Contaminated Soil Excavation at Perham Arsenic Site

State Project Number SR0000056 Contaminated Soil Excavation at Perham Arsenic Site
A. The work will be done under one prime contract that includes: General, Mechanical, and Electrical construction.
B. The following summary is a general guide to the scope of work. It should not be construed as a detailed list of work included in the contract.
The Minnesota Pollution Control Agency (MPCA) has hired Bay West LLC (Bay West; the “Engineer”) to perform a soil removal corrective action of arsenic contaminated soils at the Perham Arsenic Site (the Site) (Figure 1). The Site is currently vacant and owned by the State. The property immediately north is owned by the City of Perham and used for the fairgrounds. The building, treatment system and rabbit shed were demolished in 2024.
The U.S. Department of Agriculture distributed lead arsenate to several agricultural fields in Minnesota as insecticide to combat grasshopper infestation in the 1930s and 1940s. The grasshopper control was dispersed around farm fields to prevent crop loss. Otter Tail County, located in northwestern Minnesota, was included in the arsenic-based grasshopper bait distribution program. The present-day location of the East Otter Tail County Fairgrounds, in the City of Perham, was used as a mixing station and depositor for pure lead arsenate and unused arsenic-based grasshopper bait. In 1947, an estimated 200 to 2,500 pounds (lb) of unused arsenic-based grasshopper bait was buried in a shallow pit in the southwest corner of the fairgrounds. The pit dimensions were approximately 15 by 20 ft with an approximate depth of 3 to 6 ft. The buried grasshopper bait—contained in burlap bags, wood crates, or other biodegradable material—is believed to have been composed of more than 50 lb of technical-grade lead arsenate. The arsenic concentrations pose a risk to human health and the environment. The primary project objectives are: removal and disposal of the bulk of the arsenic contaminated soil beneath the project site property (Site), removal and disposal of the infiltration gallery and select abandoned monitoring wells in the excavation footprint, and site restoration, including restoring grade and adding cover crop to prevent erosion.
The Contractor shall:
1. Visit and review the Site with the Engineer; 2. Prepare and provide the Engineer with a Soil Excavation and Disposal Plan, Groundwater Management Plan, Site Safety & Health Plan, and any other submittals required in this specification; 3. Obtain and comply with all necessary permits to complete the work; 4. Conduct startup including mobilization of labor, equipment, and materials; 5. Conduct pre-survey of excavation boundaries; 6. Provide and maintain temporary facilities and controls including temporary utilities (electricity/water), sanitary facilities, construction facilities, traffic controls, site and excavation security (e.g. barricades, temporary fencing); 7. Abide by the air monitoring plan and health and safety protocol; 8. Conduct public and private utility locates; 9. Provide erosion controls and stormwater controls; 10. Provide and install plastic sheeting to any non-impacted soil stockpiled; 11. Determine haul truck traffic patterns, setup loading station(s) and stockpile location(s); 12. Setup stockpile locations, if necessary; 13. Install shoring or other engineered controls (at Contractors’ discretion where shoring is necessary to achieve excavation depths and meet all applicable regulations); 14. Remove any permanent fencing in the excavation area that impedes completion of excavation activities; 15. Remove asphalt (both sides of former commercial building), concrete and gravel surfaces and remove remaining building slab and foundations; 16. Dispose of asphalt, concrete, gravel, and building slab and foundations; 17. Excavate soil within designated limits and to designated depths. Note: Excavation will largely be GPS guided excavation work given the limitations for field screening of arsenic and the comprehensive 3D modeling data available for the plume extent. Soils will be excavated utilizing existing plume map boundaries including the segregation of clean versus impacted soils. 18. Seal and abandon extraction well lateral piping in place per the Minnesota well code; 19. Cut four abandoned extraction well casings 2 feet below grade and backfill to grade/restore; 20. Remove remnants of abandoned MEW-1 and MEW-1A in excavation footprint; 21. Install dewatering well network, as necessary; 22. Implement dewatering/treatment system and manage water, as necessary; 23. Remove and dispose of infiltration gallery; 24. Transport and dispose removed impacted soil; 25. Conduct waste management and tracking documentation; 26. Apply and mix additive (FerroBlack® or Engineer approved equivalent) into bottom of excavation prior to backfilling activities; an estimated 56,500 lbs will be mechanically mixed in to the impacted bottom of the excavation; 27. Partially backfill and compact excavation area with previously removed/stockpiled clean overburden; 28. Provide and import additional soil for backfill and complete backfilling and compaction of excavation; 29. Restore any sidewalks, curb and gutter damaged or removed as a result of the excavation and construct new curb and gutter as necessary; 30. Provide, set and grade topsoil to match the grade documented in pre-excavation survey, replace sod and add new cover crop where building/south asphalt lot were following the specifications laid out in the MnDOT Seeding Manual, utilizing the 2024 2575.608 seed two year cover crop or engineer approved equivalent; 31. Complete in-kind replacement of north asphalt lot. 32. Remove temporary fencing following completion of work; 33. Replace any permanent fencing that was removed following completion of work; 34. Conduct decontamination activities and management; 35. Clean Site and complete site restoration; In addition, restore and reconnect any permanent and active utilities that were temporarily moved, padded, braced, disconnected, and/or removed due to the excavation activities (if necessary). 36. Conduct post-survey of excavation boundaries; 37. Demobilize from the Site; 38. Provide one-year warranty for settling and erosion repairs; 39. Provide all project planning, project closeout submittals, and execution documentation, as requested by the Engineer.
The estimated total volume of soil to be excavated is 20,006 cubic yards (CY). The estimated excavation volume assumes shoring will be used and a final depth of approximately 30 feet (Figure 3). It is at the Contractors’ discretion where shoring is necessary to achieve excavation depths and meet all applicable regulations. The estimated amount of in-place soil to be used as backfill material is 15,084 CY. The total estimated amount of in-place arsenic impacted soil to be excavated and disposed off-site at an Owner-approved landfill is 4,922 in-place CY. For this specification, the amount of arsenic-impacted soil to be excavated and disposed off-site is 9,800 tons. This figure is based on 4,922 in-place CY plus 10% additional volume and a weight per volume ratio of 1.8 tons/CY. The estimated amount of imported fill to be provided is 6,650 CY.
The Engineer will manage the soil and debris removal corrective action and oversee the Contractor in performing the removal activities. Soil excavation activities including engineering controls, dewatering if necessary, on-Site and perimeter dust monitoring (per the air monitoring plan), dust suppression (per the air monitoring plan), removal, disposal, providing soil for backfill, backfilling, compaction and restoration will be completed by the Contractor. The Engineer will provide oversight of Contractor, guide excavation progression, provide GPS data to guide proposed excavation (available in RockWorks model and/or X,Y,Z coordinates), quantify/track soil removal, and complete field documentation, reporting, and any other activities associated with the soil removal corrective action and treatment that are not assigned to the Contractor.