Project Objectives
Geo-Solutions, Inc. (GSI) was subcontracted by Code Environmental Services, Inc. (Code) who was contracted by Akzo Nobel to install the groundwater collection trench. The purpose of the collection trench was to collect and treat potentially impacted groundwater at the perimeter of the site.
Description of Work
GSI’s scope of work was limited to the installation of the groundwater collection trench. To mitigate risks associated with dewatering and water management inherent to an open cut approach, GSI installed the trench via the Bio-Polymer Slurry (BP) Trenching Method. Due to the small size of the trench, GSI excavated the trench in its entirety before placing the pipe and drainage media. The following summarizes trench dimensions and properties:
Trench Length: 100 Lineal Feet
Trench Width: 3-feet (nominal)
Maximum Depth: 16.5-feet below work-platform surface
Average Depth: 16-feet below work-platform surface
Backfilll: #57 Stone and Excavated Soil
Pipe: 2 x 6-inch HDPE – Perforated – Solid Risers on Each End.
Bio-Polymer: Rantec DP-10,000 (cellulose)
Project Challenges
The biggest challenge during installation of the collection trench was installing the double drain pipe. Because of the relatively short trench length (100 ft) GSI was able to excavate the entire trench and install the pipe at once. This was made possible by using the cellulose BP product that is more stable and has greater longevity as opposed to standard guar gum. Using multiple pieces of equipment, the pipes were suspended over the trench and sunk to the necessary depth using weighted cement blocks.
Upon completion of the collection trench installation, the bio-polymer slurry did not breakdown as quickly as anticipated. After consultation with the bio-polymer manufacturer (Rantec) an enzyme breaker specific to the DP-10,000 (LEB-DP) was shipped to site and used to break the remaining BP slurry. Despite the slurry being broken, fine soil particles were still found to be in suspension in the fluid in the trench and in the frac tanks. After another consultation with Rantec, a flocculent was used to drop the suspended fines out of the trench fluid to allow the collection system to resume proper function.