Permeable Resin-Bound Surfacing in Pittsburgh, PA

PWSA's fee, its permeable pavement rule and how it treats porous ground

PWSA's stormwater fee is based on impervious area measured from aerial photography. One equivalent residential unit (ERU) is 1,650 square feet; residential parcels fall into three tiers, and non-residential parcels pay per ERU. PWSA's credit program covers practices such as rain gardens and underground storage systems: a residential customer with a qualifying practice drops to the next lower tier, and non-residential properties can receive up to 60% off under the City's 2019 stormwater standards, or up to 45% under the 2016 standards. Credits are renewed every three years with a current photo of the practice.

Permeable pavement is handled differently. PWSA says permeable pavement or pavers designed with a sub-base for stormwater infiltration are not eligible for a credit, but can be deducted from the parcel's impervious area. No PWSA rule names resin-bound surfaces, so whether a resin-bound system counts as permeable pavement is PWSA's call. Expect to document the reservoir, infiltration data and maintenance when you ask for the deduction. Gravel is impervious by default, with case-by-case appeals for gravel built for high permeability, and the City's zoning guidance counts gravel as impervious unless compaction or infiltration tests meet the City Stormwater Design Manual.

Hillsides, combined sewers and three rivers

The separate storm sewer area runs under a joint MS4 permit held by PWSA and the City. Everything else flows to ALCOSAN, whose Clean Water Plan adds regional tunnels along the Ohio, Allegheny and Monongahela rivers, and whose GROW program supports projects that cut flow at the source. Keeping rain out of combined pipes is the main stormwater benefit a permeable section can offer here.

The ground is the harder part. Steep slopes, landslide-prone soils, clay and old fill or undermined areas make concentrated infiltration risky on many hillsides, so the project engineer may call for a geotechnical review, a lined bed with an underdrain, or terraced reservoir cells. An underdrained section provides detention and treatment, not volume reduction. Freeze-thaw cycles are frequent and road salt is heavy, so check base depth against frost and specify vacuum cleaning rather than sanding.

Where it fits in Pittsburgh

• Non-residential parking lots: every 1,650 square feet of pavement is an ERU on the bill, so replacing part of a lot with permeable pavement that PWSA removes from the billed impervious area is worth evaluating.
• Projects seeking zoning performance points: Section 915.07 rewards capturing a share of the first two inches of runoff with preferred technologies under the City Stormwater Design Manual.
• Rowhouse yards and parking pads: if PWSA accepts the permeable section and deducts it, a smaller billed impervious area can move a home into a lower tier.
• Riverfront trails and plazas: flatter sites where infiltration is more feasible than on the hillsides.

For simple resurfacing of a sound slab, see our Pittsburgh concrete resurfacing page; that work does not change your stormwater fee.

Approvals: City Planning, PWSA and the county

Private stormwater facilities are regulated mainly by the City under its Stormwater Management Code, and PWSA's developer manual sends applicants to the Stormwater Management Officer in the Department of City Planning. PWSA handles sewer and storm connections, and the Allegheny County Conservation District runs the NPDES construction stormwater program. Once the surface is built, ask PWSA separately to remove it from your billed impervious area; permeable pavement is handled that way rather than through the credit program.

Resin Rock supplies UV-stable binder, stone blends, trims and the Rock Crete permeable sub-base, with technical data sheets for the review package. We do not install. Find an installer to be matched with an approved installer, usually within 24 hours.