ENVIRONMENTAL CONSTRUCTION AND REMEDIATION

Insitu Soil Stabilization
Shallow Soil Mixing (SSM)
Columbus, Georgia

Geo-Con completed an SSM stabilization project at a former Manufactured Gas Plant (MGP) site adjacent to the Chattahoochee River in Columbus, Georgia. The site was to be converted into a city park. A site assessment determined the extent of MGP materials, primarily coal tar, present in the soil and groundwater on the site. The assessment found petroleum hydrocarbons and other man-made materials present at depths ranging to 35 feet. The site soils consisted of fill materials and stream alluvium underlain throughout the site by saprolite. The evaluation of remedial action alternatives for the site determined that the most appropriate technology was the in-situ stabilization of the soils containing MGP-related materials that were below and just above the water table. Total polynuclear aromatic hydrocarbon (PAH) concentrations in the soil ranged from 1,545 ppm to 26,416 ppm.

The MGP site location and characteristics dictated that the in-situ stabilization technology should provide a uniform mix of the affected soils and have provisions to control organic vapors and dust. For these reasons Geo-Con's SSM system was chosen to perform the in-situ soil stabilization.

The remedial design called for the following treatment criteria:

  • The treated soils shall have a minimum Unconfined Compressive Strength (UCS) of 60 psi after 28 days;

  • The permeability of the treated soil shall be less than 1 x 10-5 cm/sec; and

  • Leachate from the treated soil, obtained from TCLP extraction, must not contain total PAHs greater than 10 ppm.

Bench scale treatability test results indicated that the treatment criteria would be met with a 10 percent (by dry weight of soil) addition of Portland Cement.

The 82,000 cubic yards of in-situ stabilization was accomplished within the 20 week fast-track schedule by working around the clock, seven days a week. The effectiveness of the SSM stabilization system in providing the correct dosage, thorough mixing, and adequate coverage of the subsurface zone to be treated was confirmed by the fact that only one column out of over 1800 was remixed due to a questionable UCS test result. The analytical results of the stabilization QA/QC sampling program showed permeabilities in the 10-7 cm/sec range. UCS results averaged in the 100 to 200 psi range and the total PAHs in the TCLP test were well below the 10 ppm limit set in the treatment criteria.

  • Start: 1/3/92
  • Completion: 5/14/92


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