Azavea began working with the Philadelphia Water Department (PWD) five years ago when the agency started restructuring the way it charged customers for management of stormwater.  Stormwater runoff is produced when the ground is unable to absorb the amount of precipitation that falls during a storm event.  In Philadelphia, and most urban areas, where the ground is substantially impervious (think streets, sidewalks and buildings), a large portion of precipitation turns to runoff.  Instead of slowly infiltrating into the ground or evaporating back to the atmosphere, it heads directly for the sewers.  When the amount of rainwater in the Philadelphia sewer system hits a critical point, untreated wastewater flows directly into the rivers, and sometimes residents’ basements.  There are essentially two options to help mitigate that outcome: either invest in expensive additional infrastructure or try to reduce the amount of runoff that enters the sewer system.

At the time, the stormwater component of non-residential property water bills was based on the size of the incoming water supply line, which served as an approximation of the size of the property and, therefore, the amount of stormwater runoff being produced.  However, with the right land cover data, that amount of stormwater runoff could be calculated more precisely so that bills could accurately reflect what it cost PWD to manage.  Not only does this distribute the cost of stormwater management more equitably, but by generating charges as a product of the actual landscape characteristics on a property, PWD can incentivize property owners to improve those characteristics as a way to lower their bill.

With the restructured billing policies in place, PWD created a collection of management practices and systems that private property owners could implement to reduce the amount of runoff coming from their properties.  The systems work by either diverting stormwater runoff to an area where it can either slowly soak and infiltrate to the ground, or be stored until it can be released back into the sewer system when the load is lower, reducing the risk that there will be an overflow.  Property owners who install and maintain these systems receive credits to their monthly stormwater charge for the reduced runoff.  Azavea helped design the billing system that PWD uses to manage this program, and also created the PWD Stormwater Billing Parcel Viewer, which enables customers to get a detailed assessment about the impervious makeup of their property and a breakdown of the various components that go into their bill.  With this knowledge, an experienced engineer or PWD employee could calculate potential savings to help a customer to decide if a project made sense for their property.

But PWD wanted to make this process easier and more straightforward for customers, from basic education about the program, to information about installing stormwater reduction systems, to understanding exactly how these systems can reduce the monthly stormwater charge.  Last month, we released the PWD Stormwater Billing Credits Explorer to let people do just that.

The app turns any non-residential property into a canvas where a user can sketch out ideas of up to 5 different types of “Stormwater Tools”, including Green Roofs and Rain Gardens, Permeable Pavers and different types of storage basins.  The tools allow you to lay out potential changes while keeping realistic limits for that given property. As Stormwater Tools are added or removed, the application updates the monthly stormwater charge for that property. Users can rapidly get a sense of the feasibility and effectiveness of adding stormwater management systems, but just as importantly, PWD hopes to use the tool to educate the public on how stormwater management systems work.  New features are planned, including a component for evaluating various types of common Philadelphia housing stock and showing the options available to those homeowners for reducing the amount of runoff produced.  Residential owners can’t apply for credits to their bill since they all receive a flat stormwater fee, but there are still plenty of ways to take action that will help keep our rivers clean and healthy.