A permeable pavement BMP for pedestrian routes
Flexus is a poured-in-place permeable pavement system engineered to function as a stormwater Best Management Practice (BMP) — supporting Low Impact Development (LID) design, MS4 compliance programs, and runoff reduction objectives. Tested under ASTM F1551 for permeability and EPA Methods 1311 / 1312 for leaching.
Engineered as a stormwater BMP
Flexus performs the same hydrologic function as other permeable pavement BMPs recognized in state stormwater design specifications and EPA guidance — capturing rainfall at the surface, detaining it in an open-graded aggregate reservoir, and discharging via infiltration or underdrain. The difference is the surface: bound stone and recycled rubber instead of porous concrete, porous asphalt, or PICP.
Stormwater design properties
Reference data for stormwater engineers preparing infiltration calculations, BMP sizing, and treatment train design. Project-specific values depend on subgrade infiltration rate, contributing drainage area, and reservoir storage depth.
| Parameter | Flexus value | Reference / notes |
|---|---|---|
| BMP category | Permeable pavement (source control) | Equivalent functional category to PICP, porous concrete, and porous asphalt in most state BMP manuals (e.g. VA DEQ Spec No. 7, MN Stormwater Manual) |
| Surface permeability | > 200 in/hr | ASTM F1551. Engineered well above typical design storm intensities for pedestrian drainage areas |
| Reservoir layer | Open-graded aggregate (No. 57 / No. 2) | Sized per project — combines structural support and stormwater storage. Voids ratio typically 0.35–0.40 |
| Underdrain | Optional, raised-elbow recommended | Specified when subgrade infiltration is insufficient (< 0.5 in/hr) or where 24–48 hr drawdown is required |
| Setbacks | Per local code | Typical: 50–100 ft from water supply wells; ≥ 3 ft above seasonal high groundwater (reference local stormwater manual) |
| Runoff reduction credit | Per jurisdiction | Determined by local BMP manual. Flexus functions as a permeable pavement BMP — credits typically follow that category |
| Pretreatment | Not required from sheet flow | Run-on from impervious areas should be minimized or treated upstream to limit sediment loading |
| Maintenance | Periodic debris clearing; low-pressure rinsing as needed | Surface infiltration can be restored if sediment accumulates. Protocol in installation guidelines |
Compared to other permeable pavement BMPs
Flexus belongs to the same BMP functional category as PICP, porous concrete, and porous asphalt — but with a different surface technology suited specifically to pedestrian routes.
| Property | Flexus | PICP | Porous concrete | Porous asphalt |
|---|---|---|---|---|
| Application | Pedestrian routes | Pedestrian + vehicular | Pedestrian + vehicular | Vehicular (light) |
| Surface permeability | > 200 in/hr | Variable, depends on joints | Typically 100–700 in/hr new | Typically 100–600 in/hr new |
| ADA surface | Firm, stable, slip-tested | Joint width affects ADA performance | Firm, stable | Firm, stable |
| Recycled content | SBR rubber component | Varies by manufacturer | Minimal | RAP possible |
| Maintenance | Surface rinsing | Joint vacuuming | Vacuum sweeping | Vacuum sweeping |
| Submittal package | Single spec pack, Division 32 | ASCE 68-18 reference standard | ACI 522 reference standard | NAPA reference |
Flexus is positioned for pedestrian-route applications where PICP joints, exposed aggregate concrete, or sealed asphalt are not the design intent. For vehicular applications, refer to PICP, porous concrete, or porous asphalt per ASCE 68-18 and applicable BMP guidance.
Stormwater engineer FAQ
Questions from civil and stormwater engineers evaluating Flexus as a permeable pavement BMP.
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Yes. Flexus is a permeable pavement system that functions as a stormwater Best Management Practice for pedestrian routes. Like other permeable pavements recognized in state and EPA stormwater design specifications, Flexus captures rainfall at the surface and allows it to infiltrate through the bound aggregate matrix into an open-graded aggregate reservoir, where it is detained and either infiltrated into native soil or discharged via underdrain. The surface is engineered to a > 200 in/hr permeability target, tested per ASTM F1551.
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Flexus is suitable for inclusion in MS4 (Municipal Separate Storm Sewer System) stormwater management programs as a permeable pavement BMP. Specific runoff reduction credit values are determined by the local jurisdiction or state stormwater design specification. We recommend referencing the applicable state BMP manual (e.g., VA DEQ Spec No. 7, MN Stormwater Manual, NJ Stormwater BMP Manual) and consulting with the local stormwater authority when specifying Flexus for an MS4 program. Flexus does not assign credit values itself — those are determined by the regulating authority.
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Flexus is engineered to a permeability target of greater than 200 in/hr at the surface, tested per ASTM F1551 (Standard Test Method for Permeability of Granular Soils). Actual long-term system performance depends on base preparation, contributing drainage area, sediment loading, and maintenance practices. The full ASTM F1551 test report is included in the spec pack.
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Yes. Flexus is positioned as an LID surface for pedestrian routes — paths, plazas, trails, and walkways where impervious cover would otherwise contribute to surface runoff. Flexus reduces effective impervious area, supports on-site infiltration of pedestrian-scale rainfall, and integrates with bioswales, rain gardens, and infiltration trenches as part of an LID treatment train. The surface counts as pervious for impervious-cover calculations where the local code recognizes permeable pavement.
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Yes. Flexus has been tested under EPA Method 1311 (TCLP — Toxicity Characteristic Leaching Procedure) and EPA Method 1312 (SPLP — Synthetic Precipitation Leaching Procedure), as well as for RCRA metals including mercury. Reports are included in the spec pack. These tests address common concerns about leaching from recycled SBR rubber components in permeable pavement applications. Results are within applicable regulatory thresholds for the tested parameters.
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Flexus is a source-control BMP — it manages runoff at the point of generation by allowing infiltration directly through the pavement surface. It can stand alone for small pedestrian drainage areas, or be combined with downstream BMPs (bioretention, swales, infiltration trenches) for larger or more complex sites. Where subgrade infiltration is constrained, an underdrain with raised elbow can be specified to detain stormwater for 24–48 hours before discharge to a downstream BMP or storm sewer.
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Setbacks follow the applicable state or local stormwater manual for permeable pavement BMPs. Typical guidance includes a minimum horizontal setback of 50–100 feet from water supply wells, a minimum 3-foot vertical separation between the bottom of the reservoir layer and seasonal high groundwater or bedrock, and minimum subgrade infiltration of approximately 0.3–0.5 in/hr where infiltration is the primary discharge mechanism. Where these conditions cannot be met, an underdrain system can be specified.
Spec it. Verify it. Build it.
Download the spec pack for ASTM and EPA test reports, CSI Division 32 specification language, and cross-section details. Request a physical sample to verify surface character before specifying.