Hennepin County road workers ran into a costly surprise this fall while rebuilding a road along Elm Creek Park Reserve: a 100-year-old dump containing mercury and other contaminants.

The dump, found under the Goose Lake Road bed north of 109th Av. N., contains household, farm and automotive wastes that date to the early 1900s, project supervisor Don Hannan said. Excavating and removing the debris could cost $700,000 in addition to almost $2 million budgeted for the mile-long stretch of new road extending from 109th to Elm Creek Parkway, he said. The stretch of county road is on the border between Champlin and Dayton, which are sharing a small part of the road cost.

So far the dump has cost an additional $25,000 to drill test holes and haul six truckloads of dump material to an Iowa landfill, Hannan said. He said more test holes will be drilled this week to confirm how big the dump is and see whether contaminants have leached down a steep slope toward nearby Goose Lake in Elm Creek Park.

Workers have unearthed a half-dozen vehicle batteries and brake parts, glass bottles with stoppers, a piece of asbestos, roofing debris and other junk at the landfill, which has been covered with dirt until cleanup work resumes.

The mile-long road project is nearly done. Closed since May, it is to reopen this month with an 800-foot detour around the dump. It will close again for several months when work resumes in the spring, Hannan said.

Contaminants of concern

The debris is contaminated with four metals: mercury, lead, arsenic and selenium, said John Evans, senior environmentalist for the county's environmental services department. He said mercury is the primary concern because tests found levels considered unsafe, though not hazardous, by the state Pollution Control Agency. Debris with the mercury at that level is barred from Minnesota landfills, so it was sent to one in Lake Mills, Iowa, Evans said.

The other three metals are at levels not acceptable for property used for residential construction, he noted.

Project officials are applying for up to $700,000 in grant money from the county's Environmental Response Fund, which usually covers such cleanups, Evans said. The request will go before the Hennepin County Board for approval in December. The environmental fund gets money from mortgage registry fees and deed taxes, he said.

The dump, originally on the slope beside an old trail that later became Goose Lake Road, appears to be at least 50 feet wide and 300 feet long, officials said. Evans estimated that up to 100 dump-truck loads of debris might have to be removed to ensure contaminants don't leach into ground water or the lake and get into the wildlife food chain.

Mark Schmitz said he has lived more than 40 years on Goose Lake Road. The man he bought the house from said he had the old dump covered over, Schmitz said. He said he relayed that information to county engineers and surveyors before the work began.

"I am not concerned" about water contamination, Schmitz said. "I've been here 47 years on my well. I am 76. I am not going to start worrying about it now."

Hannan said that he had talked with Schmitz but heard nothing about the dump, and that workers were surprised to discover the landfill in September.

The project was delayed until August, Hannan said, because it took months to get approval from Schmitz and his neighbor to be on their land.

Previously, the stretch of road has averaged more than 500 vehicles a day, a figure Hannan expects to double when the work is finished next summer.

Jim Adams • 612-673-7658