In Situ/Ex Situ Stabilization

In Situ Solidification/Stabilization (ISS) can be achieved using a variety of methods including single vertical auger mixing, multi-auger vertical mixing, mixing with specialty tools (such as the Lang Dual Axis Remediation Blender), backhoe mixing, and jet grouting. Vertical auger mixing (VAM) generally involves hollow stem augers with mixing heads between 3 and 12 feet in diameter. Ex Situ Solidification/Stabilization (ESS) can also be performed using a variety of methods including back hoe mixing in place or in tanks or containers; pugmill mixing; or treatment in lay down areas using discs or soil stabilizers. Back hoe mixing is the simplest and most commonly used method when treatment objectives are relatively simple and readily achieved. When soil or waste characteristics are more complex and a higher degree of performance certainty and process control are required, pugmill or treatment pad mixing are more commonly used. We own automated batch plants for optimum efficiency and high volume grout preparation. Forgen has the experience to help clients evaluate the methodologies that will best meet their project objectives.

Mount Pleasant, TX

  • Pugmill treatment of 247,000 tons of impacted soil

  • Excavation of 195,250 cy of soils

  • Demolition, salvage, and/or disposal of 25,000 lf of pipe

  • Demolition and disposal of 8,000 lf of ACM-wrapped steel pipe

  • Demolition of 47 aboveground structures

Forgen was contracted by for soil remediation services for the treatment of impacted soils under the TCEQ Voluntary Cleanup Program (VCP) at the former petroleum refinery located in Mount Pleasant, Texas. The former refinery was constructed in 1938 and ceased operations in 1984. During its operation, it was a topping refinery for the production of gasoline, diesel, naphtha, and asphalt to process crude oil from the Northeast Texas oil fields. The refinery infrastructure was removed between 2007 and 2015.

Forgen was to provide the final corrective measures to the client’s self-directed remediation of the site. The scope of work includes services to address the remaining soil contamination by utilizing a pugmill for ex situ soil treatment to reduce the mobility of constituents meeting the remedial cleanup objectives. Soil treatment entailed the excavation of 247,000 cy of potentially impacted material, processing, and final treatment with Portland cement through a continuous mixing automated pugmill system. The treated material was segregated into 1,500 lots for TCLP testing to verify the project’s leachability performance criteria; following confirmation, the subject material was backfilled into the designated areas.

Work also includes the demolition of remaining refinery structures and removal of all defunct (above and belowground) piping and conveyances. The demolition portion of the site work included the removal of over 32,000 ft of various types of underground pipe, including asbestos-wrapped steel, plain steel, and reinforced concrete pipe. These piping networks were used for storm drainage, fire suppression, and product transfer. The exposed pipes required cold tapping numerous times to determine if petroleum products were present. Forty other features ranging from standing structures, underground foundations, pump stands, and separators were removed once decontaminated. All ferrous and non-ferrous metals were recycled and an estimated 14,000 tons of concrete debris was crushed to produce a usable base course product for site restoration. The existing asphalt roads were milled in-place to generate additional base course material.

The project demolition was completed in March of 2018 and ex situ soil treatment was completed with original scope items during the summer of 2018.

Fort Worth, Texas

  • In Situ mixing of impacted clay soils 28 feet below land surface with sodium permanganate
  • Installation of an engineered excavation and support structure supporting excavation up to 28 feet below land surface
  • Installation and operation of dewatering and treatment system

Forgen was contracted to treat soils within a chlorinated hydrocarbon PCLE Zone to the top of bedrock (approximate depth of 28 feet below land surface) using In Situ soil mixing with sodium permanganate injection to oxidize the contaminants with the underlying ground water plume. The treatment was completed with a RH-20 Delmag Rig turning a 6 feet auger attachment to inject and mix the sodium permanganate into impacted soils. The treated soils were excavated and disposed of at a Class 2 disposal facility.  Following the excavation of treated soils the area was back-filled with select fill. Additional features of work included asphalt removal/haul off and resurfacing, installation of an excavation support structure and dewatering and treatment system with the ability to support excavation of 28 ft below land surface, and excavation/haul off and backfill of cadmium impacted areas and chlorinated hydrocarbon PCLE area.

