By Rene Marsh and Gregory Wallace, CNN

(CNN) -- The Environmental Protection Agency is beefing up security measures surrounding Administrator Scott Pruitt to an unprecedented level, CNN has learned, as members of Congress are asking if the costs are a "potential waste or abuse of taxpayer dollars."

Pruitt's security detail is in the process of expanding by hiring a dozen more agents, according to a source with knowledge of the situation, as the number of threats against the agency leader increase. The incoming agents will grow the team that works in shifts to provide him around-the-clock protection, something unheard of for Pruitt's predecessors.

Salaries alone for the full team will cost at least $2 million per year, according to figures compiled by CNN from public documents. The numbers do not include costs such as training, equipment, and travel.

The spending increase comes as the Trump administration has laid out plans to cut the agency's budget by 30%, including major cuts to the agency's enforcement work and staffing as well as the elimination of some programs. Pruitt told Congress in June that the EPA "can fulfill the mission of our agency with a trimmed budget, with proper leadership and management."

Pruitt's travel spending has also come under scrutiny following news reports outlining frequent trips to his home state of Oklahoma, as well as several flights on charter and government aircraft.

EPA administrators, whose public profiles and security arrangements are typically smaller than other members of the Cabinet, haven't had anywhere close to the level of security being assembled for Pruitt. (CNN has withheld specific details about the size of Pruitt's security detail.)

No previous EPA chief has ever received a 24/7 security detail, the agency's inspector general said. Two prior administrators were guarded primarily when traveling.

The EPA's inspector general's office, which investigates threats, says Pruitt has received more death threats than any of his predecessors. The office has launched more than 70 investigations into threats against Pruitt and others, the agency said.

"We have at least four times -- four to five times the number of threats against Mr. Pruitt than we had against Ms. McCarthy," said assistant inspector general Patrick Sullivan, referring to Gina McCarthy, who held the post under President Barack Obama.

"The EPA is a lightning rod. We get threats from both sides of the spectrum," Sullivan added. "Some people believe the EPA is not doing enough to enforce environmental laws, and they're upset about that. Other people think the EPA is doing too much, vis-à-vis enforcing environmental laws and they're upset about that."

Asked for comment on this story, EPA spokeswoman Liz Bowman said, "We decline to comment on security measures taken months ago to protect the administrator."

New security and a soundproof room for Pruitt's office

Security enhancements are also being added to Pruitt's third-floor office inside the EPA's Washington headquarters, where sources have previously described restricted access to even the hallway near his office.

The agency recently made arrangements with a security vendor to have "two access control card readers" installed for his office, according to federal contracting documents reviewed by CNN. That security system, including an additional access card reader for the security office and an alarm in the office to alert agents, costs $15,780, the documents showed.

Pruitt also purchased a secure soundproof communications booth for his office at a cost of nearly $25,000, purchasing records show, even though EPA already has a similar room elsewhere in the building.

The company that builds the booth told The Washington Post the EPA was concerned that the box not be vulnerable to hacking or eavesdropping.

EPA officials have considered using biometric security system, such as a fingerprint scanner, a source with knowledge told CNN. But it was not clear if a biometric system had been installed or continues to be under consideration.

Access to Pruitt's office appears to be a longstanding concern. Publicly released schedules show that, starting in early April, an aide to Pruitt was responsible for opening his office at 7 a.m. on weekdays for cleaning staff, rather than allowing them to enter on their own.

In the hallway around Pruitt's office, security employees check government IDs against a list of employees who are approved for access, according to individuals who work at and have visited the building.

It's unclear if Pruitt and his staff are guarding against outside threats, internal leakers, or both. EPA sources have described Pruitt as distrustful of career staffers at the agency.

Former EPA Administrator Christine Todd Whitman, who served under President George W. Bush, told CNN that cleaning staff access to her office had not been a concern under her tenure.

"I guess they entered once I was gone," she said. "There were no restrictions or anyone overseeing them while they were in my office."

Security jobs pay in six-figures

The positions on Pruitt's detail pay between $103,000 and nearly $162,000, according to the job posting and a source familiar with the positions, who described how the role is called criminal investigator or agent, and said it qualifies for a 25% bonus paid to federal law enforcement officers, who work unusual hours.

The position of criminal investigator at the EPA that usually involves investigating environmental crimes involving pollution or waste dumping.

But an online posting for the jobs described the responsibilities as including "assisting with conducting of advances, motorcade logistics, physical security, site security, and conducting or coordinating investigations of individuals or groups who may present a physical danger to the protectee."

In addition, the cost of the team goes well beyond their salaries. The number of government vehicles used by Pruitt's security detail will also grow, allowing each agent his or her own vehicle.

Democratic members of Congress have expressed concerns with the costs of his protection.

Reps. Peter DeFazio and Grace Napolitano asked the EPA inspector general to investigate their concerns that "taxpayer funds are being misused." Their letter states Pruitt's security costs "during his first quarter as EPA administrator is nearly double what the two previous administrators spent on security over that same timeframe." That was before the new agents were hired.

Pruitt's spending on travel, security and the soundproof room is "symptomatic of a troubling culture that appears to have swept through this administration," the Democrats wrote.

"This culture, which is reflected in travel and lifestyle choices from the President on down, seems to embolden senior, politically appointed officials of the Trump administration to undertake lavish spending of taxpayer dollars for their sole and personal benefit, and not for the benefit of Americans paying the tab," they added.

Sen. Tom Udall has asked the EPA for additional information about the detail, including an accounting of costs and whether the increased security measures may be pulling resources away from enforcement programs.

Previous administrators have not requested nor received the same level of protection.

McCarthy was driven to and from work by an agent, according to a person familiar with McCarthy's security arrangements while in office. Her security detail included a total of five agents, and typically three agents would accompany her on official travel outside of the DC area.

McCarthy had an open-door policy for EPA staffers, and she would leave her office door unlocked when leaving for the night.

Whitman, who served both before and after the September 11 terror attacks, did not use a security detail on a daily basis. Agents accompanied her only when traveling, and she also said she did not lock her office door. Whitman walked by herself to work.