A CASE STUDY: GEOLOGY AND THE INVESTIGATION, REMEDIATION, AND REDEVELOPMENT OF A RAILROAD SHOP BROWNFIELD SITE IN ST. PAUL, MN

A case-study approach can be used to introduce students to the work that geologists do as environmental consultants. Data used by environmental consultants for a Brownfield site that is currently undergoing redevelopment in St. Paul, MN has been adapted for in-class study, either as a series of short exercises, or as part of a larger project. Data available for the RR engine repair shop include various types of soil borings, trench profiles, ground-penetrating radar, electrical resistivity surveys, and data from nested monitoring wells, as well as local published geological information. The contaminants identified on the site include: lead and asbestos from painting and welding activities; polynuclear aromatic hydrocarbons (PAHs) from cinders, clinkers and railroad ties; volatile organic compounds (VOCs) from degreasing solvents; and petroleum from leaking storage tanks, pipelines, fill stations and an asphalt plant.

The local geology consists of: 10-20 ft of uncontrolled fill on top of mixed glacial, alluvial and peat deposits, which overlie Decorah Formation shales, Platteville Limestone, Glenwood Shale and St. Peter Sandstone. Surficial sediments thicken towards the NE across the site, which sits on the edge of a bedrock valley. The thick layers of uncontrolled fill and peat make for more expensive remediation and building foundations. In addition, a clay till layer at 40 ft depth is acting as a barrier to further transport of dense non-aqueous phase liquids (DNAPLs) such as degreasing solvents to deeper drinking water aquifers.

The remediation process involved the excavation of the upper 12 feet of the site for lead, asbestos, PAHs and petroleum. There was ‘hotspot' cleanup of VOCs with excavation of VOC laden heavy tar, a soil vapor extraction system, and passive bioremediation of the groundwater. Redevelopment on most of the site requires a GeopierTM foundation system for light industrial buildings. A parking lot is planned for the southwest side of the site because expensive and complicated piling would be required for any building due to the thick layers of uncontrolled fill and peat and the clay till barrier. The RR has retained control of the north side of the site for railroad use, although alternatives are being considered.