Former Sunflower Army Ammunition Plant Contaminated Pipe Removal


Location De Soto, Kansas
Contract Value $25,000,000
Period of Performance October 2016 – September 2021 (estimated)
Role Prime Contractor

Significant Project Features

  • Work performed under the direction of the U.S. Army Corps of Engineers, Kansas City District
  • Removal of approximately 170,316 ft. of piping contaminated with TNT
  • Removal of 445,337 SF of concrete foundation slabs
  • Excavation of 18,700 CY of contaminated soils
  • Responded to differing site condition involving mercury contamination in a timely and efficient manner
  • Transportation and disposal of an expected 350 tons of burn debris at an offsite disposal
  • Removal and transportation of 2,330 tons of sewer line debris for reuse
  • Completed, to date, 100,000 safe workhours without a lost-time incident

History & Location Details

Located near De Soto, Kansas, the Former Sunflower Army Ammunition Plant (SFAAP) encompasses approximately 9,060 acres located 20 miles southwest of Kansas City, Kansas. In 1942, the SFAAP commenced smokeless powder and propellant production for small weaponry, cannons, and rockets. The installation also manufactured and regenerated nitric and sulfuric acids and ammunitions proving. Since 1971, most of the facility has been operationally defunct; Nitroguanidine production ceased in 1992. The current owner of the SFAAP is the Sunflower Redevelopment Limited Liability Corporation (SRL). Across the 9,060-acre expanse of the SFAAP property, there are several high-priority sites, ranging in size and severity of contamination, impacted by munitions-related pollutants.

Project Description

Site Preparation

Sevenson mobilized the following fleet of company-owned equipment to the job site: D-61PX dozer; D-65 dozer; two PC-490 backhoes; two HM-300 articulating dumps; WA-470 loader; and a PowerScreen. Before transporting the equipment to Kansas, Sevenson armored all heavy soil-removal equipment with 3-in.-thick Plexiglas at our fabrication facility in Niagara Falls, New York.

Sewer Piping Removal & Disposal

The SFAAP installation had approximately 170,316-ft of subsurface sewer piping, all of which Sevenson is contracted to remove and thermally decontaminate atop on-site burn pads. The diameter of the piping ranged from 1/2-60-in, and the depth of the piping varied with the average depth of 8-ft BGS. The sewer piping was exposed in increments of 200-ft and inspected for safety and health risks. Metal piping was severed into manageable lengths for transportation; unknown piping was further inspected for residual contamination. Sediment removed from the piping was tested to determine if there were any explosive contaminants.

Temporary burn pads were utilized to thermally decontaminate sewer piping. Each pad had a concrete floor and was visually inspected for cracks greater than 1/8-in, floor drains, or voids to prevent the spread of burn debris. A minimum 100-ft fire break was constructed around each burn pad and was inspected by an Army representative prior to use/reuse and placement of sewer piping. The fuel used for the burn consisted of fuel oil, wooden pallets, and other clean non-hazardous dunnage materials. Following thermal decontamination via open burn, materials remaining were screened using a power sifter equipped with a screen size of 3-in. Any material that passed through the sifter was collected and transported to the onsite staging area for offsite disposal. Material that did not pass was collected and transported to the onsite staging area to await reuse.

Removal of Foundations, Outside Sewers, and Environmental Soils

Approximately 33 building foundations contaminated by potential explosive hazards were identified for removal. Sevenson removed the foundation using a manned armored excavator. Slabs were removed by peeling and breaking up the concrete. Sevenson screened concrete debris for explosives. When explosives were found, the debris underwent in-situ thermal decontamination. When debris was free of explosives, it was recycled onsite or used as backfill. Confirmation sampling was performed within the soil outside sewer line. It was assumed that residual contamination from the leakage of the sewers overtime impacted the soil surrounding the sewers. If the confirmation samples failed, excavation commenced on all soil aligned with the sewer system.

Mercury Contamination

While excavating the outside sewer lines, Sevenson onsite personnel visually identified mercury contamination (a major differing site condition) in areas near fume exhaust system accounts and defunct laboratory buildings. The pipe removal team visually inspected bell joints, bottoms of pipe runs, traps, manholes, and the soil directly beneath piping at these locations for traces of mercury contaminants. Crews isolated the contaminated area; the SSHO established a demarcated mercury work zone, which included establishing a zone 15 ft. from the identified mercury location; and conducted an interview and inquiry session with personnel who encountered the mercury contaminants to determine appropriate abatement measures. One major concern following worker contact with mercury is volatilization. Uncontained (or free) mercury readily vaporizes and continues to do so until it is collected. Sevenson’s SSHO performed initial and continual air monitoring in areas flagged for free mercury contamination using a real-time mercury vapor analyzer in order to determine appropriate PPE levels, as well as changed conditions during mercury abatement activities. Respiratory protection was required in real-time mercury vapor readings exceeded a concentration of 0.025 mg/m3  in the designated breathing zone areas.

Mercury handling procedures included utilizing Mityvac® hand vacuum pumps, granular zinc-infused sponges, PIG® mercury absorbent powder, and MERCON contamination wipes. Before the removal of the mercury-contaminated soil and piping, field personnel used visual observation and/or a gas vapor analyzer to determine whether mercury exists within the excavation zone.

Following mercury abatement, field personnel collected all mercury-contaminated tools and materials used during abatement activities and place them into mercury disposal buckets with sealed lids. Once boxes or drums reach capacity, they were sealed, properly labeled, inspected, and removed from the demarcated work zone and transported to a designated storage area located at Sevenson’s laydown yard. Containers remained in the storage area until disposal/recycling were coordinated through Sevenson’s Regulatory Specialist. Prior to releasing the mercury abatement area for unrestricted use, Sevenson personnel tested the atmosphere and surface area for residual indication of mercury vapors with a real-time mercury vapor monitor. Areas contaminated with mercury were sampled and analyzed in accordance with the Interim Corrective Measures Implementation Work Plan (ICMIWP) after cleanup to verify that remaining soil was below the specified Project Action Levels.

Site Restoration

 Once confirmation sampling indicated that project action levels for both explosives and environmental constituents were achieved, the excavations were backfilled with clean soil. On-site and/or off-site borrow sources were used as backfill material for the project. After the excavations were backfilled, the ground surface was rough graded and seeded to establish vegetative cover to minimize soil erosion. The areas were seeded with contractor grade K-31 tall fescue grass seed.

Rooted in Remedial Construction
Expanded into Environmental Dredging

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