ANTIOCH -- When there's a questionable charge on a utility bill or store purchase, Louis Ramos promptly asks his wife, Irene, whether it's legit.
But when it came to their property bill, there were no surprises.
Or so they thought.
Last year, the Antioch couple learned they were being charged for Delta Diablo Sanitation District sewer service despite never being connected to the district's system. Their home, built in 1980, is on a septic tank.
"We were shocked," said Irene Ramos, 64, a retired mortgage professional. "I looked at it and said, 'What's all this about.' You would think we would have paid attention, but we didn't."
According to records, the couple had paid taxes to the sanitation district for sewer service and street sweeping since 1987.
Recently, the Ramoses received a refund of about $5,700 from Delta Diablo. The total included an annual interest calculation of 5.1 percent.
Such billing errors are unfortunate but happen on occasion, especially with public agencies being understaffed, county Assessor Gus Kramer said.
Because of confusion over annexations, dividing parcels, school district borders or other snafus, there are one to two dozen Contra Costa cases each year of taxes being incorrectly assessed, he said.
Computerization has minimized but not eliminated errors.
"Computers and human beings are not infallible," Kramer said. "It comes down to property owners doing a little homework on their bill."
Louis Ramos, a retired sheet metal worker, says he and his wife acquired the land for their home in 1979 and moved in a year later. When Antioch annexed the land south of Oak View Cemetery in the 1980s, the Ramoses were given a choice of connecting to sewer or keeping their septic tank.
"I guess I took it for granted," Louis Ramos, 78, said.
Delta Diablo's sewer lines were installed in the mid-1980s for the Almondridge subdivision, located across the street from the Ramoses' Willow Avenue home. An explanation of the situation to Delta Diablo officials led to an investigation by the company's finance department.
It's a district's responsibility to maintain parcel records and inform the county if an assessment needs to be corrected, said Bob Campbell, the county's auditor/controller.
"We get our information from the county tax rolls, so as soon as it was brought to our attention, we looked into it and took it very seriously," said Angela Lowrey, the sanitary district's spokeswoman. "We see it as a relationship and honoring our customers."
The Ramoses received a refund for four years without interest, which is the district's policy. They later requested a full refund for the sewer services they had erroneously paid.
The district board granted their request, as state law has special refund provisions for a property where no service was provided.
The Ramoses' property tax bill still includes a charge for street sweeping, which they are pleased to receive.
Pittsburg, Antioch and Bay Point receive sewer service from Delta Diablo, though rates differ based on the number of scheduled street sweepings and collection systems.
The Ramoses hope the ordeal serves as a cautionary tale to others.
"People have to be astute and be sure to check both online and the hard copies," Irene Ramos said.
Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.