Ripon Manufactured Gas Plant Site

Ripon, Wisconsin

Arrowhead was awarded a competitively bid $1.6M prime contract to conduct a coal tar-contaminated sediment removal action at a former MGP Plant site (now a city park) owned by a large Midwestern Utility Company. Key elements of the work scope included utilizing a water based drill rig to characterize contaminated sediments, mechanically dredging over 2,000 cubic yards of heavily contaminated sediments, stabilizing the sediments prior to disposal, and installation of a State approved subaqueous cap.

Site support activities included: establishing site security measures/fencing; providing temporary offices, utilities, and restroom facilities; and establishing staging areas, air monitoring stations, and site ingress & egress provisions. Subsequent dredging operations began based on the information gathered during the preliminary investigation. Arrowhead crews utilized a spud barge with a long-stick excavator to conduct sediment dredging. An initial 2-feet of sediments were removed from prescribed areas of the pond. An additional 2-feet of sediments were surgically removed from the center area of the pond. All dredging was directed by GPS controlled equipment. Dredged sediments were direct-loaded on to waiting haul-barges for transport to shore. Utilizing a Sennebogen off-loader, crews transferred the contaminated sediments from the haul barges to a staging area for calciment stabilization/mixing. The sediment was then tranfered to tri-axle dump trucks destined for transport to the landfill. The subaqueous cap was installed above the excavated areas of the pond. As per the specifications and Wisconsin DNR, the subaqueous cap was designed to be comprised of a vent layer overlain by a geosynthetic liner. The entire cap system was designed and installed to passively vent any vapors to the shore side for atmospheric dissipation.

Substantial completion of the project was achieved in January of 2014 with demobilization conducted the following spring, due to subzero temperatures. Final site restoration was completed in April 2014. The work was conducted with little or no impact to the park, the shoreline, or the surrounding community.