The residents of Rio Vista could smell trouble.

In 2001, in this wind-whipped Sacramento River Delta town, 17 people in the town of about 4,500 lodged complaints with the council office about a strange odor brought about during the mid-afternoon by southeastern winds. They complained of flies and odor, said the town’s then-Mayor Marci Coglianese.

“It made you feel energy-less,” said Bob Tillisch, 58, a resident and retired U.S. Army chief engineer who first noticed the smell. A little digging revealed that a farmer upwind was applying a old load of biosolids, the term used by U.S. EPA to refer to treated sewage sludge.

“But smell is not a legitimate complaint,” Tillisch said. “No one is tracking illnesses.”

And that is the problem.

Phone calls about public health complaints come in at regular intervals to county health boards, city council offices, state departments of health or environment. Many places do not log the calls, and if they do, investigations into health complaints do not extend beyond a particular truckload of waste. Certainly no one is looking into whether applying sludge to the ground can have health effects.

And given the nature of the uncertainties involved and the bureaucracy that some researchers say exist within the industry, the answer to this question has remained hard to come by.