Many manmade waterways, independent of size and function, are constructed in permeable or marginal soils that are not ideally suited to hold surface water. If native substrates cannot be relied upon to maintain desired water levels on their own, three fundamental options are typically contemplated during construction:
- Importing and mechanically compacting one to several feet of clayey (low permeable) soil (“clay”) from a near-site or off-site source;
- Amending locally available soil with additives (e.g. powdered or granular bentonite) to provide a supplemental reduction in permeability; or
- Lining the entire basin with a geomembrane (“rubber liner”) made of HDPE, PVC, EPDM, or other synthetic material.
While all three of these traditional alternatives have a longstanding track record of use and success, each also comes with its own challenges and technical shortcomings.
Compacted Clay Basins:
- Sourcing clay with desired properties can be problematic (especially from on-site)
- Inconsistency in clay (e.g. rocks, debris, sand, organics) can lead to a reduction in performance
- Extensive/costly material handling in manpower & machinery* (i.e. excavation/removal of undesirable soils, delivery/distribution of borrow clay, proper/systematic mechanical compaction)
- Time consuming (due to high material volumes and extensive material handling)
- Performance shortcomings (e.g. natural inconsistencies, insufficient or inconsistent mechanical compaction, prone to cracking during extensive drought – without potential to “re-heal”)
* Extensive material handling is only further complicated when desirable (low permeable) clay needs to be trucked in from off-site. Even a shuttle distance of a mile or two can add substantially to the installed cost of a compacted clay/earthen liner.
Amended Clay Basins:
- Difficult to gauge appropriate application rate of amendment media versus native substrate to achieve desired results
- Often requires specialized contractor/installer and blending equipment
- Extensive/costly material handling due to physical characteristics of amendment media (i.e. dusty, fine-grained, low density, and often applied at very low rates)
- Time consuming (due to meticulous material handling)
- Performance shortcomings (e.g. inherent inconsistencies, insufficient mechanical compaction, prone to cracking during extensive drought – with limited potential to “re-heal”)
Geomembrane Lined Basins:
- Typically requires specialized contractor/installer and application equipment
- Often requires seaming and special care at transitions (which become points of future vulnerability)
- Time consuming (depending on complexity of design and shape/contours)
- Potentially QAQC-intensive
- Performance shortcomings (e.g. prone to permanent degradation from UV exposure, mechanical punctures/tares from animals, ice, etc. – with virtually no potential to “re-heal”)
- Ineffective unless used over entire basin footprint (i.e. not viable for spot-treatment)
AquaBlok is not intended to be a sweeping replacement for the established sealing methods detailed above. However, its unique “composite” design and physical attributes – both as a dry bulk material and as a hydrated sealant media – offer distinct advantages under certain situations and circumstances.
The stone-bentonite composite that is AquaBlok can serve to replace or dramatically reduce borrow clay in settings where low permeable material is simply not locally available (or cost-effectively available). AquaBlok can also dramatically simplify the process by which a targeted quantity of bentonite (e.g. 2-lbs/SF) is applied over a target area. Significant cost savings can be realized using AquaBlok in both cases – through simplified site preparation, dramatic reductions in material handling, and collectively through significantly faster execution in the field.
As an engineered composite, AquaBlok will cost more than “raw” or traditional bentonite on a material-to-material comparison. But the significant labor savings of a simple broadcast application (no field blending or compaction needed) coupled with the consistency of coverage (AquaBlok’s workhorse sealant material is a consistent 20% bentonite by dry weight) makes it a compelling alternative when amendment field mixes are being contemplated.
And while it is common for designers and contractors to immediately think in terms of “full-basin” applications (sealing the entire bottom and side slopes of a new basin), AquaBlok also offers the unique ability to spot-treat finite regions of the broader excavation. If 90-percent of the basin is anticipated to be competent based on a traditional compacted clay approach, but 10-percent is anticipated to be prone to losses associated with a sand and gravel seam or outcropping of bedrock, AquaBlok can be used to address only this isolated area of vulnerability.
Finally, AquaBlok is being utilized with increasing frequency in situations where geomembrane installation tends to be problematic. Beyond its use as a reinforcement and repair tool with synthetic liners, AquaBlok finds a home in basins that are designed to have complex shapes and contours as well as in settings that are prone to environmental conditions that would compromise traditional synthetic alternatives. A prime example would be the use of AquaBlok as a sealant within a shallow biorention basin prone to extensive freeze/thaw cycles or other physical stressors.
For a full basin AquaBlok lining with reasonable access, belt-driven conveyance equipment like stone slingers or telebelts offer a reliable and cost-efficient method of applying AquaBlok consistently over large site footprints. Other placement options include long-reach excavator buckets or crane-mounted clamshell buckets which can hold large volumes of product and cover large areas quickly and efficiently. Even small payloaders/trackloaders or skid steerers (e.g. Bobcats) can address tens of thousands of square feet in a standard work day, depending on application rates and site conditions. Concrete floats or steel rakes are effective tools to manually level dry AquaBlok to further insure uniform coverage.
