Electricity, Poop, and That Bastard Edison

San Francisco's Secret DC Grid:

Nikola Tesla's alternating current may have "won" the War of Currents at the end of the 19th Century, but the defeated incumbent -- direct-current distribution, aggressively championed by Thomas Edison -- endured. [...] Remnants of DC power distribution kept performing their assigned tasks for decades as the AC grid thickened around them.

In fact, a few live on to this day. One of the best examples is in San Francisco, where 250-volt DC power still flows through underground and overhead cables across the city. These DC lines peacefully coexist with their AC counterparts; you can see this mix of currents straddling utility poles in the city's South of Market district. DC's perseverance in that neighborhood seems fitting, for it was just a few blocks away that the tiny California Electric Light Co. -- a forebear to California's dominant Pacific Gas and Electric (PG&E) -- became the first power company in the United States, and possibly the world, to supply electricity to multiple customers from a central generating station. It was in September 1879 -- a full three years before Edison turned on his famous Pearl Street generating station in New York City -- that California Electric began burning coal, raising steam, and driving dynamos in a wooden shack at the corner of Fourth and Market streets to feed current to its customers' electric lights. [...]

DC endures in San Francisco because more than 900 of PG&E's customers still need it. Most of the utility's customers transitioned to AC lightbulbs and appliances easily enough as competing power distributors coalesced within PG&E and harmonized their equipment around AC. But for some of these building owners, however, elevators were a problem.

DC-driven winding-drum elevators -- the leading design until the 1930s -- use a DC motor in the basement that winds and unwinds the elevator's steel cable on a steel drum, thus lifting and lowering the car from pulleys atop the elevator shaft. DC drive was the only way to go at the time for a speedy elevator, because only DC could deliver variable-speed operation for smooth starts and stops. The DC motors were also energy efficient, capable of something that has only recently become possible with modern elevator designs: regenerating power when the elevator descends.

However, safety was a weak point. If a winding drum's control system fails, its motor can drive the elevator through the roof, according to San Francisco -- based elevator consultant Richard Blaska. As a result, says Blaska, new installation of winding-drum elevators was banned in the 1940s and 1950s in favor of traction elevators, whose cable will simply slip and hold the car at the top floor if the control system fails. Traction elevators can be engineered for either AC or DC operation.

Existing DC winding-drum elevators, however, have stubbornly resisted exile to the scrap heap, in no small part with support from local elevator repair firms such as Erik Bleyle's. Bleyle Elevator makes replacement parts, rebuilds DC motors, and designs custom circuits to sustain these machines from a bygone era. Bleyle admits that repairs can be pricey, especially hand-rewinding a DC motor, which can run between US $30 000 and $40 000. But he says even a refurbished motor looks cheap compared with the $500 000 cost of replacing the elevator, not to mention the months of involuntary stair climbing during the upgrade.

"Usually people just go for the motor," says Bleyle. [...]

The DC grid was also always difficult to troubleshoot because faults are hard to localize on a single large circuit -- a challenge that Austin says is compounded by the scant support this forgotten technology gets from equipment vendors. Austin adapted a circa-1990 AC/DC hammer drill to create his own diagnostic tool for so-called phantom voltage -- tiny dribbles of DC flowing across blown fuses that can hoodwink unsuspecting "troublemen" and their trusty voltmeters. Austin knows he's found a phantom when he clips his modified Black & Decker Macho III hammer drill onto a circuit, pulls its trigger, and gets a whimper instead of a roar. [...]

"When you had a failure out there like a fire in a manhole, the DC grid saw it as a load and just kept on pumping power at it," says Austin. The Tenderloin fire provided fuel for critics of PG&E's maintenance record and prompted the utility to accelerate and complete an ongoing redesign of its DC supply system. PG&E finished the job and shut down its two old rectifiers at the end of 2010.

I had no idea that this lunacy was all around us here! What the!

It reminds me of the fact that our fair city also has... unique... notions about how sewers should work. (After all, no discussion of electricity is complete without a plumbing analogy.) It's one of the few cities in the world that uses the same pipes for sewage and rain drainage. Doing it that way fell out of favor some time between the Romans and the London cholera die-offs in the 1800s.

San Francisco Combined Sewers:

San Francisco collects both sewage and stormwater in the same network of pipes, then treats and discharges the combined flows to San Francisco Bay or the Pacific Ocean. Except for portions of Old Sacramento, all other cities in California have separate sewer systems, which means there are two sets of pipes in the ground. One set of pipes takes sanitary waste to the treatment plant while a second set carries stormwater runoff from street drains directly into creeks, lakes, or the ocean. [...]

San Francisco's combined system holds these large volumes of water in underground storage vaults called transport/storage (T/S) structures, which encircle the city. San Francisco built the T/S structures in the 1980s and 1990s to prevent pollution of the bay and ocean during large storms. All combined flows pass into and through these structures on their way to the treatment plants. This upgrade greatly reduced the number of sewage overflows. The current system is designed such that overflows to the bay or ocean now occur on average one to ten times per year, depending on the rainfall and the watershed.

WHY A COMBINED SYSTEM? Many United States cities built prior to 1900 had combined sewer systems. At that time, sewage treatment was not available and sewers simply directed sewage into local water bodies. When sewage treatment became necessary to protect public health, newer cities built separate systems to save on the costs of treating stormwater. Some of the older cities opted to separate their combined systems. San Francisco, already a dense urban environment, decided that separation was too costly and disruptive to the residents.

