DarinRay,
You have the right tool to do the job. The spoils must be processed (mixed) and have at least 30% clay content, then replaced into the trench and compacted. Two thoughts here. One...if you are dealing with layered, fractured formations underground, the spoils, when mixed, are excellent to backfill the trench. But, if you are strictly dealing with porous soils, sand, loam, that sort of thing, you will need to mix clay or bentonite with your spoils before backfilling and compacting.
There's an excellent publication for you...USDA's publication #520, distributed by the NRCS. It's all about pond construction and has excellent engineering data about core trenches and their requirements.
