Sixty 7th graders at Cole Arts and Science Academy readied for Democratic delegates from California, New York and New Jersey to come help them evaluate Denver’s ecosystem on the third day of the Democratic National Convention.

The project, headed by Frontrange Earth Force was one of more than 30 held around the Mile-high City in an effort to allow delegates the chance to thank the city they’ve swarmed by the thousands this week.

“The people of Denver are putting up with a lot to have us here,” said California delegate Tim Allison of Santa Barbara, a convention first-timer. “It’s an opportunity to send the message that we want to give back.”

Delegates assisted the students at stations designed to help measure the city’s pollution.

“They’ll be doing water quality testing,” Earth Force’s professional development head Tasha Mitchell said while waiting for delegates to arrive. “They are looking for the levels of phosphates in the water” to help indicate toxins.

Delegates were also trained in “macro invertebrate identification” — spotting species of insects and Platte River-dwellers that indicate high or low tolerance of pollutants. Seeing crayfish, for example, means the waters are very clean.

Kathleen Klein of Lafayette, Calif., said delegates were given a few options for places to help out.

“A lot of people are helping students write letters to politicians to help them get into the political process,” she said.

Klein, who has worked on every Democratic presidential campaign since John F. Kennedy’s 1960 run, said Sen. Barack Obama’s candidacy makes this convention particularly important to her.

The candidate himself, who will become the Party’s nominee Thursday evening, spent the morning packing boxes for troops in Iraq and Afghanistan for his contribution to Delegate Service Day, while wife Michelle, along with the wife of Vice Presidential candidate Joe Biden, kicked off the event with opening remarks.

“These projects are our way of saying thank you to the people of Denver, our gracious hosts this week,” Mrs. Obama, who co-chaired the day’s events with Mrs. Biden, said in a press statement. “We hope the more than one thousand delegates taking part in the many service projects across Denver today will carry that commitment to service back to help their communities long after our Convention is over.”