Tara Withington, with her two young sons in tow, combs the aisles of Hannaford Bros. Co. supermarket for what she deems healthy enough to feed her family. Besides reading ingredients and studying her fruit for bruises, Withington says she needs a guarantee the organic foods she buys are kept far, far away from the store's conventional products.

"I need to know it's natural and I'm not giving them chemicals," said Withington, 33, of Milton, playfully tapping her 1-year-old son's hand as he reached out of his shopping cart seat for a jar of pickles. "I'm trying to keep them healthy, and this reassures me that they are not coming into contact with anything I don't want them to."

Chasing the success of Whole Foods Market Inc., and the announcement last year that Wal-Mart Stores Inc. would double its organic products, several regional grocers are going deeper into the market with a government-backed seal as "certified organic retailers." In recent years, smaller supermarket chains such as The Kroger Co., Lund Food Holdings Inc. and now Maine-based Hannaford represent a growing number securing the certification.

While organic foods are certified by the U.S. Department of Agriculture as free of pesticides and hormones, this designation says the retailer will comply with handling standards nearly as meticulous as those for kosher or vegan foods.

At its simplest: Organic broccoli cannot be stacked atop conventional broccoli, organic apples cannot be washed with regular apples, and organic ham cannot be exposed to the same deli slicer as the traditional cold cuts, for fear that chemicals will be transferred.

Sam Beattie, a specialist at Iowa State University's Institute for Food Safety and Security, said the certification is the best way for regular supermarkets to get a leg up in the organic food industry, where sales in the United States went from $6 billion in 2000 to $14 billion in 2005.

"They recognize that the organic foods industry is increasing in leaps and bounds over the last decade," he said. "In stores like Whole Foods where all of the food is organic, there's no issue associated with segregation. But regular grocery stores, where maybe a quarter of the food is organic, become suspect."

Beattie said it's crucial for supermarkets to do everything possible to avoiding co-mingling and cross-contamination.

"That's why this certification is critical," he said. "It's the only way for a store to address these issues."

The stores voluntarily agree to subject themselves to on-site inspections by San Diego-based Quality Assurance International, one of a number of third parties chosen through the U.S. Department of Agriculture. The group also certifies Whole Foods and grocery-selling SuperTarget, a division of Target Corp.

The move by Hannaford is being watched carefully by other chains considering similar measures, such as Massachusetts-based Shaw's Supermarkets Inc. and Stop & Shop Supermarket Co., according to spokesmen for both companies.

Perhaps the most challenging requirement for certification is getting documentation in order that chronicles the life of each food — exactly where it came from, how it was grown and the course it took to get to the store.

The certification in May took Hannaford about four months of staff training and meant completely revamping all of its 159 stores. In the delis, counters and equipment are set aside for handling unprocessed meats. Breads with organic status are in separate ovens in the bakeries.

Placed high on the coolers' shelves far from traditional fruits and veggies are boxes of fresh produce. They are carefully taken to the organic section islands with bright, large dividers to emphasize their distinction and guard them from other foods. Special chemical-free cleaning agents are used for those products, and employees stand by to monitor the area and answer customers' questions.

To maintain the title of certified organic retailer, a chain of Hannaford's size pays a fee of about $500,000 a year. That cost covers annual inspections, but not the cost of new equipment, training or reorganization of the stores.

Santo Carnabuci, who manages the Hannaford in Quincy, said customers were beginning to demand reassurance as they became more in tuned to what organic really means.

"People that are totally into buying organic foods, they understand that it cannot co-exist with something that isn't organic," he said. "Our responsibility is making sure the products stay organic from point A to point B, when it's in your hands. If you don't take all of the steps and keep things separate, it nullifies it."

There has been a push since the certification to steer customers towards healthier eating, Carnabuci said. At the stores, there is at least four times more produce than there was just four months ago, and about 10 percent of items on the shelves are under Hannaford's organic brand name "Nature's Place."

And, there are products that customers would be surprised to find a healthy alternative for, popping up alongside them in the aisles — the best example being organic beer.

Barbara Haumann of the Organic Trade Association said the certification is important to the industry because the Department of Agriculture doesn't have enough personnel to monitor grocery stores throughout the country.

"One of the advantages of a retailer becoming certified is that it shows they are taking that extra step," Haumann said. "It's important to know that if you're eating something organic, water from another food didn't drip on it in a storage room."

Rosanne O'Hare, 47, of Quincy, said she likes knowing someone is looking over her grocer's shoulder.

"It makes a difference to me," she said. "If my food is prepared with other foods that have pesticides, it would be contaminated and it wouldn't be organic. It would defeat the whole purpose."

If it weren't for that watchful eye, the customers would never know what they were eating, Carnabuci said.

"If that product is touching something it shouldn't be, is it really going to be that different? Probably not. But then it's no longer organic."