AP Environmental Science

## Learning Outcomes

- Understand why subsurface coal mining is usually more expensive than surface mining
- Identify the main cost drivers in underground coal mining, including labor, ventilation, and safety systems
- Explain hidden environmental costs such as subsidence, acid mine drainage, and methane release
- Carry out a productivity calculation using short tons per employee hour
- Compare subsurface and surface coal mining in terms of economic and environmental trade-offs
- Apply this topic to AP Environmental Science multiple-choice and free-response questions

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand subsurface coal mining cost, with a focus on the following syllabus points:

- Know that **subsurface coal mining** is used for deeper coal seams, while surface mining is more common for shallower deposits
- Explain why underground coal mining is generally more expensive than surface mining
- Identify the major cost drivers of underground mining, including lower productivity, ventilation, roof support, water pumping, and safety systems
- Understand that underground mining can have a smaller visible surface footprint but still creates major environmental costs
- Explain how subsidence, methane emissions, groundwater disruption, and acid mine drainage increase the total cost of subsurface mining
- Distinguish between **productivity**, **sales price**, and true extraction cost
- Use the formula for labor hours per ton from productivity data
- Recognise that laws and regulation add planning, reclamation, and damage-repair costs to underground coal mining

## 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. Why is subsurface coal mining usually more expensive than surface mining?
2. What is subsidence, and why does it matter economically as well as environmentally?
3. How do you convert short tons per employee hour into labor hours per ton?
4. Name two hidden costs of underground coal mining besides the direct cost of digging the coal.
5. Why is it wrong to treat the sales price of coal as the same thing as the mining cost?

## Introduction

## Introduction

Coal can be mined at the surface or below ground. For AP Environmental Science, the key idea is not just that underground mining is dangerous or damaging, but that it is also usually **costlier per ton** than surface mining. That higher cost affects land use decisions, energy choices, and the scale of environmental damage.

Subsurface coal mining can look less destructive at first because it does not remove as much land at the surface as strip mining or mountaintop removal. However, that smaller visible footprint can hide major economic and ecological costs underground. Deep mines need shafts, tunnels, ventilation, roof support, pumping, methane control, and long-term management of land and water damage.

> **Key Term: subsurface coal mining**
> Mining coal below Earth’s surface through shafts and tunnels rather than removing overlying soil and rock from above.

### Why subsurface coal mining costs more than surface mining

The simplest reason is **productivity**. Surface mining usually removes more coal with fewer labor hours. Underground mining is slower because workers and machinery operate in confined tunnels, with more hazards and more steps needed to reach and remove the coal.

> **Key Term: productivity**
> The amount of coal produced per unit of labor, often measured as short tons per employee hour.

A useful comparison comes from recent U.S. coal data. Underground coal mining productivity was about **3.24 short tons per employee hour**, while surface mining was about **8.94 short tons per employee hour**. That means a surface mine can produce far more coal in the same labor time.

Why does this happen?

- Surface mining uses larger machinery in open space
- Underground mines must move workers, equipment, and coal through narrow tunnels
- Coal extraction below ground requires more safety checks and operational delays
- Underground conditions can slow work because of roof instability, gas, dust, and water

This is the main economic idea students should remember: if a mine gets fewer tons per hour of labor, each ton mined carries more labor cost.

We can show this with a worked example.

### Worked example: converting productivity into labor hours per ton

The formula is:

$$
\text{labor hours per ton} = \frac{1}{\text{tons per employee hour}}
$$

Using underground productivity:

$$
\text{labor hours per ton} = \frac{1}{3.24} = 0.309 \text{ hr/ton}
$$

Using surface productivity:

$$
\text{labor hours per ton} = \frac{1}{8.94} = 0.112 \text{ hr/ton}
$$

Now compare them:

$$
\frac{0.309}{0.112} \approx 2.76
$$

So underground mining requires about **2.76 times more labor hours per ton** than surface mining.

This does not prove labor is the only cost, but it clearly shows why underground mining tends to be more expensive.

