Heavy rainfall in May and June that overwhelmed an Eden Prairie sewer system and caused a mudslide that nearly sent a home falling over a ravine will cost the city $1 million — double what was expected.

This week, the city continued to approve extra expenses as crews finish building the new and bigger sewer system near Burr Ridge on Purgatory Creek that was overwhelmed during the May and June rains.

“It was one of, if not the biggest, rainfall, and unfortunately we were working on a big project,” said Robert Ellis, the city’s public works director.

In May, heavy rainfall overflowed the neighborhood’s 37-year-old sewer system, eroding land between two homes on the ridge.

The city hired crews to replace the system with a larger pipe, and they were almost done when more heavy rain June 1 washed away much of the work.

“If we had another week or two, we would have been able to complete it,” Ellis said.

Instead, heavy rains caused a mudslide, opening up an 80-foot ravine in back yards as land gave way and slid down the Purgatory Creek valley. That sent the porch and deck of David Zurn’s home teetering over the huge hole.

The city made an emergency decision to demolish his house and is now in the process of buying his property to stabilize the slope and build the bigger sewer system, which will have a channel handling four to 10 times more stormwater than the old system, Ellis said.

“It provides a level of protection that neighborhood has never had,” he added.

But it comes with a cost.

What was initially expected to cost no more than $500,000 instead will double to about $1 million to fix the area, build the larger sewer system and pay $99,000 to repair erosion to Zurn’s neighbors’ yard.

And more expenses are expected. The City Council met in executive session this week to discuss buying Zurn’s property, but no price has been disclosed yet. It’s the first time the city has had to purchase an entire residential property for work like this, Ellis said.

Zurn declined to comment Wednesday but said he has hired an attorney.

The city’s sewer work is expected to finish by mid-August.

All the extra expenses from the flooding and expanded project probably will mean the city will delay other sewer work a year or longer, Ellis said.

Eden Prairie is also among the cities that hope to receive federal assistance if the county qualifies.

Last month’s record rainfall across Minnesota caused $32 million in damage to public structures, including $14 million in Hennepin County.