Project Features:
- 8,500 CY of In-Situ Soil Mixing (ISS)
- Jet Grouting of Impacted Soils – over 100 columns
- 3,679 Tons of Off-Site Disposal – Excavated Soils, ISS Spoils and Former MGP Structures Demolition, load-out, and disposal of impacted soils and former MGP structures.
- 2,100 Tons of Common Fill and Topsoil for 2 Foot Clean Cap
Project Background:
The project included the remediation of a portion of the Lancaster MGP (Manufactured Gas Plant) Site. After the MGP operations ceased, the site has continued as an operation and maintenance facility. This portion of the remediation included closure of two former gas holders – Gas Holder 13 (GH13) and Gas Holder 14 (GH14).
Description of Work
Site preparation required the installation of temporary construction facilities, portable fencing, 30-inch diameter compost filter sock for erosion control, a stabilized construction, site control zones, and installation of a mat access road to allow trucks to access the work area without contacting contaminated soil. A foaming unit and Rusmar short duration foam were mobilized to control vapors, as needed. Strict and diligent use of odor (Rusmar foam) and dust controls were necessary throughout the excavation, jet grouting and soil mixing phases of the project.
Jet grouting was used to stabilize the annular space between the brick outer wall and steel inner wall present within GH14. The 18-inch gap around the perimeter of the 105-foot diameter holder was filled with a combination of impacted soils and tar. GSI mobilized an owned Soilmec SM-14 drill equipped with a jet grouting package and owned high-pressure jet grouting Metax MP-7 pump to perform the jet grouting. Twenty-two foot deep jet grout columns were installed on 3-foot spacing to create a stabilized monolith in the annular space.
Following jet grouting, approximately 1,000 CY of non-impacted surface soils located above the top of GH13 were stockpiled onto 40-mil HDPE liner and covered to be used later as backfill. A long reach stick was installed on a Komatsu PC490 excavator to perform the deep bucket mixing in both holders. ISS was used to stabilize 8,500 CY of impacted soils to a depth of 19-feet (GH14) and 22-feet (GH13) below the workpad surface. The grout was prepared at a 0.6:1 water to cement ratio to limit the introduction of water into the matrix resulting in high unconfined compressive strengths (UCS).
Over 3,600 tons of excavated soils, ISS spoil and demolished MGP structures were loaded out for disposal. All waste was treated by bioremediation at Clean Earth’s New Castle, Delaware facility. Backfilling of the site was performed with stockpiled soils to within two feet of final grade. Gravel backfill and topsoil were imported and placed to create a two-foot clean cover across the remediated footprint. A local landscaping company performed the hydroseeding of the one-acre site.
All jet grouting and ISS quality control samples met the project requirements of greater than 50-psi UCS and less than 5×10-6 cm/sec permeability.
