Braun Intertec conducted a multiple-phase remedial investigation at a 41-acre parcel of a former railroad yard used for locomotive maintenance and refueling operations.

The objectives were to define the nature and extent of site contamination to determine remedial alternatives that would allow it to be redeveloped.

Challenges

The primary contaminants consisted of various petroleum products present in soil and groundwater. Remediation systems installed and operated included a bioremediation system, a soil bioventing system, and a groundwater extraction/free-phase product recovery system. The project was coordinated with the Minnesota Pollution Control Agency’s Voluntary Petroleum Investigation and Cleanup Program (VPIC).

A preliminary investigation consisted of installing six monitoring wells and advancing 22 soil borings. Contaminated soil and groundwater were identified, prompting a more detailed subsurface investigation. This consisted of installing six more wells and completing 71 additional soil borings. Petroleum contamination was identified in three areas.

Solutions

A closed-loop bioremediation system consisting of two fixed-film bioreactors and a closed-loop groundwater extraction and infiltration system was installed. Native microorganisms inoculated within the bioreactors consumed the petroleum contaminants as a food source. The remediated groundwater was amended with nutrients and discharged into contaminated soils via a subsurface infiltration gallery. Cleanup goals were achieved, and after one year of follow-up groundwater monitoring, the MPCA granted site closure.

The site was redeveloped with a 40,000 sq. ft. office/warehouse facility. This project earned us the Minnesota Consulting Engineers Council’s Engineering Excellence Grand Award and was named a national finalist in the American Consulting Engineers Council’s contest.

Soil bioventing and vacuum-enhanced groundwater extraction/free-phase product recovery systems were installed in the northwestern zone. These systems use geologic analysis and computer modeling to determine optimal locations and spacing of vent wells and groundwater extraction/free-phase product recovery wells.

The insitu bioventing system used both injection and withdrawal of air to accelerate the rate of natural biodegradation of the contaminants. The bioventing system had essentially achieved its soil cleanup goals after four years of operation, with the calculated biodegradation of over 40,000 gallons of fuel oil. The MPCA granted bioventing system closure in 1997. A portion of the ground-water extraction/free-phase product recovery system was modified and reconfigured to allow construction of a 28,600 sq. ft. office/bus maintenance facility. Groundwater extraction/free-phase product recovery system operations ceased in August 2000.

A feasibility study prepared for the western zone concluded that due to technological constraints, a "No Action Alternative" was preferred. This alternative was approved by the MPCA.