> **Key Term: labor hours per ton**
> The amount of worker time needed to produce one ton of coal; found by dividing 1 by productivity.
>
> **Test Tip:** If an APES question gives productivity in tons per worker hour, do not stop there. Convert it into labor hours per ton if the question is asking which method is more labor-intensive.

Students often make three errors here:

- They compare the raw numbers without explaining what they mean
- They forget to invert the productivity value
- They confuse greater productivity with greater environmental safety

Higher productivity means more output per labor hour. It does **not** mean a mining method is better for the environments.

### Direct operating costs underground

Lower productivity is only the first reason underground mining costs more. The mine also needs extra systems that surface mines either do not need or need at a much lower level.

First, shafts and tunnel networks must be constructed. Before coal can be removed, access has to be created. That means excavation, engineering, lining, transport systems, and maintenance.

Second, underground mines require **ventilation**. Air has to move continuously through the mine to reduce methane buildup, lower dust concentration, and keep oxygen available. Ventilation is not optional. It uses large fans, monitoring systems, and energy.

Third, mines need **roof control**. The rock overhead can collapse if it is not supported or managed correctly. This requires plans, inspections, support structures, and equipment.

> **Key Term: roof control**
> The methods used to prevent mine roof collapse and protect workers in underground mining.

Fourth, water must often be pumped out. Underground workings can intersect groundwater or collect seepage. If water builds up, it can halt operations, damage equipment, and raise safety risks.

Fifth, safety and emergency systems are extensive. Underground mines need gas monitoring, communications, evacuation routes, rescue capability, and regular inspections. These are real costs even before one more ton of coal is sold.

This is why saying “underground mining is more expensive because it is deeper” is too vague for exam answers. A stronger answer explains _how_ depth creates cost:

deep seam → shafts and tunnels → ventilation, pumping, support, and safety systems → lower productivity and higher cost per ton

> **Test Tip:** In a free-response answer, build a chain: deeper coal seam → more infrastructure and labor → higher extraction cost → greater economic disadvantage.

### Sales price is not the same as extraction cost

Students often see a coal price and assume it is the cost of mining. That is incorrect.

A reported **sales price per short ton** is what the coal sells for, not what it costs to extract. Price reflects market conditions as well as production cost. Underground coal may sell at a higher average price, but that does not mean it is more efficient. It often means the opposite: higher prices can reflect higher mining costs.

For example, recent U.S. figures show average sales prices of about **$85.88 per short ton** for underground coal and **$29.61 per short ton** for surface coal. This supports the idea that underground coal is usually costlier, but price itself is not a direct operating-cost number.

> **Key Term: sales price**
> The price received when coal is sold; it is not the same thing as the cost of extracting that coal.

A strong APES answer would say:

- underground coal often has a higher sales price than surface coal
- this is consistent with higher production costs
- but sales price and extraction cost should not be treated as identical

### Hidden environmental costs of underground coal mining

Underground mining may disturb less land at the surface than strip mining, but that does not mean its environmental impact is low. Some of its most serious costs appear later or away from the mine entrance.

One major problem is **subsidence**.

> **Key Term: subsidence**
> The sinking or collapse of land above underground mine workings when mined-out spaces below can no longer support the ground.

Subsidence can damage buildings, roads, pipelines, streams, and farmland. Economically, that means repair costs, compensation costs, and land restoration costs. Environmentally, it can alter habitats and drainage patterns.

A second major cost is **acid mine drainage**.

> **Key Term: acid mine drainage (AMD)**
> Acidic water formed when exposed sulfur-bearing minerals react with air and water, often polluting streams and groundwater.

In coal mining, sulfur compounds such as pyrite may become exposed. Water moving through these materials can form acidic drainage that carries metals and lowers stream pH. This damage can continue long after mining stops, so the mine may leave behind treatment and restoration costs for years.

A third hidden cost is **methane emissions**. Underground coal seams often release methane. Methane is a strong greenhouse gas, and underground coal mines are a major emitting sector. Methane has to be monitored and managed for safety, but even with controls, some escapes through ventilation or other systems.

