Posit the question "How do they clean the sewers in San Francisco" and you'll be surprised. Unless, of course, your answer was "They roll out a device resembling a Victorian-era laboratory contraption painted tomato red, emitting more noise than a diesel locomotive, and employing technology more often seen in fountains and vacuum cleaners." If that was your answer -- you're on the money.
As to what, exactly, the Department of Public Works is cleaning out of the sewers with the aforementioned contraption -- there, too, you'll be surprised. The answer we were given Monday at the corner of Fourth and Berry was "bricks from 1860."
Here's how "The Sewer Hog" and "The Grit Gator" work:
The "Sewer Hog" -- which really does resemble something devised by Jules Verne via Bugs Bunny -- is a massive, rectangular device the color of Dorothy's slippers and equipped with more knobs, gauges, and needles than the Apollo XI command module. A thick hose is lowered down a hole into the afflicted sewer pipe and snaked through the filth of ages until it reaches its desired location. At this point, water is fired backwards toward the filth between the nozzle and the hole. This water, by the way, is shot at 1,500 to 2,000 pounds per square inch -- roughly 10 times the pressure of a firehose, according to Department of Public Works personnel we chatted with. If fired straight in the air, the plume of water would clear a 20-story building. You do not want to drink from this hose.
But what happens to the rocks, sand, bricks, and -- let's face it -- shit fired backwards by the high-pressure beam of water? That's where "The Grit Gator
" comes in.
A fire engine-colored box resembling a dumpster, the Grit Gator is, essentially, the biggest filter you've ever seen. The sewer filth and the water used to loosen it are vacuumed up into the box, where a series of sieves separate the solids from the liquids. The water is pumped back out, on a circuit, and will run through the Sewer Hog and be blasted out the hose again. But the bricks, rocks, etc. are stuck for good. The Hog holds 33 cubic yards of sewer goodness.
Both are operated by Brenford Environmental Systems, which was subcontracted out on this job by Yerba Buena Engineering & Construction.
Sewers underneath flat areas of San Francisco, intuitively enough, gather more detritus than those beneath the hills. This stretch of sewers, according to the DPW, hadn't been cleaned since 1955 -- so some of the crap they dislodged was pretty big. Depending on the subterranean layout, various sewer systems require a cleaning once a year, once a decade, or even less.
Despite the 55 years without a scouring, DPW officials didn't expect the Grit Gator to be more than half full by the end of the day. And, comparatively, that's pretty clean -- they recently spent a good five days cleaning out the sewers on Harrison near the Best Buy. Insert your own "full-of-you-know-what" joke here.