Ogden, Utah

  • Wetland Project Setting
  • In Situ Soil Stabilization
  • Construction of 10,624 lf of composite slurry wall to a depth of 38 feet
  • Excavation of RCRA SWMUs
  • Consolidation Area Placement
  • Quarry and Borrow Area Development
  • Access Road Construction
  • Site Grading and SWPP BMPs
  • Onsite Crushing Operations
  • Recycling of packaged materials and unused HDPE Sheetpiles

This multi-faceted remediation project was conducted at an active chemical plant in Utah. The scope of work included: the development and reactivation of an on-site quarry to produce rock needed for berm and barrier wall platform construction, In Situ soil stabilization to support barrier wall platform construction and improve seismic stability, barrier wall work pad construction, soil-sepiolite slurry wall construction, HDPE sheet pile installation, and final dike construction and rock slope protection. The project also included remediation of two RCRA Solid Waste Management Units (SWMUs) and placement of excavated material in an on-site consolidation area.

Performed as an RCRA corrective action under the regulatory authority of Utah’s Department of Environmental Quality, the barrier wall was constructed around a series of evaporation ponds to prevent process residuals and waste byproducts stored in the ponds from migrating off-site. Since the project was situated in the former dry lake bed of the Great Salt Lake, due to soft underlying soils and groundwater at or near the existing grade, a five-foot working platform had to be constructed in order to provide a stable working surface for barrier wall construction. Working platform construction consisted of placing 1.5 ft of material, produced at the on-site quarry, and stabilizing the lower 3.5 ft of subgrade with In Situ soil stabilization.

The soil stabilization effort required stabilizing 30 percent of the lower 3.5 feet of the working pad to meet the seismic requirements of the design and help strengthen the subgrade below the upper 1.5 feet of the work pad. Chemical constituents in the existing soils and groundwater elevations, relative to the finish grade of the working pad, varied throughout the site. To meet the unconfined compressive strength requirements for In Situ stabilized soils, Forgen had to continually monitor the grout mix to account for variable subsurface soil conditions and the presence of destabilizing constituents such as sodium chloride, ammonium chloride, sodium hypochlorite, and raffinate.

Forgen successfully completed In Situ soil stabilization by making consistent and ongoing adjustments to the amount of grout added and water to cement ratio of the grout mix while monitoring preliminary unconfined compressive strength testing throughout the project. The In Situ soil stabilization was performed during the winter and required additional effort to prevent the grout from freezing in the batch plant, hoses, and mixing equipment. This was accomplished by working 24 hr per day and utilizing specialized heating units. Upon completion of the In Situ soil stabilization, the site was shut down for the remainder of the winter.

Construction of the composite HDPE/soil-sepiolite slurry wall commenced in May of 2013. In total, 11,000 lf of slurry wall was constructed around the ponds to a maximum depth of 38 feet. Construction progress was accelerated utilizing a two shift per day schedule and the wall was completed in less than one month. The performance specification for the slurry wall backfill permeability was 1 x 10-7 cm/sec. Actual permeability measured post installation was 5 x 10-8 cm/sec. A total of 275,000 sf of HDPE sheeting were installed in the center of the soil-sepiolite slurry wall using a custom-made mandrel to ensure the structural integrity of each panel. A hydraulic sealant was applied to each joint of the Forgen also utilized an in-house, custom designed and fabricated slurry batch plant for mixing the soil stabilization grout and slurry trench backfill.

Additional work included grading to improve site drainage, installation of various drainage pipelines and outfalls, construction of a perimeter site access road, and placement of rip-rap for dike slope armoring around the outer perimeter of the new dike construction.