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Good practice Imported

Philadelphia's Green City, Clean Waters — 25-Year Green Stormwater Infrastructure Programme

United States of America · Philadelphia · See the United States of America profile

Evidence: Observational / pre–post Top 40% 47/100 · Ask Evidence Copilot about this practice

Under a 2011 EPA/PA DEP consent order, Philadelphia Water Department has built 3,850+ 'greened acres' of rain gardens, bioswales and green roofs, keeping billions of gallons of combined sewer overflow out of local rivers at roughly a quarter of the cost of an all-grey alternative

3,850+ acres
Greened acres delivered (15-year mark)
1,100+ projects
Completed projects
~3 billion gallons/year
Stormwater/overflow diverted annually
~2.1 USD billion
Planned public investment
8-13 USD billion
Comparable grey-infrastructure-only cost estimate
~85 %
Target combined-sewer-overflow reduction
Philadelphia's Green City, Clean Waters — 25-Year Green Stormwater Infrastructure Programme

Details

Maturity
Scaling
Promoter
Philadelphia Water Department
Period
2011-2036
Keywords
green stormwater infrastructure, combined sewer overflow control, urban water management, green roofs, rain gardens

Context

In 2011 the City of Philadelphia signed a Consent Order and Agreement with the U.S. EPA and Pennsylvania DEP, committing to a 25-year, largely green-infrastructure-based plan (through 2036) to cut combined sewer overflows into the Delaware and Schuylkill rivers by roughly 85%, instead of expanding conventional 'grey' sewer tunnels.

Activities

The Philadelphia Water Department builds and inspects rain gardens, permeable pavement, bioswales and green roofs on public and private land, counted toward a regulatory 'Greened Acre Performance Standard'.

Results

At the programme's 15-year mark, PWD reported more than 3,850 greened acres delivered across 1,100+ completed projects, with infrastructure now keeping roughly 3 billion gallons of stormwater and sewer overflow out of local waterways annually. Independent estimates put a comparable grey-infrastructure-only expansion at $8-13 billion, versus Philadelphia's roughly $2.1 billion mostly-green plan.

Conclusions

Recent reporting has questioned whether the programme can meet its full 2036 targets given rising per-acre construction costs and uneven build-out pace, and a 2024 hydrology study found the measured streamflow benefit varies by watershed and storm size.

Implementation
Indicative cost
Very high (> €5M)
Time to results
Long (> 3 years)
Staffing & skills
Philadelphia Water Department

Conditions for success

  • Legally binding EPA/PA DEP consent order with a defined performance standard
  • Roughly a quarter of the cost of an all-grey infrastructure alternative

Common failure modes

  • 2024 reporting questions whether the programme can meet full 2036 targets given rising per-acre construction costs and uneven build-out pace
  • 2024 hydrology study found measured streamflow benefit varies by watershed and storm size

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