INTRODUCTION
As engineers begin to understand the multiple facets of a ClosureTurf® design, they realize there are many more benefits than previously understood. The original version of ClosureTurf brought many unique changes to the landfill design process. Maintenance was cut by more than 95%. The need for final cover vegetative soil was removed. The need for compacted soil profiles below the geomembrane were no longer needed. Monitoring for storm water quality also became a non-issue. Further improvements in the design of the product will now allow for changes in the way landfills have historically been designed.
CLOSURETURF® WITH ARMORFILL™
An environmentally friendly binding agent called ArmorFill can now be added to the sand infill component of ClosureTurf that will increase the performance of the product. In the typical landfill design, slope lengths must be limited or soil will begin to migrate due to shear forces. Historically, landfill designs have incorporated diversion berms (benches) and down slope channels to move the water off the cover as quickly as required. With the introduction of ArmorFill, landfill designers can utilize a rarely used concept; Benchless Design.
ClosureTurf with ArmorFill is a specially designed binder that is sprayed into the Sand Infill Component of ClosureTurf after the sand installation is completed. ArmorFill binds the sand infill within the Engineered Turf Fibers, coats the sand particles, yet is porous and allows storm water to flow through to the drain liner without eroding the sand infill. The bound sand will now have no drainage length limitation. This is a game changing event for landfill design. It means no requirement for diversion berms or down slope channels.
ClosureTurf® can now be utilized with geomembranes that have a lower drainage profile such as AGRU’s MicroSpike® geomembrane. One advantage is being able to reduce costs by utilizing a 40mil MicroSpike instead of the more aggressive 50 mil AGRU Super Gripnet® product. Note that on very steep slopes, the Super Gripnet may still be the best choice for high interface friction values.
HYDROLOGIC METHOD
The addition of ArmorFillTM to the typical ClosureTurf profile completely changes the hydrology of landfill design. Because ArmorFill binds the sand infill within the Engineered Turf, the sand is capable of handling higher storm water shear values. This allows the designer to utilize the maximum distance for sheet flow rather than channelizing the flow in diversion berms. Contrast that with the typical method of 90-100 feet of sheet flow, then the rest of the distance to the pond confined to channel flow. Reducing concentrated flows will increase overall Tc values, and pond sizing may also be beneficially affected. With an ArmorFill design, the storm water can stay in sheet flow for the maximum distance before being converted to shallow concentrated flow. Channel flows will not occur until the water reaches the perimeter channels. This innovative concept will also reduce the need to dissipate the converted energy that channelized water and gravity cause with steep slopes.
It is important to note that with a ClosureTurf Final Cover System, storm water is ‘de’tained rather than ‘re’tained. Since there is not a significant sediment contributor that would degrade water quality, the storm water is detained only long enough to safely convey peak storm events. This allows the pond size to be smaller and more efficient. It could also allow for natural vegetation in the pond area that will not be killed off by sediment buildup since there will be none.
CONCLUSION
Further analysis is recommended to fully appreciate the value the above ideas may add to the design. The particular cost saving items that a ClosureTurf with ArmorFill design may include are:
- Reduction/elimination of Diversion Berms and Down Slope Channels.
- Reduction/elimination of Energy Dissipation devices.
- Reduction/elimination of sediment storage and water quality volumes.
- Detention of storm water rather than Retention allowing for smaller pond volume.
- Reduction/elimination of maintenance.
ClosureTurf is changing forever the parameters used in the design of landfill/CCR caps.