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Pavement is a culprit in flooding

Hard surfaces worsen runoff, contamination during heavy rain

By Beth Daley

Boston Globe, Monday, April 5, 2010

Do you blame Mother Nature for last week’s apocalyptic flooding?

Your own driveway might have contributed to the mess.

State and federal environmental officials say flooding in many places has been exacerbated by the roads, patios, parking lots, and, yes, driveways that define our urban and suburban landscapes.

Instead of rain seeping into soil around homes and malls to be stored in the earth, it pours off rooftops, sidewalks, and streets into storm drains, which quickly funnel the water to streams and rivers. That increases the likelihood of flooding from already swollen rivers — and of pollutants reaching waterways.

About 56 percent of Boston is paved over; Somerville tops out at 77 percent, according to the Charles River Watershed Association.

“The collective way we live as a society creates acres and acres of impervious surfaces we didn’t have before,’’ said Maria Rose, Newton’s environmental engineer. “Larger homes, bigger box stores, and shopping centers — as well as tennis courts, pools, and patios, have all added to the problem.’’

State and federal officials said they have no data on how much pavement has contributed to flooding, but a 2002 United States Geological Survey report noted that river flows near densely paved areas in Massachusetts were almost 10 times as high as those near less paved areas.

Rain runoff also carries contaminants from the built-up landscape — dog feces, oil, bits of metal from cars, and lawn chemicals. The state Depart ment of Environmental Protection is requiring managers of drinking water supplies in flooded areas to test water more frequently this week. So far contamination has been low — possibly because the amount of water diluted the pollutants.

The state also suggests that private well owners whose well caps were under water should boil their water and disinfect their wells. Contaminants in standing water could seep into wells.

“Our near-term focus is to protect public health — we are very concerned about this amount of moving water,’’ said Laurie Burt, the state environmental protection commissioner.

The enormous amount of runoff is also likely causing a significant number of sewage treatment plants across the state to be overwhelmed with storm water and sewage — communities have until today to report — and as a result diverted the dirty mixture into the state’s waterways.

Worries about pollution and flooding have led some communities to see pavement as a liability — and even to tax it.

Since 2006, Newton has charged residential property owners a flat $25 a year for paved surfaces on their property. The typical single-family property is 20 percent to 30 percent paved. Business properties, which can be as much as 90 percent paved, are charged more.

Reading has charged for pavement since 2007 — about $37 annually per household, and more for businesses. George Zambouras, town engineer, said the community takes in about $400,000 a year from the fees, which are used to upgrade its drainage system, clear catch basins, and buy equipment.

Other towns probably will levy similar fees, he said, as federal water quality rules tighten for the state’s waterways. The US Environmental Protection Agency is strengthening storm water-discharge permits for the Charles River and elsewhere across the state. The town of Franklin is among several communities investigating whether to assess a pavement fee, according to the Charles River Watershed Association.

Because water flows a great distance, efforts to reduce runoff in the suburbs can have a big payoff for Boston and other downstream communities. Some places, like Boston’s Back Bay — once a vast marsh — could have flooded this week if not for six giant pumps that can get rid of 3.7 million gallons of water from the swollen Charles River every minute. A vast wetland in Millis, Medfield, and Medway, set aside as preservation land in the 1970s, also helps absorb water that would otherwise pour into the lower Charles.

“It’s like a big sponge — there is this huge 8,000-acre-plus wetland that is helping the Back Bay not flood,’’ said Kate Bowditch, director of projects for the Charles River Watershed Association.

Ideally, water experts say, water should be “kept local’’ and allowed to percolate into the ground, where it travels far more slowly to rivers and streams. The water also is cleansed that way, with contaminants binding to soil or eaten by microbes.

Homeowners can take steps to reduce runoff. Recommended measures include placing crushed stone near drainpipes so the water seeps into the ground and buying barrels to capture rain that falls off the roof, which then can be used to water lawns by attaching a soaker hose to it. Homeowners can also replace asphalt or concrete pavement with stones that allow water to seep into the ground between them.

Bowditch’s organization even recommends that people convert their lawns into rain gardens, replacing grass with native plants that are better able to absorb rainwater.

“We want to capture that [rain] runoff,’’ said Lynne Hamjian, surface water branch chief for the EPA in New England.

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