In the plane next to me, Mira Kilpatrick cranes to see a small patch of green tucked alongside the tanks. It's a tiny farm, less than three-quarters of an acre. Kilpatrick has spent the last couple of summers at the Somerton Tank Farm as an apprentice farmer, planting seeds, pulling weeds and plucking bugs. No pesticides, no chemicals, 100 varieties of crops are groomed almost entirely by hand.

Kilpatrick loves it, and she says she's ready to strike out on her own. She wants to make a living as a professional urban farmer, and she's looking for usable land somewhere in the city. She scans the land below for some arable patch hidden among rows of homes that extend to the horizon. So far, she's had no luck, but she hasn't given up yet.

The Somerton Tank Farm below us is located on Philadelphia Water Department (PWD) land. This isn't a hobby garden. The project is sponsored by PWD's Department of Economic Development: It's got to be profitable, and it is.

Kilpatrick's mentors are Nicole and Steve Shelly. Their farm is winning praise nationally, featured recently in the prestigious "New Farm" newsletter and in the PBS book Edens Lost and Found: How Ordinary Citizens Are Restoring Our Great Cities.

PWD has started bringing eco-tourists and VIPs to visit their model farm. But getting politicos to buy into the program means producing more than bushels of pretty veggies. PWD is looking for hard numbers to trace how the benefits of locally grown food will cascade into the community. So the Institute for Innovations in Local Farming—a Philadelphia-based nonprofit that's partnered with the water department—has just commissioned an analysis to quantify the results.

Meanwhile, the numbers the Shellys are getting are growing: from $26,000 to $38,000 to $52,000 last year, and climbing still.

Fifty grand a year isn't living large. But for the Shellys, it's all-they-can-eat—and they probably eat better than almost anyone. Besides, Steve would rather push a tiller than jockey a mouse.

The institute hopes to spawn a new generation of professional, college-educated urban farmers to follow their example. And Kilpatrick—in her late 20s, with a degree in biology from Smith, living in Center City—fits that profile perfectly.

Kilpatrick is ready to go to the head of the elusive "creative class"—the young professionals who bring innovation and life to the city. Unfortunately, the bulk of Philly's creative class get their education here, but then take their talents elsewhere.

I fear the same fate for Kilpatrick. If she can't find public land in the city to farm, she says, she will leave.

There's plenty of demand for local, sustainably grown produce, say the Shellys. The farm sells through a buying club, which is now closed to new members. They also go to farmers' markets in Rittenhouse Square, South Street and South Philly.

At the South Philly location recently, older residents and new arrivals swapped recipes with the three farmers. They snapped up salads of ruby amaranth and iridescent Swiss chard. There were piles of purple-tipped onions, Italian and Japan-ese basils, and baby fennels with lacy fronds. Little bags of zucchini blossoms moved quickly: Picked this morning, the bright orange flowers will be filled and batter-fried tonight.

This is real artisanal food, too delicate to survive a trip through a supermarket. And way cheaper than Whole Foods.

The Shellys are ready to graduate Kilpatrick. She's ready to run a farm of her own. But though the water department has some 100 acres of potential land, Kilpatrick has yet to get an offer. I've asked, and I can't find out why. Except for the whispered excuse that bureaucrats fear potential terrorism.

Like she's gonna dump tofu in the water supply?

C'mon. Get real. This is a model that works. It's time to bet a farm on Mira.