Lancaster city might have found a small answer — or many small answers — to a very large problem.

Whenever the city experiences a heavy rain, stormwater runs into the sewer systems and overwhelms the capacity of its wastewater treatment plant, causing raw sewage to overflow into the Conestoga River.

It happens on average more than 100 times annually and dumps nearly 1 billion gallons of untreated wastewater into the river.

The federal Environmental Protecting Agency, which is now overseeing the cleanup of the Chesapeake Bay, is putting increasing pressure on the city to reduce overflows by 60 percent.

The way to do that with traditional "gray infrastructure" is to build additional sewage treatment capacity, build huge storage tanks to hold wastewater to be treated after storms or rebuild the city's 19th-century sewer system with separate stormwater and sanitary sewer systems.

The least expensive of those fixes — the construction of storage tanks — would likely cost between $200 million and $300 million, Charlotte Katzenmoyer, the city's public works director, said. Either the construction of additional treatment capacity or separate sewer systems would likely costs three times that amount or more, Katzenmoyer said.

On Thursday, consultant CH2M Hill presented an alternative.

After a four-month study, the group presented a draft of a "green infrastructure" plan for the city.

Instead of building expensive public works facilities at the edges of the city, likely behind wire fences, the green plan calls for myriad of small low-cost changes at the neighborhood level.

Those changes are intended to capture the rainwater before it runs into the sewer system.

Those would include using porous asphalt for baseball courts in three city parks and five city parking lots to let rainwater drain through instead of run off. Green roofs on buildings would catch rain and nourish plants, and much of it would evaporate.

Rainwater from residential downspouts could be directed into alleyways paved with porous asphalt. "Rain gardens" and additional trees planted along city streets also would catch rainwater, Brian Marengo, a water resources project manager for CH2M Hill, said.

Ten pilot projects already have been identified, and funding is in place for them, according to Danene Sorace, president of LIVE Green, an urban environmental organization that joined the city in sponsoring the study.

Much of that funding is coming from a $400,000 National Fish and Wildlife Foundation grant the city received last month.

A second and third set of projects also have been identified, she said.

Sorace maintained that gradually doing green projects as city streets and alleys are repaved or other improvements are made will make a huge difference in the amount of stormwater running into the sewer system. After 25 years of gradual improvements, raw sewage overflows would be completely eliminated, she said.

"It's all about scale. It's year after year after year. It has to be integrated," she said.

One of the ways greening would become integrated is by requirement. The city could alter ordinances to require green improvements be made when redevelopment is done.

The city also could levy a tax or fee on property based on the amount of rainwater runoff, Marengo said. Philadelphia recently implemented such a fee in which 20 percent is based on the total area of property and 80 percent is based on the amount that is impervious, meaning it allows rainwater to pass into the ground below.

Marengo said some land uses cause significant water runoff but pay nothing toward the city sewer system. A homeowner pays a water and sewer bill while providing only a small impervious surface area. A parking lot owner may pay no sewer bill for that property if it doesn't have sewer service, but the paved lot is responsible for significant runoff, he said.

Such a fee would fund the city's green infrastructure changes and provide incentive for property owners to add impervious surfaces on their own, he said.

City planning staff have started drafting ordinance modifications that would require the changes, Katzenmoyer said. Any change would be subject to City Council approval.

A final "green infrastructure" plan is expected to be presented next month. Public meetings will be held to present the proposals.

bharris@lnpnews.com