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[WATER SPLASHING] DAN OLSON: Water from a late summer rain shower splashes off a roof onto a driveway and courses into a Minneapolis City street. At the end of the block, water rushing off roofs, driveways, and sidewalks has grown from little rivulets into a stream that tumbles into a storm sewer grate.

Minnesota Department of Natural Resources Watershed coordinator, Michele Hanson, says the water carries pollutants.

MICHELE HANSON: There's gasoline, there's metals. If we leave our leaves and grass on the surfaces, there's nutrients that go down to our resources.

DAN OLSON: Nearly all of the rain that falls onto forests and fields soaks into the ground. However, in the Twin Cities, where about 13% of the land, more than 250,000 acres is covered with impermeable surfaces, shingles, concrete, and asphalt where over half the rainfall runs off.

Cliff Aichinger, who directs the Ramsey-Washington Watershed District, stands in a parking lot at a St. Paul neighborhood mall. Most stormwater in older cities, he says, is untreated.

CLIFF AICHINGER: This area in highland here has nothing. It's piped directly to the Mississippi River. A lot of St. Paul, a lot of the first ring suburbs are that way.

DAN OLSON: Stormwater runoff is one reason state officials have declared the Mississippi that flows through the Twin Cities impaired or polluted. Stormwater is separate from what we send down our kitchen drains and toilets. Sewer or wastewater goes off to treatment plants, not stormwater.

University of Minnesota stormwater specialist Ron Struss says, in newer suburbs, some is diverted to ponds.

RON STRUSS: About 50% of the sediment and the nutrients to settle out. So we get about a half cleaning job in newer communities, but even that's not meeting our water quality goals.

DAN OLSON: Most stormwater doesn't look polluted. Some looks clear enough to supply a trout stream. But a closer inspection of the surface of stormwater reveals the rainbow effect that comes from traces of petroleum products.

GARY OBERTS: It doesn't take much gasoline, for example, to have a taste and odor problem in a body of water.

DAN OLSON: Gary Oberts is a consultant who works for the Oakdale-base water resource consulting firm EOR. He's hired by developers and others to help them comply with the layers of rules put in place to control stormwater runoff. Oberts says amounts of pollution measured in parts per million, even billion, can spell disaster for an ecosystem.

GARY OBERTS: It doesn't take much phosphorus to turn a lake green. It doesn't take much of different contaminants to be toxic to fish or to be toxic to frogs. They are all small numbers and we are all the source of the problem.

DAN OLSON: Some of the foulest stormwater is found in the hundreds of ponds near suburban Twin Cities office and shopping centers. A pond near the newly rebuilt Apache Plaza in St. Anthony Village is a pit the size of an Olympic swimming pool. It's surrounded by a fence to prevent people from falling in.

Water from the nearby parking lot has washed a collection of plastic bottles, wrappers, and newspapers into it. The color of the water on a bright, sunny day is black.

Dan Huff is a watershed specialist for the Friends of the Mississippi River, a St. Paul-based clean water advocacy group. He says ponds were considered state of the stormwater collection art 20 years ago, but they're a relic now.

A cheaper and more effective approach, Huff says, is to dot big impervious areas like parking lots with smaller sunken rain gardens and grassy collection basins. They keep stormwater closer to where it originates and do a better job of cleaning.

Many of the old ponds, he says, aren't maintained until the property changes hands, and then the new owners, often the city, encounter a big cleanup.

DAN HUFF: You have to drain it, get in there with heavy equipment, load all these dump trucks full of polluted sediment, and then take it somewhere. Hundreds of thousands of dollars in maintenance. Who pays for that? More than often it's the city taxpayers who pay for that.

DAN OLSON: Minnesota's progress in adopting new stormwater control ideas is slow, Huff says. States have the job of enforcing the Clean Water Act, the landmark federal legislation approved 33 years ago by Congress, which sets water pollution standards.

Huff says years of staff layoffs have created a climate of perpetual reorganization in Minnesota agencies. The result is cities and counties are confused about who to ask for help. State officials are writing a new document to try to untangle some of the confusion.

The huge manual is like a Bible of stormwater management. When completed, it will be a guide for how to comply with stormwater control rules and regulations, and there are plenty of them.

Anyone planning to build on or in some other way modify an acre or more of land in Minnesota needs a stormwater permit. The permit must include a plan for controlling runoff. At the moment, experts say nothing surpasses agriculture in Minnesota as a cause of water pollution, but Twin Cities construction activity makes a huge contribution.

With every rainfall, thousands of tons of soil and other sediment wash off urban and suburban construction sites into lakes, rivers, and streams. The company putting townhomes on this 28-acre parcel in Eagan has spread blankets of straw and created sediment catch basins to slow the runoff.

Dakota County Soil and Water conservationist Mike Isensee watches with an approving eye. The developer is spending extra money and taking extra time to contain erosion that could choke a nearby marshland.

MIKE ISENSEE: Construction sites can load sediment at up to 10 to 20 times than an agricultural field can, because the first thing we do when we come in and start a urban construction site is we strip off the topsoil, exposing the subsoils, which are silts and clays, and they're very difficult to drop out of the water column.

DAN OLSON: Isensee helps landowners devise ways to control runoff, but he's also a kind of stormwater sheriff. If he spots problems, he can write up a complaint that can result in landowners being fined tens of thousands of dollars for not complying with stormwater runoff rules.

Some of the rules are created by a layer of government in Minnesota called watershed districts. Most areas of the state have them, but the elected watershed board members don't have a very high profile. However, they make rules that, if enforced, can have an impact.

For example, Ramsey-Washington Watersheds Cliff Aichinger says, some Twin Cities area watershed boards are adopting a rule that developers building on more than an acre of land must plan for a way to capture the first half inch of rainfall. The reason Aichinger says is the first half inch carries most of the pollutants.

CLIFF AICHINGER: The first half inch of rainfall has to infiltrate. It can't run off. And that's probably about 80% of our rainfall events are under half an inch.

DAN OLSON: One result is developers are searching for pervious or porous alternatives to long stretches of impervious concrete driveways, parking lots, and sidewalks.

Virtually unchecked development in the fast growing Twin Cities area is adding acres of impervious surfaces every year. Officials say the challenge is to accommodate the growth while cleaning up the pollution already fouling the region's lakes and streams. Dan Olson, Minnesota Public Radio News.