Street-Smart Sustainability

Summer 2013

Incorporating permeable surfaces in Lancaster, PA’s stormwater management plan proves highly cost-effective

by Alicia Lasek


Street-Smart Sustainability

alley5In 1795, the city of Lancaster, PA, had the good fortune to be the terminus of the first long-distance gravel-surfaced road in the United States, the 62-mile Philadelphia and Lancaster Turnpike. At the time, road engineering in the U.S. was at its most basic level, and this simple stone surface was a boon to local travelers, ensuring that the road remained passable, versus muddy and rutted, during the spring thaw. More than 200 years later, this city of 60,000 is again a public works pioneer. Since implementing a long-term, integrated green infrastructure plan in 2011, including about 210 acres of planned permeable paving, the city has become a showcase for how an urban municipality can cost-effectively tackle required stormwater management upgrades.

In 2009, Lancaster officials faced an estimated $330 million-plus for required gray infrastructure upgrades to the city’s stormwater management system, including new underground storage tanks. According to the Environmental Protection Agency (EPA), the city is one of about 770 U.S. cities that employ a combined sewer system, designed to capture city sanitary sewage, industrial wastewater, and rainwater runoff and funnel it to wastewater treatment facilities before discharge into nearby waterways. Today, severe rainstorms and heavy snowmelts routinely overwhelm these aging systems. In Lancaster’s case, combined sewer overflows (CSOs) can amount to about one billion gallons of untreated combined sewage flowing into the Conestoga River yearly, says Lancaster Director of Public Works Charlotte Katzenmoyer.alley2

Under EPA rules, Lancaster, with other municipalities in the area, is on a timetable to greatly reduce the incidence of CSOs, meet groundwater pollutant caps and reduce nutrient and sediment runoff as part of a larger cleanup effort of the region’s rivers flowing into the Chesapeake Bay.

In response, Lancaster commissioned a study of the long-term efficiencies of green infrastructure in capturing and filtering stormwater, including permeable pavement systems in alleys, parking lots, sidewalks and streets; infiltration and bio-retention areas; green roofs and rain barrels. Using a customized calculator, the city estimated that it could reduce average annual runoff by one billion gallons for a total cost of approximately $141 million over 25 years. When considered as a marginal or increased cost of incorporating green infrastructure into other public works projects and private redevelopment, the estimate dropped to $77 million.

With those numbers in hand, in 2011 Lancaster officially adopted an integrated Green Infrastructure Plan that has become a springboard for green projects throughout the city.

“The plan envisions a long-term strategy to green the city and use that as a primary mechanism to reduce combined sewer overflows as well as address pollution in the separate sewer areas,” says Andrew Potts, senior watershed services technologist at CH2M Hill, the city’s strategic consultant. Guided by the plan, Lancaster examines each project in the concept stage, comparing green and gray infrastructure costs on a per-gallon basis, says Katzenmoyer. “Then we make a case, based on a self-imposed threshold, that [green infrastructure] will cut that cost at least in half,” she explains. “If we can do that, we are spending the limited resources that we have wisely.”

Covering the costs

The Green Infrastructure Plan helped the city kick-start a quick succession of demonstration projects on public and private land. And with a new green infrastructure showcase, Lancaster was able to successfully pursue grants and other funding. In January 2013, the city was awarded $7 million in low-interest loans from the Pennsylvania Infrastructure and Investment Authority (PENNVEST). With private land accounting for the majority of the city’s impervious surfaces besides roadways, PENNVEST funds allow the city to incentivize owners by offering 90 percent coverage of construction costs for installing city-approved green stormwater capture elements.

alley3To date, the plan and completed projects have shown that Lancaster can construct enough green infrastructure to eliminate the need for a $70 million storage tank that would have addressed one of the city’s CSO basins.

“We’ve found that the incremental cost of green infrastructure is much less when you incorporate it into another project,” says Katzenmoyer. Buoyed by this success, city officials are negotiating with the EPA under the agency’s new integrated planning framework to continue to meet stormwater management requirements with green infrastructure, and not involve gray infrastructure at all, she says.

Word on the street: permeable pavers

By June of 2013, Lancaster had about 140 green infrastructure projects in planning, design or development with permeable paving making a strong showing in the plans. According to Katzenmoyer, Lancaster predicts it will have runoff from about 24 acres (9.7 ha) managed or 20 million gal. (75,700 L) of stormwater captured by the end of 2014. “This includes gray infrastructure, rain gardens and other green infrastructure, and permeable paving systems play a significant role,” she says.

The city identified streets and alleys needing complete reconstruction that are good candidates for green infrastructure. Since 2011, four out of 14 completed green ground projects (excluding green roofs) have used about 8,000 sf (740 m2) of permeable pavers, according to Potts. In addition, the city plans to repave all 20 mi. (32,000 m) of its alleys with a combination of conventional pavement and permeable interlocking pavers. In 2011, it unveiled Alley 148, a green demonstration project that used permeable interlocking concrete pavers in a center strip over an infiltration trench, flanked by concrete paving designed to handle city service vehicles.

Concrete pavers were chosen for their cost-effectiveness, says project contractor Doug Lamb of Doug Lamb Construction in Elizabethtown, PA. Lamb says he began to notice an uptick in bids involving interlocking concrete pavers right around the time stricter CSO reduction rules kicked in, in 2009. “About four or five years ago we started seeing more requests for them,” he says.

The city estimates that the project’s costs amounted to 10 percent more than if it had reconstructed the alley with 8-in (200-mm) reinforced concrete. Yet this and the cost of future maintenance are offset by the green alley’s ability to capture and naturally filter pollutants in an estimated 200,000 gal. (750,000 L) of stormwater per year, says Katzenmoyer.alley4

The city has also found that, beyond replacing a mechanical sweeper with a $300,000 vacuum sweeper, there is no further maintenance cost for the necessary cleaning of the permeable pavers in public ways, Katzenmoyer notes.

Vacuum sweeping duties are assigned to city crews as part of their routine maintenance schedule.

Embracing green

In Lancaster, the use of permeable paving systems has proven to be an important tool for reducing runoff pollutants and CSO overflows, and for protecting public and environmental health, says Katzenmoyer. She suggests that those considering green solutions to EPA stormwater requirements can begin by encouraging their local, state and national contacts to look beyond the traditional stormwater engineering mindset and more closely at green solutions.

“They need to first work to dispel the perception that green infrastructure costs so much more; we have learned that it does not,” Katzenmoyer says. In the case of permeable paving systems, for instance, the construction and maintenance is not as daunting as they might think. Over their lifespan they are more cost effective and have multiple benefits compared to single-purpose solutions such as an underground storage tank, including aesthetics, which benefits the property owners, and the alleviation of [damage from] the winter freeze-thaw cycle.

“In addition, continuing to add piping and storage to handle storm water overflows and runoff is not only very costly, it simply increases the velocity of the stormwater, making it more erosive,” says Katzenmoyer. “U.S. municipalities and the EPA are starting to get away from the traditional gray engineering model and are looking at more natural systems to clean stormwater.”