Project Features:
- In-Situ Stabilization (ISS) by Large Diameter Auger Shallow Soil Mixing (SSM) method of 7,590 Cubic Yards (CY) of impacted Soil.
- Target Unconfined Compressive Strength of greater than 30 psi at 28 days
Background:
The 40.5-acre former Baltimore Aircoil Company (BAC) facility is located near Merced, California. The former BAC facility was an industrial manufacturing site operated from 1961 to 1994 for cooling tower fabrication. In 1969, a wood pressure-treating system was installed at the facility that used treatment solutions containing arsenic, copper, and chromium. During the operations of the wood treatment system, waste treatment solution was discharged to soils and groundwater at the facility, creating a condition of pollution or nuisance. In 1975, BAC, then a subsidiary of Merck & Co., Inc. (Merck), purchased the cooling tower fabrication operation. Merck sold BAC to Amsted Industries, Inc. (Amsted), in 1985. Amsted ceased cooling tower manufacturing operations and closed the facility in February 1994.
The property around the BAC site is still occupied by active businesses. The ISS project was undertaken to mitigate the impacts to the soil. Specific volatile chemicals of concern are heavy metals, specifically Arsenic, hexavalent chromium, chromium, and copper.
Project Objectives:
Geo-Solutions was subcontracted by to perform the In-Situ Solidification (ISS) of the soils at this site. The ISS reagents and limits of treatment were designed to prevent the contaminants from migrating outside the limits of the site.
Description of Work:
ISS was completed using a Delmag Model RH-34 track mounted rotary drilling rig fitted with Geo-Solutions’ 8-foot and/or 4-foot diameter auger. The Delmag RH-34 has an operating weight of 189,600 pounds (lbs) and approximately 247,083 foot-lbs. of torque available to turn the mixing auger plus a crowd (down) force of 74,200 lbs. ISS was completed up to 40 feet below ground surface (fbgs) to the confining soil layer. The site was divided into multiple treatment zones that were treated to different depths based on the zones of contaminants.
A mixture of water, ferrous sulfate, and Portland cement grout was created in Geo-Solutions’ batch plant and pumped through a hollow-stem Kelly bar to the mixing auger. Columns were mixed in an overlapping pattern to provide the specified 100% coverage of the treatment area. 7,590 Cubic Yards (CY) were completed using this method. Samples of the soil mix were collected daily or every 500 Cubic yards and tested for Unconfined Compressive Strength to ensure the contaminants are immobilized within the solidified soil-reagent monolith. Laboratory confirmation testing was conducted on samples of the stabilized soil. The stabilized soil attained strength of over 30 psi prior to the specified 28-day cure period.
