Significant Project Features:
- Slag-Cement, Cement-Bentonite Cutoff Wall (SCCB Wall)
- Permeable Absorptive Barrier (PAB)
- Gravel Collection Trench
- Low overhead pipe racks and narrow work areas
Background and Objectives:
Geo-Solutions provided technical support to Brasfond, a leading geotechnical contractor in Brazil, to implement the SCCB Wall, PAB and Gravel Collection Trench at the Confidential Client Site in Sao Paulo. Prior to mobilization, Geo-Solutions and Brasfond assisted the international consultant (CH2MHILL) in developing the design.
Industrial activities at the site began in 1950 with the production of phthalic anhydride. In 1964, the manufacturing process was expanded with the installation of the plasticizers unit. In 1970 the production of fumaric acid began. The Confidential Client acquired the site in 1998 producing phthalic anhydride, fumaric acid, maleic anhydride and plasticizers. The production of maleic anhydride ceased in 2001.
The site encompasses a total of 137.543,43 square meters (m2) with approximately 21.539,20 m2 of the area developed. The plant was built on a channelized stream which flows through the property from southwest to northeast. The studies conducted for the area indicate that this stream acts as the principal groundwater discharge mechanism in the area.
The land use of the area downstream consists of residences, local Club and commercial establishments. There is also the presence of vegetation and small farms.
The site has been subject to a number of environmental efforts including preliminary, confirmatory, detailed and supplementary investigations, risk assessment studies and remediation measures. The presence of free phase products was confirmed by such studies in the Plasticizer area in 1994. Remediation actions were commenced in 1999 with the installation of a Multi-phase Extraction system (MPE). This system has been continuously running since then and has removed approximately 66,650 liters of product since November 2012.
The goals of the project were to protect surface water resources, most specifically the channelized Creek, by:
- Intercepting the contamination before it reaches the creek;
- Collecting free phase products (LNAPL);
- Removing organic compounds from groundwater.
Description of Work:
- Installation of a PAB at the intersection of the two CB walls consisting of sand, organophilic clay and activated carbon. Total depth of the PAB was 4 meters with approximate final dimensions of 4 meters by 3.5 meters
- Installed using a sheetpile bracing system
- Pre-blended of the PAB mixture using a concrete mixing truck prior to backfilling
- Flooded backfilled PAB with fire protection system water and dewatered rapidly through the gravel collection trench to prevent long term settlement of the low strength material that is located in the middle of the main access road to the site
- Design support and installation of two CB Walls that were 66 and 26 meters long respectively, 0.8 meters wide and 4 meters deep.
- The trench was excavated with an excavator using Cement-Bentonite slurry, which acts as hydraulic shoring during excavation and cures in the trench to become the permanent backfill material. The self-hardening slurry included a combination of a Slag cement, Portland cement, and bentonite slurry. The proportions of the mixture were developed during a laboratory testing program that evaluated various candidate mixtures.
- Design support and Installation of a 30 meter long, 0.8 meter wide and 2.8 meter deep gravel collection trench.
Project Challenges:
- Logistics in coordinating overall work between international consultant, Prime Contractor and local material suppliers
- Aiding in coordination of materials for the PAB imported from the United States
- Working along the main intersection of the plan under the 2 roadways most heavily traveled by trucks and equipment
- Installation of trenching below 4 separate low profile pipe Racks
- Excavation through historically poorly placed fill
- Excavation through and abandoning over a dozen abandoned utilities unknown to the site
- PAB shoring system modified in the field to fit site conditions
- Placement of a geotextile filter within the gravel collection trench prior to backfill