Material quantities vary dramatically based on target coverage area and basin design. Fifty-pound bags of AquaBlok are typically only utilized for very isolated spot treatments or in situations where site access is extremely limited. Most blanket applications involve bulk material packaged in one cubic yard (2,400-lb) bulk bags. The product is heavy – even treatment over relatively small basins (1-acre or less) require truckloads of AquaBlok to achieve a full basin lining. Five dry pounds per square foot is considered a light application rate. Conversely, 20-lbs/SF would be considered a heavy application rate. Most blanket applications fall in the range of 7- to 10-lbs/SF – particularly where water depths are designed to be 10-feet or less.
AquaBlok Packaging Options – Contact any of our distributors to receive help estimating quantity need and to receive a custom quote.
Tips & Observations
- To achieve a 1-inch layer of dry AquaBlok (which will hydrate to ~2” when surface applied over standing water) apply right out of the packaging at 7-lbs/SF.
- No blending with on-site soil or physical compaction of the product is needed (nor recommended) in this type of an application to create a reliable seal.
- Think of spot treatment like placing a band-aid – allow for enough AquaBlok so that the dimension of the blanket of product extends well beyond the suspected area of concern (i.e. by at least three feet in all directions).
- When contemplating the installation of an AquaBlok sealant layer over the entire basin, consider treating only the basin floor and perhaps the transitional “toe” going up the side slopes as a means to reduce material need and overall project cost. Under certain site conditions, soil types are such that a full lining – including all side slopes to the top of bank – will only have a minimal impact on overall containment. Because head pressure is highest in the deepest water environments, sealing the bottom provides the “biggest bang for the buck.” Additionally, supplemental AquaBlok can always be placed up the side slopes as a second phase in the installation (months or even years later), should additional containment be deemed desirable.
- For the most uniform and consistent application, placement of dry AquaBlok is preferred (as opposed to attempting to apply hydrating or hydrated product).
- Provided the equipment can access the site, a stone slinger is an extremely effective and cost-efficient tool for AquaBlok placement: they have a carrying capacity of 18-20 tons, are remote operated and can be run by a single person, can off-load in 15 minutes or less, and have a reach of 70 to 90-feet.
- When applying AquaBlok from a payloader or track-driven skid steerer (either from the bucket or directly from the original packaging/bulk bag) it is preferred if the applicator “paint himself out of the room” such that the equipment is not driven over the newly applied AquaBlok. While the dry product is durable enough to withstand the associated weight, instability of the underlying substrate can cause differential settling. Track marks themselves can cause differences in product thickness and create unnecessary points of vulnerability.
- When spot-treating around points of vulnerability like overflow/water control structures, pipes, etc. consider the possibility of limited (and careful) exploratory excavation to ensure stability beneath the area that will be supporting the AquaBlok.
- Consider substrate conditions prior to the placement of AquaBlok. Ideally, the surface that will be receiving the AquaBlok will be firm (or at least stable) and flat (or at least devoid of large inconsistencies like rocks or clods of clay) – the more consistent the base, the more consistent the layer of AquaBlok will be.
- More gentle slopes (e.g. 4:1 or less) are simpler to seal than steeper slopes (e.g. 3:1 or steeper). The texture of the earthen base and the length of the slope will influence stability. AquaBlok will typically adhere to a 3:1 slope, provided the length of slope is < 20-feet. If you have questions relating to stability on slopes contact us or one of our distribution partners.
- Water need not be added to make AquaBlok effective. T)ypically in this application, precipitation, surface run-off, and moisture from underlying soils will eventually hydrate the individual particles into a single body of material. However, if any fill material (e.g. sand, armor stone, organic media) is to be placed on top of the AquaBlok as part of the final design, care should be taken to wait until the individual particles have hydrated/coalesced together before the fill is placed. A light watering from atop the newly placed AquaBlok will accelerate this hydration such that fill material can typically be added within 30-60 minutes.
- Cover media (e.g. sand, soil, or stone) atop the AquaBlok adds ballast and can contribute to overall stability. An armor layer can also provide erosion protection (from wind and ice), help lock in moisture in areas prone to drawdown (due to evaporative loss), and provide site safety and visual appeal.
- Photo documentation of the application, particularly when spot-treating an isolated area, can be very helpful. If a given treatment area is well identified, one can always come back and apply more product (over the same area or to expand the treatment area), should seepage rates slow but remain unacceptably high.
- Sample calculations: If targeting 7-lbs/SF (~1” dry, ~2” hydrated product thickness), then each 2,400-lb bulk bag would cover ~342 SF (2,400/7); if targeting 10-lbs/SF (~1.5” dry, ~2.7” hydrated product thickness), then each 2,400-lb bulk bag would cover ~240 SF (2,400/10).
Examples from the Field