State researchers spent the summer looking at Lancaster city's trees.

Now, city officials and representatives of LIVE Green Lancaster are looking at numbers.

Those numbers include:

• The number of the city's street-side trees: 5,489.

• The city's tree canopy coverage: 28 percent.

• The recommended city coverage: 40 percent to 45 percent.

• The number of trees that would have to be planted to reach 40 percent: 1,200 per year for 25 years.

Trees beautify the city, reduce air and noise pollution and even save energy costs. But that's not what this is about.

Planting trees is one of the simplest and best steps the city can take to reduce the amount of stormwater that flows to the sewer system during heaving rains, city Public Works Director Charlotte Katzenmoyer said.

A larger, second set of numbers show the intent behind the initiative:

• The annual average amount of stormwater 1,200 trees would absorb: 4.13 million gallons.

• The number of gallons of stormwater the city must contain or remove to meet federal mandates to protect the Chesapeake Bay: 1 billion.

• The estimated cost of measures to meet that goal: $140 million.

• The estimated cost of building massive storage tanks to treat the stormwater overflows through conventional water treatment methods: $300 million.

During storms, rainwater from street curb inlets and from parking lots and other surfaces floods the sewer systems and overwhelms the city wastewater treatment plant. When that happens, the plant overflows and raw sewage pours into the Conestoga River and ultimately the Chesapeake Bay.

The federal Environmental Protection Agency is cracking down on bay pollution and is requiring city action on overflow sewage.

Katzenmoyer would rather the city do that with "green infrastructure." That means planting trees, putting porous pavement basketball courts in city parks and alleyways, encouraging vegetative "green" roofs on buildings and other measures to divert rainwater into the ground before it gets to the sewer system.

"The bottom line is, if we don't meet this goal in 25 years, we're going to have huge, major 'gray infrastructure' projects that everybody will have to pay for," she said of building storage tanks that would contain overflow stormwater until it could be treated later.

"This is much more cost-effective," she said.

Before setting out to plant more trees, Katzenmoyer and Fritz Schroeder, program director of the non-profit LIVE Green, an urban environmental group, first wanted to know the status of the city's trees.

For that, people looked high and low this summer.

From above, the state Department of Natural Resources surveyed Lancaster County from aircraft using near infrared technology called Light Detection and Ranging. Using the LIDAR technology, researchers were able to look through the tree canopy and get a more accurate picture of its density.

The aerial survey found 28 percent tree canopy coverage in the city.

Meanwhile, four college students literally measured and assessed the city's trees the old-fashioned way.

Two graduate students from the Penn State University School of Forest Resources and two Millersville University undergrad interns used tape measures to find the trunk size of all 5,489 street trees in the city.

Between late June and early August they also identified the trees by species, assessed the health of the trees — excellent, good, fair and poor —!q and recorded them by address and location on a property.

Although their report isn't expected for a few weeks, Schroeder said preliminary data showed a wide variety of trees in the city. In addition to the common red maples, there also are single specimens of the dawn redwood, sumac and American beach.

The students found 35 dead trees and 1,200 empty tree wells, despite a city ordinance that requires street trees to be replaced if they are cut down. If property owners don't want to replace trees, a provision in the law allows them to pay to have another tree planted in another location.

The $12,000 Penn State survey was funded jointly by the state Department of Natural Resources and the city's Shade Tree Commission.

The survey report will provide a baseline inventory that will be used by city Public Works crews. It will be consulted and updated when a tree is added or removed, Katzenmoyer said.

Schroeder said data from both surveys will make it easier to identify areas where trees should be planted.

But, Katzenmoyer said, 1,200 trees a year are too many for public land alone.

The implementation plan, to be developed this winter, also will include efforts to include homeowners and other private property owners in the tree-planting effort, Schroeder said.

The plan will include specific trees that will be offered that are most likely to survive and thrive in an urban environment, he said. Those trees may have to deal with compacted soils, road salt and heat radiating from nearby macadam surfaces.

For street-side trees, the city will prepare the site and plant the tree for the property owner. The value of that labor has been placed at $750, Katzenmoyer. The only cost to the property owner is the tree itself. That cost, between $150 and $250, is the below-wholesale cost the city pays, she said.

The city hopes to begin planting the trees in the spring.

bharris@lnpnews.com