Braun Intertec performed the remedial investigation, feasibility study and remedial action work for the extension of Interstate 35 in Duluth, Minnesota.

This segment of the freeway extension is approximately 2 miles long and runs through an older mixed industrial/residential district of Duluth. The investigation included 65 individual parcels, some of which have been contaminated with petroleum derivatives from past land uses. Among the parcels was one 10-acre parcel which had been a railroad maintenance yard for both steam and diesel locomotives.

Other parcels included bulk oil storage facilities, present and former gasoline stations, and light industrial areas. Our work concentrated on identifying the contaminated parcels and their contaminants, providing an approved cleanup method and disposal of the contaminated soils so construction could begin.

Challenges

We performed the Phase I site reconnaissance, a review of historical documents and aerial photographs, drilling and chemical analysis of soil from 27 borings on 17 parcels within a one-month period. Our Phase II work included performing an additional 140 borings, as well as Phase I work on parcels not included in the original study area. The results of these investigations yielded contaminants ranging from heavy metals to solvents and petroleum.

Solutions

The remedial action we developed was unique in that it remediated approximately 40,000 cubic yards of contaminated soils by a passive method. We proposed that an earthen berm made of contaminated soils be constructed in the median of a nearby divided highway presently owned by Mn/DOT. This strategy was chosen due to the large volume of contaminated soils, their clayey nature and other economic factors such as transport costs. This method will be very cost effective and was approved by State regulatory authorities.