Arnegard Dam, ND

Prototype 3

IMS was engaged by the North Dakota Fish and Game Department to remove 40,000 cubic yards of sediment from the Arnegard Reservoir and demonstrate the Geo-Pool dewatering technology.

Arnegard Dam

On prototype 3, we used the type 2 frames, added bulk water release doors (Dump Doors), and tested a different type of geotechnical fabric. We used the prototype 3 Geo-Pools for 2 seasons at Arnegard Dam.

When we sampled Arnegard dam, none of our samples indicated the presence of bentonite in any significant amounts, nor did the regulators bring it to our attention. We decided to use a fabric with smaller pores and divided the pool into two smaller pools in an attempt to achieve greater overall size than the terrain otherwise allowed.

Even though we continued to work the two smaller Geo-Pools for the full season, we found that we had to change the fabric back to the larger pore size after the second fill. The Bentonite present in the local soils clogged the filters immediately, limiting production. In order to get the fabric to filter, we had to wait until the bentonite dropped out of suspension before working the fabric. We also found that having smaller Geo-Pools wasn’t appropriate as we had, at the last minute, upgraded our dredge to an IMS 5012 HP which pumped much more material at a faster rate.

This overloaded the Geo-Pools’ ability to dewater as it kept the slurry with the bentonite in suspension for a longer time.

To correct the issue at the beginning of the second season, we reconfigured the Geo-Pool into a single oval shaped pool and added larger frame sections due to the lack of space to dewater and stock pile.

Our testing demonstrated that due to the energetic nature of the material as it is pumped into the pool, it needs time and distance to drop out of suspension and dewater at the necessary rate. We also found that once active pumping had ceased, the material dropped out of suspension rapidly and we had massive amounts of clear water in the top layer of the pool. This took time to filter through the geotechnical fabric.

During this project, we tested our first bulk-water release doors (Dump Doors), which were vertical sliding doors. We found that it worked to bleed the clear water. However, the first doors were too limited to deal with the massive amounts of water when the pool was almost full. This design was improved to manage larger volumes of water.

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