When fracking causes controversy, it’s often because of wells — either the ones used to inject chemicals and water into the ground to break up gas-rich shale rock or the ones used to dispose of all the waste and water left over from the injection process.

Often overlooked is a another way to dispose of that waste: massive surface ponds in which fracking water is stored until it can be recycled or buried or is left to slowly evaporate. Those ponds, which can grow to several acres in size, dot the landscapes of virtually every state that produces natural gas.

Now environmentalists say a recent controversy over the ponds in Utah highlights their increasing impact across the U.S.

The scandal at Danish Flats Environmental Services, in Clark County, next to Colorado, began as soon as the ponds were developed in 2007. The facility, which consists of 14 ponds filled mainly with oil and gas wastewater from Colorado, had been allowing the water to evaporate without an air quality permit from the state. Until early August the state considered the facility — and every other wastewater pond in Utah — below the de minimis pollution standard, meaning it wasn’t emitting enough to be regularly inspected by air quality regulators or to need a permit.

But after an updated analysis of its emissions was conducted, regulators found that Danish Flats was allowing fracking chemicals like methanol and other volatile organic compounds into the air and fined the facility $50,0000 in early August.

“These places are the size of football fields, they’re all across the state, and none of them were declared above de minimis,” said Chris Baird, director of the Canyonlands Watershed Council, a western Utah environmental group. “They’ve just kind of resisted regulatory control.”

Now the state is looking into the dozens of other wastewater facilities across the state.

But as Utah begins to clamp down on the facilities, environmentalists say the type of ponds that got Danish Flats in trouble is still an environmental concern elsewhere as hydraulic fracturing expands across the U.S.

The fracking process requires thousands of gallons of water. There’s the fracking fluid, a mixture of water, sand and chemicals that’s used to break up rock thousands of feet below the surface. And then there’s flow-back water, which pours out of the well during the fracking process and includes some of the fracking fluid as well as the very salty water that’s naturally in shale rock.

As tens of thousands of wells are drilled each year, billions of gallons of contaminated water are left over. Environment America estimates 280 billion gallons of wastewater were produced by fracking wells in 2012 alone (PDF).

Increasingly, there seems to be no completely safe option for this water. Injection wells may prevent air quality issues, but they also might cause earthquakes. Treating the water and releasing it into the environment might save water, but it also might irradiate streams and rivers.

In the arid West, allowing the water to slowly evaporate is an attractive option for natural gas companies. But the ponds have environmental effects, including possibly leaching toxins into the air, water and earth. And they can be death traps for birds that confuse the ponds with fresh water.

It’s unclear how many wastewater ponds exist in the U.S., but experts believe the number is undoubtedly well into the hundreds. In North Dakota, Montana and Texas, almost 50 percent of all fracking waste is stored in ponds, according to industry publication WaterWorld.

“They’re usually in rural areas where not that many people see that they’re there or see the damage they can cause” said Natural Resources Defense Council senior policy analyst Amy Mall. “No one really knows where all these places are.”

As of now, Utah has relatively lax regulations. There’s currently no requirement for groundwater monitoring, and companies aren’t required to present plans for how to remedy the effects of water and toxins released into the environment.

Other states are beginning to impose stricter regulations. Pennsylvania might be a sign of things to come for pond regulations. In 2010, after the state had a spate of high-profile fracking water spills, including one that spilled 50,000 gallons of wastewater at a drilling site, the state beefed up enforcement of environmental regulations regarding ponds and now has some of the most stringent regulations in the nation, including requirements for groundwater monitoring and environmental remediation.

Those requirements not only make the ponds safer, according to David Yoxtheimer, a professor at the Penn State Marcellus Center for Outreach and Research, but they’re also making the industry search for other options like wastewater recycling and closed-tank storage.

“Where there’s hydraulic fracturing, there’s going to be flow-back water, so you need a way to store it that’s environmentally friendly,” he said. “But these [ponds] are relatively expensive, they tend to leak, and regulations are getting more stringent, so the industry is starting to turn away.”