Bio-Polymer (B-P) slurry trench method is used to install collection or recharge trenches. The B-P trench method is different from the bentonite slurry trench method in two areas. First, the slurry used to support the trench walls during excavation is made from a biodegradable material such as guar gum or polymer. Second, the trench backfill is a pervious material such as permeable sand or pea gravel. After the trench is backfilled, the slurry is treated to allow it to biodegrade or break down. It is then flushed out of the drain material. Other than this difference, the construction technique of trench excavation and backfilling are very similar to normal slurry trench method.
Drains installed by the bio-polymer method are usually deeper than 15 to 20 feet and have achieved depths of nearly 70 feet. This technique is used when the groundwater or soil conditions would result in an unstable situation without a trench shoring system, or where contaminated groundwater exists. In the latter case, the B-P trench method eliminates the need for dewatering, thereby greatly reducing the necessity for costly treatment or disposal of contaminated water from dewatering operations. B-P trenches have been used to install pump and treat systems, air sparging trenches, groundwater collection and reinjection galleries and groundwater barriers.
B-P drains also have uses in civil engineering including applications such as toe or chimney drains for earthen dams, groundwater diversion trenches, and dewatering for slope stabilization. All structures placed in a B-P trench must be weighted to sink into place through the slurry. Standard manufacturer’s recommendations are available for placing some types of pipes under water or slurry. Fabrics must be designed not to trap the polymer in its weave. In general needle punch fabrics are not recommended, whereas woven fabrics are better suited. HDPE liners can be placed in the trench using special frames, rollers, and other construction aids. However it is not possible to weld joints under the slurry. Often a complex design can be simplified by substituting well casings for manholes and flexible corrugated slotted drain pipe for rigid pipe. A soil-bentonite or cement-bentonite cutoff wall can be used as a containment device in conjunction with a B-P drainage or recharge trench to eliminate the necessity of a HDPE liner in the B-P trench.