BERKELEY — University of California regents and UC Berkeley have been slapped with two lawsuits, one from the city of Berkeley and another from a neighborhood group, over the university’s unbridled enrollment growth — an issue both plaintiffs claim was swept under the rug in planning documents for the university’s latest expansion project that regents approved last month.

From 2005 to 2018, the campus population grew from 31,800 to 40,955, and will increase by another 4,000 students by 2022.

In 2005, the university projected that the student population would only rise about 5 percent through 2020. But by 2018, the increase in the number of students had shot up close to 29 percent. By a Berkeley consultants’ estimate, the increased enrollment puts a $21 million strain on the city, and city officials want the university to pay its fair share of those costs.

Though the city’s lawsuit doesn’t make a monetary demand, it calls on the university to analyze the impact the increased enrollment has on services such as police, fire, roads and public transportation in an environmental impact report. Such a report could strengthen Berkeley’s demand on the university to increase its annual payment to the city, which the two parties are currently negotiating.

Rather than conduct a separate report into the impact, city officials say, the university tucked the enrollment increase into a report for the “Upper Hearst Project” at Hearst and La Loma avenues — a proposal to which includes a 150-unit dorm with parking and a four-story academic building. The lawsuit alleges that a report into the impact of the increased number of students should have been separate under the state’s Environmental Quality Act.

“What they’ve tried to do is bury their campuswide enrollment impact into a report about two buildings,” city spokesman Matthai Chakko said in an interview Thursday, adding that the city isn’t against the Upper Hearst Project itself.

UC Berkeley spokesman Dan Mogulof said university administration would be happy to crunch the numbers and negotiate a fair compensation to the city, but that Berkeley opted to “proceed with costly litigation” instead, which will only delay the construction of “urgently needed student housing.”

“We cannot address the housing crisis through the courts, only through construction,” Mogulof said.

The city’s lawsuit, filed last week, calls for the regents’ approval of the project and certification of the environmental impact report to be scrapped and for the project to be put on hold until it comes into compliance — which the city says would include conducting an environmental review into the enrollment growth.

Mogulof also pointed out that the university makes an annual payment of $1.8 million to the city to compensate for the strain its students put on city services such as police and fire, roads and public transportation — per a 2005 settlement of an earlier lawsuit. However, when that settlement was reached, the university projected that the student population would only rise about 5 percent through 2020.

The city is seeking the university to pay upward of $21 million, the consultant’s estimate of what is the true impact of students on Berkeley.

Mogulof said the campus is offering to increase its payments by 30 percent, but raising the payments by more than 1,000 percent would be “unprecedented.”

Chakko said the city would be willing to drop the lawsuit if the university would conduct a separate, data-driven review of the impact on the enrollment growth.

The lawsuit filed by Save Berkeley’s Neighborhoods also calls for the approval of the project to be voided and for a separate environmental impact report to be conducted. It also alleges that the environmental impact report fails to assess the effects the project may have on “community aesthetics, including increases in street trash and littering.”