This means underground coal mining adds to climate change in two ways:

- methane released during mining
- carbon dioxide released later when the coal is burned

A fourth hidden cost is groundwater disruption. Tunnels and subsidence can alter how groundwater moves through the area. Wells, springs, or surface water supplies may be reduced, contaminated, or interrupted. That creates ecological harm and can also require replacement water supplies or compensation.

### Regulation and why it adds to cost

Mining costs are not just labor and machines. Regulation adds planning, monitoring, and repair obligations.

For underground coal mining, operators must include a **subsidence control plan** in the permit process. This plan identifies structures, land, and water supplies that may be damaged by subsidence and explains how impacts will be prevented, reduced, or corrected.

If damage occurs, operators may have to repair structures, restore land, or compensate affected owners. This means subsidence is not only an environmental risk but a likely financial liability.

Worker safety also adds cost. Underground coal mines must follow approved roof control and ventilation plans. These rules are necessary because underground mining is dangerous, but they also increase operating expenses.

A good APES answer should not treat regulation as separate from economics. Regulation affects cost because it requires:

- more planning before mining
- more monitoring during mining
- more restoration and repair after damage

### Comparing underground and surface mining as an APES trade-off

AP questions often reward comparison. The key is to avoid one-sided answers.

Underground mining has one possible advantage relative to surface mining: it usually causes **less immediate visible surface disturbance** at the mining site. Less overburden is removed, and entire hillsides are not stripped in the same way as surface mining.

But this advantage has limits. Underground mining can still cause:

- subsidence
- acid mine drainage
- methane release
- groundwater disruption
- dangerous working conditions
- high reclamation and damage-control costs

Surface mining is usually cheaper and more productive, but often causes greater immediate land disturbance and habitat loss at the surface.

So the trade-off is:

- **surface mining**: lower cost, higher productivity, greater direct surface damage
- **subsurface mining**: higher cost, lower productivity, smaller visible footprint, but large hidden environmental and social costs

That final phrase is useful in free-response answers: **smaller visible footprint, but large hidden costs**.

### How this appears in AP Environmental Science questions

You may see this subtopic tested in several ways.

One type is a direct comparison question:
“Explain one economic disadvantage of subsurface mining compared with surface mining.”

A strong answer:
Subsurface mining is more expensive because it has lower labor productivity and requires extra infrastructure such as shafts, ventilation, roof support, and water pumping.

Another type is a trade-off question:
“Identify one advantage and one disadvantage of subsurface mining.”

A strong answer:
One advantage is that it usually disturbs less land at the surface than strip mining. One disadvantage is that it can cause subsidence, which damages land and infrastructure and increases restoration costs.

A third type is a data question using productivity values. If given underground and surface tons per employee hour, calculate labor hours per ton and explain which is more expensive.

A fourth type is an environmental-cost question:
“Describe one long-term environmental cost of underground coal mining.”

A strong answer:
Underground mining can create acid mine drainage when sulfur-bearing minerals are exposed to air and water, producing acidic runoff that pollutes streams and increases cleanup costs.

When writing FRQs, keep your answer specific. Name the mining method, the process, and the consequence.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Subsurface coal mining removes coal through underground shafts and tunnels
- Underground coal mining is generally more expensive than surface mining
- Lower productivity is a major reason underground mining costs more
- Productivity can be measured in short tons per employee hour
- Labor hours per ton are found by dividing 1 by productivity
- Underground mining requires more labor hours per ton than surface mining
- Additional underground costs include ventilation, roof control, water pumping, and safety systems
- Sales price per ton is not the same as extraction cost per ton
- Subsidence can damage land, buildings, and infrastructure above underground mines
- Acid mine drainage can create long-term water pollution and cleanup costs
- Underground coal mines can release methane, a strong greenhouse gas
- Underground mining may have a smaller visible surface footprint than surface mining, but it still creates major hidden environmental and economic costs

## Key Terms and Concepts

- subsurface coal mining
- productivity
- labor hours per ton
- roof control
- sales price
- subsidence
- acid mine drainage (AMD)


Impacts of Mining - Subsurface coal mining cost