On my way to assignments I am always on the lookout for images. Such was the case in Providence, RI, where half sun-drenched/half shadowed rows of concrete columns edging a parking garage beckoned me, as did a street cleaner clad in yellow, trundling along with his similarly hued trash bin. Though tasty, neither visual morsel seemed worth running late for, so I put them on the back burner.

Done with my shoot, back in the garage, I had time to revisit the columns that were situated near my 4th floor parking spot. I happened to glance down at the street. There was the sanitation worker! Bingo.

I thought I was done.

I had spent years photographing the Big Dig: a massive public works project that took an interstate highway that cut through Boston and put it in tunnels under the city.

However, the tunnels have developed leaks, one major breach and hundreds of minor seams. So I joined a group of other journalists and construction managers and headed down into the project in the middle of night when the tunnels are closed so the workers can work.

Some construction defects require concrete and steel patching. In other inaccessible locations, grout is injected into the walls to keep the water out. A white-suited technician prepared the grout in this heated, mobile, grout-mixing unit. Via hoses, the grout is pumped up to injection crews working in the ceiling.

Up in the roof of the tunnel, leak-sealer Pat Joyce, worked on a leak. It's a cramped business.

At the end of a bay between girders, engineer John Rich described a leak in the wall. He told me how talented the leak sealers are - that pumping grout requires constant vigilance and the use of senses other than your eyes because you can't see what is going on inside the wall.

You need to listen for water or cracking, he explained. Also, you listen to the pump with your hands, noting that if the hose bulges or the pump's vibration level shifts, it may indicate that the hole is filled or a problem is developing.

Surely you don't use your sense of taste? Oh yes, he assured me. He tastes leaked water to determine its origin: seawater, for example, or deep groundwater.

Rich has spent years of his life underground and reminisces fondly about when construction was in full swing. Like giant hydraulic woodpeckers, hoe rammers removed unwanted concrete. Hi-voltage electric arcs cut off old steel. Generators generated. Cranes groaned.

“The sounds were dynamite,” says Rich, “like a big jam session.”

It was four a.m., and the tour was over, but I couldn't resist one last photo when the safety officer offered to take me out on The Leonard P. Zakim Bunker Hill Bridge.