As of Friday, earth-eating machines had dug nearly 80 percent of the pit, which will bottom out at 10.5 feet below grade. Without engineering safeguards, this hole would be a public menace.

Dirt walls must be shored up with steel beams and thick boards, with steel tie-backs anchored in concrete that radiate 30 feet under city streets.

“We don’t want to lose streets, sidewalks, stores possibly,” said Nelson Dougherty, the construction superintendent, talking up the importance of these safety measures.

The hole at Napa Square has been getting deeper and deeper these past four weeks as big Caterpillars rumbled and a parade of trucks pulled up for dirt fill-ups.

By Friday, two giant Caterpillars — a “mud Cat” ’dozer and an excavator — stood atop a mountain of dirt in the center of the pit, seemingly stranded. On the Franklin Street side, a concrete pumper sat marooned in muddy water from the recent rains.

Yet the action along the pit walls was one of furious drilling and concrete pumping under sunny skies.

“I know California needs rain,” Dougherty said, “but this is what I need to get the job done — good weather.”

Rain and the water table, located 8 feet down, have the potential of stopping the project in its tracks, so precautions have been taken.

To keep the ground water at bay, 14 wells were dug, with pumps 20 feet down. After time in a settling tank, the water is dribbled onto Franklin Street at the rate of less than two gallons a minute, Dougherty said.

To survive heavy rain, additional pumps lift murky surface water into another tank for filtering and storm drain release. That marooned concrete pumper will have to sit there until the earth is pumped dry, Dougherty said.

It will be another two years before tenants occupy the $25 million Napa Square project. Until then, Dougherty of Zcon Builders is in charge.

“It’s what I do for a living,” said Dougherty, who moved to Napa from Shingle Springs to live closer to the project. “They pay me to push the job and make sure it comes in on time.”

Ten men were on the job site last week. Over the coming year, the project will be crawling with up to 75 workers representing more than a half dozen trades, including steel workers, plasterers and tile setters.

Some subcontractors will be local, but many workers are likely to be commuting to the job site from throughout Northern California, Dougherty said.

Zcon strives to build to the “American standard,” said a patriotic Dougherty. The core of that standard is “hard work and knowledge,” he said.

But first the pit, which is producing 660 truckloads of dirt to cap the old American Canyon landfill.

Before a permanent drainage system and a concrete shell can be constructed, workers must complete wood retaining walls supported by steel I-beams and radiating tie-back rods. To make sure the walls wouldn’t collapse, the city required multiple reviews of the engineering plans, Dougherty said.

If things go well, steel framing rising up to 50 feet above ground will begin appearing this summer. The new structures will be three stories, standing head and shoulders above the adjacent one-story buildings.

An even taller five-story hotel, the Inn at Town Center, is scheduled to start construction by late spring at a cleared site just across First Street.

What about those two Caterpillars seemingly stranded atop the dirt mound in the center of the pit?

Not to worry, Dougherty said. They will use the dirt to build a temporary ramp out of the pit onto School. Later, the dirt will be shifted to the east side of the pit where the permanent entry ramp off Franklin will be located.

Gawkers should have a field day in coming months as the project rises out of the hole, Dougherty said. “This is going to be a busy place.”