Parking lot runoff and Ohio River quality

I did this short story at work today, based on a news release I got from the EPA this morning. It has to do with the EPA not liking the amount of rainwater running off the asphalt and concrete in my city of Huntington WV. As a person with no college-level training in hydrology or the chemistry of water that runs off parking lots into the Ohio River, I am kind of mystified that it would be such a major contributor to water quality problems in a river as big as the Ohio, but what do I know?