Alpharetta’s downtown redevelopment budget grew by almost 5 percent to more than $32.2 million this week, the result of late adjustments and unforeseen costs.

The City Council approved the increase because the project’s contingency fund — $1.7 million — has already been depleted.

Alpharetta voters approved a $29 million bond issue in 2011 to fund the project, which had been estimated to cost $30.7 million. Plans call for a new city hall, a parking deck with 460 spaces, a park and green space set aside for possible future development. The city has also left three acres for a 25,000-square-foot Atlanta-Fulton County Library branch, funded through a county bond issue.

The chief culprit for unexpected overruns was the recent discovery of unstable soil at the site of the new city hall. Before a foundation could be laid, contractors had to install pylons up to 70 feet deep at an additional cost of $500,000.

The project also has absorbed additional costs due to changes after the original design was adopted early last year. Public outcry for more green space spurred city leaders to add a five-acre pocket park between the new city hall and library at a cost of $500,000. Redesigns to those buildings to accommodate the park tacked on $200,000.

Another $450,000 went to the addition of restrooms and space for future expansion to the first floor of city hall. City leaders said the restrooms would be a welcome addition near the park, and the added space to the first floor could be used for offices if the future need arose.

Council members Monday approved funding of the first-floor projects, then voted 5-2 to commit another $1 million from unallocated capital improvement funds to the contingency fund.

“We’re taking this money and moving it from one account to another,” Councilman Mike Kennedy said. “It doesn’t mean we’re authorizing the expenditure of this money.”

Councilman Jim Gilvin argued against approving the full amount.

“If we only took half a million (dollars) from unallocated capital, and should it be necessary to reach that other half million, we as a board would be forced to look at cuts,” he said.

Councilman Chris Owens argued for full funding.

“This is a project our citizens have committed to,” he said. “It’s an imperfect process because we’re imperfect beings. That’s why we have budgets. That’s why we have allowances. That’s why we have contingencies.”