oil sands that does not flow easily.

This is one of the most tested distinctions. Students often think tar sands are a separate fuel, but the usable petroleum is the **bitumen** inside the sand mixture. Bitumen is the part that can eventually be turned into fuels such as gasoline, diesel, and jet fuel.

Conventional crude oil usually flows more easily from underground reservoirs. Bitumen does not. That is why oil sands are called an **unconventional** fossil fuel source. They require either mining or underground heating before the petroleum can be moved.

Most major oil sands deposits are found in **Canada**, **Venezuela**, and the **Russian Federation**. Canada is the most important APES example because its oil sands are especially concentrated and economically significant. Recent reserve data also show how central oil sands are to Canada’s petroleum supply.

> **Key Term: proved reserves**
> Quantities of a fossil fuel that can be recovered with reasonable certainty under current economic and operating conditions.

Canada had about **163 billion barrels** of proved oil reserves as of January 2024, and about **97%** of those reserves were in oil sands. That tells you why oil sands remain a major energy issue: the resource base is enormous.

A second exam trap is assuming that a large reserve automatically means a great energy source. It does not. APES often asks students to weigh **size of supply** against **environmental cost** and **energy return**.

> **Test Tip:** If an APES question asks why oil sands are “unconventional,” focus on the fact that bitumen usually cannot be pumped directly like conventional crude. It must be mined, heated, upgraded, or diluted.

### How extraction works: surface mining and in situ methods

The extraction method depends mainly on **depth**. Shallow deposits can be mined directly. Deep deposits cannot.

#### Surface mining

If oil sands are close enough to the surface, companies remove the overlying material and excavate the deposit. This is a form of surface mining, much like other mining methods you study in APES land-use topics.

The basic sequence is:

1. Remove overburden and vegetation
2. Dig up the oil-sand ore
3. Crush or process the material
4. Separate bitumen from sand, clay, and water
5. Store waste materials, often in tailings ponds

This method causes major direct land disturbance. It clears boreal forest, removes soil layers, disrupts wetlands, and fragments habitat. Because the material itself has to be dug up and processed, the operation also uses a lot of machinery and energy.

#### In situ extraction

If the deposit is too deep to mine economically, producers use **in situ** methods. “In situ” means the bitumen is extracted while still underground.

> **Key Term: in situ extraction**
> A method used to recover deep oil sands deposits by heating or otherwise treating the bitumen underground so it can flow to wells.

The most important example is **SAGD**.

> **Key Term: steam-assisted gravity drainage (SAGD)**
> An in situ oil sands extraction method in which steam is injected underground to heat bitumen so it flows downward and can be pumped out.

SAGD usually uses two horizontal wells. Steam is injected into the upper well. The heat lowers the viscosity of the bitumen. Once the bitumen becomes less thick, gravity helps it drain into the lower well, where it can be pumped to the surface.

Why this matters for the exam:

- **Surface mining** causes greater direct land disturbance
- **In situ** extraction causes less visible surface removal but still needs roads, pipelines, well pads, water, and fuel for steam generation

Students often oversimplify this and assume in situ is “low impact.” It is not. It usually disturbs less surface area than mining, but it still has high energy use and greenhouse gas emissions because steam has to be generated, often by burning natural gas.

#### Surface mining vs in situ extraction

- **Surface mining**
  - Used for shallower deposits
  - Removes vegetation and overburden
  - Creates major direct land disturbance
  - Produces large tailings ponds

- **In situ extraction**
  - Used for deeper deposits
  - Leaves bitumen underground during extraction
  - Requires steam, wells, roads, and pipelines
  - Usually has less direct surface disturbance than mining, but still significant total impact
    > **Test Tip:** If a question asks which method causes greater direct land disruption, choose **surface mining**. If it asks which method often needs large amounts of steam energy, choose **in situ extraction**, especially SAGD.

### Processing bitumen into usable fuel

Getting bitumen out of the ground is only part of the story. Bitumen is too thick and impure to behave like typical crude oil. It often contains a relatively high sulfur content and needs additional processing.

There are two main routes after extraction:

1. Upgrade it into a lighter oil-like product
2. Dilute it so it can move through pipelines
   > **Key Term: upgrading**
   > Processing bitumen to produce a lighter petroleum product that is easier to refine into fuels.
   >
   > **Key Term: synthetic crude oil**
   > A crude-like petroleum product made by upgrading bitumen from oil sands.

Synthetic crude oil is closer to conventional crude in how refineries handle it. This is why AP materials often say oil sands contain bitumen that can be processed into **synthetic crude oil**.

The second route is transport by dilution.

> **Key Term: diluted bitumen (dilbit)**
> Bitumen mixed with lighter hydrocarbons so that it can flow more easily, especially in pipelines.

This distinction matters:

- **Synthetic crude** = upgraded bitumen
- **Dilbit** = bitumen mixed with diluent for transport

Students often confuse the two. Synthetic crude is a processed product. Dilbit is mainly a transport mixture.

This also explains why pipelines are such a major part of the oil sands debate. Bitumen is not naturally easy to move long distances. It must either be upgraded first or diluted.

### Why tar sands oil has lower efficiency and higher emissions

The APES lens here is energy return and environmental trade-offs. Oil sands can provide a very large fuel supply, but they do so with a lower energy return than conventional crude.

> **Key Term: EROI**
> Energy returned on energy invested; a measure of how much useful energy is obtained relative to the energy used to get it.

