B47 BLOCK CONTAINMENT SYSTEM
Freeport, Texas

In the environmental remediation industry, Remedial Construction Services, L.P. (RECON) is recognized for its ability to provide innovative, first-of-a-kind solutions to complex and challenging projects. Such was the case at a chemical plant´s former landfill adjacent to the Brazos River in Freeport, Texas.

Total encapsulation of the 200-acre landfill area was required to prevent the flow of groundwater contaminated with numerous Volatile Organic Compounds (VOCs) and Semi-Volatile Organic Compounds (SVOCs). A soil-attapulgite slurry trench, keyed a minimum of two feet into the underlying clay, provided the majority of the containment. Attapulgite, a naturally occurring clay with similar properties to the more commonly used bentonite, was selected for this project by the consulting engineer because of its compatibility with the contaminants. Where the alignment of the slurry trench encountered two water crossings continuous, unspliced, steel sheetpiling was specified to complete the encapsulation.

Scope and Execution of Work

Prior to the work, RECON conducted a significant amount of research and development on the stability and use of attapulgite slurry to ensure the long-term effectiveness of the completed barrier. The 10,100-foot long, 3-foot wide trench was continuously excavated under the stabilizing slurry to an average depth of 90 feet using a company-owned Koehring 1466 hydraulic excavator, specially customized to achieve a reach of 102 feet. The excavated material was blended at the side of the trench with dry and hydrated attapulgite in ratios calculated to meet the permeability requirement of 1x10-7 or less, and placed in the trench using the lead-in method. After backfilling was completed, a compacted clay cap was placed to ground level.

The continuous, unspliced steel sheet piles were installed to depths ranging between 78 and 104 feet. To accomplish this, RECON designed and constructed special driving templates two stories tall, and drove the sheets in place using 250-ton cranes with specially designed vibratory impact hammers, and using biodegradable hydraulic fluid.

Construction Milestones

This project marks a significant advance in slurry trench construction. At the time of completion, RECON was:

• The first to construct a soil-attapulgite slurry wall of this magnitude
• The first to dig a 100-foot deep slurry wall with a hydraulic excavator
• The first to drive 105-foot long, unspliced sheets of steel piling