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One-Pass Trenching Gallery
Soil-Bentonite Slurry Trench for Decommissioned Nuclear Plant
ISSUE:
In the decommissioning of the Big Rock Nuclear Facility site, it was determined that any potential sub-grade contaminants that may be capable of impacting the local ground water table must be contained.
OBJECTIVE:
Installation of a 1,200 lineal foot soil-bentonite wall that encircled the site in a horseshoe fashion. The natural aquiclude that the wall was to be keyed into averaged 18 vertical ft. below existing ground surface. MERSINO was retained to construct the barrier wall to mitigate the flow of any impacted water entering Lake Michigan.
REQUIREMENTS:
The wall needed to be constructed such that it had a maximum in-place permeability of 1 x 10-7 cm/sec or lower. According to information provided, the soils consisted of fine-grained sands and silts. MERSINO installed the 1 1/2 ft. wide soil-bentonite slurry containment wall via the one-pass trenching method. MERSINO utilized an Inter-drain 6050 HT powered by a 520 hp engine, fitted with an adjustable environmental boom capable of extending to depths of 28 ft. below ground surface.
The dehydrated bentonite was mixed with water utilizing a hopper, jet pump and venturi, and a mixing tank. Upon reaching the appropriate hydrated levels, confirmed by viscosity tests using a Marsh funnel, the bentonite was pumped and injected into the digging chain to the bottom of the slurry wall cut. The rotating cutting chain homogenized the bentonite slurry and native soils in-situ.
OUTCOME:
In addition to the client having a full time third party inspection service at the site, MERSINO performed on-going testing and inspection of the slurry and backfill materials throughout the project to assure the design criteria was exceeded. Testing consisted of monitoring viscosity, filtrate loss, density of the slurry, sand content, pH levels, and density of the constructed wall. All phases of the construction were performed in a timely manner. The Health and Safety Plan submitted for the project was adhered to at all times. The project was successfully completed meeting all of the engineering requirements of the wall design.
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