The house on the edge of the old side of town seemed like the best place for Bob and Frieda Helgerson to grow old together.

Located in tiny Randolph in southern Dakota County, the house has been in Bob Helgerson’s family since 1943. When the couple moved in a decade ago, the place was affordable enough that they could make some major improvements: a larger driveway, fresh stucco and a new septic system.

It turns out, though, a lot of the neighbors never replaced their septic systems, and many are failing. Local leaders have to figure out a solution — and fast — to stop wastewater contamination that’s already threatening the Cannon River watershed — and Randolph’s drinking water supply.

Options include requiring homeowners to upgrade failing systems, connecting to an existing municipal system in nearby Cannon Falls, or building a new citywide treatment system.

“It’s not an easy problem, but I think as a responsible steward of the water supply, number one, and as a responsible participant in the community of Randolph, we’ve all got an obligation to consider all options,” Bob Helgerson said.

A few years ago, the City Council voted to give up its authority over septic system monitoring, inspection and enforcement.

In keeping with state law, the responsibility then fell to Dakota County.

“Oh, boy, that’s a loaded question,” Mayor Robert Appelgren said when asked recently why the council voted to release its authority.

He did not respond to requests for additional comment, and council members could not be reached.

Of 149 systems inspected after the county took over, 43 were found to be failing and 106 were deemed compliant. Of those 106, though, about 30 could fail in the next few years.

Pollution from untreated sewage is a big issue in the Cannon River watershed, threatening already-impaired water bodies including the Cannon River and Lake Byllesby.

In Randolph, some septic systems are so old that they drain directly into sandy soil, which is too porous to act as a proper filter.

Over time, that untreated wastewater makes it way into the aquifer that supplies the town’s drinking water, said Cannon River Watershed Partnership program manager Aaron Wills, who works with Randolph and other small communities to solve sewage treatment problems.

Randolph has commissioned a study to examine solutions.

The costs of building a new system or connecting to one elsewhere aren’t yet clear, but replacing individual septic systems could cost homeowners between $8,000 and $15,000 each, said county water resources manager Brad Becker.

That price tag could be a burden for Randolph residents, some of whom are on “very fixed incomes,” said Commissioner Mike Slavik, who represents rural Dakota County.

The situation in Randolph has spurred the creation of a county program that would assess the cost of a new septic system to a homeowner’s property tax payments, so they don’t have pay all at once. It would complement an existing county cost-sharing program for low-income residents.

If city leaders choose to build a municipal system or connect to one elsewhere, residents could be hit with pricey assessments — even if, like the Helgersons, they already have a working septic system of their own.

“If we have to do it, we’ll do it,” Frieda Helgerson said.

For now, county officials are waiting to see what the City Council does.

“We’ll react to whatever decision they make,” Becker said.