“It doesn’t make any sense,” he said.

Carle, an attorney, said he wonders whether different materials were used in the construction of the infrastructure of Coffey Park, Wikiup and Fountaingrove. He urged the city to be completely transparent about the problem going forward.

“I think all of us want to be tracking this, and if we feel some level of concern, we’d potentially want to bring our own experts,” Carle said.

Real estate agent Tammra Borrall is listing a burned property on West Bristlecone Court for $299,000. She said she had not been told by the property owner about any issues with the water quality, which would be something that would have to be disclosed to future buyers. She said her client said she was unaware of the issue.

Burke said the city has been focused on the health of the people living in the homes, and hasn’t sent letters to owners of destroyed properties, though she said some of the information is on the recovery website.

City officials say they are confident the contamination is limited to the 184 acres in Fountaingrove.

Hundreds of samples from the area immediately surrounding the advisory areas and other parts of the city, such as Coffey Park, have found no issues. A single slightly elevated result was found east of the advisory area but did not return after that section of the system was flushed out, Burke said.

To ensure this remains the case, the city has isolated the contaminated area with a series of valves that allow water to flow in but not flow back out, Horenstein said. Water pressure in the area, which is about 600 hundred feet above the valley floor, is currently strong, but has had issues in the past.

The water actually going to the homes left standing contains levels below 1 part per billion, and that has been the case since the crisis began, with a single exception that was resolved with a component replacement, she said.

Lower contamination at homes left standing makes some sense, Horenstein said.

Existing homes, and likely the immediate area and ground around them, would have been exposed to lower heat levels than those that burned, lending support to the idea that the heat from the fire is at fault, he said.

The problem is that test results don’t fully support the theory that burned components are solely to blame for the contamination, Horenstein said.

“The data is really still too uncertain and confusing to make those conclusions,” he said.

That’s because in some cases, the city has isolated an individual court, removed all the meters and replaced plastic service lines, flushed the system with fresh water, waited a while, retested, and found that benzene levels eventually crept back up again after an initial drop.

That would suggest something else is at play, he said.

Benzene is an organic compound that is formed from both human activities, such as gasoline production, and natural processes, such as forest fires.

It could be that the water mains, which are typically made of high-strength cement, or the service laterals, which are usually made of a high-density polyethylene, have somehow absorbed the benzene and are releasing it back into the water, he said.

It could also be that there are underground storage tanks in proximity to the compromised lines, Horenstein said, though he acknowledged that this seems less likely given the number of different hot spots identified by the tests. This area of Fountaingrove was largely pristine hillside until it was developed as homes in the 1980s and 1990s.

It’s also possible that the low water pressure the area experienced during and immediately after the fire drew in contaminants, but nothing is conclusive.

“We know the cause of the contamination is the fire, but exactly how is what we’re trying to figure out,” Burke said.

The longer the problem persists and the longer the investigation fails to conclusively pinpoint a cause, the more likely it is that a full replacement of the water system in the area will be needed, Horenstein said.

“At this point, it seems possible if not likely that we may have to do a wholesale replacement of the majority of the infrastructure in that area,” he said.

You can reach Staff Writer Kevin McCallum at 707-521-5207 or kevin.mccallum@pressdemocrat.com. On Twitter @srcitybeat.