Colorado-based Abound Solar has been ordered to remove and bury in cement thousands of leftover solar panels “deemed unsellable” by the Colorado Department of Public Health and Environment (CDPHE). The company must also clean up other hazardous waste at a number of facilities statewide, according to the Northern Colorado Business Report (NCBR).

The cleanup is expected to cost at least $2.2 million.

The company, a recipient of a $400 million Department of Energy loan guarantee, received approximately $70 million before it shuttered its operation. The bankruptcy will cost taxpayers $40 million to $60 million.

State health officials pointed to the carcinogenic metal cadmium in the panels as the source of concern. “At the time of the inspection these 2,000 pallets of solar panels were deemed unsellable and a viable agreement for reclamation of the solar panels was not evident,” the inspector’s report says. “Therefore, the department views these 2,000 pallets of solar panels as a characteristic hazardous waste for cadmium.”

The Denver Post estimates more than 2,000 total pallets of solar panels remain that are either unsellable or defective. Abound’s manufacturing facility still contains more than 4,000 gallons of cadmium-contaminated liquids, The Post said.

At the height of Abound’s production, CDPHE estimated a “waste stream” of 630 pounds of hazardous cadmium-laced materials produced per month, according to a report from Complete Colorado.

Following the company’s bankruptcy, an investigation by the Environmental Protection Agency (EPA) revealed that the warehouse in Denver storing the unsold panels did not have a hazardous waste permit. The cleanup, NCBR reports, will require encasement and burial:

There’s only one treatment facility in the state, a landfill near Last Chance in eastern Adams County. The panels would likely be treated, mixed in cement and buried, Schieffelin said.

Violating state hazardous waste regulations carries an administrative fine of as much as $15,000 daily and a civil fine of as much as $25,000 per violation per day, according to the state.

The news report concluded, “Any [Abound] panels that cannot find a buyer would be deemed hazardous waste.”

So far, the state has refrained from imposing the fines as it expects the company to pay for the cleanup.

Cadmium’s toxicity has led to a host of regulations, including a new set of guidelines issued in December 2012 by the EPA. The Occupational Safety Health Association’s listing on cadmium notes the danger posed by the metal:

Cadmium and its compounds are highly toxic and exposure to this metal is known to cause cancer and targets the body’s cardiovascular, renal, gastrointestinal, neurological, reproductive, and respiratory systems.

An Associated Press story earlier in February detailed the problem faced by solar companies in handling and disposing of hazardous waste and toxic chemicals within the industry. As much as 46.5 million pounds of contaminated materials and water was produced by solar manufacturers in California alone between 2007 and 2011, including cadmium-contaminated water from the now-bankrupt Solyndra.

Abound still faces a fraud investigation as well as a Congressional document probe after a Daily Caller report in October revealed faulty and defective panels that suffered “catastrophic failure.”