Permeable pavement: Plan review

Plan checklist

1. Do the plans include an appropriate construction sequence that is specific to the construction of the permeable pavement?
2. To avoid soil disturbance and compaction during construction, will the proposed infiltration area be clearly marked before any site work begins?
3. Do the plans include an appropriate cross-sectional detail for the permeable pavement?

Design checklist

1. Verify the drainage area directed to any proposed porous pavement. If DCIA runoff from other areas on-site, in addition to the direct (1:1) rainfall onto the porous pavement, is directed onto porous pavement, the porous pavement cannot be considered disconnected. It must instead be considered, and modeled as, a porous pavement structural SMP. The porous surface must be considered, and modeled as, DCIA. Porous pavement structural SMPs require infiltration testing. [Section 4.2.1]
2. For porous pavement structural SMPs, if infiltration is feasible, verify that the porous pavement design meets all Design Guidance Checklist design standards noted in Appendix F.10, Subsurface Infiltration. [Section 4.2.3, 2]
3. For porous pavement structural SMPs, if infiltration is infeasible, verify that the porous pavement design meets all Design Guidance Checklist design standards noted in Appendix F.14, Subsurface Detention. [Section 4.2.3, 3]

For porous pavement DIC systems:

1. Verify that the porous pavement DIC is installed on-site such that it does not create any areas of concentrated infiltration or discharge. [Section 4.2.3, 1a]
2. Verify that the surface slope in any direction across porous pavement does not exceed 5%. [Section 4.2.3, 1b]
3. Verify that the choker course depth is a minimum of two inches. [Section 4.2.3, 1c]
4. If an underdrain is proposed, verify that the first 1.5 inches of runoff are stored below the lowest invert of the underdrain. [Section 4.2.3, 1d]
5. Verify that an appropriate porous pavement curve number value is used when performing Flood Control calculations. [Section 4.2.3, 1e]
6. Verify that the stone storage bed depth is a minimum of eight inches, except when located beneath walkways or play surfaces, for which a depth of four inches is allowable. [Section 4.2.3, 6a]
7. Verify that stone is separated from soil media by a geotextile or a pea gravel filter to prevent sand, silt, and sediment from entering the system. [Section 4.2.3, 6b]
8. Verify that the stone storage system has a level bottom. Terraced systems may be used to maintain a level infiltration interface with native soil while accommodating significant grade changes. [Section 4.2.3, 6c]
9. Verify that pretreatment is provided for all runoff entering the porous pavement, including pretreatment of runoff from all inlets. At a minimum, this can be achieved through the use of sumps and traps for inlets, sump boxes with traps downstream of trench drains, and filter strips for overland flow. [Section 4.2.3, 4]
10. Verify that, when SMPs are used in series, the storage areas for all SMPs provide cumulative static storage for the WQv. [Section 4.2.3, 9]
11. Verify that any impervious liner, if necessary, is not interrupted by structures within the basin footprint. The plans must indicate that the impervious liner is to be continuous and extend completely up the sides of any structures that are located within the lined basin footprint to the ground surface. If additional liner material must be added to extend up the structures, the additional liner sections are to be joined to the rest of the liner with an impervious seam per the manufacturers’ recommendations. [Section 4.2.3, 10]
12. Verify that underdrains, if proposed for porous pavement DIC systems, meet the following requirements:
13. Underdrains must be surrounded by a sand or stone layer to filter sediment and facilitate drainage. [Section 4.2.3, 11a]
14. The minimum allowable thickness of a sand or stone filter layer is six inches both above and beneath the underdrain. [Section 4.2.3, 11b]
15. To prevent clogging, underdrain pipes must be surrounded by a geotextile fabric if a sand layer is used. [Section 4.2.3, 11c]
16. Verify that an adequate number of appropriately placed cleanouts, manholes, access panels and other access features are provided to allow unobstructed and safe access to the porous pavement structural SMP for routine maintenance and inspection of inflow, outflow, underdrains, and storage systems. [Section 4.2.3, 13]
17. Verify that an observation well is provided for a storage system that includes stone storage and that it meets the following requirements:
18. The observation well must be placed at the invert of the stone bed. [Section 4.2.3, 14a]
19. An observation well must be located near the center of the stone bed system to monitor the level and duration of water stored within the SMP (drain down time). [Section 4.2.3, 14b]

Adequate inspection and maintenance access to the observation well must be provided. [Section 4.2.3, 14c]

1. A manhole may be used in lieu of an observation well if the invert of the manhole is installed at or below the bottom of the SMP and the manhole is configured in such a way that stormwater can flow freely between the SMP and the manhole at the SMP’s invert. [Section 4.2.3, 14d]
2. Verify that access features are provided for all underground storage systems that are not stone storage beds. [Section 4.2.3, 15a]
3. Verify that a sufficient number of access points in the system are provided to efficiently inspect and maintain the infiltration area. [Section 4.2.3, 15b]

For cast-in-place vault systems, verify that access features consist of manholes or grated access panels or doors. Grated access panels are preferred to maintain airflow. [Section 4.2.3, 15c]

For grid storage or other manufactured systems, verify that the manufacturer’s recommendations are followed. [Section 4.2.3, 15d]

1. Verify that ladder access is proposed for vaults greater than four feet in height. [Section 4.2.3, 15e]
2. Verify that header pipes, at minimum 36-inch diameter, connected to manholes at each corner of the subsurface system are provided. Alternatively, smaller header pipes may be used if cleanouts are provided on every second manifold pipe/header pipe junction, on alternating sides of the SMP. [Section 4.2.3, 15f]

https://www.pwdplanreview.org/manual/appendices/f.-design-guidance-checklist/f.8-porous-pavement

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

A perforated pipe used to assist the draining of soils.

Filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

Soil or media particles smaller than sand and larger than clay (3 to 60 m)

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The natural ground material characteristic of or existing by virtue of geographic origin.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

Open space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

Cleanouts are "a fitting access in a drainage system or venting system that is installed to provide access for cleaning and inspection and that is provided with a readily replaceable air tight cover" (O.Reg 332/12: Building Code, 2022).