Oil sands generally have a **lower EROI** than conventional oil because energy is needed for:

- blasting and excavation
- drilling
- crushing ore
- heating bitumen
- producing steam for in situ extraction
- upgrading or diluting the product
- waste disposal
- land reclamation
- long-distance transport

That long chain matters. Each added step requires energy. Under the Second Law of Thermodynamics, every energy transfer loses some usable energy, often as heat. So unconventional oil with more processing steps usually has a lower net energy return.

This is also why greenhouse gas emissions are generally higher per barrel than for conventional crude. More energy use during extraction and processing means more combustion somewhere in the system. In in situ extraction, a major share comes from burning fuel to make steam. In mining, emissions come from heavy equipment, processing, and upgrading.

Combustion of the final fuel still releases carbon dioxide as well, because oil sands petroleum is still a **carbon-based fossil fuel**. So there are emissions both **before** and **after** the fuel reaches a consumer.

### Environmental impacts you must know

Oil sands development has several major environmental impacts, and APES questions often ask students to identify, explain, or compare them.

#### Land disturbance and habitat loss

Surface mining can destroy large areas of **boreal forest**, which is an important carbon sink and wildlife habitat. Forest clearing, wetland removal, and soil disruption reduce biodiversity and fragment habitats.

Even in situ development affects habitats through roads, pipelines, drilling sites, and support infrastructure. That can break natural systemss into smaller patches and affect migration and breeding.

#### Water use

Oil sands extraction requires large amounts of water, especially mining and steam-based in situ methods. Some process water is recycled, which reduces but does not remove the problem. Freshwater withdrawals can still be significant.

This matters in APES because it links Unit 6 energy to Unit 8 water pollution and Unit 9 global change.

#### Tailings ponds and water contamination

After bitumen separation, waste materials are stored in **tailings ponds**.

> **Key Term: tailings ponds**
> Large waste-storage ponds that hold water, clay, residual bitumen, and other contaminants left after oil sands processing.

These ponds can contain process-affected water with harmful substances such as residual hydrocarbons and dissolved chemicals. Risks include:

- wildlife exposure
- seepage or leaks
- long-term storage problems
- contamination concerns for nearby water bodies

The scale is large. Official Alberta data reported roughly **1.392 billion m³** of fluid tailings at oil sands mine sites at the end of 2022. You do not need to memorise the exact number for APES, but it shows that tailings are not a minor issue.

#### Air pollution and acid deposition

Extraction and upgrading can release **SO₂** and **NOx**, especially because bitumen-derived petroleum can contain substantial sulfur. These pollutants contribute to smog, respiratory problems, and **acid deposition**.

#### Greenhouse gas emissions

Oil sands production has high greenhouse gas emissions relative to conventional crude because extraction and processing are energy-intensive. There is also an indirect climate effect from destroying boreal forest and wetland habitats that store carbon.

#### Reclamation limits

Companies may reclaim disturbed land, but reclamation is not the same as restoring the original environment. Wetlands and peat-rich systems are especially difficult to rebuild. Recovery can take decades, and the resulting habitat may not function the same way.

### Weighing the pros and cons for exam questions

APES often frames oil sands as a trade-off rather than a simple “good” or “bad” resource.

#### Main advantages

- Very large supply
- Major reserve significance, especially in Canada
- Potential economic benefits such as jobs and revenue
- Can help maintain oil supply and affect energy security

#### Main disadvantages

- Lower EROI than conventional crude
- Greater direct land disturbance, especially with mining
- High water demand
- Tailings pond waste and contamination risk
- Higher greenhouse gas emissions than conventional crude
- Air pollutants including sulfur oxides and nitrogen oxides
- Habitat fragmentation and biodiversity loss
- Continued dependence on fossil fuels

An excellent APES answer will connect these points. For example:

Oil sands may improve fuel supply in the short term, but because extraction is energy-intensive and damages boreal forest carbon sinks, the climate and habitat costs are higher than for conventional crude.

That is stronger than merely listing pros and cons.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Oil sands and tar sands are interchangeable APES terms for deposits containing bitumen
- Bitumen is a heavy, sticky, highly viscous form of petroleum that does not flow easily
- Oil sands are an unconventional fossil fuel source because bitumen usually cannot be pumped directly like conventional crude
- Shallow deposits are typically extracted by surface mining, while deeper deposits are extracted in situ
- SAGD is an in situ method that uses steam to heat bitumen so it can drain and be pumped out
- Surface mining causes greater direct land disturbance than in situ extraction
- Bitumen can be upgraded into synthetic crude oil or diluted into dilbit for transport
- Oil sands generally have a lower EROI than conventional crude because extraction and processing require more energy
- Major environmental impacts include boreal forest loss, water use, tailings ponds, air pollution, and greenhouse gas emissions
- Tailings ponds store contaminated waste left after bitumen separation and create wildlife and water-quality risks
- Oil sands remain a major global petroleum reserve, especially in Canada
- Oil sands still produce carbon dioxide when the final fuel is combusted because they are a fossil fuel source

## Key Terms and Concepts

- oil sands (tar sands)
- bitumen
- proved reserves
- in situ extraction
- steam-assisted gravity drainage (SAGD)
- upgrading
- synthetic crude oil
- diluted bitumen (dilbit)
- EROI
- tailings ponds


Fuel Types and Uses - Crude oil from tar sands