Part of the nearly $1 billion upgrade to the Silicon Valley Clean Water system — the joint powers authority that accepts, treats and cleans all the sewage from Belmont down to the northern parts of Menlo Park — involves upgrading the main pipelines that feed into the facility at the eastern edge of Redwood Shores.

The existing pipelines are large — about 4.5 feet in diameter — but the new pipelines are huge: 10 feet in diameter! And they are contained within a 16 foot wide tunnel 40 feet or more underground. Extending from just south of San Carlos Airport, under the airport and then out to the shore.

Naturally such a large pipeline couldn’t be laid by the simple expedient of digging a ditch, laying the pipe, and burying it. That would involve moving staggering amounts of dirt and muck and, more importantly, would drastically impact the airport and a lot of businesses, homes, roads, etc. Upgrading infrastructure that serves a large and growing community — and must exist inside the community — is a challenge.

So instead the engineers went a different route: they ordered a custom-built tunnel boring machine and dug out a tunnel under the ground, lining it with concrete walls, all without disturbing anyone living or working above them.

Today I got to walk through part of the first completed section, which basically runs underneath the airport for about a mile. Here’s the north end where we started, just south of the San Carlos Transfer Station (aka “the dump”):

Things get surreal pretty fast walking through the tunnel. Pretty soon you’re lost in the darkness except for the light cast by the work lights:

• 

• 

We stopped about a thousand feet in, after the last turn¹. From that point it’s straight shot for almost a mile to the south end:

Which makes it look suspiciously like a rumored secret government installation built in the 1960s… 🙂

---

1. The boring machine has a 650 turning radius…which doesn’t sound like much, but when you remember it’s a 600+ foot long machine — made of multiple connected cars, each of which performs a function necessary to cutting and building the tunnel — it’s actually pretty impressive. ↩