Also: A Rare Look at the Tunnels Under San Francisco:

In the early '90s my friends and I used to tape flashlights to the handlebars of our bikes and go riding around in underground storm drain tunnels. There was a whole network of these tunnels under the city that sat empty for most of the year. We would go for miles snaking up and down the sides of the tubes, clapping and yelling to see how far our echoes would carry, eventually popping out in some other part of the city covered in cobwebs and bat guano. When the tubes got too small, we laid down on skateboards and kept going. If we found a flooded part, we taped garbage bags around our legs and crossed our fingers.

Previously, previously, previously, previously, previously, previously, previously, previously.

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17 Responses:

  1. berdario says:

    Problem 1: Having the same pipe for sewage and rain drains might promote cholera outbreaks in SF
    Problem 2: The high population density of SF made it too expensive to separate the two pipe systems



    • Travis Roy says:

      Why would having the same pipe for sewage and rain drains cause that if it's treated?

      • berdario says:

        "The current system is designed such that overflows to the bay or ocean now occur on average one to ten times per year, depending on the rainfall and the watershed."

        I understood that to mean that such overflows wouldn't be treated... the waste would be diluted, but still untreated

        and the bigger the flood the worse it could get, I assume

        Then again, my previous comment was just for its comedic value... Please forgive if there're some inaccuracies or wrong assumptions in it :)

  2. Nick Lamb says:

    "Doing it that way fell out of favor some time between the Romans and the London cholera die-offs in the 1800s."

    Actually, Bazalgette's London sewers built in the 19th century are a combined sewer exactly like the one you have in San Francisco. And London is currently (and will be for many years) slogging through the process of getting its huge resident population of BANANAs to accept that we're going to build more overflow storage (under the Thames river because there's nowhere else left) or else they are going to be holding their "not in anyone's backyard" placards while standing knee-deep in their own shit.


  3. Not really unique. London still has its' combined network with no plans for a divorce (they're presently boring - at great expense - a new transport and tunnel storage deep below the city to increase capacity). Many older cities and towns in the UK still have combined sewers as well - at least in some areas. There is a tendency to separate for new development, but old builds are left as is.

    The confusion is actually somewhat problematic - there are teams of people who have the full time job of going around inspecting storm drain manholes to check nobody's accidentally plumbed, say, a sink into one.

  4. Scott Louis says:

    this was a really cool article!

  5. Other jamie says:

    Somehow, we still live in SOMA. Maybe some of like living here. Go figure.

  6. Karl Shea says:

    Milwaukee has a combined sewer system as well, and spent about $4b starting in the late 70's to build the Deep Tunnel project to hold wastewater. It helped to greatly reduce overflows into Lake Michigan to about 3 per year, which is a very small number compared with other cities with combined sewers.

    Of course instead of focusing on facts it has turned into a huge political issue every time there's a big storm resulting in an overflow, and now the Milwaukee Metropolitan Sewerage District spends over $1m/year on PR.

  7. Jeff Warnica says:

    I can't believe that there aren't a few options to get out of this insanity (at least on the street)

    * PG&E puts a 20 year window on things (requiring individual buildings to put in industrial rectifiers), even going so far as to pay bonuses to buildings that switch over (possibly when whole blocks switch over; game the fuck out of the neighbous)
    * PG&E hangs rectifiers on poles, only distributing DC from the street to the building, not around town

    ... unless, PG&E is charging absolutely insane rates for DC. Which still might motivate them to do the second option.

    And as others have pointed out, SF isn't unique in combined sewage systems. Here in Halifax, the city is now just about compete a $500 mil (CAD) project to cap off the combined sewage outfall (CSO)'s around the shorelines, pipeline that to new plants for treatment. At some indefinite time in the future net-new storm sewers will be run everywhere, turning the now combined lines to sanitary only. Since treatment was going to happen, for maybe 50 years new streets have two systems, and for maybe 30 rebuilt streets have had two. As far as the end of the block, when tying into the single, legacy, combined system. The isolated combined systems may take 50 years to be replaced. There remain select "private" direct discharges to the harbor, including some 50 unit apartment buildings.

    For extra fun, where as it sounds like San Fran has been treating the CSO for decades, with occasional incidents of overflow, Halifax was, until 5 years ago, not treating the CSO at all. We have only upgraded (@ $500mil) to "infrequent" discharges. Presumably a plant built in 2008 handling everything 358 days a year is better then the SF plant from 1980 doing the same.

    No word on how the reduction in... biologicals... has had on the exceedingly common Navy diver lobster poaching.

    • Chris says:

      Winnipeg has combined sewers in most of the older neighborhoods (central Winnipeg and the parts of the surrounding pre-unicity towns). A long-term project to separate them is in progress.

  8. DaveL says:

    Currently, Boston has approximately 235 miles of combined sewers and 37 active CSO outfalls. ... To correct this situation, over the years, Boston Water and Sewer Commission (BWSC) has undertaken a number of easy-to-install improvements as well as more costly improvements such as sewer separation projects. Six sewer separation projects have been completed, for a total of approximately 43 miles of new storm drains. Presently, there are other sewer separation projects in various stages of construction and design.

    Boston Combined Sewer Systems and Outfall Maps

    You can actually swim in the Charles now, if you are careful.

  9. Jef Poskanzer says:

    At least SF is on an ocean shore, so when they do spill shit it doesn't get sucked up as drinking water by folks downstream. Except for the fish, and they don't vote.

  10. Jens Kilian says:

    Eeeyarg. They swam in that in Big Trouble in Little China.