New data suggests that Pittsburgh sewer overflows may be 15 percent greater than prior estimates, which were based on data from 2003. A new report from the RAND Corporation analyzes data collected by ALCOSAN between 2004 and 2013.
Furthermore, the volume of water overflowing from local sewers could rise in coming decades, according to Jordan Fischbach, co-director of RAND’s Water & Climate Resilience Center.
He said one factor is climate change. More rain could fall in the future or rain events could become more intense. Other potential changes include population growth and the ways land is used.
“That’s primarily asking the question how much more pavement would we put in if there was additional population growth in and around Pittsburgh in the combined sewer service area,” Fischbach said.
Non-permeable surfaces such as roads, parking lots and sidewalks are contributors to the county’s sewer overflow problem. Other issues include cracks and leaks in the aging sewer system, homeowners’ gutters that run directly into the sewers and combined sewers that collect both storm water and wastewater.
“The ALCOSAN system was designed for another era of sanitation, when diluting
wastewater before draining into streams and rivers was state of the art,” reads the RAND report. “Now, the system is an aging patchwork across many municipalities, including poorly maintained and leaking or broken pipes.”
The RAND analysis looked at 18 possible scenarios for how rainfall, population growth and land use could affect future overflow volumes and evaluates potential strategies for addressing the problem.
Those strategies include green storm water infrastructure, inflow and infiltration reduction, treatment plant expansion and deep-tunnel cleaning.
Green infrastructure refers to things like rain gardens, bioswales and permeable pavement. Reducing inflow and infiltration involves fixing cracks in sewer lines, while deep-tunnel cleaning would increase the capacity of the existing sewer system by clearing out silt that has collected.
ALCOSAN’s current plan also includes a $335 million expansion of the wastewater treatment facility on the North Side and the addition of more tunnels and holding tanks.
Fischbach said a successful plan to address the sewer overflow problem will include a combination of multiple strategies, and will seek to stabilize the system for the next 50 to 100 years.
“These plans should take into account a larger volume of overflow and try to address tomorrow’s overflow challenge, not just solve today’s,” he said.
Fischbach said, from a technical perspective, a solution is possible, but would require much more than the $2 billion investment ALCOSAN is currently proposing.
ALCOSAN praised RAND for its work on the report.
“This study demonstrates the need for speed in moving ALCOSAN’s clean water plans forward,” said ALCOSAN Executive Director Arletta Scott-Williams in a statement. “That is why we already have undertaken multimillion projects at the wastewater plant itself, and why we have invested $9 million this year alone in municipal projects to reduce excess flow throughout our service area.”
The U.S. Environmental Protection Agency has ordered ALCOSAN to fix the overflow problem by 2026, though officials said an extension is likely.
*UPDATED: Wednesday, April 26, 2017 at 9:25 p.m. to include the dates of the data that new and previous estimates of sewer overflow were based on.