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ENVIRONMENTAL CONSTRUCTION AND REMEDIATION In-Situ Soil Stabilization This project involves in-situ Shallow Soil Mixing (SSM) of impacted soil (LNAPL and DNAPL) over an area of approximately 2.2 acres. Approximately 103,000 cy of soils will be stabilized in-place to an average depth of 22 feet bls for this project.
The property is the former location of a Manufactured Gas Plant (MGP). Past MGP operations resulted in the release of hazardous chemicals to the soil and groundwater. Hazardous chemicals, including but not limited to volatile and semi-volatile organic compounds, are present in soil and groundwater at concentrations greater than Reportable Concentrations specified in the Regulations for the State of Massachusetts.
The project is being performed as a Release Abatement Measure (RAM) under the provisions of Massachusetts Environmental Regulations. The scope of work includes but is not limited to the following: Mobilization, Site Preparation, Site Clearing, Excavation of Subsurface Structures, Soil Stabilization Field Demonstration Test, Full Scale Soil Stabilization, On-site Management of Materials, Off-site Transportation of Materials and Demobilization and Site Restoration.
The equipment being used to perform the stabilization includes the following; a 4000 series Manitowoc crane, a rotary drill table (Caldwell CH-200 capable of developing 350,000 ft-pounds of torque), a 10-ft diameter mixing tool, a batch plant and a Soil-Vapor Extraction (SVE) system, shroud and carbon filter. The SVE system is being used to collect and treat any hazardous gases that may be released during the stabilization process. Cement-Kiln Dust (CKD) and Bentonite are the mixing reagents.
A spacing of 8.67 feet between the center of adjacent columns is being implemented based on the effective ten-foot column mixed by the ten-foot diameter-mixing tool. This pattern layout allows for mixing of 100% of the soil mass and includes approximately 35% overlap of each interior column. The SSM operation will require approximately 590 columns for treatment of the LNAPL impacted soils and approximately 1620 columns for treatment of the DNAPL impacted soils inside the treatment boundry.
All columns within the LNAPL stabilization area are being stabilized to a depth of 12 feet below the existing ground surface. In areas where both LNAPL and DNAPL are present, stabilization occurs to a depth of 2 feet below the clay surface. All columns within the boundry of the DNAPL stabilization area are being stabilized to a depth of 2 feet below the clay surface.
A field demonstration test program was implemented prior to full-scale soil stabilization. The
purpose of the test program was to; refine the soil-reagent mix ratio, evaluate the bulking characteristics of the stabilized soils, evaluate mixing methods and equipment performance and determine the sampling methodology and define performance criteria. Currently, full scale production is ongoing.
Prior to stabilizing the soil, excavation is performed within the limits of the stabilization area to locate and remove historical subsurface structures to a depth of approximately 22 feet below the existing land surface. The subsurface structures consist of gas holders, tar tanks, boiler house and other structures. The structures are either removed or broken in place and then removed. The existing ground water elevation is approximately 8-10 feet below land surface. To reduce the odors generated during the excavation of the substructures, the area is constantly foamed during excavation. most of the excavation is performed under water and foam.
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