Inspection and Maintenance: Permeable Pavement

Inspection & Maintenance Guidance of a built vstormwater best management practices that treats the stormwater that falls on them and can be designed to also receive runoff from adjacent impermeable surfaces (e.g., pavements and roofs) as either sheet flow or from a pipe (e.g., roof downspout) connected to the washed gravel base, where captured water is temporarily stored in the base where it later soaks into underlying native soil or sent to a municipal stormsewer/other BMP via underdrains (TRCA, 2016)

Overview

Permeable Pavement Permeable pavements contain many small openings (i.e., joints or pores) that allow rainfall and snowmelt (i.e., stormwater) to drain through them instead of running off the surface as it does on impervious pavements like conventional asphalt and concrete. An overflow outlet is needed to safely convey flows during flood events. Depending on the permeability of the underlying soil and other constraints, the pavement may be designed with no sub-drain for full infiltration, with a sub-drain for partial infiltration, or with an impermeable liner and sub-drain for a no infiltration practice. The sub-drain pipe may feature a flow restrictor (e.g., orifice cap or valve) for gradually releasing detained water and optimizing the amount drained by infiltration into the underlying soil.

Key components of Permeable pavements to pay close attention to are the:

• Inlets
• Aggregates
• Choker layer
• Underdrains
• Pavement Surface
• Contributing Drainage Area
• Geotextile
• Overflow outlets

Associated Practices

• Permeable Interlocking Pavers (i.e., Block Pavers) – Precast modular units made of concrete, pervious concrete or rubber/plastic composite designed to create open joints between pavers that are filled with fine, washed aggregate and installed on an open graded aggregate (i.e., clear stone) base and sub-base.
• Permeable Interlocking Grid Systems (i.e., grid pavers) – Precast concrete or manufactured plastic grids with open cells that can be filled with aggregate or a mixture of sand, gravel and topsoil and planted with grass or low-growing ground covers and are installed on an open-graded aggregate base.
• Pervious Concrete – a rigid pavement installed on an open-graded aggregate base that uses a cementitious binder to adhere aggregate together, similar to conventional concrete, except that the fine aggregate component is minimized or eliminated which results in the formation of connected pores throughout.
• Porous Asphalt – a flexible pavement installed on an open-graded aggregate base that uses a bituminous binder to adhere aggregate together, similar to conventional asphalt, except that the fine aggregate component is minimized or eliminated which results in the formation of connected pores throughout.

Inspection and Testing Framework

Permeable articulated block system at the LSRCA headquarters in Newmarket, ON is designed for heavy loads. This example shows an appropriate pavement surface condition when conducting any of, construction, assumption, routine or verification inspections.

Visual Indicators Framework - Permeable Pavements

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Contributing Drainage Area
	CDA condition	x	x	x	x
Perimeter
	BMP dimensions	x	x		x
Filter Bed
	Standing water		x	x	x
	Trash		x	x
Vegetation
	Vegetation cover	x	x	x	x
	Vegetation condition		x	x
	Vegetation composition	x	x	x
Underdrain & Monitoring Well
	Monitoring well condition	x	x	x	x
	Sub-drain/Perforated pipe obstruction		x		x
Outlets	Overflow outlet obstruction	x	x	x	x
Pavement Surface	Pavement surface condition		x	x
	Pavement surface sediment accumulation	x	x	x	x
	Control structure condition	x	x	x	x
	Control structure sediment accumulation	x	x	x	x

Permeable pavement in need of maintenance as excess sediment and unwanted vegetation growth has begun to occur near the perimeter of the installation. Source: (TRCA, 2016)..

Testing Indicators Framework - Permeable Pavements

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Testing Indicators
	Surface infiltration rate testing		x		(x)
	Natural or simulated storm event testing		x		(x)
	Continuous monitoring		x		(x)
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

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

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

Toronto and Region Conservation Authority

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

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

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

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

Penetration of water through the ground surface.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Lake Simcoe Region Conservation Authority

Water ponded on the ground surface.

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.

Structure to control the volume or rate of flow of water through or over it.

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 rate at which stormwater percolates into the subsoil measured in inches per hour.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

Sustainable Technologies Evaluation Program