Pervious Porphyry pavement has a role to play in numerous parking lanes, alleys, driveways, motor courts and walkways in Philadelphia.  What if your business water bill was not just based on how much water you used, but on how much storm water run off your property caused?  That is what is happening in Philadelphia as a result of a major effort to curb the amount of storm water entering the system.  It is called the Parcel Based Billing Initiative and is a storm water utility fee.  Along with prescribed incentives that offer credits, the initiative charges non-residential properties based on the ratio of impervious surface to gross property area.  In one of our country’s oldest cities and one that has many historic and cultural public squares, permeable Porphyry pavers can benefit the redevelopment of these spaces to storm water management jewels.

Porphyry Paving Permeable SetDiagram Credit – Milestone Imports, More Drawings, PDF and CAD at

Philadelphia’s Problem

48% or 64 sq. miles of Philadelphia operates on a Combined Sewer System.  Sewage and storm water flow through a common pipe to the treatment plant.  When storm water is greater than the system can manage, there is a discharge of sewage and storm water to nearby rivers and streams including the Delaware and Schuylkill. This is called Combined Sewer Overflow or CSO. With one of the nations oldest water infrastructure systems and faced with compliance to many federal as well as quality of life requirements, the city looked at its options.

Separating the combined system and building enormous storage tunnels for storm water could run $8-10 billion dollars.  Instead, a comprehensive plan to convert 4,000 acres of impervious coverage to “greened acres” is underway at an estimated cost of $2.5 billion over 25 years.  The city owns 45% of the impervious coverage in the city, including streets, so it is not entirely on the shoulders of private business to bear the costs.  This urban comprehensive plan is know as Green Cities, Clean Waters.  To download a copy of this plan click below.


A Greened Acre

Each greened acre represents an acre of impervious cover within the combined sewer service area that has at least the first inch of runoff managed by storm water infrastructure.  One acre receives one million gallons of rainfall each year.  Green storm water infrastructure will result in a renewal of urban landscapes and streetscapes guided by sustainable urban design in both development and redevelopment.

Permeable hard surfaces, such as Porphyry in a permeable set, are referenced throughout this plan frequently due to the density of the urban landscape and the number of pedestrian and vehicular pathways.  See the blog of permeable grout for pavers here —–EcoSystems Grout – Permeable Joint Material for Porphyry


Porphyry’s composition determines its high compression strength, resistance to stains, slip resistance, and high freeze/thaw ratings.  The stone is the most popular paver in Europe, and is favored for its flexibility in design, beauty, durability and low maintenance requirements. ADA Compliant Porphyry pavers are also adaptable to a permeable paving set. The stone is by far one of the most durable pavers in the world.  These materials are available from Milestone Imports.   –