What Is an Operable Unit?

An Operable Unit — often shortened to OU — is simply a way to organize cleanup work at a very large Superfund site.

Think of it as a way to break a massive, interconnected problem into smaller, more manageable pieces.

Why do Operable Units exist?

The Butte–Silver Bow Superfund site covers a large area and includes many different kinds of environmental challenges:

• contaminated soils
• mine flooding
• groundwater movement
• stream and floodplain contamination
• tailings ponds
• industrial sites

Trying to study and clean all of this at once would be impractical.

Operable Units allow investigators and cleanup teams to focus on specific problems, design appropriate solutions, and move some areas forward while others are still being studied.

This approach allows cleanup to begin sooner, rather than waiting for every question across the entire site to be answered.

Operable Units are based on place and problem

An Operable Unit usually focuses on a particular geographic area or a specific type of contamination.

For example:

• Butte Mine Flooding focuses on underground mine workings and pit water
• Butte Priority Soils focuses on residential areas
• Streamside Tailings focuses on Silver Bow Creek and its floodplain
• Warm Springs Ponds focuses on tailings capture and downstream protection

Each Operable Unit has its own history, risks, and cleanup approach.

Explore the cleanup by area →

Why do some areas move faster than others?

You may notice that some areas appear "finished," others are under construction, and some are still being studied.

This does not mean that certain areas are being ignored.

Different Operable Units move at different speeds because:

• contamination types differ
• risks to people and the environment differ
• technical solutions vary in complexity
• new information may require re-evaluation

Superfund is designed to be protective first, even if that means taking more time to get decisions right.

How Operable Units fit together

Although Operable Units are managed separately, they are environmentally connected.

Water flows between areas. Groundwater moves beneath boundaries. Floods can carry sediments downstream.

Because of this, cleanup decisions are coordinated across Operable Units to make sure actions in one area do not create problems in another.

This is one reason cleanup planning can take time — but it is also how long-term protection is achieved.

How Superfund decisions are made →

What does this mean for me?

You do not need to understand Operable Units to:

• know if your drinking water is safe
• get soil or attic testing
• use trails and recreation areas
• participate in public meetings

Operable Units are an organizational tool — not a requirement for understanding or involvement.

Common misunderstandings

"An Operable Unit means cleanup is finished."
Not necessarily. Some OUs move into long-term monitoring after construction, but oversight continues.

"Each Operable Unit is isolated."
No. OUs are managed separately, but environmental connections are always considered.

"If my area isn't active, nothing is happening."
Investigation, monitoring, and planning are active parts of the cleanup process.