Derby ? It’s a pretty sure bet that Carl Rose is going to name his new dog “Derby.”

Rose and other Derby city workers — from wastewater treatment employees to firefighters — helped rescue the black lab Thursday from the bottom of a concrete tank about 20 feet deep.

Here’s the story:

Rose, superintendent of the Derby Wastewater Treatment Plant, went to work at about 7 a.m. Thursday. One of his employees, Terry Meek, a wastewater operator, was going out to turn on a pump when he walked by what’s called a clarifier pit used to treat water and noticed “that there was a dog in the bottom.”

The pits usually have water in them, but this one was empty.

Meek called Rose in the office.

“He said, ‘Uh, we have a problem.’ I’m like, ‘Oh boy, what’s going on?’ ” Rose said.

Meek told Rose that there was a dog in the bottom of the clarifier pit.

“What?” Rose asked “Is it dead?”

“No,” Meek answered. “It’s sitting here looking at me.”

Rose rushed out there.

“A couple other people went with me out of sheer curiosity,” Rose said.

Sure enough, there was a dog in the bottom of the hole. He appeared to have broken his leg.

Nobody is sure how he got into the plant, which is fenced off, and into the clarifier, which has rails around it.

Probably slipped through a gate, Rose guessed.

“We’re standing there looking at him, and we can tell he’s hurt,” Rose said.

Rose called the fire department, and firefighters showed up.

“I had already set up a ladder,” Rose said. “One of my guys was down in the basin with this dog and trying to calm him down and keep himself from hurting himself any further.”

The dog was scared but calm. He wasn’t wearing a collar or ID tag.

A firefighter, Cody Larson, went down into the clarifier, put the dog over his shoulder and carried him out of the pit up the ladder.

Throughout the ordeal, Rose said, the guys were telling the dog, “It’s going to be all right. We’re going to get you out.”

Then the search was on to find someone to mend the dog’s leg.

The first veterinary clinic workers called said it would be about $1,500 to fix up the dog.

El Paso Animal Clinic in Derby “quoted me about $1,000,” Rose said. “One of my employees’ wives works there. So I called my wife and said ‘We’ve got to do this.’ My wife said, ‘I know, you’re right, we have to do it.’ “

The Roses lost one of their dogs about eight months ago. They also have a Chihuahua.

So the Roses will take him home.

Brad Smith, fire chief for the Derby Fire Department, said firefighters have “had a few occasions where we’ve rescued animals. We had a dog that went through the ice in one of our retention ponds.”

If firefighters have the time, they’ll help, he said. “Obviously if we’re running an emergency call for a human being, that will take precedent,” he said.

Veterinarians have estimated that the shiny black dog is between 6 months and a year old.

The good news for “Derby” — or whatever his name ends up being — is that his leg should heal.

The bad news for him is that after that, he’s scheduled to be neutered.